Hi all,

Would anyone who has used a petrol powered tool like a big garden
chipper believe the automatic (centrifugal/(petal?)) clutch to only
engage once you were a (fair?) bit above tickover?

I've taken the clutch off and everything is free and there are no
broken (but could be weak) springs but even on tickover it feels like
the clutch is fully engaged?

I will email the manufacturers and it could well be that the clutch is
only there to aid sub tickover revs, eg, *just* whilst being started
(so you don't have to pull start the entire mech), a bit like a
de-compressor?

Cheers, T i m

T i m wrote:
Hi all,

Would anyone who has used a petrol powered tool like a big garden
chipper believe the automatic (centrifugal/(petal?)) clutch to only
engage once you were a (fair?) bit above tickover?

I've taken the clutch off and everything is free and there are no
broken (but could be weak) springs but even on tickover it feels like
the clutch is fully engaged?

I will email the manufacturers and it could well be that the clutch is
only there to aid sub tickover revs, eg, *just* whilst being started
(so you don't have to pull start the entire mech), a bit like a
de-compressor?

Cheers, T i m


The only similar clutch I have experience of is the one fitted to
Suffolk Punch lawn mowers and this certainly had to be significantly
above tickover to drive the machine.

On Sat, 30 Jul 2016 23:31:35 +0100, Bob Minchin
wrote:

T i m wrote:
Hi all,

Would anyone who has used a petrol powered tool like a big garden
chipper believe the automatic (centrifugal/(petal?)) clutch to only
engage once you were a (fair?) bit above tickover?

I've taken the clutch off and everything is free and there are no
broken (but could be weak) springs but even on tickover it feels like
the clutch is fully engaged?

I will email the manufacturers and it could well be that the clutch is
only there to aid sub tickover revs, eg, *just* whilst being started
(so you don't have to pull start the entire mech), a bit like a
de-compressor?


The only similar clutch I have experience of is the one fitted to
Suffolk Punch lawn mowers and this certainly had to be significantly
above tickover to drive the machine.

Thanks for that Bob.

I wonder though if the difference there is that the clutch affects
it's drive (assuming you mean cutters and / or being self propelled)
whereas this clutch just drives the hammermill / flales / disk cutter
etc.

eg, This chipper isn't going to move if the clutch is engaged and you
wouldn't want your fingers anywhere near it if it was running
(internally).

So, the $100 question is is this particular clutch simply to leave the
engine output disconnected from the workings just while you start it
or should it also stay disengaged when it's ticking over.

I've since emailed the makers and am awaiting their reply.

Cheers, T i m

On 30/07/2016 22:24, T i m wrote:
Hi all,

Would anyone who has used a petrol powered tool like a big garden
chipper believe the automatic (centrifugal/(petal?)) clutch to only
engage once you were a (fair?) bit above tickover?

I've taken the clutch off and everything is free and there are no
broken (but could be weak) springs but even on tickover it feels like
the clutch is fully engaged?

I will email the manufacturers and it could well be that the clutch is
only there to aid sub tickover revs, eg, *just* whilst being started
(so you don't have to pull start the entire mech), a bit like a
de-compressor?

It sounds the springs are weak.

Can you check the spring pull needed for the clutch to engage and from
the weight of the shoes etc determine when the spring tension would be
overcome and so engage?

Are you sure the clutch doesn't bind in some other way? I don't know
what you mean by "even on tickover it feels like the clutch is fully
engaged".

Is it possible that the clutch is only to ensure that when the blades
are jammed you don't have the full weight of the engine on them in
self-destruct mode?

On Sat, 30 Jul 2016 23:56:49 +0100, Fredxxx wrote:

On 30/07/2016 22:24, T i m wrote:
Hi all,

Would anyone who has used a petrol powered tool like a big garden
chipper believe the automatic (centrifugal/(petal?)) clutch to only
engage once you were a (fair?) bit above tickover?

I've taken the clutch off and everything is free and there are no
broken (but could be weak) springs but even on tickover it feels like
the clutch is fully engaged?

I will email the manufacturers and it could well be that the clutch is
only there to aid sub tickover revs, eg, *just* whilst being started
(so you don't have to pull start the entire mech), a bit like a
de-compressor?

