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Old 08-08-2019, 05:10 PM   #41
GOSFAST
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Default Re: 1CM Merc Crank In A 40?

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Originally Posted by JSeery View Post
I happen to have a Scat 4 1/4 crank laying around, just measured it and it is 2.000". Interesting.

Just looked at their site, they have both throw sizes listed for a 4 & a 4 1/8, but not 4 1/4. Shouldn't be much of an issue to produce a larger dia throw on a 4 1/4 though.
We don't use the aftermarket (Eagle) shafts with any rod journals other than the 2.000" pieces.

I believe Eagle doesn't make any shafts with the OEM journal size (2.139") with the exception of the 4.000".

The problem I can foresee is getting the 4.250" arm in with the 2.139" journal, never tried it, but I don't think it'll go without hitting water! Could be wrong, but I don't think so?

Thanks, Gary in N.Y.

P.S. Every one of these Flathead builds really should be done on the 2.000" journal. They simply run/perform much better! The 2.000" rod journal crank would definitely be a bit lighter, this would be the right direction to go in, lighter.
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Old 08-08-2019, 07:11 PM   #42
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Default Re: 1CM Merc Crank In A 40?

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P.S. Every one of these Flathead builds really should be done on the 2.000" journal. They simply run/perform much better! The 2.000" rod journal crank would definitely be a bit lighter, this would be the right direction to go in, lighter.
The 2.000 journal is fine but where am I going to find Merc. pistons to fit the 221 block? I'm not building an 8BA. Bore is 3 1/16".
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Old 08-08-2019, 07:20 PM   #43
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Default Re: 1CM Merc Crank In A 40?

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The 2.000 journal is fine but where am I going to find Merc. pistons to fit the 221 block? I'm not building an 8BA. Bore is 3 1/16".
Only way I know of is custom - call Ross firsts, then J&E and Wiseco. It will take somebody who has a forged blank that will work. It gets a bit expensive - probably $100+ per piston.
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Old 08-08-2019, 07:21 PM   #44
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Default Re: 1CM Merc Crank In A 40?

Why not have the block sonic tested and see what bore it can go too? You can probably get to 3 3/16 - then you have piston options. I would go with a 2" journal crank - depending on the bore you can get too, either 91A or 21A rods - or SCAT.
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Old 08-08-2019, 07:41 PM   #45
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Default Re: 1CM Merc Crank In A 40?

If you use the 6.75 rod, you an use std factory, 3 1/16 pistons and have the factory deck clearance, using the 4 1/4 crank. But, you will have to find a way of using the 2.138 rods.

I know it may sound strange but, if you like, I will show you the math for it.

A question for everyone:
What is the min bore to get a 2.138 rod in the block?
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Old 08-08-2019, 07:55 PM   #46
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Default Re: 1CM Merc Crank In A 40?

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A question for everyone:
What is the min bore to get a 2.138 rod in the block?
I'm fairly sure you are referring to from the top, but they can and have been installed from the bottom. You can do about anything if you are will to deal with the hassle factor.
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Old 08-08-2019, 10:10 PM   #47
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Default Re: 1CM Merc Crank In A 40?

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If you use the 6.75 rod, you an use std factory, 3 1/16 pistons and have the factory deck clearance, using the 4 1/4 crank. But, you will have to find a way of using the 2.138 rods.

I know it may sound strange but, if you like, I will show you the math for it.

A question for everyone:
What is the min bore to get a 2.138 rod in the block?
Not necessarily true - also depends on whether or not you have "skirt clearance" when the crank is 180 degrees from TDC. My guess is that the pistons may be too long (if you had a 4.250 stroke arm) - may hit the counterweights of the crank. When you see long stroke pistons, they tend to get a bit "short" - and with the 6.75" rod, you have the piston skirt 1/4" further down the bore. Also, depending on the piston design (think 4-ring) not sure where a bottom ring will end up.

Lots of little things to think about - and validate before you start buying parts.

B&S
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Old 08-08-2019, 10:43 PM   #48
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Default Re: 1CM Merc Crank In A 40?

For the stock car we cut the pistons off at the bottom oil ring, To lighten it. I still have the cheater cam. his has been a fun build, glad I don't have to pay for it.
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Old 08-09-2019, 02:30 PM   #49
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Default Re: 1CM Merc Crank In A 40?

