One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

--
*Why do we say something is out of whack? What is a whack? *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


Whilst the drive may be central isnt there still the possibility that the
axis of the new motor is 2mm further away from the flywheel axis? If not,
are the teeth on the flywheel and starter pinion deep enough to accommodate
meshing more deeply (by 2mm)?

Otherwise, Im stumped too. ;-)

Tim
--
Please don't feed the trolls

In article
,
Tim+ wrote:
Whilst the drive may be central isn‘t there still the possibility that
the axis of the new motor is 2mm further away from the flywheel axis?

No. It is concentric in the fitting ring which locates in the hole in the
engine. They also give instructions on how to alter the alignment of the
motor unit to the fitting plate if needed - say for a kit car using that
engine.

If not, are the teeth on the flywheel and starter pinion deep enough to
accommodate meshing more deeply (by 2mm)?

I suppose it must be that. Obviously the two won't be in as tight mesh as
in a gearbox, etc.

Otherwise, I‘m stumped too. ;-)

Quite. Doing my head in. ;-)

--
*I'm pretty sure that sex is better than logic, but I can't prove it.

Dave Plowman London SW
To e-mail, change noise into sound.

On 20/06/2020 12:22, Tim+ wrote:
Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


Whilst the drive may be central isnt there still the possibility that the
axis of the new motor is 2mm further away from the flywheel axis? If not,
are the teeth on the flywheel and starter pinion deep enough to accommodate
meshing more deeply (by 2mm)?

Otherwise, Im stumped too. ;-)

Tim

At first I agreed with the "spacing" idea. But, normally the
bell-housing has a circular seating for the motor, and the matching
flange on the motor is usually co-axial with the bearings, although of
course it does not have to be. So, I'd start by looking to see whether
or not they look coaxial.

One of the clever things about the involute profile is that it still
meshes OK even if actual distance between centres is not quite right
(although you get a bit more sliding and hence wear).

So you can "squeeze in" extra teeth on the same centres, obviously at
least one set has to be a little bit thinner to avoid interference.

I'm not familiar enough with gear design to know whether you could get
away with it with this 22% difference, which sounds a lot. But, starter
gears are typically pretty sloppy to accomodate debris, they don't do
very much "mileage", and they still work after a lot of wear.

My guess is that the aftermarket starter has thinner teeth. They could
easily get away with that in "strength" terms by using a slightly higher
spec and therefore stronger material.

On Sat, 20 Jun 2020 11:55:50 +0100, Dave Plowman (News) wrote:

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has
an 11 tooth pinion 29mm diameter.

This is a virtual gear simulator, might help?

https://geargenerator.com


--
Cheers
Dave.

On 20/06/2020 12:56, newshound wrote:
On 20/06/2020 12:22, Tim+ wrote:
Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but
has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is
central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


Whilst the drive may be central isnt there still the possibility that
the
axis of the new motor is 2mm further away from the flywheel axis?Â* If
not,
are the teeth on the flywheel and starter pinion deep enough to
accommodate
meshing more deeply (by 2mm)?

Otherwise, Im stumped too. ;-)

Tim

At first I agreed with the "spacing" idea. But, normally the
bell-housing has a circular seating for the motor, and the matching
flange on the motor is usually co-axial with the bearings, although of
course it does not have to be. So, I'd start by looking to see whether
or not they look coaxial.

One of the clever things about the involute profile is that it still
meshes OK even if actual distance between centres is not quite right
(although you get a bit more sliding and hence wear).

So you can "squeeze in" extra teeth on the same centres, obviously at
least one set has to be a little bit thinner to avoid interference.

I'm not familiar enough with gear design to know whether you could get
away with it with this 22% difference, which sounds a lot. But, starter
gears are typically pretty sloppy to accomodate debris, they don't do
very much "mileage", and they still work after a lot of wear.

My guess is that the aftermarket starter has thinner teeth. They could
easily get away with that in "strength" terms by using a slightly higher
spec and therefore stronger material.

As an afterthought, the increased diameter of the new gear rather
suggests that the motor axis must be moved, otherwise the new gear would
surely "bottom" in the starter ring.

Is one of the holes in the starter motor elongated as that would give you a bit of wiggle room to mesh the gear correctly?

