Is this true for an engine

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.

Total bullshit, top to bottom.

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.

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.

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.

Believe (or not) what you want.

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

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.

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

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.

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."

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

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

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

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.

And that is correct.

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