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D12 rebuild

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hunter321 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Topic: D12 rebuild
    Posted: 13 May 2022 at 9:43am
I'm 15 and need help with a d12 rebuild information
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steve(ill) View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 9:57am
Good job on the new post Hunter..

Just break it down into specific questions on what your working on first - second....

Sounds like you need ONE piston and liner, but not sure if you have a 138 or 149 inch motor ?  When you get a chance to go look at the tractor, grab that motor serial number.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 10:03am
I will
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 10:07am
I was told that I needed to lapp the valves. How do I do it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 12:24pm
IF you set the head on a table , on its side , with the intake and exhaust ports pointing UP and you are looking at the valve heads..... you pour water or gasoline into the ports and look at the valve heads and see how bad they LEAK liquid into the combustion chamber... If you have excessive leaks you remove the valves and springs, wire brush the valves and the ports and seats......

then the "LAP" is actually polishing the VALVE face to match the head SEAT face to get a better seal... you put an abrasive paste on the mating faces and rotate the valve to "lap" it in... if the valves are REALLY bad, then the seat has to be "CUT" with a grinding wheel or steel cutter to get it close enough to "LAP". ..... here is an idea.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DrAllis Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 1:23pm
Who told you to 'lap" the valves ???    If there is a compression problem, verified by a compression test, while the head was still on the engine, you need to GRIND the valves and seats. You cannot do this, unless you are a machine shop with all the valve grinding equipment that it takes to do such a job.  So, let's have the whole story. Is the cylinder head off or on the engine ????????
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PaulB Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 1:48pm
Get yourself a GENUINE Allis Chalmers service manual. A parts book is also very helpful. As mentioned there are differences in those engine depending on the serial number and what might have been done previous to you. You need to properly asses what you have to know what you need. 
If it was fun to pull in LOW gear, I could have a John Deere.
If you can't make it GO... make it SHINY
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 4:10pm
I was given this tractor by one of my moms friends and it hadn't run in years the engine was seized from water damage. When we took the engine apart only 1 pistion was stuck. We pulled all 4 honed 3 and have to pull the fourth. The head is currently at my house disassembled and the rest of the tractor is still at my moms friend's house. One of my dad's friends told me to lap the valves. I haven't but the valves are out of the head
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 13 May 2022 at 4:26pm
since it is already disassembled... you would normally clean the valves, do a little lapping and see what the seat looks like....if you hold one in and pour gas thru the port as mentioned, you can see if the "lap" is working or not... Normally a visual check can tell.

I would imagine your friend said to "LAP" , just as a standard CHECK when you have everything disassemble... to verify the seat is OK.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DrAllis Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2022 at 7:38am
If that's the plate of doo-doo you've been handed, the valves should all go in the same exact location as they came from.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 16 May 2022 at 12:02pm
This is what I found on the head.    M4831-1. B21m
I think
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 9:02am
I dont think the head number will help much.. You need the MOTOR number on the back edge on the left side.... 10- xxxx  or 12- xxxx  ............ and verify the piston diameter to prove that it has not been changed from factory parts. ... since you only want to replace ONE of the pistons, it needs to MATCH the other three.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 12:48pm
So I need the number on the engine and the number on the piston
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 3:50pm
not a piston number... just measure what the diameter is.... 3- 3/8 , 3- 7/16 ,  3- 1/2 inch ... ??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DiyDave Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 5:24pm
Image result for allis chalmers d 12 serial number location
Serial number stamped into the flange where the engine and transmission meet on the left side of the tractor.Jul 17, 2017
Type: Row-Crop tractor

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JK in Pa Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 5:36pm
If you can match the piston number you are good to go.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2022 at 8:07pm
John has a good point.. You have the other 3 pistons out of the motor... Look at the bottom side and see if there are any casting numbers...But still verify the motor serial number and piston diameter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2022 at 1:58pm
I'll check the diameter later.
I found this on the piston
I think it said
GE385.   Either a 5 or a s
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2022 at 10:01pm
The diameter is 3.47 in
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DiyDave Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2022 at 4:36am
Originally posted by hunter321 hunter321 wrote:

The diameter is 3.47 in

Sounds like a 149 C.I. engine.  IF that is an s, standard, not bored...Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2022 at 10:06am
where would i be able to find a pistion and sleeve.
diamiter is 3.47 in

also what sight has the best prices on engine parts. if i can i want to get the parts for one store but if some are cheaper elsewere i will use two sights


Edited by hunter321 - 20 May 2022 at 10:27am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2022 at 1:24pm
Should I look at a tractor salvage yard
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2022 at 9:44pm
It would sure be best to get a piston that matches the other 3.  That will keep the motor balanced and run smooth... If you cant find a "match" then your either stuck buying 4 pistons , or miss matching the 3 + 1 and see what happens..

again, your piston should be something like 3.495 if it is a  3- 1/2 inch BORE in a 149 motor......  if it really measures 3.470  ... thats ODD.... What does the cylinder bore measure ?

 if you MOTOR serial number is 10 - xxxxx then it would be a 138 inch motor and the bore would be 3-3/8 inch ( 3.375) ..... so the piston would be about 3.37 inch


Edited by steve(ill) - 24 May 2022 at 9:54pm
Like them all, but love the "B"s.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 8:14am
I'll take the piston to the tractor shop as well to make sure the measurements are correct
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 8:19am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 8:20am
The markings I found on the piston
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 9:07am
Hunter, i am not familiar with the FACTORY design on the  D12 piston... But MOST allis pistons are not domed like that. You may have an aftermarket piston already.. Maybe someone more familiar with the piston will chime in here....






Edited by steve(ill) - 25 May 2022 at 9:07am
Like them all, but love the "B"s.
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hunter321 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 9:53am
the top of the pistion is not domed
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 10:02am
so thats a shadow on top ?  The piston is FLAT or does it concave DOWN ( dished in ).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hunter321 Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2022 at 10:35am


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