Is this true for an engine
 

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.

Is this true for an engine
 

stryped fired this volley in news:4fa97790-
:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress
on
lower end parts.


You're _supposed_ to get about 50% blow-by on that motor. It was
never intended to burn the gas in the cylinders, but rather, in the
exhaust where it creates that cool exhaust tone that motor is famed
for, along with the hyper-cool tailpipe flames it makes.

You shouldn't mess with leaky valves. You'll screw up the "street
coolness" of the vehicle.

LLoyd

Is this true for an engine
 

"stryped" wrote in message
...
SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

It happened to me on an old Ford 360. The blowby was intolerable after
installing rebuilt heads.

Is this true for an engine
 

On Wed, 15 Apr 2009 07:51:00 -0700 (PDT), stryped
wrote:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.

151,000 miles is still in the new end of most engines these days.

My Ranger (3.0)..a 2001 model passed smog yesterday with flying colors,,
better by far than the minimum requirements.

Now yours IS a Dodge...but 151k is only the half way point for most
engines.

Gunner

"Somewhere a True Believer is training to kill you. He is training with
minimum food or water,in austere conditions, day and night. The only thing
clean on him is his weapon. He doesn't worry about what workout to do---
his rucksack weighs what it weighs, and he runs until the enemy stops chasing him.
The True Believer doesn't care 'how hard it is'; he knows he either wins or he dies.
He doesn't go home at 1700; he is home. He knows only the 'Cause.' Now, who wants to quit?"

NCOIC of the Special Forces Assessment and Selection Course in a welcome speech to new SF candidates

Is this true for an engine
 

On Apr 15, 8:51*am, stryped wrote:
SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.

This is the point where you get out the bore gauges and start checking
against the factory specs in the manual. If you've got no scoring,
the bore size is in spec and there's no out-of-round or taper wear,
you should be OK. But without dropping the crank and looking at the
bearings and journals and measuring same, you've got NO idea how much
more wear, if any, you can get out of the thing. And if you go that
far, you might as well commit to a rebuild.

I would have started looking for a donor engine at the local U-Pull-
its, myself. They usually go for $300-400 around here. Heads are
usually $25 or so. Certainly cheaper than messing around with machine
shop rates.

Stan

Is this true for an engine
 

Lloyd E. Sponenburgh wrote:
stryped fired this volley in news:4fa97790-
:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress
on
lower end parts.


You're _supposed_ to get about 50% blow-by on that motor. It was
never intended to burn the gas in the cylinders, but rather, in the
exhaust where it creates that cool exhaust tone that motor is famed
for, along with the hyper-cool tailpipe flames it makes.

You shouldn't mess with leaky valves. You'll screw up the "street
coolness" of the vehicle.

It works even better if you can plumb an
old air pump out of a '68 Mustang into the
exhaust header.

Is this true for an engine
 

"stryped" wrote in message
...
SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Shouldn't be a probem if you have kept up with your oil changes. A lot of
people do this every day. But do you really need a valve job? Perhaps just
disassemble, decarb, lap and reseal.



Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.

Slight fluid seepage in not unusual in even a heath head. Lapping at home
may be a good idea. You can at least see how bad it might need a valve job.
But if you just lap them, keep each valve in it's original seat. It often
makes a difference.

Is this true for an engine
 

On Apr 15, 1:25*pm, "Tim" #__#@__.- wrote:
"stryped" wrote in message

...

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Shouldn't be a probem if you have kept up with your oil changes. A lot of
people do this every day. But do you really need a valve job? Perhaps just
disassemble, decarb, lap and reseal.



Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.

Slight fluid seepage in not unusual in even a heath head. Lapping at home
may be a good idea. You can at least see how bad it might need a valve job.
But if you just lap them, keep each valve in it's original seat. It often
makes a difference.

I had low compression on two cylinders, 90 on one and 95 on the other.
Would lapping raise the compression much? My manual says 100 is the
minimum PSI per cylinder

Is this true for an engine
 

stryped wrote:
SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.


Not modern engines. Crank and bearing materials, and even more so the
lubricants, make modern lower ends very beefy. I use to do rod and main
jobs frequently in the cars I had as a kid. Haven't done a bearing job,
nor had it done, in many decades. Don't worry about it. Do the valves.

