Cracked main cap 8ba 7ra-6330 B

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OldBolts

Junior Member
I was looking to find a few caps to try out and ship back the ones that didn't. One bolt was found intact in the pan and the other sheared off. Sure seems like the one worked its way out... Not tightened? The crank journal feels smooth. Taking apart the rest of the engine next few days. Trying to figure out the numbers on the mangled bearing. Please check out the picture. Thanks, Eric
 

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Posting your address would help people respond. I can probably help out, but am in New Zealand!
 
I can't imagine a main bolt unscrewing and falling into the pan, the other bolt breaking in tension and the crankshaft being straight and useable. Not sure about flatheads but in my experience with modern engines, main and rod caps aren't interchangeable between different engines unless you make them so by machining.
 
Capt Kirk said:
I can't imagine a main bolt unscrewing and falling into the pan, the other bolt breaking in tension and the crankshaft being straight and useable. Not sure about flatheads but in my experience with modern engines, main and rod caps aren't interchangeable between different engines unless you make them so by machining.
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Depending on how the engine will be used a missed matched main cap might be just fine. I'm sure back in the day many a flattie was repaired with whatever was available. Of course for a more performance engine I would think it would have to be lined bored but that's JMO.
 
51504bat said:
Depending on how the engine will be used a missed matched main cap might be just fine. I'm sure back in the day many a flattie was repaired with whatever was available. Of course for a more performance engine I would think it would have to be lined bored but that's JMO.
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I would guess babbit bearing would be fine with mis-matched caps. I agree that line boring would be needed otherwise.
 
Ronnie said:
That is an insert brg not a babbitt. Judging from the number it should be a Michigan brg.

R
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I knew it wasn't babbit...I could see the tab. This might be a pet peeve of mine but main and rod caps go where they go...mixing and matching would take some precise measuring or machining in my opinion.
 
The facts are the Flathead blocks are machined with such consistency and within such tight tolerances as to make it entirely possible to use a residue main cap on your engine. Having a variety to choose from makes it almost a certainty. It always works for me as I have several experiences where people brought blocks to the shop with lost main caps.
 
You'd probably do better to get the numbers off the other main bearing shells. Centre and front are the same.

Mart.
 
you would be surprised with the accuracy of the machining in the Ford engine, I have gotten several engines that needed caps and ones from other engines--or NOS caps that measure out at withing specs for round and size without any machining
 
I have seen the same thing. Not every one will work, but if you have several to pick between one will most likely check out perfectly. It's amazing!
 
Thanks for all the replies. My address is:

Eric Horne
828 Hawks Hollow
Delafield, Wi 53018

Jack, I do have one from that first block I dropped off to you The one that needed the sleeve on 8. I will try one of the other bearings on it and plasti gage that. Is it strange that a 59 ab had the same casting number cap? The 7RA-6330 B? This cap has a rough outside casting to it. I will post a picture tonight.

Thanks again
 
I had just about the same thing happen to me on my high school '51 in 1958. Half the cap was still bolted to the block, while the other half was in the pan. I had the same experience as the others. The first junk cap I tried fit perfectly (checked with "Plasti-gage"), and I even used the same main bearing shell. It ran well for several years after that until I sold it. For all I know, that engine may still be out there soldiering along.

As I look back now, it's amazing what we were able to accomplish when we didn't know it couldn't (or shouldn't) be done. These days, I think I know a lot more, but it seems I can't even install a set of heads!:o
 
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A similar thing happened to me, lost a center main on my merc flathead, broke in half as well as the bolts. Was able to use another main cap with the original insert, clearance checked good. I installed a bearing cap support for insurance and peace of mind
 
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