It sounds the springs are weak.

Can you check the spring pull needed for the clutch to engage and from
the weight of the shoes etc determine when the spring tension would be
overcome and so engage?

I've not measured anything technically yet but using two screwdrivers
I prized one shoe up and the springs felt pretty tough. There are
three clutch 'shoes' that slide in guides and three springs that go
between the ends of each. So, when levering one shoe you are only
stretching the springs on both ends by half what they would normally
do.

Are you sure the clutch doesn't bind in some other way?

It feels pretty free in all other aspects and the outer (with the V
belt pulley) turns freely with the engine at rest.

I don't know
what you mean by "even on tickover it feels like the clutch is fully
engaged".

We started the chipper and after letting it warm for a bit, ran the
engine at it's slowest speed (on the tortoise) and if you put say a
block of wood on the output pulley you couldn't stop it (eg, it wasn't
just 'drag' that was making it spin).

Is it possible that the clutch is only to ensure that when the blades
are jammed you don't have the full weight of the engine on them in
self-destruct mode?

Yes, I guess that is also possible. The sales blurb only mentions the
clutch re 'easy starting'. It would make sense however that if any of
the cutting / flail stuff seized (or was jammed), especially instantly
the clutch would ensure the engine wasn't also brought to a dead halt.
However, from what I have seen so far I think it would still stall the
engine, not allow it to tickover as I imagined and as I am familiar
with similar equipment.

Cheers, T i m

T i m wrote:
On Sat, 30 Jul 2016 23:31:35 +0100, Bob Minchin
wrote:

T i m wrote:
Hi all,

Would anyone who has used a petrol powered tool like a big garden
chipper believe the automatic (centrifugal/(petal?)) clutch to only
engage once you were a (fair?) bit above tickover?

I've taken the clutch off and everything is free and there are no
broken (but could be weak) springs but even on tickover it feels like
the clutch is fully engaged?

I will email the manufacturers and it could well be that the clutch is
only there to aid sub tickover revs, eg, *just* whilst being started
(so you don't have to pull start the entire mech), a bit like a
de-compressor?


The only similar clutch I have experience of is the one fitted to
Suffolk Punch lawn mowers and this certainly had to be significantly
above tickover to drive the machine.

Thanks for that Bob.

I wonder though if the difference there is that the clutch affects
it's drive (assuming you mean cutters and / or being self propelled)
whereas this clutch just drives the hammermill / flales / disk cutter
etc.

eg, This chipper isn't going to move if the clutch is engaged and you
wouldn't want your fingers anywhere near it if it was running
(internally).

So, the $100 question is is this particular clutch simply to leave the
engine output disconnected from the workings just while you start it
or should it also stay disengaged when it's ticking over.

I've since emailed the makers and am awaiting their reply.

Cheers, T i m

The more I think about this (dangerous I know!) I can't see why the
cutter mechanism should be allowed to run at tick over speed although no
load starting feature is a must have.
Once the cutter is rotating there must be the temptation to lob
something in, forgetting to increase the revs. This would almost
certainly jam the machine and stall the engine due to insufficient
stored energy in the cutter at low rpm and insufficient engine power
(esp. if petrol) at tickover to recover from the load.
To my mind a well designed machine should not start rotating until the
revs were close to nominal engine power.

I'd expect the engine to have a governor anyway so the user control
would be much closer to a binary switch between tickover and "ready for
work" I can't really see why it would want an analogue control of speed.

Bob

On Sun, 31 Jul 2016 10:50:38 +0100, Bob Minchin
wrote:

snip


So, the $100 question is is this particular clutch simply to leave the
engine output disconnected from the workings just while you start it
or should it also stay disengaged when it's ticking over.

I've since emailed the makers and am awaiting their reply.


The more I think about this (dangerous I know!)

;-)

I can't see why the
cutter mechanism should be allowed to run at tick over speed although no
load starting feature is a must have.

Ok ...

Once the cutter is rotating there must be the temptation to lob
something in, forgetting to increase the revs.

