compression testing

steviep · Jan 1, 2017

Does anyone know how to test the compression on a 2001 JD 4300 with a yanmah 3 cylinder diesel engine.

Texasmark · Jan 1, 2017

I never did on a diesel to answer your question. However, if mine start right up, especially on a 40 degree day, I don't worry about compression.

I'd guess you'd get a tester capable of 300 give or take pounds of pressure and use an injector hole with the other injectors removed and a good, fresh battery. I think compression numbers will be around 2-300 on a diesel......all an uneducated guess. Surely a google search for compression numbers on your engine or one similar would be available.

steviep · Jan 1, 2017

My problem is I seem to be getting a lot of air blowing out the valve cover air tube, trying to check if I have a bad head gasket or maybe a bad ring.

thepumpguysc · Jan 1, 2017

You can purchase a DIESEL compression tester on ebay or harbor freight.. guage must go over 300psi,,
A master compr. tester is around 100.00 has adaptors for most injectors and glow plug holes.. a compression tester w/ adaptors to go specifically into glow plugs costs around 50.00..

Texasmark · Jan 1, 2017

If excessive compression leaks by the piston rings on the power half of the 4 cycles, it will pressurize the crankcase and all things attached to it...aka valve train and force gasses out the crankcase breather.

I have done 3 things with diesels over the years on separate tractors:

Overhauled the engine because of hard starting as I mentioned when it wasn't bad enough weather for hard starting without assistance. Top end was shot. Ford 3000

Drilled and tapped a hole in the intake manifold and with a piece of garden hose, routed the pipe outlet to that manifold because the tractor was easy to start and pulled hard. Did not seem to need overhauling (JD 4010 6 cyl)

Used Power Services and Sea Foam chemical treatments to clean up the injectors and decarbonize the pistons and ring-ring grove interfaces which about solved the problem, including blue and black smoke out the tail pipe. Ford 2000

steviep · Jan 1, 2017

Properly call the dealer Tuesday, I have been trying to find someone local but not having good luck.

Jerry/MT · Jan 4, 2017

Texasmark said:
I never did on a diesel to answer your question. However, if mine start right up, especially on a 40 degree day, I don't worry about compression.

I'd guess you'd get a tester capable of 300 give or take pounds of pressure and use an injector hole with the other injectors removed and a good, fresh battery. I think compression numbers will be around 2-300 on a diesel......all an uneducated guess. Surely a google search for compression numbers on your engine or one similar would be available.

You'll need a guage with more like 500 psi capability for most diesels. 400-500 psi is generally good compression on a diesel.

Texasmark · Jan 4, 2017

Jerry/MT said:
You'll need a guage with more like 500 psi capability for most diesels. 400-500 psi is generally good compression on a diesel.

Would certainly be better. I hadn't read the numbers in awhile. I remembered it was at least 2x what gas engines are so I just added the rubber words, "I think". Grin

I have owned and overhauled tractor diesels over the last 37 years and still don't have a meter for it, nor have ever directly measured compression. Reason was other means found the smoking gun and I didn't want to fool with finding a meter and pulling the injectors and getting them purged when finished and all that. I did get a 0-5k oil filled gauge for measuring hydraulic pump pressure on my Fords however.