Richard

On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


http://www.delcoremy.com/the-latest/...ar-differences

On 20/06/2020 13:45, Tricky Dicky wrote:
Is one of the holes in the starter motor elongated as that would give you a bit of wiggle room to mesh the gear correctly?

Richard

It's not about the bolt holes, there's a fairly big "separating force"
between the gears when the starter operates, so the starter motor body
needs to be clamped securely to the bell-housing to prevent movement.
Hence a flange with a spigot.

On 20/06/2020 13:48, Richard wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:

It's confusing my little grey cells. ;-)


http://www.delcoremy.com/the-latest/...ar-differences

Excellent link, that explains everything!

In article ,
newshound wrote:
On 20/06/2020 12:22, Tim+ wrote:
Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


Whilst the drive may be central isn‘t there still the possibility that the
axis of the new motor is 2mm further away from the flywheel axis? If not,
are the teeth on the flywheel and starter pinion deep enough to accommodate
meshing more deeply (by 2mm)?

Otherwise, I‘m stumped too. ;-)

Tim

At first I agreed with the "spacing" idea. But, normally the
bell-housing has a circular seating for the motor, and the matching
flange on the motor is usually co-axial with the bearings, although of
course it does not have to be. So, I'd start by looking to see whether
or not they look coaxial.

The mounting has a circular raised part with locates accurately in a same
sized machined hole in the engine. So all the fixing bolts do is prevent
fore and aft movement - they don't locate it side to side. And the starter
shaft is concentric to the entire mounting plate. The mounting plate is
made by the UK firm to adapt the Denso starter to an engine they don't
supply one for themselves. Like lots of classic cars. Basically the same
starter motor with a custom made mounting plate and the correct drive
pinion can fit a vast range of vehicles, old and new.

One of the clever things about the involute profile is that it still
meshes OK even if actual distance between centres is not quite right
(although you get a bit more sliding and hence wear).

So you can "squeeze in" extra teeth on the same centres, obviously at
least one set has to be a little bit thinner to avoid interference.

I'm not familiar enough with gear design to know whether you could get
away with it with this 22% difference, which sounds a lot. But, starter
gears are typically pretty sloppy to accomodate debris, they don't do
very much "mileage", and they still work after a lot of wear.

My guess is that the aftermarket starter has thinner teeth. They could
easily get away with that in "strength" terms by using a slightly higher
spec and therefore stronger material.

Yes - the teeth have a thinner profile. Other difference is the 'far' end
of the pinion has a flange which is part of the teeth. Which I suppose
would strengthen them.

Other thing is more teeth means the engine spins faster for a given motor
speed. Odd, since it is already a gear reduction type.

--
*I got a job at a bakery because I kneaded dough.*

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Richard wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


http://www.delcoremy.com/the-latest/...ar-differences

Thanks, Richard. All that does is confuse me. A minor difference I'd
likely not have noticed. A different number of teeth and a larger diameter
difficult to miss. And there is no offset on this unit.

--
*Procrastination is the art of keeping up with yesterday.

Dave Plowman London SW
To e-mail, change noise into sound.

On Saturday, 20 June 2020 11:56:01 UTC+1, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

The teeth must be the same size in order to mesh.
So, the gear must be bigger.
So, the centre of the motor must be further way from the axis of the crankshaft.
Should be easy enough to check.

On 20/06/2020 14:54, Dave Plowman (News) wrote:
In article ,
Richard wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


http://www.delcoremy.com/the-latest/...ar-differences

Thanks, Richard. All that does is confuse me. A minor difference I'd
likely not have noticed. A different number of teeth and a larger diameter
difficult to miss. And there is no offset on this unit.

But you mentioned a "mounting plate" in your other post. Seems likely in
this case that the "offset" is there.

On 20/06/2020 14:54, Dave Plowman (News) wrote:
In article ,
Richard wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


http://www.delcoremy.com/the-latest/...ar-differences

Thanks, Richard. All that does is confuse me. A minor difference I'd
likely not have noticed. A different number of teeth and a larger diameter
difficult to miss. And there is no offset on this unit.


If the replacement fits on the car and can start it then the pinion must
be further from the crankshaft axis by 2mm. You could measure the
distance between the centre of the pinion and the mounting bolt holes on
both motors. They must be different though as the difference is small it
will be difficult to measure accurately.


