426 pistons
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=170745
Printed Date: 14 Oct 2025 at 12:33pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: 426 pistons
Posted By: Kevin210
Subject: 426 pistons
Date Posted: 01 May 2020 at 9:32pm
Would it hurt a 426 3700 engine to put 4.5 pistons in it vs the 4.25 pistons.
Not going to do a whole lot of pulling maybe just a few times a year if that much.
Thanks.
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Replies:
Posted By: DrAllis
Date Posted: 01 May 2020 at 11:08pm
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Hurt ?? Not sure what you mean by that. There are 426's out there in the pulling world with 4 7/8" pistons in them. You can't expect the engine to provide the hrs of service that it would achieve with OEM size components and you sure wouldn't farm with them, would you ???
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Posted By: injpumpEd
Date Posted: 02 May 2020 at 9:43am
Anytime you can increase the cubes to get up to the 466 range, it never hurts since all the green and red guys are already there, and then some usually lol!
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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!
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Posted By: Kevin210
Date Posted: 02 May 2020 at 8:51pm
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Where would you find some sleeves and pistons that are 4.75.
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Posted By: MACK
Date Posted: 02 May 2020 at 8:58pm
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Darton will make any size you want. MACK
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Posted By: DrAllis
Date Posted: 02 May 2020 at 9:04pm
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Seems like 5020 Deere pistons can be made to do what you want. Like Mack says, Darton sleeves or L.A. Sleeves.
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Posted By: Kevin210
Date Posted: 07 May 2020 at 9:41pm
And I was told that it would best if I used a counterbalanced crank and main bearing caps also otherwise the bigger pistons would more than likely eat up bearing pretty quick.
Any thoughts guys.
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Posted By: DrAllis
Date Posted: 08 May 2020 at 7:07am
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Counterbalanced crank better?? Yes. Necessary ?? Nope. Steel main caps ?? Girdle ?? Depends on how much HP/size or turbo you intend to run. Open RPM ?? You're not telling us much...……….
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Posted By: cms
Date Posted: 08 May 2020 at 5:56pm
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You have to bore block for 4 1/2" sleeves and pistons. I can get sleeves and pistons made to do anything like this. It's going to cost more than a standard sleeve kit. Have put 4 3/4" sleeves in that block with o-ring on and still run water. 4 1/2" may run a little warmer but I think it would be ok. 4 3/4 I would not recommend doing anything other than pulling.
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Posted By: Kevin210
Date Posted: 11 May 2020 at 8:24pm
I know Dr Allis but my 91 year old dad always told me you don't even tell your best your friend you're going to whip someone after they sucker punch because your best friend will tell someone and someone else and before you know it the guy that sucker punched you knows you're coming (so to speak).
So with all that said I don't want the most cubes or the most HP simply because in my opinion you don't always need the most to win as over the years you always see the green guys making mistakes during their run and they can be beat.
Now my pump has been worked on by scheids diesel and runs great in a no speed limit class which about the time I quit because I pulled the guts out of the motor and it finally pushed the valve cover cap off during a run and covered me with very hot oil so it's been sitting for many years.
However it isn't set up right for speed limit classes in my opinion and would need reworked for speed limit classes,i ran a switzer to4 turbo and a few other things have been done.
I now have a 3700 MK II motor for it that is in shop being hot tanked along with checking the crank,cam and the head.I just thought maybe some 4.5 pistons not 4.75 as I mentioned would give it some more grunt in speed classes and I would still be able to pull my rolling plow with it and not burn it up.
Sorry to be so long.
But here at home the green guys will try anything to keep me off the track in stock classes.
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Posted By: MACK
Date Posted: 11 May 2020 at 9:11pm
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Good luck. A lot has changed in the last 2 years, not to say about 2 or 3 before that. MACK
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Posted By: DrAllis
Date Posted: 12 May 2020 at 7:19am
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Well, spending a lot of $$$$$ to make more cubic inches to still be able to farm with it and the main reason (to begin with) was to do well at the County Fair is a new one on me. "Speed Limit" classes is still very vague. There is a huge difference between a 10 MPH class and a 12 MPH class. There are even some organizations that have 15 MPH classes. While the engine size is important, the proper turbo/injection pump (not always a Roosa)/ injectors and GEARING are more important than just cubic inches. If you don't have a gear that lets you come down the track just on top of the (proper size) turbo and then throttle up the farther you come, you're not going to do very well. Your 210 tractor has a perfect gear for 10 MPH and even at 12 MPH 6th gear isn't too bad. This is assuming you are limited to 3,000 RPM, which you don't say.
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