504 Diesel compression test

F-MM · Mar 17, 2018

What do you guys use for an adaptor to do a compression test on the MM diesels? One of our Vistas just doesn't run right, It was overhauled not that long ago, new rings and heads gone through completely, pump worked on and last summer had the injectors done too and it still has a limp to it so I better see what I have for compression. I don't have any adaptor that can work so I thought Id ask. I've thought of taking an old injector apart and trying to see if there's any way to connect to that? I don't think I can adapt to the energy cells unless I drill and tap one?? Any easy way that I'm missing? Thanks.

JK2 · Mar 17, 2018

You might swap two injectors and see if the issue moves. A non contact temp probe is nice to find which one isn't firing properly.

F-MM · Mar 17, 2018

Listening to the exhaust and cracking the lines one at a time but we can't isolate it. It actually sounds like it can come from any of them which I know sounds strange. That's why I'd like to know if I'm weak on compression on one. We set the lifters over again to make sure there was no tight one. There is barely any blow by when you pull the dipstick while running. I'm pretty good at making these run right but this ones got me wondering??

carvel minne farmer · Mar 17, 2018

(quoted from post at 19:14:41 03/17/18) Listening to the exhaust and cracking the lines one at a time but we can't isolate it. It actually sounds like it can come from any of them which I know sounds strange. That's why I'd like to know if I'm weak on compression on one. We set the lifters over again to make sure there was no tight one. There is barely any blow by when you pull the dipstick while running. I'm pretty good at making these run right but this ones got me wondering??

F-MM this is a long shot but, I had a cat diesel in an older kw. years ago that I bought at auction and found out why it went to auction! it had a miss like that we could not nail down to one cylinder, had experienced hd mechs look at it, nobody had any luck until this oldtime cat guy came along, listened to it, asked me for an oil squirt can, took the can and was squirting oil between the block and manifold, about halfway down the manifold oil shot up about 2 feet in the air :shock: shut down pulled the manifold and there was 2 gaskets, one old rotten burnt one broken to pieces and one new one! turn out someone had pulled the manifold for some reason cleaned up the block installed new gasket, forgot to clean the old one off the manifold installed it and and the fun started. maybe try squirting oil along the manifold at the block ?

STEVEKLS · Mar 18, 2018

put in ear plugs. take the exhaust manifold off on diesels and start it up. look witch cylinder it is. If they are all missing could be the key on the camshaft.

jimvw · Mar 18, 2018

Better check the lift on the camshaft. You may have a valve or two that is not opening as much as it should.

F-MM · Mar 18, 2018

Thanks for some good suggestions here, two of you mentioned the camshaft. I hadn't thought of that too much before. I know the valves seemed to open and close nicely when I checked the clearance last fall but I don't recall any not moving a full stroke back then, nothing that jumped out at me anyway. But the key thing, so if it were half worn off that would make the valves late and I suppose the pump too. I had tried moving the timing last fall while on the grain vac but it still sounded the same, just not a clear exhaust sound like the 504 should make, more like a sputter, at first it was more noticeable at higher speeds but I quit using it when it seemed to even sound that way at lower rpms and when you hit the throttle it really shows up as it's gaining RPMs.

J.A.R · Mar 18, 2018

Injection pump could be at fault too. My 670 Diesel did what you seem to be having problems with. If it hasent been touched it probably could stand to be freshened up. Just my.02

F-MM · Mar 18, 2018

That injection pump was gone through when we put in the rings and did the heads, that plastic retainer or whatever is in them was out so they did everything to it that it needed and it probably has only a couple hundred hours on it since. I even questioned them about if the pump could be failing when I had them rework all the injectors last summer and that didn't make any difference either. I didn't check the energy cells now but they seemed ok when the heads went on.

molinegb · Mar 19, 2018

Have drilled energy cell cap for compression check. Doesn't tell anything. Leak down test is proper way to check. More than likely rings,valve or head gasket. MM not known for cam issues except 585.

F-MM · Mar 19, 2018

What do you mean by leak down check. How do I verify that?

molinegb · Mar 19, 2018

Several you tube video's can explain it better than me.

F-MM · Mar 19, 2018

Thanks, I checked those out now too. I'll run some tests before I try anything else.

Joe Pro · Mar 23, 2018

F-MM.
Yes, get an extra energy cell cap and drill and tap for 1/4 mpt or what ever thread adapts to your compression adapter.

What exactly is the "limp" you are referring too.
I chased a noise down in a g900 and never found anything that completely satisfied me.

504 Diesel compression test

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