--
Michael Chare

On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


It is not impossible for two gears to have the same effective diameter
(measured where the gears actually drive each other) and a different
major diameter. The real test will be to fit it and see if it works. :-)

--
Colin Bignell

In article ,
newshound wrote:
On 20/06/2020 14:54, Dave Plowman (News) wrote:
In article ,
Richard wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


http://www.delcoremy.com/the-latest/...ar-differences

Thanks, Richard. All that does is confuse me. A minor difference I'd
likely not have noticed. A different number of teeth and a larger diameter
difficult to miss. And there is no offset on this unit.

But you mentioned a "mounting plate" in your other post. Seems likely in
this case that the "offset" is there.

Keep on saying, no. According to the makers data they simply changed the
pinion. Nothing else.

--
*Hang in there, retirement is only thirty years away! *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
nightjar wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


It is not impossible for two gears to have the same effective diameter
(measured where the gears actually drive each other) and a different
major diameter. The real test will be to fit it and see if it works. :-)

Obviously if you increase the number of teeth you'd need to increase the
diameter too - to keep the distance between the teeth the same, where they
touch. ISTR the ring gear teeth don't have the same profile anyway. So
provided they mesh and the tips don't bottom in the valleys it might just
work. We're not talking about the sort of super accurate gears you'd want
inside a gearbox.

--
*Eagles may soar, but weasels don't get sucked into jet engines *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

In article ,
Richard wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)



http://www.delcoremy.com/the-latest/...tip-starting-m
otor-gear-differences

Thanks, Richard. All that does is confuse me. A minor difference I'd
likely not have noticed. A different number of teeth and a larger diameter
difficult to miss. And there is no offset on this unit.

Have you acttually checked for offset between the pinion and locating
ring at various radial points with a vernier? It wouldn't have to be
very much.
--

Roger Hayter

On 20/06/2020 11:55:50, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

A different number of teeth implies the centre of the starter gear has
moved.

Is there a way you can compare the two wrt to mounting holes, or an
appropriate point?

If the centre is further away from the flywheel by 4-5mm I would say all
is ok.

4mm in 25 is ~ 1/6, which is near enough to 2 teeth in 11.

"nightjar" wrote in message
...
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has
an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


It is not impossible for two gears to have the same effective diameter
(measured where the gears actually drive each other) and a different major
diameter.

Particularly when the pinion teeth are noticeably
smaller on the new pinion.

The real test will be to fit it and see if it works. :-)

--
Colin Bignell

Its pretty obvious that the gear ratio is different. The bigger gear
obviously has the same gear pitch but more teeth since the diameter, and
hence the circumference is larger.
The motor will, I'd say be under slightly more strain when turning the
engine of course, and we would hope it can stand the extra current, but
assuming the motore is the same it will turn over the engine a tiny bit
faster and have more teeth in contact with the flywheel gear at any one
time, I'd have thought.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Dave Plowman (News)" wrote in message
...
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

--
*Why do we say something is out of whack? What is a whack? *

Dave Plowman London SW
To e-mail, change noise into sound.

I'd imagine its within the range of adjustment myself. Many moons back when
I had sight and my Father was alive this same question came up on a much
older car. I don't quite recall which, but this does beg the question that
if this sort of issue was known back then, how is it that more modern cars
designs still make the same mistakes and retro fit the same solutions?
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Tim+" wrote in message
...
Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has
an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


Whilst the drive may be central isn't there still the possibility that the
axis of the new motor is 2mm further away from the flywheel axis? If not,
are the teeth on the flywheel and starter pinion deep enough to
accommodate
meshing more deeply (by 2mm)?

Otherwise, I'm stumped too. ;-)

Tim
--
Please don't feed the trolls

I'm confused by all of this.

Surely straight cut gears ground to the same specification will mesh
correctly regardless of their diameter.

Thinking back to my Meccano days all the gears would mesh successfully
with any of the pinions, there were pairs that one used most
frequently because the diameters added up to multiples of 1/2" but you
could use different pairs without problems if you had shafts at odd
spacings.

Isn't this why (straight cut) gears are ground the way they are?

