Compression

[Joey Allen]

I want to do a compression check on the Ty I just bought. It has 137,000 miles on it, what are some numbers I should looking for to assure me that I have good compression. Thanks

Joey Allen
'92TY1635
TY401K

 

[Sy769]

Minimum compression recorded in any one cylinder should not be less than 70% of the highest cylinder and no cylinder should read less than 100psi

 

[Tydriver]

Its not so much the #'s that you get.. Its more the fact that they are close to each other. What I mean by that statement if you have cylinders at 120# and one at 80# then you know you have a problem.. I've read else where before that anything over 110# is good, some people suggest 120+ is good..

The main thing to keep in mind, most of the cylinders should be close to each other in #'s. This indicates that the engine is equally worn, if they are all low say 50-80# then expect a rebuild sometime soon. If they are all above 110#+ I'd say all things considered you are doing fine for the age on that engine.

Thats using the standard type setup to check compression.. Personally I prefer the LEAK DOWN tester myself. I think its a better setup. Problem is, its a little more labor intensive than the normal compression checkers and gives you more choices to locate the source of any leakage (if there is any).

 

[Lynn D. Brown]

Compression readings

Compression readings

Yes, what everyone said about consistency is very important. I wouldn't like to see any more than about 10 # different in the readings.

The actual reading can vary depending on how hot it is and the cam overlap, and even how well U do the test. But typically U can expect around 120-150 Lbs. Anything less than about 110 could either be showing wear or alot of cam overlap.

 

[Irid]

Generally 18-19 times the compression is a good ballpark value. So 150PSI is probably a good value on a syty (~8.3 to 1 compression).

Make sure you open the throttle when doing the check, and I'd recommend doing it with some sort of "jumpstart" pack in parallel with your battery to keep the consistency of the readings up from the first cylinder to the last; if you have a weaker battery the readings will start to go downhill and you'll get false readings.

 

[Falco]

Last time when I checked I got 155-160 psi in all of the cylinders. Engine has less than 55k miles on it...

HTH,

 

[Tooky]

Last time when I checked I got 155-160 psi in all of the cylinders. Engine has less than 55k miles on it...

My results were quite similar. 150-160 PSI in all 6. My motor has 35K on it.

 

[TurboManiacal]

I was going to say the #'s I've seen listers and post over the years have generally been around 150-165 for the good motors. When I had mine checked I showed around 150 for 5 cylinders and 50 for the last. That would explain the rod knock now wouldn't it?