Compression question - High on two cylinders

569 Views 7 Replies 6 Participants Last post by vigman, Jan 31, 2011

tonyw

Discussion Starter · Jan 27, 2011

I bought myself a "kit" car in December. It's a '91 with 79K original miles on it. The guy I bought it from had removed the engine and trans to replace the EFI harness. I got all the parts, labeled and bagged along with the engine and trans.

I also have my sons '93 with 60K original miles on it. He lost it on ice in Oregon and ping-ponged off the jersey wall on both sides of I-5. Lots of suspension and frame damage but no engine or trans damage.

I was thinking of taking the engine out of the '93 and putting it in my '91. Then I thought the '93 would be worth more complete.

I put the trans on the '91 engine and installed the starter so I could do a compression check to see if the engine that came with the car was OK:

Firewall
(5) 170 (6) 160
(3) 220 (4) 150
(1) 210 (2) 185

The factory manual says "normal" is 186 and minimum is 142 with a max variance of 14 between cylinders.
The engine has been out of the car for at least two years. It has oil in it (clean).

Thoughts on the two high compression cylinders? The low ones?

Thanks!

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salvadoran300zx

· #2 · Jan 27, 2011

I would take out all the plugs and spray some carb cleaner in it and rotate the engine by hand first and then with all plugs out give it a couple of cranks just to get any possible water or residue of the carb cleaner out.

Start it (if it starts) let it warm up and re-test with all plugs out to keep your battery power at top shape through out the test.

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tonyw

Discussion Starter · #3 · Jan 27, 2011

It's not in the car so I can't start it. I did the compression test in my garage, on a stand.

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salvadoran300zx

· #4 · Jan 27, 2011

most likely it's got sticky lifters and un-lubricated rings... install it, it should be good to start with those numbers and then sort itself out

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dumbestone

· #5 · Jan 27, 2011

Low numbers as Sal says.
High numbers would seem to indicate there's either liquid or a lot of carbon inside. Pull the plugs and crank it to see (not looking directly over th hole) if anything shoots out.

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jzack

· #6 · Jan 27, 2011

2nd on the sticky rings. I've had good success in a similiar situation as yours by filling the offending cylinders with about 1 inch of ATF and letting things sit for 3-4 days (or more). It won't hurt anything, just be sure to use a turkey baster or similar to get all the ATF out before cranking (don't want any hydro locking issues). Good idea to also crank the engine with a rag over the spark plug opening to "ping" out anything else in the cylinder - can do that once the engine is back in the car.

Was very happy with my outcome - one example: 120 psi to 195 psi.

FYI1: I'm sure something like MMO would work too, but ATF is used by old time engine restorers for things like this -- so went that way...

FYI2: Always a good idea to do this when running a compression check with an low reading. Put a teaspoon of oil in the offending cylinder and re-test. If compression doesn't change -- very likely its NOT the rings. In this situation that means the ATF trick probably won't work.

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maxdoc

· #7 · Jan 29, 2011

tonyw said:
I bought myself a "kit" car in December. It's a '91 with 79K original miles on it. The guy I bought it from had removed the engine and trans to replace the EFI harness. I got all the parts, labeled and bagged along with the engine and trans.

I also have my sons '93 with 60K original miles on it. He lost it on ice in Oregon and ping-ponged off the jersey wall on both sides of I-5. Lots of suspension and frame damage but no engine or trans damage.

I was thinking of taking the engine out of the '93 and putting it in my '91. Then I thought the '93 would be worth more complete.

I put the trans on the '91 engine and installed the starter so I could do a compression check to see if the engine that came with the car was OK:

Firewall
(5) 170 (6) 160
(3) 220 (4) 150
(1) 210 (2) 185

The factory manual says "normal" is 186 and minimum is 142 with a max variance of 14 between cylinders.
The engine has been out of the car for at least two years. It has oil in it (clean).

Thoughts on the two high compression cylinders? The low ones?

Thanks!

Considering this is a cold engine on a test stand that has been sitting ....here is my humble opinion... 1, 2 & 3 have carbon buildup. 5 & 6 are OK for a test stand check. As for #4 see if the compression numbers change with a shot of oil in the cylinders.

MaxDoc

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vigman

· #8 · Jan 31, 2011

What do the plugs look like that came out of those holes ( assuming plugs were in the head ) ..

Shoot the ATF in...
Clean it out 3 days later...
Charge battery ( have to stay ~300 rpm )
Throttle plates open

try again

Mike

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