Besides, that high compression only comes with full throttle. When you
are at less than full throttle, the BMEP is considerably reduced. So
unless you are driving full throttle all the time you are unlikely to
hurt lower end.

Is this true for an engine
 

"stryped" wrote in message
...
On Apr 15, 1:25 pm, "Tim" #__#@__.- wrote:
"stryped" wrote in message

...

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Shouldn't be a probem if you have kept up with your oil changes. A lot of
people do this every day. But do you really need a valve job? Perhaps just
disassemble, decarb, lap and reseal.



Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.

Slight fluid seepage in not unusual in even a heath head. Lapping at home
may be a good idea. You can at least see how bad it might need a valve
job.
But if you just lap them, keep each valve in it's original seat. It often
makes a difference.

I had low compression on two cylinders, 90 on one and 95 on the other.
Would lapping raise the compression much? My manual says 100 is the
minimum PSI per cylinder

-----------------------------------------------------------------------------------

Examine your cylinders carefully. Look for any vertical scoring, and measure
the wear just below the ring wear ridge, about 3/8" down in the cylinder. If
these look good you can probably assume the compression problem was in the
valves. Most likely it is.

If your valves are not to pitted to lap smooth, you will be fine. If not,
best to have them ground. Be sure to use a wire brush on a drill or die
grinder to decarb your seats, and a wire wheel on a bench grinder to buff
your valves.

Is this true for an engine
 

In article , Don Stauffer wrote:

Besides, that high compression only comes with full throttle.

???????

Is this true for an engine
 

stryped wrote in news:4fa97790-25a5-4b12-b06f-
:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.


It's not going to make any difference, or much anyway as to the lower end.
All engines since 1995 or so are designed with a minimum "as new" life of
150,000 miles on internal components. This is due to the emissions laws.
Having the head job done shouldn't be an issue.
Your motor is just now to that stage, so only now will it begin to actually
wear to any significant amount.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Is this true for an engine
 

Doug Miller wrote:
In article , Don Stauffer
wrote:

Besides, that high compression only comes with full throttle.

???????

Consider the restriction of the throttle plate . You're *NOT* going to get
full cylinder fill , and therefore maximum cylinder pressures at
part-throttle operation .
--
Snag
every answer
leads to another
question

Is this true for an engine
 

stryped fired this volley in news:59f024dc-
:

I had low compression on two cylinders, 90 on one and 95 on the
other.
Would lapping raise the compression much? My manual says 100 is the
minimum PSI per cylinder


That's just because you were testing the motor at cranking speeds. A
ten or fifteen thousandths gap in the valves won't matter at all at
15,000 to 20,000 rpm.

Lapping is just to make the valves look pretty while you have them out
of the motor.

LLoyd

Is this true for an engine
 

stryped writes:

I had low compression on two cylinders, 90 on one and 95 on the other.
Would lapping raise the compression much? My manual says 100 is the
minimum PSI per cylinder

That's outside of spec all right... I hope they weren't next to each
other; if so, did you inspect the head gasket while you were taking the
head off?

Is this true for an engine
 

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com writes:

stryped fired this volley in news:59f024dc-
:

I had low compression on two cylinders, 90 on one and 95 on the
other.
Would lapping raise the compression much? My manual says 100 is the
minimum PSI per cylinder


That's just because you were testing the motor at cranking speeds. A
ten or fifteen thousandths gap in the valves won't matter at all at
15,000 to 20,000 rpm.

The spec is for testing at cranking speeds. It is of course completely
true that the condition of the valves will matter very little after a
few seconds at three times the engine's red line...

Lapping is just to make the valves look pretty while you have them out
of the motor.

And to correct sealing problems in the valves, of course.

Is this true for an engine
 

Is this true for an engine
 

Joe Pfeiffer fired this volley in
:

(Doug Miller) writes:

In article , Don Stauffer
wrote:

Besides, that high compression only comes with full throttle.

I expect he meant high force or high pressure.


Joe, you're _really_ going to regret feeding this troll.

He'll sap the patience of Job, and make every 'right' answer given to
him sound like blather by the time he's done.

Just read some of his prior threads.

"Which way do you turn a right-handed screw to tighten it" might be in
the genre of his questions. When you tell him "clockwise", he'll ask
if you mean viewing it from the top or the bottom.

Just wait...