We tested this yesterday (on tickover) with some light brush in though
the 'shredder' bit and it just shredded it! ;-)

You can see one in action here (albeit on full power etc):

https://www.youtube.com/watch?v=vEmLZbyBDOk

This would almost
certainly jam the machine and stall the engine due to insufficient
stored energy in the cutter at low rpm and insufficient engine power
(esp. if petrol) at tickover to recover from the load.

Understood. The side cutter (up to 3.5" diameter wood) is basically a
400 x 12mm steel disk with a small cutout and blade on one side and on
the same shaft, 24 steel flales on a 3 panel steel frame. A picture
speaks 1000 words: ;-)

https://dl.dropboxusercontent.com/u/...hammermill.pdf

And yes, it confirms what you say above in that pdf:

"Another outstanding feature of our hammermill machines is the
centrifugal clutch. It is designed for easy no-load starting while of
offering operator and engine protection not available with a direct
drive machine. The clutch will also disengage if the machine is
overloaded. This allows the engine, flywheel, and rotor RPM’s to
quickly recover to full speed and complete the task at hand."

So, whilst that confirms the 'easy starting', 'safety shock load
fuse' and 'anti-stall' roles, it doesn't actually state the clutch
would be disengaged at std tickover. ;-(

To my mind a well designed machine should not start rotating until the
revs were close to nominal engine power.

Or at least a good bit above tickover. ;-)

I'd expect the engine to have a governor anyway so the user control
would be much closer to a binary switch between tickover and "ready for
work" I can't really see why it would want an analogue control of speed.

It has (like most mowers etc) that increase the throttle (often via an
'air flap' as the revs drop.

The only other thing we haven't really investigated is the slow
running on the B&S engine and if the slow running revs are stable and
slow enough. We have the manual for the engine so should be able to
check any setup steps offered in that.

Cheers, T i m

T i m wrote:

The only other thing we haven't really investigated is the slow
running on the B&S engine and if the slow running revs are stable and
slow enough. We have the manual for the engine so should be able to
check any setup steps offered in that.

Is this an old machine? Is it possible a bit of rust in the clutch is
making it much "draggier" than normal?

Tim

--
Trolls and troll feeders go in my killfile

Tim+ wrote:
T i m wrote:

The only other thing we haven't really investigated is the slow
running on the B&S engine and if the slow running revs are stable and
slow enough. We have the manual for the engine so should be able to
check any setup steps offered in that.

Is this an old machine? Is it possible a bit of rust in the clutch is
making it much "draggier" than normal?

Tim


Doh! Just re-read the thread from the start. I see you've already had the
clutch apart. Maybe just needs greasing. ;-)

Tim

--
Trolls and troll feeders go in my killfile

On Sun, 31 Jul 2016 12:46:05 -0000 (UTC), Tim+
wrote:

Tim+ wrote:
T i m wrote:

The only other thing we haven't really investigated is the slow
running on the B&S engine and if the slow running revs are stable and
slow enough. We have the manual for the engine so should be able to
check any setup steps offered in that.

Is this an old machine? Is it possible a bit of rust in the clutch is
making it much "draggier" than normal?

Tim


Doh! Just re-read the thread from the start. I see you've already had the
clutch apart.

;-)

To answer your first question I think it's 5+ years old but we have no
idea how much use it got prior ownership but I feel 'not a huge lot'.
I think it was more neglected than worn out (like, the bearings that
should be (according to the handbook, 'greased every 8 hours use' had
never been greased at all (inside the grease nipple / entry was
completely devoid of any signs of grease)).

So, I think the clutch pads are steel and the inside of the clutch
bell was slightly 'galled' but I think I'd expect that with a steel on
steel solution.

Maybe just needs greasing. ;-)

Well, I cleaned it up with some WD40 and although it says the clutch
hub is self lubricating (large oil-lite bush) and so shouldn't be
'lubricated', I did wipe a very fine smear of bearing grease inside
the bearing pre re-assembly just to see if it made any difference. It
didn't seem to.

