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: 04 Apr 2026 at 8:58pm
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. |
Posted By: jjrosty
Date Posted: 04 Apr 2026 at 8:31am
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I did find 2 push rods not seated. ( the screws were extra long). I’ve since fixed that & now all are short. ------------- If you always do, what you always did, You'll always get, what you always got |
Posted By: jjrosty
Date Posted: 04 Apr 2026 at 8:42am
A good friend & I came up with the following possible causes: Wrong rocker arms, Wrong valves, Worn cam shaft Worn cam shaft bearing, Too thick head gasket, Wrong rocker arm pedestal Wrong ,too short lifters, Wrong head The list is endless. At this point I’m not going to fire a parts canon at it. I think I will try & put the jam nuts under the rocker arm. It will be a little more difficult to adjust but should work. ------------- If you always do, what you always did, You'll always get, what you always got |
DrAllis wrote:Posted By: tbran
Date Posted: 04 Apr 2026 at 8:53am
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As the famous Chinese pilot Sum Ting Wong stated once : somethings major wrong here. I am thinking this is going to put some bad geometry on the valve train. ------------- When told "it's not the money,it's the principle", remember, it's always the money.. |
Posted By: steve(ill)
Date Posted: 04 Apr 2026 at 8:55am
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again, LOOK at the drawing... If you have room to put the nuts UNDER the rocker, then the adjuster screws must be long enough to fit ? Unscrew the adjuster and put the nut on the top... Look to see if the PUSH ROD HEIGHT is about the same as the VALVE STEM HEIGHT...... You have to narrow down what you looking at....I doubt the head gasket could be thick enough to cause this... Rocker are TOWERS could have been changed, but WHY ? Big question is are the push rods and valve stem sticking above the head ABOUT the same height.... if you look at the drawing.. the adjuster and push rod are PARALLEL on top of each other... also the rocker arm button is parallel to the valve stem.. neither is at a big angle.. that should also give you an idea of which side ( push rod or valve) is the problem.------- as tbran said, dont put everything i a BIND by getting the angles off..  ------------- Like them all, but love the "B"s. |
Posted By: SteveM C/IL
Date Posted: 04 Apr 2026 at 10:42am
| You got a basket case tractor so unless you know your stuff on said engine I question if you have the correct parts to begin with. |
Posted By: Les Kerf
Date Posted: 04 Apr 2026 at 12:01pm
Yup. I have never so much as touched a D12 but I have rebuilt several Model C engines; could someone have swapped B/C parts onto this engine thinking they re the same? Maybe they are, maybe not. I dunno
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Posted By: DrAllis
Date Posted: 04 Apr 2026 at 3:52pm
| The original post said: "there are no lock nuts and the adjustment screws are too short for lock nuts". Now we have jam nuts and are putting them on the underside of the rocker arms with the too short adjustment screws. |