LLoyd

Is this true for an engine
 

Joe Pfeiffer fired this volley in
:

It is of course completely
true that the condition of the valves will matter very little after a
few seconds at three times the engine's red line...


One can hope.

LLoyd

Is this true for an engine
 

On Wed, 15 Apr 2009 07:51:00 -0700 (PDT), stryped
wrote:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.

There is an extremely small chance that a valve job MAY increse the
vacuum in the cyl enough to draw oil past weak rings, causing oil
consumption. USED to be a real consideration back when rings were
generally worn out, and cyls bell-mouthed, tapered, and out of round
by 60,000 miles or less.

Those days, thankdully, are behind us. Not at all uncommon to have
virtually no measureable cyl wear at 300,000km today. I've had engines
with more than that on them where you could still see the crosshatch
from the final cyl honing.

Don't waste your time and money doing a half-assed job. Lapped valves
will NOT maintain a seal long. Today ALL engines have at least a 3
angle valve job, with at least a 1 degree mismatch between the valve
and the seat to make a line contact, self cleaning seal.
Lapping cannot do this.

If you just lap the valves and put in a new set of head gaskets, the
gaskets are wasted when the valves fail, again.

To have the heads properly checked the valves come out anyway - and
they come apart to install the new valve seals.

Have them ground properly - both valves and seats, or just tow the
truck to the scrapyard and safe everyone a lot of headaches.

Is this true for an engine
 

On Wed, 15 Apr 2009 12:44:13 -0400, "ATP*"
wrote:


"stryped" wrote in message
...
SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

It happened to me on an old Ford 360. The blowby was intolerable after
installing rebuilt heads.

My guess is the engine was pretty well intolerable BEFORE replacing
the heads too. Yes - it DID happen occaisionally - but is not a common
issue today.

Is this true for an engine
 

Technically, no. What usually happens is with the increased efficiency
and power after a top end o/haul, people drive the engine harder,
enjoying the new performance. Result: marginal bearings from a lifetime
of infrequent oil changes can't handle it. bottom end failure.
JR
Dweller in the ellar

stryped wrote:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.


--
--------------------------------------------------------------
Home Page: http://www.seanet.com/~jasonrnorth
If you're not the lead dog, the view never changes
Doubt yourself, and the real world will eat you alive
The world doesn't revolve around you, it revolves around me
No skeletons in the closet; just decomposing corpses
--------------------------------------------------------------
Dependence is Vulnerability:
--------------------------------------------------------------
"Open the Pod Bay Doors please, Hal"
"I'm sorry, Dave, I'm afraid I can't do that.."

Is this true for an engine
 

Now yours IS a Dodge...but 151k is only the half way point for most
engines.

Dodge's engine were doing so good they decided to not install valve seats
and just cut them in the head. They needed something to fail. Gives
automotive machinists work, or you buy another car.
If you didn't overheat badly due to cooling system failure, the rings are
probably fine.
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty

Is this true for an engine
 

wrote in message
...

There is an extremely small chance that a valve job MAY increse the
vacuum in the cyl enough to draw oil past weak rings, causing oil
consumption. USED to be a real consideration back when rings were
generally worn out, and cyls bell-mouthed, tapered, and out of round
by 60,000 miles or less.

Those days, thankdully, are behind us. Not at all uncommon to have
virtually no measureable cyl wear at 300,000km today. I've had engines
with more than that on them where you could still see the crosshatch
from the final cyl honing.

Don't waste your time and money doing a half-assed job. Lapped valves
will NOT maintain a seal long. Today ALL engines have at least a 3
angle valve job, with at least a 1 degree mismatch between the valve
and the seat to make a line contact, self cleaning seal.
Lapping cannot do this.

If you just lap the valves and put in a new set of head gaskets, the
gaskets are wasted when the valves fail, again.

To have the heads properly checked the valves come out anyway - and
they come apart to install the new valve seals.

Have them ground properly - both valves and seats, or just tow the
truck to the scrapyard and safe everyone a lot of headaches.

Total bull****, top to bottom.

Is this true for an engine
 

In article , "Terry Coombs" wrote:
Doug Miller wrote:
In article , Don Stauffer
wrote:

Besides, that high compression only comes with full throttle.

???????