--
Chris Green
·

On Sun, 21 Jun 2020 15:46:03 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the trolling senile asshole's latest troll**** unread

--
Marland answering senile Rodent's statement, "I don't leak":
"That¢s because so much **** and ****e emanates from your gob that there is
nothing left to exit normally, your arsehole has clammed shut through disuse
and the end of prick is only clear because you are such a ******."
Message-ID:

On 20/06/2020 16:28, Dave Plowman (News) wrote:
In article ,
newshound wrote:
On 20/06/2020 14:54, Dave Plowman (News) wrote:
In article ,
Richard wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


http://www.delcoremy.com/the-latest/...ar-differences

Thanks, Richard. All that does is confuse me. A minor difference I'd
likely not have noticed. A different number of teeth and a larger diameter
difficult to miss. And there is no offset on this unit.

But you mentioned a "mounting plate" in your other post. Seems likely in
this case that the "offset" is there.

Keep on saying, no. According to the makers data they simply changed the
pinion. Nothing else.

Maybe they are wrong. Maybe the mounting plate has the necessary offset
to compensate. I would have thought that just increasing the pinion
diameter (which goes with adding another tooth, if you keep to standard
profiles) then you would end up with the pinion teeth "bottoming" in
starter ring.

But maybe not; perhaps there is plenty of clearance with the standard
pinion, so that you can get away with increasing the pinion tooth count
/ diameter.

Various sorts of tip and root relief are used on different sorts of
gears. Modern finite element analysis lets you play all sorts of tunes.

https://www.ncbi.nlm.nih.gov/pmc/art...0and%20so%20on.

On 20/06/2020 18:28, Dave Plowman (News) wrote:
In article ,
nightjar wrote:
On 20/06/2020 11:55, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


It is not impossible for two gears to have the same effective diameter
(measured where the gears actually drive each other) and a different
major diameter. The real test will be to fit it and see if it works. :-)

Obviously if you increase the number of teeth you'd need to increase the
diameter too - to keep the distance between the teeth the same, where they
touch. ISTR the ring gear teeth don't have the same profile anyway. So
provided they mesh and the tips don't bottom in the valleys it might just
work. We're not talking about the sort of super accurate gears you'd want
inside a gearbox.

No you don't. You can just machine the tips off so that the 11 tooth
pinion has the same diameter as the 9 tooth one. But, with a standard
profile, you will now find that the tips of the 11 tooth ones are too
wide to fit into the gap at the root of the flywheel pinion. So you also
have to make the teeth of the 11 tooth pinion a bit thinner.

On 21/06/2020 08:33, Brian Gaff (Sofa) wrote:
Its pretty obvious that the gear ratio is different. The bigger gear
obviously has the same gear pitch but more teeth since the diameter, and
hence the circumference is larger.
The motor will, I'd say be under slightly more strain when turning the
engine of course, and we would hope it can stand the extra current, but
assuming the motore is the same it will turn over the engine a tiny bit
faster and have more teeth in contact with the flywheel gear at any one
time, I'd have thought.
Brian

The contact ratio (the average number of teeth in contact through a
cycle of one pitch) depends on other parameters, like clearance, which
is likely to be different if the centre distance is the same.

On 21/06/2020 09:26, Chris Green wrote:
I'm confused by all of this.

Surely straight cut gears ground to the same specification will mesh
correctly regardless of their diameter.

Thinking back to my Meccano days all the gears would mesh successfully
with any of the pinions, there were pairs that one used most
frequently because the diameters added up to multiples of 1/2" but you
could use different pairs without problems if you had shafts at odd
spacings.

Isn't this why (straight cut) gears are ground the way they are?


A good way to think of this is to start with a rack, with straight
flanks. A gear of infinite diameter, if you like. If it is symmetric, it
has three parameters: the flank angle, the tooth height, and the tooth
spacing. For involute gears with an arbitrary number of teeth to mate
with this successfully they must have the same circular pitch
(circumference at the pitch line divided by number of teeth) or module
(pitch diameter divided by number of pitch). This is how you make gears
with any number of teeth mate with each other.

The pitch line is the point where the width of the teeth is the same as
the width of the gap.

There are standard values for module, all gears with the same module
will mesh. The addendum (radial distance from pitch line to tip) and
dedendum (radial distance from pitch line to root) are usually fixed
multiples of module and this works for gears with, iirc, 9 or more
teeth. For fewer teeth, something needs tweaking.

Involute geometry is not particularly sensitive to the spacing of
centres (provided of course the gears are not interfering) and gives
better performance than (for example) the peg and lantern wheel geometry
that you see in medieval water wheels, windmills, etc.

