Compression 71 240

[rtaylor]

Hi ya'll:

Prior to pulling the head on my motor due to a pinched head gasket from when I replaced the front cover due to a broken water pump bolt, where this all started, a compression test was taken. 175 across the board except for #5 which was 110 dry, 125 wet.

Do I need to yank the motor and pull the #5 piston? Or do I just do a head job? The shop is telling me they need to pull the motor and check the rings on #5. 25,000 original miles on the motor.

What to do? Thanks for the advice.

[dspillman]

HI Randy,

I'd be tempted to put air in #5 at TDC and try to determine where, if any air escapes.....Use ear/rubber hose test and listen at exhaust, at carb with throttle open, listen at front of cam cover, with valve cover off. Where is hissing the strongest?

Maybe a bent valve?

May not determine anything...Thinking out loud.

David

[LEB]

Also, have you checked your valve adjustment? It could be just a tight valve.

Happened to me.

Luck, Larry

[Arne]

Randy, the fact that the compression goes up (even a little) wet is normally a good indicator of ring problems. Whether sticky, broken or whatever. You might try simply pulling the head first to take a visual look at the bore, but if the rings are sticky you may not be able to see much.

[bpilati]

Just a thought here; is it possible that a small amount of solvent could be put in #5, then pull the coil wire and rotate the engine with the starter? Maybe it could work it's way into the rings over a few days or week. Then change the oil. Just an idea, never tried it, maybe it's stupid. Maybe add any engine flush to the oil at the same time. Brake cleaner is a great solvent, or carb cleaner.

[rtaylor]

Thanks for the responses guys. The head is off, so there is no way to run air for a leakdown test. I will wait for a report from the shop regarding the condition of the valves when they get to it. While its there, all brass valve guides will be replaced with steel guides. Arne, I agree with you on the wet/dry indication. If it is a stuck ring, the possibility is there that it wil get unstuck. I don't know how likely that is. But solvent was sprayed in the hole. I looked inside cylinder 5 and there is no scarring of the cylinder walls. But, on a side note, the tops of all of the pistons are really , really carbonized. Don't know how this could happen. It seems to me if the car was running rich that the extra gas would wash out the carbon. If lean, then no carbon would form. Is carbon deposited perhaps from leaky valves allowing oil to flow down into the chamber, or does it come from being pushed past the rings through oil pressure?

The owner of the shop, btw, thanks Stephan for the referral to Elvin at Z-Car Specialities in Upland. Seems to be quite knowledgable and honest. Quite a collection of Zs he has in his yard that no one has picked up.

Its hard to deal with an unknown qualtity such as a new mechanic who recommends needed (or un-needed as the case may be) repairs. I am always leery in case the plan of action is just a way for the mechanic to supplement his income...

[zbane]

Its hard to deal with an unknown qualtity such as a new mechanic who recommends needed (or un-needed as the case may be) repairs. I am always leery in case the plan of action is just a way for the mechanic to supplement his income...

Randy, it's always good to be careful, I'm heading into Small Claims Court for exactly the reason you have listed.

You do have the benefit, however, of having been recommeded to this particular shop by someone who genuinely knows his stuff, not to mention that this shop speciallizes in our line of autos.

Still, Caution is always needed, and second opinions (when available) are always good to get.

[JimmyZ]

But, on a side note, the tops of all of the pistons are really , really carbonized. Don't know how this could happen. It seems to me if the car was running rich that the extra gas would wash out the carbon. If lean, then no carbon would form. Is carbon deposited perhaps from leaky valves allowing oil to flow down into the chamber, or does it come from being pushed past the rings through oil pressure?

I just took a L-series motor apart and there was lots of carbon. Running rich will leave quite a deposit as will burning oil. Just sandblasted my old cast iron exhaust header and got the giant sheets of carbon/soot out. One side of the manifold had more deposits than the other which tells me that one carb was running richer. Raw fuel will not clean out the carbon. Running lean for a short time will burn off some of it but be careful not to overheat/melt anything. Pilots often lean an engine out momentarily to unfoul a plug during preflight.

When having your head redone insist on a three angle valve job like the factory did. Double check that they actually did a three angle job. Ask to see the head and parts before it is assembled. Check that they replaced and didn't just knurl the old guides. I had a shop shaft me once even though I specified three angle. They also billed for replaced guides but knurled all of them instead. Talk about pissed! This is an expensive thing to fix if any parts need to be replaced due to someone's negligence.

Jim