Consider the restriction of the throttle plate . You're *NOT* going to get
full cylinder fill , and therefore maximum cylinder pressures at
part-throttle operation .

I guess it depends on exactly what is meant by "high compression". The
compression *ratio* is invariant, determined *only* by the length of the
piston stroke. Compression *pressure* is certainly higher with a full cylinder
fill.

Is this true for an engine
 

On Wed, 15 Apr 2009 07:51:00 -0700 (PDT), stryped
wrote:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.


My experience, I did exactly that, pulled the heads, cleaned them
up, hand lapped the valves, and put on new valve stem seals, put heads
back on and I now had a rod knock. Guys I talked to said the bottom
end most likely had excessive clearance to start with and the better
valve seal and higher cylinder pressure now made I knock I could hear.
Local auto machine shop had a 10 week wait on crank grinding, I bought
a factory regrind and all was well.

OTOH, this was in a truck I had bought at auction, 90K miles and was
owned by the NJ/DE toll bridge commission so It most likely had
another 100K worth of wear sitting on the side of the road idling. Who
knows about oil changes.

If you are pulling the engine out, check the bearings, if you're doing
the heads with the motor in the truck then just try it. If you
maintained the oil you should be OK.

Thank You,
Randy

Remove 333 from email address to reply.

Is this true for an engine
 

Doug Miller wrote:
In article , "Terry Coombs" wrote:
Doug Miller wrote:
In article , Don Stauffer
wrote:

Besides, that high compression only comes with full throttle.
???????
Consider the restriction of the throttle plate . You're *NOT* going to get
full cylinder fill , and therefore maximum cylinder pressures at
part-throttle operation .

I guess it depends on exactly what is meant by "high compression". The
compression *ratio* is invariant, determined *only* by the length of the
piston stroke. Compression *pressure* is certainly higher with a full cylinder
fill.
Strange, but somehow I thought that compression ratio was determined by
a ratio of the volume (cylinder volume plus combustion chamber) at BDC
to the volume (cylinder volume plus combustion chamber) at TDC. Piston
cutouts also included of course. My diesel in my truck has similar
stroke length to many gas engines but a whole lot higher ratio, actually
21.1 to 1.

YMMV

Is this true for an engine
 

"George" wrote in message
...
Doug Miller wrote:
In article , "Terry Coombs"
wrote:
Doug Miller wrote:
In article , Don Stauffer
wrote:

Besides, that high compression only comes with full throttle.
???????
Consider the restriction of the throttle plate . You're *NOT* going to
get full cylinder fill , and therefore maximum cylinder pressures at
part-throttle operation .

I guess it depends on exactly what is meant by "high compression". The
compression *ratio* is invariant, determined *only* by the length of the
piston stroke. Compression *pressure* is certainly higher with a full
cylinder fill.
Strange, but somehow I thought that compression ratio was determined by a
ratio of the volume (cylinder volume plus combustion chamber) at BDC to
the volume (cylinder volume plus combustion chamber) at TDC. Piston
cutouts also included of course. My diesel in my truck has similar stroke
length to many gas engines but a whole lot higher ratio, actually 21.1 to
1.

YMMV

That IS correct. The confusion here is actual combustion pressure at normal
operating rpm will change greatly based on the throttle position.

Is this true for an engine
 

On Thu, 16 Apr 2009 01:19:33 -0500, "Tim" #__#@__.- wrote:


wrote in message
.. .

There is an extremely small chance that a valve job MAY increse the
vacuum in the cyl enough to draw oil past weak rings, causing oil
consumption. USED to be a real consideration back when rings were
generally worn out, and cyls bell-mouthed, tapered, and out of round
by 60,000 miles or less.

Those days, thankdully, are behind us. Not at all uncommon to have
virtually no measureable cyl wear at 300,000km today. I've had engines
with more than that on them where you could still see the crosshatch
from the final cyl honing.

Don't waste your time and money doing a half-assed job. Lapped valves
will NOT maintain a seal long. Today ALL engines have at least a 3
angle valve job, with at least a 1 degree mismatch between the valve
and the seat to make a line contact, self cleaning seal.
Lapping cannot do this.

If you just lap the valves and put in a new set of head gaskets, the
gaskets are wasted when the valves fail, again.

To have the heads properly checked the valves come out anyway - and
they come apart to install the new valve seals.