This is not a bad article, which also shows something of the geometry of
"conformal" gears like the Wildhaber Novikov.

https://www.geartechnology.com/issue...x/Involute.pdf.

Conformal gears are *very* sensitive to the spacing of centres.

For an engineering product of true beauty, I recommend the main gearbox
of the Lynx helicopter but sadly I have not been able to find any images
of the internals on-line. (In the 1970's I used to run across people
from Westland and Imperial College, who collaborated closely on gears
and bearings).

In article ,
Roger Hayter wrote:
Thanks, Richard. All that does is confuse me. A minor difference I'd
likely not have noticed. A different number of teeth and a larger diameter
difficult to miss. And there is no offset on this unit.

Have you acttually checked for offset between the pinion and locating
ring at various radial points with a vernier? It wouldn't have to be
very much.

Absolutely no need. The unit has instructions on how to rotate it within
the adaptor plate if needed - which would also involve drilling new holes.
This might be needed in a kit car etc fitted with this engine to clear the
exhaust or whatever. If there were an offset, they'd have made this plain
in those instructions. The fixing holes, adaptor plate to engine, are 180
apart, and assuming clearance to other things, the unit could be mounted
upside down.

--
*I want it all and I want it delivered

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Brian Gaff \(Sofa\) wrote:
I'd imagine its within the range of adjustment myself.

No adjustment possible, Brian. The unit is an exact fit to the hole in the
engine. Both 'hole' and 'sleeve' machined.


Many moons back when I had sight and my Father was alive this same
question came up on a much older car. I don't quite recall which, but
this does beg the question that if this sort of issue was known back
then, how is it that more modern cars designs still make the same
mistakes and retro fit the same solutions?

Not quite clear what your question is?

--
*My dog can lick anyone

Dave Plowman London SW
To e-mail, change noise into sound.

"Fredxx" wrote in message
...
On 20/06/2020 11:55:50, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has
an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

A different number of teeth implies the centre of the starter gear has
moved.

Not if the new teeth are smaller/thinner.

Is there a way you can compare the two wrt to mounting holes, or an
appropriate point?

If the centre is further away from the flywheel by 4-5mm I would say all
is ok.

4mm in 25 is ~ 1/6, which is near enough to 2 teeth in 11.

On Mon, 22 Jun 2020 08:18:33 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the trolling senile asshole's latest troll**** unread

08:18, you clinically insane 86-year-old trolling senile pest? STILL some
SIXTEEN HOURS of your insipid trolling ahead of you, eh, cretin? LOL

--
Richard addressing senile Rodent Speed:
"**** you're thick/pathetic excuse for a troll."
MID:

On 21/06/2020 23:18:33, Rod Speed wrote:


"Fredxx" wrote in message
...
On 20/06/2020 11:55:50, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but
has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is
central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

A different number of teeth implies the centre of the starter gear has
moved.

Not if the new teeth are smaller/thinner.

Which means the profile of the teeth will be wrong for the flywheel. You
don't seem to know anything about teeth, involute or otherwise.

For the avoidance of doubt:
https://en.wikipedia.org/wiki/Involute_gear

The alternative is going to be less efficient and very noisy.

"Fredxx" wrote in message
...
On 21/06/2020 23:18:33, Rod Speed wrote:


"Fredxx" wrote in message
...
On 20/06/2020 11:55:50, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has
an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is
central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

A different number of teeth implies the centre of the starter gear has
moved.

Not if the new teeth are smaller/thinner.

Which means the profile of the teeth will be wrong for the flywheel.

Wrong with thinner, as the new pinion is.

On Tue, 23 Jun 2020 14:54:26 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the trolling senile pest's latest troll**** unread

--
about senile Rot Speed:
"This is like having a conversation with someone with brain damage."
MID:

On 20/06/2020 14:49, Dave Plowman (News) wrote:
In article ,
newshound wrote:
On 20/06/2020 12:22, Tim+ wrote:
Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)


Whilst the drive may be central isn‘t there still the possibility that the
axis of the new motor is 2mm further away from the flywheel axis? If not,
are the teeth on the flywheel and starter pinion deep enough to accommodate
meshing more deeply (by 2mm)?

Otherwise, I‘m stumped too. ;-)

Tim

At first I agreed with the "spacing" idea. But, normally the
bell-housing has a circular seating for the motor, and the matching
flange on the motor is usually co-axial with the bearings, although of
course it does not have to be. So, I'd start by looking to see whether
or not they look coaxial.

