Wisemen needed, low compression

[Spoolin18]

Here is the story, I noticed my car will idle low when you come to a stop, I also noticed a slight miss at idle. The car is completly stock, never seen more than stock boost. It has 95,800 on the clock. I took it to my mechanic, he did a compression test and the results are as follows. #4=145, #3=142, #2=138, #1=110. It holds excellent oil pressure, better than any dsm I've ever seen and i've seen plenty of them. It holds about 18-20 inch HG vaccumm at idle and the needle will slowly snap back when you rev it. But I do have a prosport boost/vac gauge, not sure if that plays a part in it or not. I heard their gauges aren't the best in the world. It has good power. I tried the hill/stomp gas pedal scenario and it didn't smoke. It has sit a long time, probably put 20 miles on it since march. It smokes a little blueish-whiteish color at startup and will do so at idle until it is drove for a few minutes, the smoking goes away. My mechanic has narrowed it down to either a failing headgasket or a valve not sealing all the way on the #1 CYL. I meant to ask him if the compression test was done at a cold start, or warm. I'm thinking it might be a bad seal and when it gets warm, the seal soaks up the oil and the valve seals all the way, but I can't say for sure since I don't know how the test was performed. In any case, could it be rings? He was going to do a t-belt job, until we found this problem. The timming was off slightly, but when they adjusted it, it was still low. I need help and guidance. Should I tell him to pull the head and see for sure what the heck is going on? Anything I should do while the head is off? should the head/block be shaved or something? Could the piston rings be replaced with std. bore rings, and leave the block in the car. I need answers fast. Its been at his shop for a month and our paitence is wearing thin. Thanks.

 

[cruisintalonawd]

you can do that as long as the block doesn't need machined

 

[spoonman]

I would perform a leak down test on the #1 cylinder, this will pinpoint if the valves are not sealing or if head gasket/rings are the culprits. This is a really good write up on Leak Down tests. http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-test-vs-leak-down-test.html

 

[Spoolin18]

He said there was no 100% full proof way of pinpointing it down exactly. Which if you read the write up, it says exactly that. I'm in a pickle and looking for answers. I'm thinking of letting him do the t-belt job and drive it until it falls apart, then buy a built engine.

 

[saechao04]

+1 on a leak down test. I thought for sure my piston ring was broken so I pulled the motor and it ended up being valve stems.

 

[Spoolin18]

+1 on a leak down test. I thought for sure my piston ring was broken so I pulled the motor and it ended up being valve stems.

What was your symptoms?

 

[kp116]

A leak down test won't tell you if its your valve stem seals. You could perform a dry and wet compression test but if your vacuum is where it should be I wouldn't think it would be rings. I would perform a leak down and see if you try to pinpoint where it is leaking from.

 

[Spoolin18]

A leak down test won't tell you if its your valve stem seals. You could perform a dry and wet compression test but if your vacuum is where it should be I wouldn't think it would be rings. I would perform a leak down and see if you try to pinpoint where it is leaking from.

Thats what I was thinking, it holds good vaccum, good oil pressure. He has it narrowed down to two things, leaking head gasket or valve not sealing all the way. Should I go ahead and tell him to pull the head?

 

[spoonman]

If you do decide to pull the head the head gasket will have to be replaced, I suggest you use only an OEM composite head gasket, not copper or MLS. It would be wise to have the head checked for straightness and leveled if it is warped. Although I do not recommend reusing the head bolts that were on the engine, if you really do not have the cash they will work for a low HP engine. To check if the valves or the valve seats are the problem the head will have to disassembled and the valves must be "lapped" to to ensure they are sealing properly. If the procedure shows shows that there is compression loss due to deformed valve seat, the valves must be ground and the valve seat must re-cut. This could all cost a substantial amount of money $500-$875 for an old engine with deteriorating components. I suggest that you live with the problem (if possible) and wait to buy a new long block.

 

[Spoolin18]

He says it could also be a burnt valve. I think I wil take the advice someone gave on here and live with the problem and experiment on this engine for my next setup, tunnibg, boost, etc. In the mantime, I'm gonna be hunting a better mechanic. Thios guy is very smart, ase certified, takes classes every year to stay up to date. Had a 09 rx8 in his garage, but I don't think DSMs are his thing.

I think it has a mistimming issue, which is not allowing the valve to fully close on the number 1 cyl. @ TDC. The mechanic says it seems in line, I think its one tooth off.

 

[okm12346]

a burnt valve will cause more than just little start up smoking. You shoul pop the valve cover and see if the 4 valves are closed when any of the cylinders is at TDC

Check timing, turbo seals