Have them ground properly - both valves and seats, or just tow the
truck to the scrapyard and safe everyone a lot of headaches.

Total bull****, top to bottom.


Believe (or not) what you want.

Is this true for an engine
 

On Thu, 16 Apr 2009 09:07:24 -0500, Randy wrote:

On Wed, 15 Apr 2009 07:51:00 -0700 (PDT), stryped
wrote:

SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

Or I thought about just laping the valves at home. I put fluid in one
of the heads and it seeped out slowly of every valve but one.


My experience, I did exactly that, pulled the heads, cleaned them
up, hand lapped the valves, and put on new valve stem seals, put heads
back on and I now had a rod knock. Guys I talked to said the bottom
end most likely had excessive clearance to start with and the better
valve seal and higher cylinder pressure now made I knock I could hear.
Local auto machine shop had a 10 week wait on crank grinding, I bought
a factory regrind and all was well.

OTOH, this was in a truck I had bought at auction, 90K miles and was
owned by the NJ/DE toll bridge commission so It most likely had
another 100K worth of wear sitting on the side of the road idling. Who
knows about oil changes.

If you are pulling the engine out, check the bearings, if you're doing
the heads with the motor in the truck then just try it. If you
maintained the oil you should be OK.

Thank You,
Randy

Remove 333 from email address to reply.

Most likely had antifreeze get into the oil and take out the bearings.
Nothing to do with the valve job.

Is this true for an engine
 

On Thu, 16 Apr 2009 09:39:58 -0500, George
wrote:

Doug Miller wrote:
In article , "Terry Coombs" wrote:
Doug Miller wrote:
In article , Don Stauffer
wrote:

Besides, that high compression only comes with full throttle.
???????
Consider the restriction of the throttle plate . You're *NOT* going to get
full cylinder fill , and therefore maximum cylinder pressures at
part-throttle operation .

I guess it depends on exactly what is meant by "high compression". The
compression *ratio* is invariant, determined *only* by the length of the
piston stroke. Compression *pressure* is certainly higher with a full cylinder
fill.
Strange, but somehow I thought that compression ratio was determined by
a ratio of the volume (cylinder volume plus combustion chamber) at BDC
to the volume (cylinder volume plus combustion chamber) at TDC. Piston
cutouts also included of course. My diesel in my truck has similar
stroke length to many gas engines but a whole lot higher ratio, actually
21.1 to 1.

YMMV
There is "theoretical" or "mathematical" or "static" compression
ratio, and then their is "Dynamic" and "effective" compression ratio.
Dynamic compression ratio is lower than theoretical - and depending on
cam timing can be significantly lower at low RPM. Effective
compression ratio is affected by the breating efficiency, AKA
Volumetric Efficiency of the engine as well as the "dynamic"
compression. Effective CR is higher at lower speeds than at higher
speeds, generally speeking.

Is this true for an engine
 

On Thu, 16 Apr 2009 09:48:32 -0500, "Tim" #__#@__.- wrote:


"George" wrote in message
.. .
Doug Miller wrote:
In article , "Terry Coombs"
wrote:
Doug Miller wrote:
In article , Don Stauffer
wrote:

Besides, that high compression only comes with full throttle.
???????
Consider the restriction of the throttle plate . You're *NOT* going to
get full cylinder fill , and therefore maximum cylinder pressures at
part-throttle operation .

I guess it depends on exactly what is meant by "high compression". The
compression *ratio* is invariant, determined *only* by the length of the
piston stroke. Compression *pressure* is certainly higher with a full
cylinder fill.
Strange, but somehow I thought that compression ratio was determined by a
ratio of the volume (cylinder volume plus combustion chamber) at BDC to
the volume (cylinder volume plus combustion chamber) at TDC. Piston
cutouts also included of course. My diesel in my truck has similar stroke
length to many gas engines but a whole lot higher ratio, actually 21.1 to
1.

YMMV

That IS correct. The confusion here is actual combustion pressure at normal
operating rpm will change greatly based on the throttle position.

Called "pumping losses" - a spark ignition engine (and very few
deisels) is air throttled - at reduced throttle settings the cyl only
partially fills

Is this true for an engine
 

wrote in message
...
On Wed, 15 Apr 2009 12:44:13 -0400, "ATP*"
wrote:


"stryped" wrote in message
...
SOmeone saif that doing a valve job on an old engine is a
gamble,becasue the increased compression will put increased stress on
lower end parts.

