Compression Check.

[Leeland07]

Question Gents and Ladies.

Compression, how much per cylinder, and how many percent do you allow before you look at it ascance and start thinking repair time. I have a number one at 60-65 PSI cold motor and dry, then about 70 PSI in 2 and three, also cold and dry, then 80-ish in number 4. Not a huge difference, but big enough to cause a bit of a rough idle down low and maybe a broken crank if a few variables fall into line. So what is your cut off? If this were an 8 cylinder, I would be off in a new direction, but a 4 is a little different in my thinking. What you folks got for ideas? I don't need diagnostics on WHY I have compression issues, just what you think as for IF it is a problem. Thank you folks! this forum is always a great source of entertainment and information for me. Thank you all !

 

[Leeland07]

Now why cant I post a picture? Any ideas Guys and Gals?

 

[Den N Ms]

You need a few more post to post pics.

 

[Mike Groom]

Anything under 100# is cause for concern, you either have ring problems or valve problems or both. I would do a teardown.

 

[Hobo,NC]

The gold standard is 20% so anything below 90 something is losing its ability to seal at an efficient level.

 

[jimtrs]

(quoted from post at 02:51:54 06/16/22) Question Gents and Ladies.

Compression, how much per cylinder, and how many percent do you allow before you look at it ascance and start thinking repair time. I have a number one at 60-65 PSI cold motor and dry, then about 70 PSI in 2 and three, also cold and dry, then 80-ish in number 4. Not a huge difference, but big enough to cause a bit of a rough idle down low and maybe a broken crank if a few variables fall into line. So what is your cut off? If this were an 8 cylinder, I would be off in a new direction, but a 4 is a little different in my thinking. What you folks got for ideas? I don't need diagnostics on WHY I have compression issues, just what you think as for IF it is a problem. Thank you folks! this forum is always a great source of entertainment and information for me. Thank you all !

A more meaningful test is done with engine warm. Min spec is 90, but they will run down lower. 60's & 70's will show loss of power and/or oil burning

You Say - Not a huge difference - WRONG. The difference between #1 and #4 is 15 -- 20 psi. (In the range of 20% -- 25% difference). Too much. Problem? - Yes, depending on what you're doing. If the numbers are valid, a rebuild is in your future

Broken crank? Because of the variance? - Doubt that would ever happen. Usually you get sick of the smoke / loss of power / changing of spark plugs / hard starting etc.

 

[Eman85]

Is it burning oil? Does it run OK? maybe do a leak down with the cyl on TDC so the valves are closed and use regulated air and see where the air goes. No oil useage most likely poor valve sealing.

 

[Leeland07]

(quoted from post at 06:59:30 06/16/22) Is it burning oil? Does it run OK? maybe do a leak down with the cyl on TDC so the valves are closed and use regulated air and see where the air goes. No oil useage most likely poor valve sealing.

OK, so I guess I DO have issues... interesting. Looks like you folks are calling 90-110 is the gold standard here. I was actually thinking I had a reasonable engine. it don't smoke, burns a little rich, but that is the carb I have yet to mess with, it idles reasonable at 500-600 and will pull unreasonably well in my guess. I move a 5000-5500 LB trailer with it regularly down a sandy drive and down the road about 4 miles to fill all the fuel tanks I have. (other tractor, diesel tank, and fuel cans for small motors around the place.) and starts fast ! I can't get off the button that quickly kind of fast. and oh, errr... sorry I did forget to say I just finished a head gasket on it. had a bit of water seep to the alternator corner. found rust and loose head bolts... The compression check was after that. My bad in not doing one before the fact...

I think I am going to run the poop out of it for a little bit and see if anything changes.

I think I need to make me a compression adaptor for this thing I can sneak under the gas tank.... :lol: