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Old 09-05-2020, 09:03 PM   #21
Brian
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Default Re: Oversize OD main bearings for 37 21 stud block

Front and center main bearing liners, .015 os;

68 6333 X .020 us
68 6333 Y .030 us
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Old 09-05-2020, 09:06 PM   #22
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Default Re: Oversize OD main bearings for 37 21 stud block

front and center main bearings .015 os;

68 6333 X .020 u.s
68 6333 Y .030 u.s.
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Old 09-08-2020, 02:12 PM   #23
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Default Re: Oversize OD main bearings for 37 21 stud block

I have a question on this:

Has anyone rebored the mains for the 2.500 main bearings? Is there any problems in doing that?
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Old 09-09-2020, 12:37 AM   #24
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Default Re: Oversize OD main bearings for 37 21 stud block

+1 I was just looking at that this evening, there appears to be room for the larger diameter between the studs. Has anyone done this?
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Old 09-09-2020, 06:28 PM   #25
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Default Re: Oversize OD main bearings for 37 21 stud block

If there is enough meat between the studs, boring to the bigger size would seem to be the easiest way.
You sound like you have sleeved main bores back to standard before. That is another reletavley easy way to go.
As a last resort, you could make aluminum bearings to fit. Just give them .002 more clearance than stock.
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Old 09-09-2020, 10:19 PM   #26
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Default Re: Oversize OD main bearings for 37 21 stud block

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if you decide to do this...big job, you'll need to narrow the centre main; the later cranks are narrower there and won't fit the block, also, the rear main is still .010" too short; something else to deal with.
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Old 09-10-2020, 08:02 AM   #27
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Default Re: Oversize OD main bearings for 37 21 stud block

If the brg bores are .015 oversize, could the block be "decked" on the oil pan rail and the brg caps cut a few thousands, then line honed like a SBC to a standard size?
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Old 09-10-2020, 10:37 AM   #28
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Default Re: Oversize OD main bearings for 37 21 stud block

L-head - at .015 over you'd have to move the bore centers way too far up into the block to be useful afterward.


Brian, how much narrower are the later center mains? Milling that to size seems like the easy part of the job.


Pete - Sounds like you have made and run aluminum bearings? How has that worked out long term? What alloy would you recommend?
I made some Durabar bearings for a rotary engine running 70 lbs boost on alcohol because the OE bearings were getting destroyed, but I never got to see the results.


Putting a later crank in the 36-37 block opens up a lot of possibilities for a hot rod 21 stud. I think I could put a 38-42 crank in and use 21A rods with 38-42 rod bearings, this would allow use of new production bearings and make them easier to find and buy. I could put a Merc crank in for a stroker or even a 4-1/8 stroke - is the crank compartment of the early engine the same as a 59A as far as fitting a stroker?
With flat top .100 over pistons I have here I could offset grind a 59A crank to 3.875 stroke and turn about .020 off the top of the pistons to get the deck height I want without decking the block much and get a few extra cubic inches on the cheap.


Please forgive some of the basic questions, I'm only really familiar with 35-37 engines, don't have much else to look at/measure without traveling.
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Old 09-10-2020, 12:29 PM   #29
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Default Re: Oversize OD main bearings for 37 21 stud block

On the cheap? Can't you find the correct bearings?
A while back, I built a 255 cube 21 stud....I used a 37 block like you've got, first operation was to ultrasonic check all cylinders to ensure sufficient 'meat' after a rebore to 3 3/16". The machinist assured me there was adequate thickness to allow yet another .020" bigger again. I used a Scat 4" stroke crankshaft for a 221, another story in itself to make that work, and got Ross to make me custom flatop stroker pistons @ 3 3/16" dia. Bores were finished to correct size incorporating torque plates as recommended by Ross.
Recently had the heads off....the rh bank, all combustion chambers were oily, lh side exhibited just normal carbon deposits. All cylinders, particularly rh bank were scored. #7 piston particularly, could be rocked a lot! Pulled engine to bits....all pistons and cyl walls were scuffed/scored. Again, measured everything. The pistons had .0045 clearance. The scoring was not as a result off insufficient clearance of the forged slugs. If you look into the water jackets of a flattie, you'll observe that the cylinder walls step up in thickness about 1 1/4 below the deck. Well, the afore mentioned #7 cylinder had a crack that followed that step.
I believe, that boring a 21 stud out too much allows cylinder walls to flex and distort, which led in my case to the above problems. Just because one can bore a 37-38 block out to 3 3/16, doesn't mean one should!!
If you want a Scat 4" crank to suit your block, let me know! I have one going cheap.
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Old 09-10-2020, 12:36 PM   #30
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Default Re: Oversize OD main bearings for 37 21 stud block

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On the cheap? Can't you find the correct bearings?
Not so far, that's why started this thread. I'm still hoping to find them, other wise I'm starting over with another block or modifying this one. If I have to modify it, I may as well make it extreme, right? Maybe 2 motors...
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Old 09-10-2020, 01:37 PM   #31
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Default Re: Oversize OD main bearings for 37 21 stud block

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Pete - Sounds like you have made and run aluminum bearings? How has that worked out long term? What alloy would you recommend?
They went in a customer's engine so I never got to find out the long term results.
The alloy was 75T.
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Old 09-10-2020, 01:44 PM   #32
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Default Re: Oversize OD main bearings for 37 21 stud block

The Ford factory spec for the 21 stud engines cylinder wall OD, is 3.380, that only leaves .095 wall thickness, at best (no core shift or corrosion).

Once I obtain the Ford drawings, I decided that the most I should bore my '37 block, was .080 and not the 239 size, I had intended. 3.188 bore doesn't leave much sealing area at the bottom stud, either.
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Old 09-10-2020, 01:46 PM   #33
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Default Re: Oversize OD main bearings for 37 21 stud block

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They went in a customer's engine so I never got to find out the long term results.
The alloy was 75T.
What did you do for the tangs and splitting them?
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Old 09-11-2020, 05:07 PM   #34
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Default Re: Oversize OD main bearings for 37 21 stud block

I am going through my stash of bearings and it would be nice to know the aftermarket bearing numbers , some of these don't have the ford numbers penciled on the boxes.so it would be helpful Clawson Balls , Johnson Bronz, Monmouth, Thompson, federal mogul, ring true, Toledo.
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Old 09-11-2020, 06:18 PM   #35
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Default Re: Oversize OD main bearings for 37 21 stud block

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What did you do for the tangs and splitting them?
No tangs. I just pinned them.
I made 2 sets to get one full size one.
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Old 09-12-2020, 12:59 AM   #36
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Default Re: Oversize OD main bearings for 37 21 stud block

Thank you, Pete.
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Old 09-30-2020, 09:58 AM   #37
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Default Re: Oversize OD main bearings for 37 21 stud block

I found 2 pairs of -.030 +.015 inserts for the front and center mains at Red's Vintage auto parts, thanks to Red Hamilton and Marilyn. I'm running out of folks to ask, the few who understand what I'm looking for don't seem to even want to talk to me about it.
I'm close - If I can find a rear main bearing, I can grind up another crank and I have it solved. Anyone have other sources of old OEM parts you are willing to share?



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