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MEP-831 Compression Test

zapp

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Hello - new member. I am in the process of acquiring an MEP-831 and noticed in a lot of the threads reference to engine compression checks to verify engine start/run. I looked through the TM's but didn't see steps on how to test. Did I miss it, or is this so fundamental it's not documented? Never done one on a diesel engine so just looking for any guidance. Thanks!
 

zapp

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Ohio
I download the ones in the TM forum for the MEP-831a (TM 9-6115-639-13&P, TM 9-2815-257-24, and MEP-831A-OPERATOR-UNIT-AND-DIRECT-SUPPORT-MAINTENANCE-MANUAL-INCLUDING-REPAIR-PARTS-AND-SPECIAL-TOOLS-LIST-TM-9-6115-639-13P), and searched for "compression". Nothing really came up. I am just trying to understand where/how to test to determine if compression is okay. Assuming I can get a test kit at Harbor Freight.
 

Ray70

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I doubt the Harbor freight Diesel compression tester will work for you right out of the box. I'd be very surprised if it comes with an appropriate adapter to go in place of the Yanmar injector.
 

Ray70

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I just took a quick look as well, I don't see anything in the engine TM's as far as procedure , special tools or acceptable readings for compression.
All I found was "check for leaking valves" and "check for leaking head gasket"
Essentially you need to remove the injector and find / fabricate an appropriate adapter to adapt it to a pressure tester, most of which use 1/4" NPT threads on the gage fittings and quick connect fittings.
Most other mil. diesels seem to need a min. of 325 PSI when cranking them dry.
I'd assume the 831 would be in a similar range?
 

2Pbfeet

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Mt. Hamilton, CA
I just took a quick look as well, I don't see anything in the engine TM's as far as procedure , special tools or acceptable readings for compression.
All I found was "check for leaking valves" and "check for leaking head gasket"
Essentially you need to remove the injector and find / fabricate an appropriate adapter to adapt it to a pressure tester, most of which use 1/4" NPT threads on the gage fittings and quick connect fittings.
Most other mil. diesels seem to need a min. of 325 PSI when cranking them dry.
I'd assume the 831 would be in a similar range?
Yanmar lists a special tool, TOL-97190060, but I can't find a compression number or a procedure in any of the Yanmar technical or service manuals that I have. The tool seems to be readily available online from several vendors, but not inexpensive.
IMG_1437.jpeg

Also mentioned in a thread by @AfghanVeteran2010;

All the best,

2Pbfeet
 
Last edited:

Ray70

Well-known member
Steel Soldiers Supporter
2,648
6,150
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Location
West greenwich/RI
Yanmar lists a special tool, TOL-97190060, but I can't find a compression number or a procedure in any of the Yanmar technical or service manuals that I have. The tool seems to be readily available online from several vendors, but not inexpensive.
View attachment 938659

Also mentioned in a thread by @AfghanVeteran2010;

All the best,

2Pbfeet

Definitely a bit pricey!
For testing the 002/003 and 802/803's I just made "Dummy" injector bodies out of plain mild steel and tapped a 1/4" NPT thread in the end to screw my gage into. then put an O-ring groove in the bottom to seal it to the head.
It just bolts in place of the injector, which is exactly what the "Tool Set" appears to be.
The only similar adapter in the Harbor Freight kit is meant for a Detroit I believe, and probably way too big.
 

zapp

New member
4
2
3
Location
Ohio
I just took a quick look as well, I don't see anything in the engine TM's as far as procedure , special tools or acceptable readings for compression.
All I found was "check for leaking valves" and "check for leaking head gasket"
Essentially you need to remove the injector and find / fabricate an appropriate adapter to adapt it to a pressure tester, most of which use 1/4" NPT threads on the gage fittings and quick connect fittings.
Most other mil. diesels seem to need a min. of 325 PSI when cranking them dry.
I'd assume the 831 would be in a similar range?
Thanks for the info, makes sense. I can make an adapter so will take a look and check it out.
 
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