Compression Test results...kinda wierd...opinions?

Did you buy it to drive or strip down ?

Service and/or Italian tune-up plus drive some then maybe next winter see what the test looks like if you must and even then probably not get into a rebuild until it obviously needs it

 

Get her up to temperature and give her the beans. Then redo the test.

Might just have some build up.

 

Those numbers are probably okay. I don't think cleaners will affect the compression.

I would warm the engine up first. Then let it cool enough to work on it. Pull all the plugs out. Crank the engine for 7 seconds, for the test. Clean the plugs with a propane torch since you have them out.

Fantastic car. Congrats.

 

The lower numbers on bank 1 is likely because the timing is off.

 

Wonder how the numbers would be it tested in reverse order?

 

Beat me to it. That's exactly what was wrong with mine.

They reset the timing during the engine out and that fixed it completely.

 

Be careful guys. You are starting to sound like there is no point in doing a compression test because if it's off it's because the timing is off. So far the engine detectives have determined that bad compression = bad timing, carbon build up on valves, rust on valves, stuck rings,... Have I missed any. I guess a leak down could help thin that herd, unless the timing is off enough that the valves got bent a little. Doesn't take much.

All I'm trying to say is that bad compression = problem. From there it's speculation as to why w/o proper diagnostics. If you want to gamble on a guess, that's your prerogative.

 

Yes, of coarse it's speculation given the data that has been provided to us

99.9% of posts on this forum are via speculation

He did a compression test and provided the values. The cylinders of each bank are close to each other, relatively, with bank 1 being lower in value. That's the data that caused me to "speculate" my response

 

Just by reading the cold compression numbers alone, and seeing that all cylinders on the same side are close to each other but uniformly different from the other bank, I would also conclude (speculatively, I am not there doing the test) that there is a slight difference in cam timing from one bank (bank1) to the other.

I certainly would not tear the motor down reading these numbers. I suggest doing a leak down test while the engine is out and repeating the compression test AFTER verifying the cam timing.

$50 says bank 1 cam timing is 3 degrees out on one of the two cams.

 

As I recall, several times such numbers have been posted where bank 1 is consistently lower than bank two on a cold compression test, but other wise acceptability uniform. Is my memory failing or is there something too this? Dave, wasn't the case, more or less, with your 955 project car?

1 = 177
2 = 170
3 = 156
4 = 135

5 = 238
6 = 212
7 = 210
8 = 210

Was that a cam timing issue? I don't recall what you found re timing.

 

Yes - those are the values for my 95 project car. The timing was NOT consistent from side to side (but not too far off) - see values. And, the leak rate was greater on bank 1 (which to your point, has nothing to do with timing). But, my bank 1 compression results are not as close (cylinder to cylinder) as the OP
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Unlike car A there is no consistency in this compression test.


I or those directly under me have done compression tests on hundreds of 355s and I concur it is most likely a cam timing issue.

As far as those concerned about it being cold, how many here have done back to back tests on 355s with good motors cold and hot? Have a look at the ring gap specs sometime. Cold or hot if the compression is no good the motor is junk.

 

Brian - thank you for confirming this. This was my thoughts, although I've only done the cold vs hot (warm) experiment once.

What about WOT or closed? I did this again, one time, and did not see a difference, but as a SOP, I now do WOT.

 

Some types of cars it makes a difference. Most it does not.

 

When you pull the motor, before taking stuff apart, check your current timing. You could then correct and check again before even installing new belts.

 

Much appreciated.

 

Well, the leak down would (should) shed light on whether its timing related. I would certainly do that before taking the engine apart. Please post results when you have them.

Also, I do agree with Dave that you might consider checking timing before taking the old belts off.


I was using Dave's data as an example of my observation that the lower compression numbers seem to commonly occur on the 1-4 bank, as I recall.

I also recall that the 1-4 header tends to fail first. And it has been said by one of the pros here that 1-4 tends to run hotter.

Why is it always (or commonly) the 1-4 bank?

 

John, if you recall, my situation one bank had wet heads and the other dry (combustion chamber). I think the wetness of the one bank allowed for less carbon than the other but I'm not 100% certain I'm remembering that correctly.

Given the OP's bank 1 numbers today, it all seems very obvious to me.

 

#2 runs the hottest followed by #7. Every motor ever designed has hotter and cooler cylinders.

I do not believe a 355 motor should ever be removed without a leak down first. Compression tests are fine and a good diagnostic tool but will never replace a leak down test. A leak down test shows much more about basic condition. When embarking on a major service I find no value in knowing about the status of cam timing. I want to know if there is enough motor left to justify tuning.

 

These are some temperature measurements I made about 7 years ago. Car was idling at operating temperature. Temperature numbers are roughly where the measurement was made on each header. I don't recall if I used infrared or if it was a contact pyrometer. Not very scientific and a number of variables involved (location on pipe, could have some cylinders running lean etc.).

I'm thinking (hoping?) cylinders #1 and #2 are much hotter due to the proximity of heat reflecting material.

NOTE: photos of headers were taken during installation after ceramic coating and not during temperature tests.
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Temperatures at idle mean nothing and a sample of one car means very little more. Ask anyone who has been working on 355 since 1995 which tubes burn out first and which valve guides go bad first. I knew a lot of guys in the earlier days who never even tested any other cylinders.