Flathead Main Cap Bolt Lengths - Different lengths?

[Ziggster]

I have a C69 block and just came back from the machinist and he said the main cap bolts I purchased from Speedway (link below) are too long for the types of main caps that were with my block when I purchased it. He said the shoulders on my caps were shorter than some others he had. Speedway says they are for 32-53. Were there different lengths depending on the year or cap type?

https://www.speedwaymotors.com/ARP-M...ord-V8,17.html

[34PKUP]

Originally probably had studs, not bolts.
Good possibility that they can be shortened to make work.

[flatjack9]

59AB and back had studs, (48)49 - 53 had bolts.

[Ziggster]

It's interesting that Speedway advertises the bolts for 32-53 and yet some blocks used studs. He had a block I think from the same year as mine and it had studs. There were no studs in my block when I got it and I'm sure the "originsl" bolts are at the machinists somewhere.

[flatjack9]

The 8BA had 2 different bolt lengths. The center and rear mains used lock washers, so the bolt was slightly longer.

[Brian]

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The C69A block uses bolts, same configuration as flatjack9 describes.

[51 MERC-CT]

Call out for 8BA/8CM looks like 6 bolts (PN B4A-6345-A)
All are (1/2"-13 x 2 7/8" long) and use either 4 or 6 ( 1/2" lock washers)

[Ziggster]

The Speedway bolts are 3" long and come with hardened flat washers.

[Brian]

Actually...whenever I build a C69A, I toss the original bolts and fit studs. I prefer studs and safety wire like the earlier engines had. As I result, I've no doubt several sets of original 69A main bearing bolts kicking around. Without hunting them out and examining them, all I can remember is that indeed some positions had spring washers, whilst others didn't, and I think there was two different length bolts used.

[flatjack9]

Originally Posted by 51 MERC-CT

Call out for 8BA/8CM looks like 6 bolts (PN B4A-6345-A)
All are (1/2"-13 x 2 7/8" long) and use either 4 or 6 ( 1/2" lock washers)

That may be replacement specs, but originally they were as I posted above.

[3twinridges]

When I put my main caps in, I am pretty sure all of the bolts were the same size, and had lock washers, all 6 of them. However I see in the manual now that the front cap didn’t take lock washers, I wonder why?

Jonathan

[Ol' Ron]

I noticed that the front bolts have a depression in the center of the head. I use a harden flat washer under the bolt head. Started doing that back in the 60's. not sure why??

[Ziggster]

Does anyone have a source for the correct bolts or studs?

[JSeery]

Well, as I read the Green Book it is not real straight forward.

Studs for 32-36 1/2-13 & 1/2-20 x 3.07
Studs for 37-48 1/2-13 & 1/2-20 x 3.30

BUT, there are also bolts sizes listed, the base stud number is 6345 and it list front, center and rear all the same length.

On the Bolts it list front and rear main as 1/2-13 x 2.72 with a lock washer and the center as 1/2-13 x 3.26 and no listing of a lock washer. The years are a little rumbled up as well. The bolt uses the same base number of 6345. It appears to be a little mixed up to me on the bolt side!

[flatjack9]

Measuring the stock bolts I have, they measure around 3.2 and 2.91. The thickness of the lock washer is .135. That 2.72 measurement is suspect.

[Kohnke Rebabbitting]

Originally Posted by Ol' Ron

I noticed that the front bolts have a depression in the center of the head. I use a harden flat washer under the bolt head. Started doing that back in the 60's. not sure why??

Mr. Ron, with out the hardened flat washer, the hardened lock washer, will dig into the cap, and chew it up some., and even with a normal lock washer, it will do it.

Mr. Ron, you are even more clever then you thought, and can't remember why.

That sounds like a prime example of the saying, of some one forgetting more then other people will ever know!

Herm.

[Ziggster]

From Reds Vintage Parts

https://reds-vintage-parts.com/red-s...eners-jan-2016

Damn this is confusing.

[flatjack9]

Originally Posted by Kohnke Rebabbitting

Mr. Ron, with out the hardened flat washer, the hardened lock washer, will dig into the cap, and chew it up some., and even with a normal lock washer, it will do it.

Mr. Ron, you are even more clever then you thought, and can't remember why.

That sounds like a prime example of the saying, of some one forgetting more then other people will ever know!

Herm.

Ford did not use flat washers on the main bolts. I have never seen any evidence of galling on the main caps.

[Brian]

These photos are of original C69A main bearing bolts. They differ in the head configuration; the ones that use spring washers have six slots and a recess, whereas the non washer using bolts have six slightly raised ridges around a raised 'B'. Both bolts measure at 2 15/16" long.

[Ziggster]

Interesting. Thanks for the pics. I'm going to see if I can drop by the machinist again today to check the lengths of original bolts. I guess the two forward cap studs/bolts didn't use washers so that the bolt heads could clear the oil pan according to the Reds article! The difference between 2-15/16" and 3" in bolt lengths does explain the issue I'm facing as they were closer to 1/4" too long. Do you have pics showing the lengths of the shoulders of the main caps? This is what is likely causing the issue. Seems the Ford "authorized" rebuilders in the day just slapped in whatever worked for them at the time. Lol.

[Brian]

No, sorry, I have no pictures of main caps. I don't have a C69A apart at this time. As I said in an earlier post, i always fit studs in those blocks anyway.

[Ol' Ron]

I;m not that smart. I think Bill Barth told me that. I saw him doing that to a SBC. Also JWL does it aswell. There are allot of smartpeople out there and I just pass it along.

[GOSFAST]

Just a tip, forget using any bolts, put in a stud kit and be done>

All our builds nowadays get main studs, we put the kits together in-house using all ARP fasteners!

They use .125" thick flat-washers under each nut. We spot-face the original registers on the main cap for a fresh surface!

Thanks, Gary in N.Y.

P.S. Here's a shot of one laid out with the studs, the nice part about the studs we use they can be adjusted in or out up to a .625" or so as needed! The other shot is one with main cap straps included, these studs are just a bit longer O/A however!

[Ziggster]

Stopped by the machinist this morning. The Speedway/ARP bolts are about 1/4" too long. Also the shoulder just under the head which is a larger dia than the shank interferes slightly with the bore in the cap. The orig bolts have a much larger head and appear to be in good shape, so I'm sticking with them. Lock washers were originally used, but I'll swap out those with the flat washers that came with the new bolts. I'll call Speedway next week to see if they can explain what the issue is.

[marko39]

Originally Posted by Brian

These photos are of original C69A main bearing bolts. They differ in the head configuration; the ones that use spring washers have six slots and a recess, whereas the non washer using bolts have six slightly raised ridges around a raised 'B'. Both bolts measure at 2 15/16" long.

On my 51 block the bolts are like the ones you show except the front two are the slotted ones and center and rear that use washers are the other ones and are longer, about 3 1/16. When I took to machinist for alighn honing he told me to leave lock washers off the front cap.

[Ziggster]

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All the bolts that were on my block (it was rebuilt at some point by a Ford authorized dealer) are like the slotted ones in the attached pic. My machinist and I are still not clear how washers under the two front bolts can interfere with the pan. Looking at the shape of the cap and where the heads of the bolts are located, I can't imagine how the thickness of a washer could cause an issue.