Farm Equipment - Military surplus 3500 generator engine in a D21

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Military surplus 3500 generator engine in a D21

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=209644
Printed Date: 10 Jan 2026 at 3:00am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: Military surplus 3500 generator engine in a D21

Posted By: pirlbeck
Subject: Military surplus 3500 generator engine in a D21
Date Posted: 08 Jan 2026 at 10:51pm

I have spoken for a rebuilt military surplus 3500 engine with the intentions of putting it in a D21 with series ll conversion that I have had sitting here way too long waiting for me to rebuild an engine to put in it. I am aware that the timing cover, the front engine plate and hydraulic pump drive will need to be swapped from the D21 engine to the new engine.

I don't know if the rebuild engine has a crankshaft driven oil pump or the earlier cam driven oil pump, but will the oil pan on a 3500 engine with the crank driven oil pump clear the D21 front axle without modification?

This rebuilt engine also has a right angle tachometer drive coming out of the tach drive location on the block, so it either has the cam driven oil pump or some sort of stub tachometer drive.

I am also aware that I will need to swap a lot of the engine accessories, most of the fuel system, along with the rear engine plate and flywheel.

I would like to to look as close to "stock" as possible so I plan on using the D21 parts wherever possible.

Any other possible surprises that I may not be thinking of?

Thanks!

Replies:

Posted By: PeteMN
Date Posted: 08 Jan 2026 at 11:16pm

Steve Fisher probably knows as much about those military engine conversions as anyone. He sold a bunch of them.

Posted By: injpumpEd
Date Posted: 09 Jan 2026 at 8:20am

Strip it down to a long block, and go back with the D21 parts as needed. They are both the early style blocks.

-------------
210 "too hot to farm" puller, part of the "insane pumpkin posse". Owner of Guenther Heritage Diesel, specializing in fuel injection systems on heritage era tractors. stock rebuilds to all out pullers!

Posted By: Michael V (NM)
Date Posted: 09 Jan 2026 at 10:17am

I was gonna do this with my 220,, but,,with the help of this forum , hav pretty much figured out that it more than likely has the original engine,, so I'm jus gonna rebuild it..
That being said,, I now have one of these military rebuilds for sale,, still in the crate...

Posted By: orangereborn
Date Posted: 09 Jan 2026 at 1:52pm

if the engine conversation is about the unit Lad/orange knight had listed, this should be the engine tag.. Would not that tag be toward the end of the series? Thanks...Dale

Posted By: Kcgrain
Date Posted: 09 Jan 2026 at 2:32pm

If you want the original Allis Chalmers engine tag on the military block, we stock both the tags and the rivets so it looks original

Posted By: pirlbeck
Date Posted: 09 Jan 2026 at 2:40pm

injpumpEd wrote:

Strip it down to a long block, and go back with the D21 parts as needed. They are both the early style blocks.

We have put 2900 combine engines in tractors before, so I know there is a fair amount of parts transferring to be done.

Thanks for the help!

Posted By: pirlbeck
Date Posted: 09 Jan 2026 at 2:44pm

Michael V (NM) wrote:

I was gonna do this with my 220,, but,,with the help of this forum , hav pretty much figured out that it more than likely has the original engine,, so I'm jus gonna rebuild it..
That being said,, I now have one of these military rebuilds for sale,, still in the crate...

My block has a hole in it behind the hydraulic pump so there is no rebuilding it. When I bought the tractor it came with a short block that looks like it has sat outside with not head on it. My intention was always to just rebuild it, but as expensive as parts and machine work are I think this rebuilt engine will be a cheaper way to go.

Thanks for your input!

Posted By: pirlbeck
Date Posted: 09 Jan 2026 at 2:55pm

orangereborn wrote:

if the engine conversation is about the unit Lad/orange knight had listed, this should be the engine tag.. Would not that tag be toward the end of the series? Thanks...Dale

Yes, the engine is the one in the classified here listed by Lad.

Besides the factory style tag on the rear LH corner of the block, the picture also shows another tag farther forward on the LH side........maybe this tag has some rebuild SN or component information. If it is that late of production engine, would it likely have piston cooling jets in it?

Thanks for your help!

Posted By: pirlbeck
Date Posted: 09 Jan 2026 at 3:06pm

Kcgrain wrote:

If you want the original Allis Chalmers engine tag on the military block, we stock both the tags and the rivets so it looks original

I will keep that in mind, depending on how original it ends up looking. Can you stamp the tag?

Thanks!

Posted By: Michael V (NM)
Date Posted: 09 Jan 2026 at 3:20pm

pirlbeck wrote:

Thanks for your input!

Well,, a hole in the block don't leave much choice

mine still run,, although it's really tired,,

Posted By: pirlbeck
Date Posted: 09 Jan 2026 at 3:50pm

Michael V (NM) wrote:

pirlbeck wrote:

Thanks for your input!

Are you in New Mexico? I am going to be driving through there in a couple of weeks.
Well,, a hole in the block don't leave much choice

mine still run,, although it's really tired,,

Posted By: pirlbeck
Date Posted: 09 Jan 2026 at 5:24pm

orangereborn wrote:

if the engine conversation is about the unit Lad/orange knight had listed, this should be the engine tag.. Would not that tag be toward the end of the series? Thanks...Dale

Lad sent me a picture of the tag and as you stated, it is the same date of MFR and the same engine SN as your picture above. Is the date of MFG and the engine SN the original one from Allis when the engine was built? I would think it would be.

Anyone know what the A suffix means in the model number?

The other tag shows the rod and mains as being .010 & .010 and overhauled at OSMS, OREGON

Thanks!

Posted By: concretepumper
Date Posted: 09 Jan 2026 at 8:50pm

I have done this swap on 2 d21s and a 210, the ones I have swapped in all had the front crank shaft driven or 210 style oil pumps
As ed mentioned, I stripped the long block down and exchanged rear covers
If the motor is crank driven, you will need a deep 210 style oil pan and front cover
The deep oil pan does clear the front axle
One of the differences I found are the cranks do not have dowl pins for the flywheel, they have Japan cranks, and standard rods
One thing I would for sure check is the oil cooler, finding out the hard way, sitting in storage, the copper in the cooler had deteriorated and upon start up, mixed coolant with the oil
Other than that, pretty straightforward, I use one in a 210 pulling hot farm class

Posted By: DrAllis
Date Posted: 09 Jan 2026 at 9:56pm

The suffix "A" would mean it is a first generation 3000 series engine. This would mean the oil filters are positioned to run oil down the side of the block when you remove them and if equipped with an oil cooler (turbo'd engines) it is vertical in location right behind the injection pump. Typically, we would see them in D-21, 210 and 220 farm tractors. I don't think piston cooling jets would be there as the cam driven style oil pump didn't have enough GPM's for that feature, or maybe they blocked the jets with the blank main bearing shells? . The crankshaft driven pump was the same as a 7030/7050 tractor which the 7050 has piston cooling.