I think we need to know what it is *supposed* to do before we can
determine if it is doing it or not (which was sort of my question).
;-)

Cheers, T i m

T i m wrote:


I think we need to know what it is *supposed* to do before we can
determine if it is doing it or not (which was sort of my question).
;-)


I must admit, like you I would expect the clutch to disengage at idle but
that's not the same as knowing how it's meant to work. I imagine you've not
got a lot of variables to play with. Idle speed, clutch spring strength and
friction. You've already said that the idle is very slow and it would be
odd for the springs to have lost their strength in 5 years of occasional
use. Might the "galling" be significant?

Tim

--
Trolls AND TROLL FEEDERS all go in my kill file

On Sun, 31 Jul 2016 17:09:58 -0000 (UTC), Tim+
wrote:

T i m wrote:


I think we need to know what it is *supposed* to do before we can
determine if it is doing it or not (which was sort of my question).
;-)


I must admit, like you I would expect the clutch to disengage at idle but
that's not the same as knowing how it's meant to work.

Quite. ;-(

I imagine you've not
got a lot of variables to play with. Idle speed, clutch spring strength and
friction.

That's about it Tim.

You've already said that the idle is very slow

Well, it seems to be but I think I'd like to re-visit that in general
to see what adjustments are available on that particular engine (re
throttle position / fuel - air mix etc). Unlike say an outboard or
motorbike where the tickover is simply set conventionally, these
things use the air pressure flap governor thing so it seems awkward to
set tickover. That said, once I read the engine handbook there may be
a procedure for disconnection that governor and then setting the
tickover without interference. ;-)

If the carb has been as poorly maintained as the rest of the machine I
wouldn't be surprised if it isn't way out of adjustment.

and it would be
odd for the springs to have lost their strength in 5 years of occasional
use.

Agreed, not but not impossible? Batch fault or something? It may be
that it is a Briggs and Stratton supplied clutch and / or I might be
able to get some more information on it, as we did with the Taper-Lock
bush that holds the main cutter / flywheel on the main shaft. [1]

Might the "galling" be significant?

Depending on how the metallurgy works at that level it could well
cause the clutch to 'hang on' later than it might before low rev / pre
stall disconnection but I can't see how it could impact how soon it
engages initially?

Cheers, T i m

[1] https://dl.dropboxusercontent.com/u/...Taper-Lock.jpg

(you can just see the main cutter blade and the pass-through slot on
the left)

http://www.linngear.com/part/s16-6/

Not sure if it's actually this make but it gives a good idea about how
it works and how you are supposed to deal with it.

I had to learn similar with the self centring bearings and the (cotton
covered Kevlar reinforced) drive belt. ;-)

https://dl.dropboxusercontent.com/u/...oodman%201.jpg
https://dl.dropboxusercontent.com/u/...oodman%202.jpg
https://dl.dropboxusercontent.com/u/...oodman%203.jpg
https://dl.dropboxusercontent.com/u/...oodman%205.jpg
https://dl.dropboxusercontent.com/u/...man%20belt.jpg

Steel on steel clutch? Or whatever was lining the plates has worn away
completely?

On Mon, 1 Aug 2016 11:54:55 +0100, GB
wrote:

Steel on steel clutch?

Yup, it looked and felt (hardness and weight) like it.

Or whatever was lining the plates has worn away
completely?

I think the 'shoe(s)' was(were) far too thick and solid for it(them)
to have ever had a lining.

And if that were the case, you might have thought the issue would be
the clutch slipping not gripping. ;-)

However, I think the role of this 'clutch' is more like a 'dog
(clutch)' than what we might traditionally consider to be a clutch,
with it's gentle slipping / gripping action.

I'm still waiting for a reply from the American manufacturers so that
might explain things better.

Cheers, T i m

On Sun, 31 Jul 2016 00:34:27 +0100, T i m wrote:

snip


Is it possible that the clutch is only to ensure that when the blades
are jammed you don't have the full weight of the engine on them in
self-destruct mode?

Yes, I guess that is also possible. The sales blurb only mentions the
clutch re 'easy starting'. It would make sense however that if any of
the cutting / flail stuff seized (or was jammed), especially instantly
the clutch would ensure the engine wasn't also brought to a dead halt.
However, from what I have seen so far I think it would still stall the
engine, not allow it to tickover as I imagined and as I am familiar
with similar equipment.

