How to check compression on diesel engine

Brad in WI · May 30, 2008

What is the easiest way to check the compression on the diesel side of an MD. I know using a gauge for a diesel is a good start but how would I insert it into the injector hole and have minimum leakage. Any advice on this is good advice as I am stumped. I can check it on the gas side by threading into the spark plug hole and checking like that. I will not get a reading with out the diesel injectors in place though and they are removed currently.

Allan in NE · May 30, 2008

Down, fast and dirty.

If it's getting fuel and air but won't start, it probably has bad compression.

Allan

Anonymous-0 · May 30, 2008

keep the injectors in, close the decompression valves, check just like it was a gasser. Bleed off fuel beforehand.

the tractor vet · May 30, 2008

To do a proper comp. test ya have to remove the injectors clean the injector well and have the proper fitting that looks like a injector and use a new sealing ring and torque it in just like you would when ya install the injector. then you hook up your gauge and turn the engine over. Then move to the next hole.

Brad in WI · May 30, 2008

one would figure that

but how do I tell if the injectors are out now and I do not have an injection pump yet.

Brad in WI · May 30, 2008

is there another way I could check for compression? I am sure that I do not have anything near what I need to do it somewhat properly.

Janicholson · May 30, 2008

Find or make an adapter that will allow your Gas compression gauge to be placed in the Injector hole.
Leave the plugs in, set it to gas side operation and crank it All pressures will be equal in a closed system, so it will be as if the injectors are in. JimN

the tractor vet · May 31, 2008

The only thing you can check with out the proper tools is the comp. on the gas side ain't no other way . Go find and old injector and gut it and install a fitting into it then you can do the job wright.

TomA in CA · May 31, 2008

Cat does not use a compression check to diagnose engine problems. They recommend a leak down test. I made a leakdown tester from an air blowgun and 1/4" pipe fittings. Tee in a pressure gauge. Set the cyinder at TDC and put it in gear or lock the engine somehow. Pressurize the cylinder through the injector hole. I used the tip off of a gas compression gauge which fit on a 1/4" pipe nipple. You can easily hold it against 100 psi.

Use your compressor to presurize the cylinder to your max pressure. Shut off the air and see if it will hold. If air leaks try to locate where it is going. Intake or exaust manifold indicates valve. Into crankcase, piston or rings. Or into the dreaded cooling system may mean cracked head.

Tom

How to check compression on diesel engine

Brad in WI

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Allan in NE

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Anonymous-0

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the tractor vet

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Brad in WI

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Brad in WI

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Janicholson

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the tractor vet

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TomA in CA

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