I thought the French SUMB engine rods for the 4-inch crank were 6 7/8". All they wanted them for was so both engines could use the same Ford type pistons.
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Old 08-09-2019, 08:33 PM   #50
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Default Re: 1CM Merc Crank In A 40?

Yo Roto - you're probably correct . . . and that makes sense from a perspective of saving money . . . and God only knows that would be the tendency of the French! LOL
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Old 08-10-2019, 08:31 AM   #51
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Default Re: 1CM Merc Crank In A 40?

I would think that re locating the wrist pin, would be allot cheaper than forging a new rod?????
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Old 08-10-2019, 08:37 AM   #52
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Default Re: 1CM Merc Crank In A 40?

Ron the military often has different ways of thinking about this kind of stuff. It might be an inventor/stocking issue, who knows.
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Old 08-10-2019, 09:20 AM   #53
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Default Re: 1CM Merc Crank In A 40?

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Originally Posted by Bored&Stroked View Post
Why not have the block sonic tested and see what bore it can go too? You can probably get to 3 3/16 - then you have piston options. I would go with a 2" journal crank - depending on the bore you can get too, either 91A or 21A rods - or SCAT.
This is a new NOS block and I can't see boring it.
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Old 08-10-2019, 06:22 PM   #54
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Default Re: 1CM Merc Crank In A 40?

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This is a new NOS block and I can't see boring it.
It is all just choices in the end. If you want to increase the stroke of the engine, you're going to need new pistons . . . so they'll have to be custom in this situation. Also, you'll need to run the 21A or 91A rods that will fit through your bore - which means a 2" rod journal crank. A good combination would be a 4" late Merc crank - offset ground to 4 1/8" stroke . . . using the 2" rod journal.

Should be a fun project - once you get past the piston purchase (which will be a bit pricey - but not that bad). I'm not sure a 4.250 stroke crank will fit in it (from the perspective of the rods hitting the bore) - not sure there is an issue, but something that needs to be known. Of course there are many situations where one has to "notch" the bottoms of bores to clear crankshafts . . . just not sure if there is an issue in your case.


if you have any questions about anything, feel free to PM me.


Best of luck,

B&S
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Old 08-10-2019, 06:42 PM   #55
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Default Re: 1CM Merc Crank In A 40?

Wonder if any anybody has done this. As long as flatheads and earlier pre-8BA engines
have been around, I would think somebody has stroked one.
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Old 08-10-2019, 06:46 PM   #56
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Default Re: 1CM Merc Crank In A 40?

Re the 6-7/8" rods. I used those rods, a 4" crank and 3-5/16" Ford pistons in the French motor I built for my roadster. The pistons had to be clearanced at the skirt because they were hitting the crank at the bottom of the stroke. I made a jig that passed the piston over a cutter held in the lathe and trimmed away the skirt until they cleared ok. I also had to leave out the lower oil ring.

In other words, although the French motors use a 7" rod in the 3-3/4" stroke engine and a 6-7/8" rod in the 4" stroke engine, the French pistons are not the same as a Ford piston, they are designed to clear the 4" crank. I think they are 3 ring, also, rather than 4.

But nonetheless a Ford piston, in the case of this thread, a 3-1/16" one could be modified to work.

I don't know if there would be clearance issues from rod to cylinder at the base of the bore, though.

I don't have the parts at my disposal to do a dummy build. The mains would need to be reduced, for a start.

Mart.
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Old 08-10-2019, 09:33 PM   #57
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Default Re: 1CM Merc Crank In A 40?

Just a thought

Most of the new early blocks that I have seen are sleaved, both 37 21 stud style and 24 stud style. If you have one of these blocks the sleeves can be pulled to give a larger bore.
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Old 08-10-2019, 10:20 PM   #58
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Default Re: 1CM Merc Crank In A 40?

the merc 4" crank can be installed into the 36 Lb to early 38 21 stud block by boring to 3 3/16 and turning down the Mains to 2 .398 . THis has been done on many early blocks. I did this with a n 8BA crank just to see if it could be done. Wish I used a Merc crank.

Just remember"It's the journey, not the destination"
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