So, I got a reply from their engineer yesterday and it confirmed that
the 'clutch' is really only there for two things ... to allow easier
starting (not having to spin over all the chipper gear) and to protect
the engine in the even of a seizure within the chipper mech.

So that's good then as it means it's working as designed. ;-)

Thanks to those who offered thoughts. ;-)

Cheers, T i m

T i m wrote:
On Sun, 31 Jul 2016 00:34:27 +0100, T i m wrote:

snip


Is it possible that the clutch is only to ensure that when the blades
are jammed you don't have the full weight of the engine on them in
self-destruct mode?

Yes, I guess that is also possible. The sales blurb only mentions the
clutch re 'easy starting'. It would make sense however that if any of
the cutting / flail stuff seized (or was jammed), especially instantly
the clutch would ensure the engine wasn't also brought to a dead halt.
However, from what I have seen so far I think it would still stall the
engine, not allow it to tickover as I imagined and as I am familiar
with similar equipment.

So, I got a reply from their engineer yesterday and it confirmed that
the 'clutch' is really only there for two things ... to allow easier
starting (not having to spin over all the chipper gear) and to protect
the engine in the even of a seizure within the chipper mech.

So that's good then as it means it's working as designed. ;-)

Thanks to those who offered thoughts. ;-)

Cheers, T i m

Thanks for feeding back Tim.
I can tick this off my list of outstanding queries!
Bob

On Wed, 10 Aug 2016 19:46:09 +0100, Bob Minchin
wrote:

T i m wrote:
On Sun, 31 Jul 2016 00:34:27 +0100, T i m wrote:

snip


Is it possible that the clutch is only to ensure that when the blades
are jammed you don't have the full weight of the engine on them in
self-destruct mode?

Yes, I guess that is also possible. The sales blurb only mentions the
clutch re 'easy starting'. It would make sense however that if any of
the cutting / flail stuff seized (or was jammed), especially instantly
the clutch would ensure the engine wasn't also brought to a dead halt.
However, from what I have seen so far I think it would still stall the
engine, not allow it to tickover as I imagined and as I am familiar
with similar equipment.

So, I got a reply from their engineer yesterday and it confirmed that
the 'clutch' is really only there for two things ... to allow easier
starting (not having to spin over all the chipper gear) and to protect
the engine in the even of a seizure within the chipper mech.

So that's good then as it means it's working as designed. ;-)

Thanks to those who offered thoughts. ;-)

Cheers, T i m

Thanks for feeding back Tim.

You are welcome Bob, in fact, the answer came by email but in the form
of a .pdf and 'in response to several queries on this matter'
document. ;-)

The chipper has been since used and the reports are that it's working
very well. ;-)

I can tick this off my list of outstanding queries!

I did thank the tech guy for his reply and asked for further
clarification on greasing and the bearings.

According to the user handbook the bearings should be greased every 8
hours. However, upon stripping the machine / bearings it was obvious
the grease nipples had never been used (as the internal pathways
between nipple and bearing were devoid of any signs of grease).

The bearing and housing looks like this:

https://dl.dropboxusercontent.com/u/...oodman%203.jpg

And the (self centring) bearing out of the housing looks like this:

https://dl.dropboxusercontent.com/u/...oodman%205.jpg

You should be able to see that the grease would enter through the
nipple, go down into the groove in the inside of the spherical part of
the casting, go round the groove till it finds the holes in the
bearing outer and then pass though into the bearing itself. Except,
when you apply grease it just comes out between the bearing and
casting? Now, that either suggests the grease isn't getting to the
holes in the bearing (alignment issue), or that there isn't anywhere
for the grease to get out of the bearing so it finds the lest path of
resistance and comes out the sides. Maybe when the bearing seal lip
wears slightly, that will allow us to 'purge' the bearing with grease?

Or maybe the instructions are wrong and these (particular) bearings
are sealed for life?

I have read of people who regularly grease such (chipper / arb
machinery) bearings till they see grease coming out and others say
that if the bearing is sealed for life, that you can blow the seals
out by doing so (and maybe that's happening but they don't realise if
it's an inner bearing)?

Again, I'll await the official reply. ;-)

Cheers, T i m