#1 & #2 main bearing cap bolt lengths

[John Haynes]

I have been cleaning a lot of main bearing cap bolts from motors which were disassembled and I discovered that there are two lengths of bolts for the #1 and #2 bearing caps. Some are 5 5/8 long and some are 6 1/8 long. I have a 24 block and it will take the long bolts. Can anyone tell me what year the change in the bolt lengths was made?

[Kerry]

I'd have to say in doing many T engines from all years, I've never come across a 1/2" difference in main bolts.

[Mark Gregush]

Could be Model A main bolts. The Model A and T main bolts look the same.

[Dan McEachern]

The shorter ones are Model A/B.

[John Haynes]

Thank you Gentlemen!

[Mark Gregush]

I would have to do some checking, but during Model A production, the caps went from cast to forged and got thinner. The early cast caps may have used the same bolts as the T. The forged type, the area where bolted to block was thinner so may have used a shorter bolt.

[Dan McEachern]

Mark- all Model A/B front and center caps are steel forgings and use the same length bolt. Early Model A rear caps were steel forgings as well. Later A and all B rear main caps are cast iron. The early A rear main cap uses a shorter bolt that the later cast rear main caps.
The result is there are three similar looking but different length T/A/B rear main bolts out there. Hope this clarifies things a bit.

[Mark Gregush]

Yes, thank you Dan.