D12 rocker adjust studs too short
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=210624
Printed Date: 03 Apr 2026 at 9:57pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: D12 rocker adjust studs too short
Posted By: jjrosty
Subject: D12 rocker adjust studs too short
Date Posted: 03 Apr 2026 at 10:41am
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I acquired a D12 last year as a pile of parts. The rocker arm adjusting screws did not have lock nuts & the adjustment screws are too short for locknuts, they are bottomed out in the rocker arm. The push rods are the correct length 9.25” The possible causes are endless. What would be the best way to resolve this situation. I think B push rods are 9.8” long could I replace them? Any useful opinion for a fix would greatly be appreciated . ------------- If you always do, what you always did, You'll always get, what you always got |
Replies:
Posted By: DrAllis
Date Posted: 03 Apr 2026 at 12:28pm
| The adjustment screws should be long enough for a jam nut. So, get some that are long enough and the problem is solved. |
Posted By: steve(ill)
Date Posted: 03 Apr 2026 at 12:35pm
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are you saying the adjusting screws MIGHT be the right length, but they are screwed in 1/2 inch too far ? If that is the case, there should be a LOT OF THE SCREW sticking out of the rocker arm ??.. If you adjust the screw out so it looks "like a good location".. can you get the nut on and the pushrods are just 1/4 - 1/2 inch too short ?? Do the valve springs look like the valves are long enough sticking out of the top of the head ? Valves not compressed too much ?
not an exact science, but the ROCKER should set about perpendicual to the valve stem and the pushrod... just a visual check for "normal" rocker position. ------------- Like them all, but love the "B"s. |
Posted By: steve(ill)
Date Posted: 03 Apr 2026 at 12:56pm
here is a drawing from the "B" service manual.. Shows the rocker arm setting about horizontal.... You should visually be able to tell of your rocker is too far toward the pushrod or too far toward the valve... That would tell you which side the problem is on... assuming your adjusting screws are proper length to have the ball sticking out on the bottom and the nut installed on the top... ------------- Like them all, but love the "B"s. |
Posted By: jjrosty
Date Posted: 03 Apr 2026 at 4:33pm
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I’ve thought of that. Where would someone source longer rocker arm screws? ------------- If you always do, what you always did, You'll always get, what you always got |
Posted By: jjrosty
Date Posted: 03 Apr 2026 at 5:19pm
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my understanding is that the head was “rebuilt”. I’ve looked for specs on valve spring height, rocker screw length, rocker tower height etc etc. but have found nothing. I’m not sure what was used for the “rebuild “ ------------- If you always do, what you always did, You'll always get, what you always got |
Posted By: DrAllis
Date Posted: 03 Apr 2026 at 5:27pm
| You must have jam nuts on your adjusting screws to keep the valve lash setting locked to where you set it at (.015" cold). You say the screws are too short. So, you must have the wrong (too short) screws and are missing the jam nuts. I'm fortunate to have salvage yards not far from where I live. I guess if it was my problem, I'd just buy a complete used rocker arm shaft assembly from a salvage yard. D-10-12-14-15 engine parts should be all the same I think in this area. Not so sure parts from a B-C-CA might work too. |
Posted By: SteveM C/IL
Date Posted: 03 Apr 2026 at 6:00pm
| Are the push rods in the lifters or setting beside them? |
Posted By: steve(ill)
Date Posted: 03 Apr 2026 at 7:55pm
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look at the drawing above... is the HEIGHT of the PUSH ROD above the head ( valve cover face) about the same as the height of the valve SPRING above the head ???
SteveM has a good question ......... about seating the push rods correctly. ------------- Like them all, but love the "B"s. |