The mounting has a circular raised part with locates accurately in a same
sized machined hole in the engine. So all the fixing bolts do is prevent
fore and aft movement - they don't locate it side to side. And the starter
shaft is concentric to the entire mounting plate. The mounting plate is
made by the UK firm to adapt the Denso starter to an engine they don't
supply one for themselves. Like lots of classic cars. Basically the same
starter motor with a custom made mounting plate and the correct drive
pinion can fit a vast range of vehicles, old and new.

One of the clever things about the involute profile is that it still
meshes OK even if actual distance between centres is not quite right
(although you get a bit more sliding and hence wear).

So you can "squeeze in" extra teeth on the same centres, obviously at
least one set has to be a little bit thinner to avoid interference.

I'm not familiar enough with gear design to know whether you could get
away with it with this 22% difference, which sounds a lot. But, starter
gears are typically pretty sloppy to accomodate debris, they don't do
very much "mileage", and they still work after a lot of wear.

My guess is that the aftermarket starter has thinner teeth. They could
easily get away with that in "strength" terms by using a slightly higher
spec and therefore stronger material.

Yes - the teeth have a thinner profile. Other difference is the 'far' end
of the pinion has a flange which is part of the teeth. Which I suppose
would strengthen them.

Other thing is more teeth means the engine spins faster for a given motor
speed. Odd, since it is already a gear reduction type.


I think it's fair to say, as someone already has, that a starter motor
under good charge can produce a lot of torque. I have heard of friends
get the car to a garage on a starter motor.

So the engine gets turned 11 teeth per starter gear rotation and the
extra torque generated by the extra 2mm radial length is eaten up. A
faster engine turnover is what you get.

In article ,
RayL12 wrote:
Other thing is more teeth means the engine spins faster for a given motor
speed. Odd, since it is already a gear reduction type.


I think it's fair to say, as someone already has, that a starter motor
under good charge can produce a lot of torque. I have heard of friends
get the car to a garage on a starter motor.

So the engine gets turned 11 teeth per starter gear rotation and the
extra torque generated by the extra 2mm radial length is eaten up. A
faster engine turnover is what you get.

Gearing it up, ie 11 rather than 9 teeth, will result in a higher speed
but less torque.

--
*HOW DO THEY GET DEER TO CROSS THE ROAD ONLY AT THOSE YELLOW ROAD SIGNS?

Dave Plowman London SW
To e-mail, change noise into sound.

On 22/06/2020 16:06, Fredxx wrote:
On 21/06/2020 23:18:33, Rod Speed wrote:


"Fredxx" wrote in message
...
On 20/06/2020 11:55:50, Dave Plowman (News) wrote:
One for the engineers here.

The original Lucas starter motor on my old Rover has a 9 tooth pinion
measuring 25mm diameter, top of tooth to top of tooth.

Have bought an aftermarket replacement.

That is clearly marked as being for the correct make and model, but
has an
11 tooth pinion 29mm diameter. And a note saying that improves the
performance. Ie, not to worry about it being different.

Not fitted the new starter yet, but curious how different pinions could
mate OK with the same ring gear. The drive in all the motors is
central -
no offset to the centre of the pinion possible.

It's confusing my little grey cells. ;-)

A different number of teeth implies the centre of the starter gear
has moved.

Not if the new teeth are smaller/thinner.

Which means the profile of the teeth will be wrong for the flywheel. You
don't seem to know anything about teeth, involute or otherwise.


It's your ignorance which is showing. You can still have the same
involute profile for the contact face with a thinner tooth.

On 23/06/2020 16:48, Dave Plowman (News) wrote:
In article ,
RayL12 wrote:
Other thing is more teeth means the engine spins faster for a given motor
speed. Odd, since it is already a gear reduction type.


I think it's fair to say, as someone already has, that a starter motor
under good charge can produce a lot of torque. I have heard of friends
get the car to a garage on a starter motor.

So the engine gets turned 11 teeth per starter gear rotation and the
extra torque generated by the extra 2mm radial length is eaten up. A
faster engine turnover is what you get.

Gearing it up, ie 11 rather than 9 teeth, will result in a higher speed
but less torque.

Aye. Ye canna change the laws of physics, Captain!