D2 Decompression not working

Check the valve push rod lengths. I rebuilt a D315 that had badly worn push rods and rocker arm seats and adjusters. The button and shaft look good on yours. Your valve stems may be too short also [ground].

so if i understand what rome thinks, the push rods being too short due to being reground to dress them. means the rocker adjusters are wound out enough so that the decomp mech doesnt contact them properly and the solution is check the cam followers(lifters, some engines have lifters others have followers) for correct length and replace any under size parts.

this does happen with automotive engines with hydraulic lifters the lifters become worn in there bores or collapse inside and the you dont get proper valve lift that could also be the issue. and the d315 has lifters according to my parts book.

a little wear everywhere can add upto a lot of wear. find your self a manual for the engine itself and get measuring.

Rome - good to know the button looks good. Thought it was after I saw both sides. Trainzkid - I have a manual but there are no specs for push rod length. It does give a spec of .120-.125 clearance between the rocker arm and the decompression shaft (I assume the flat section), and I'll measure that when I reinstall the rocker arms on the head.. I could measure the push rods but wouldn't know if they are the correct length or not. Also, for clarification, this is a D311 engine, not D315. Thanks for your input. If anyone else has any ideas, I'd appreciate hearing them.

I can whip the rocker cover off my 5U this weekend Bruce, and get some measurements.

im sure they would be similar internally and there would be details available somewhere. as they would have had a national stock number since they were military issue machinery if you google the push rod part number you maybe able to find a nsn listing which could have the details. you could also try the dealer they may still have that info if they can supply the part. they will have cam followers all pushrod engines do and the face that works on the cam must be slightly convex so they will rotate as they are worked by the cam lobe some things are just the same on all engines.

some thing else to check is are the push rods straight and thats easy roll the on a flat surface they should have no deviation bent rods will not give correct valve lift and excess rocker adjustment. that brings the question why did they bend is there a valve stem or valve spring binding. did something get out of time. if only someone had a brand new push rod and lifter they could measure for you you could compare yours.

so if i understand what rome thinks, the push rods being too short due to being reground to dress them. means the rocker adjusters are wound out enough so that the decomp mech doesnt contact them properly and the solution is check the cam followers(lifters, some engines have lifters others have followers) for correct length and replace any under size parts.

this does happen with automotive engines with hydraulic lifters the lifters become worn in there bores or collapse inside and the you dont get proper valve lift that could also be the issue. and the d315 has lifters according to my parts book.

a little wear everywhere can add upto a lot of wear. find your self a manual for the engine itself and get measuring.

[quote="trainzkid88 post=231955 userid=11838"]so if i understand what rome thinks, the push rods being too short due to being reground to dress them. means the rocker adjusters are wound out enough so that the decomp mech doesnt contact them properly and the solution is check the cam followers(lifters, some engines have lifters others have followers) for correct length and replace any under size parts


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I think there is an issue with the valve stem length. The length of the lifters and push rods will have no effect as the decompression shaft is in the head. Never assume all engines are the same internally. Older engines have the decompression lever lift the cam followers while later engines work on the rocker arms.

Check the height of the valve stems themselves and compare them to Neil's measurements if they aren't in the manual. Also as Rome said check for excessive play in the rocker arms.

"Upon inspection of the intake rocker arm, there is a slight gap between the button on the intake rocker and the decompression shaft when it is in run mode."

In run mode the button should be in the recess in the shaft with clearance and in start mode the button should be riding on the straight part of the shaft. If there is still a slight gap when the shaft is rotated so the button rides up on the parallel shaft then there is an issue with the valve, rocker arms or rocker arm bushes.

Regards

Phil

It's no problem Bruce, it's easy. Adding to what everyone else has suggested, the decompression shaft is probably snug in its journals right? otherwise you would have mentioned it, so we can rule that out
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