Crank counterweight November 29, 2022 12:58PM
In process of getting a plan for a no rpm limit motor,currently crank is not counterweighted.is this nessisary?
Engine will have a spark ignition
Will have 4.75 to 5 inch bore
Stock stroke is 5 inch
It's a diesel conversion
Will turn as hard as it wants to
Looking to get to 600ish cu.in
Is counterweighting the crank nessisary now or not
Hoping for 500 plus hp
Fuel will be alcohol
If it needs done any recommendations
I have heard of cummins crank working in the block which would add stroke
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Re: Crank counterweight November 29, 2022 01:13PM
Well I cant tell you exactly how to make the alcohol work but if you want to make the cubic in easily, I would do a 4 7/8 bore with a 5.35 (466 stock crank) stroke. I dont think that putting a Cummins crank in it would be worth your custom parts needed or the money spent. The bore and stroke that I talked about would put you at 600ci and then it would be semi stock parts other than the pistons. Good luck seems like a cool project.
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Re: Crank counterweight November 29, 2022 01:50PM
I think you need to share more about this build. What engine are you using? What about head? NA? Factory rods or aluminum? Are you carb limited? Are others running this combo or are you blazing a trail?

Most factory cranks have some counterweight, but not enough to offset the weight of heavy factory diesel rods and pistons. I have seen some cranks with almost no factory counterweight.

Presuming you are blazing a trail, your head, cam, and/or carb are going to dictate the RPM’s. You need to start there and figure out RPM’s first. Then the factory crank design and rod & piston weight will let you make an educated guess on whether additional counterweight will be required to make the crank live.
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Re: Crank counterweight November 29, 2022 11:32PM
The crank currently has no counterweight of any kind.
Will be naturally aspirated with a nar9 stromberg carb.
Planning on using aluminum rods,tho stock rods are angled cap and look very strong in the beam.
It does have 7 main bearings.
Rpms are unknown,not using a governor.
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Re: Crank counterweight November 30, 2022 12:19AM
You will have a lot less main and rod bearing problems if you go with a counter weighted crank especially if your planning on running over 6000 rpms. Well worth the money and time in the long run.
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Re: Crank counterweight November 30, 2022 01:23AM
Must be a Case motor??
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Re: Crank counterweight November 30, 2022 01:04AM
Your rpm is gonna be dictated by head & cam. Depending on the brand, I may have a used billet crank that will get you 5 steps ahead.
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Re: Crank counterweight November 30, 2022 03:18AM
Weight of rotating assembly is a factor in RPMs, bro.
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Re: Crank counterweight November 30, 2022 05:54AM
If you would like to chat about counterweighting, would be glad to talk about cost, process, advantages, disadvantages, etc,. Send your contact information to RPJINDUSTRIESINC@gmail.com. We have successfully done a couple of diesel and alcohol cranks.
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