I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am
debating with having a valve job done or not. I will have it crack
checked and milled if necessary.

It happened to me on an old Ford 360. The blowby was intolerable after
installing rebuilt heads.

My guess is the engine was pretty well intolerable BEFORE replacing
the heads too. Yes - it DID happen occaisionally - but is not a common
issue today.

As I said, it is an old engine- 1970. I don't doubt that there was some
blowby before the job but it definitely increased after the job.

Is this true for an engine
 

Is this true for an engine
 

Gunner Asch wrote:

My Ranger (3.0)..a 2001 model passed smog yesterday with flying colors,,
better by far than the minimum requirements.


My Ranger 2.9 made 236,500 before it cracked a ring. Not bad for a 4x4.

Less than 200K if you change the oil, I'd feel like I was screwed.

Wes

Is this true for an engine
 

On Thu, 16 Apr 2009 12:22:57 -0500, George wrote:

wrote:

There is "theoretical" or "mathematical" or "static" compression
ratio, and then their is "Dynamic" and "effective" compression ratio.
Dynamic compression ratio is lower than theoretical - and depending on
cam timing can be significantly lower at low RPM. Effective
compression ratio is affected by the breating efficiency, AKA
Volumetric Efficiency of the engine as well as the "dynamic"
compression. Effective CR is higher at lower speeds than at higher
speeds, generally speeking.
Exactly, I was just "gently" trying to point out what seemed a major
mis-statement. Static is what is always stated in engine specs, but cam
timing plays a major part in dynamic CR. Ed Iskenderian had lots to say
about volumetric efficiency, but that was "back in the day."


Leaning towards the pedantic:-

Compression ratio is regarded as swept volume/unswept volume.

Pressure ratio is the end result under any particular working condition.

Pressure ratio is what counts.

Mark Rand
RTFM

Is this true for an engine
 

Mark Rand wrote:
On Thu, 16 Apr 2009 12:22:57 -0500, George wrote:


wrote:



There is "theoretical" or "mathematical" or "static" compression
ratio, and then their is "Dynamic" and "effective" compression ratio.
Dynamic compression ratio is lower than theoretical - and depending on
cam timing can be significantly lower at low RPM. Effective
compression ratio is affected by the breating efficiency, AKA
Volumetric Efficiency of the engine as well as the "dynamic"
compression. Effective CR is higher at lower speeds than at higher
speeds, generally speeking.

Exactly, I was just "gently" trying to point out what seemed a major
mis-statement. Static is what is always stated in engine specs, but cam
timing plays a major part in dynamic CR. Ed Iskenderian had lots to say
about volumetric efficiency, but that was "back in the day."



Leaning towards the pedantic:-

Compression ratio is regarded as swept volume/unswept volume.

I've always seen it as (swept volume + unswept volume) / unswept volume .

Pressure ratio is the end result under any particular working condition.

Pressure ratio is what counts.

Mark Rand
RTFM

Is this true for an engine
 

On Apr 16, 5:23*pm, Wes wrote:
Gunner Asch wrote:
My Ranger (3.0)..a 2001 model passed smog yesterday with flying colors,,
better by far than the minimum requirements.

My Ranger 2.9 made 236,500 before it cracked a ring. *Not bad for a 4x4..

Less than 200K if you change the oil, I'd feel like I was screwed.

Wes

Do 4x4's not last as long for some reason?

I have a 96 chevy truck with a 350 and is 4x4 that currently has
302,000. It was owned by my dad and ironically, had coolant in the oil
due to a head gasket leak at 200 xxx. Head gasket was replaced at a
Chevy dealer.

It does use the dex cool stuff. It seems like I read that the stuff
was designed not to hurt bearings as much as regular coolant but I may
be wrong.

Is this true for an engine
 

"David Billington" wrote in message
...
I've always seen it as (swept volume + unswept volume) / unswept volume .


And that is correct.

Is this true for an engine
 

"Randy" wrote in message
...
Most likely had antifreeze get into the oil and take out the bearings.
Nothing to do with the valve job.

No antifreeze, I can guarantee that.
Thank You,
Randy

You had something, a fresh valve job does not have the ability to create a
rod problem.