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Old 01-15-2007, 08:41 AM   #1
Seijirou
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351M/400 wrist pin

Hey guys. I can't find out what the diameter of the wrist pin is for these engines. I know the W/C used a .912 wrist pin, but all I can find about the M blocks is that the wrist pin is "slight bigger" Does anybody know how much bigger it is? Or is it not bigger at all?

Side note, if it is bigger but your rod is designed for a .912 pin, what are your options?

Thanks!
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Old 01-15-2007, 08:56 AM   #2
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The stock 351m/400 wrist pin diameter is .975". Bushing the stock rods to accept a smaller wrist pin - and then it's full floating instead of press-fit - is quite commonly done. IF you are going to use a rod that has the smaller .912 pin, however, then you need pistons that use that pin size too. What are you trying to put together?
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Old 01-15-2007, 09:22 AM   #3
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Originally Posted by bmc69 View Post
The stock 351m/400 wrist pin diameter is .975". Bushing the stock rods to accept a smaller wrist pin - and then it's full floating instead of press-fit - is quite commonly done. IF you are going to use a rod that has the smaller .912 pin, however, then you need pistons that use that pin size too. What are you trying to put together?
W crank, C rods, 351M pistons is what I'm trying to put together.

Not sure how I'm going to find M pistons with a .912 pin.
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Old 01-15-2007, 09:37 AM   #4
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Because the 351m was a crude destroke of the 400, the pistons are very tall and very much an oddball design..hence are also one-of-a-kind with zero aftermarket suport for anything other than stock. What block are you trying to stick that combination of parts in to? I've built a lot of old-school strokers and such..but what you listed is not a combination I've run across yet. 351M pistons, in particular, are used only in stock 351m rebuild..and nothing else.
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Old 01-15-2007, 09:50 AM   #5
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With an 88 Windsor block, that rod/piston combo gives me 0.026 deck clearance, so that I can fit some M heads ontop. The idea is to stay away from the expensive specialty pistons for clevors. I discovered that the 300 I6 engines also use the 0.975 pin, any chance you would know the lenght on those rods?

Edit: found the info

I240: rod 6.7947 length, piston c.h. 1.577
I300: rod 6.2079 length, piston c.h. 1.740
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Old 01-15-2007, 10:14 AM   #6
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The HD rods with the .975" pin are 6.209" center to center. The LD rods have the .912 pin and are 6.22" long..
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Old 01-15-2007, 10:38 AM   #7
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So is there any reason why I can't take the little end of the cleveland rod out to .975?
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Old 01-15-2007, 10:41 AM   #8
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"probably" OK..but that is a fair amount of meat to remove and would require machining before honing..lot of work.
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Old 01-15-2007, 10:44 AM   #9
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Looks like nomatter what I do someone is going to get paid.

Ahwell, I'd rather pay my machinist anyway :)
I'll talk to him this afternoon and see what he thinks.
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Old 11-29-2007, 10:27 AM   #10
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Originally Posted by Seijirou View Post
Looks like nomatter what I do someone is going to get paid.

Ahwell, I'd rather pay my machinist anyway :)
I'll talk to him this afternoon and see what he thinks.

Oh yeah, I forgot about this.

My machinist thinks I'm out of my mind.
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