Main bearing cap bolts

[tpepmeie]

Howdy gents,

Reading the FSM, it appears that the main cap bolts are Torque to Yield, and are recommended to be replaced after use. Is this, in fact, the case?

If so, where is the best place to get replacement bolts (2-bolt motor)? Are there any upgraded bolts or studs? I know Bill K used to sell the stud kit, but I think it required some machining of the block and loss of the alignment dowels.

Thanks in advance,

Todd

93 #411

[phrogs]

good luck finding some.

I have been searching for a while for my spare motor, try kurt he has some of them but I am missing the washers as well and he doesnt have those I think he might have the main cap bolts.

I don't think they must be replaced

[Polo-1]

Sent you a pm

[flyin ryan]

Originally Posted by Polo-1

Sent you a pm

This will be good

[A26B]

Todd,
I had this very discussion with Graham last year at BG. You were there too, sure wish you had been there for the talk-about.

Summary: Torque to yield doesn't actually mean the bolt exceeded yield strength and suffered permenant deformation which would occur if yield had been exceeded. The differential thermal expansion rates of steel & aluminum would however, place additional longitudinal stress on the bolts, for which no empirical data was ever obtained. It could be calculated but would probably assume "0" deformation under the bolt head or through the thread engagement.

Bottom line: Graham didn't think there would be any adverse results from reusing them. FWIW, this same line of thinking also applied to the head bolts.

He also went on to say that he was opposed to increasing the main bolt dia because of the possibility of encountering casting porosity during the bolt thread enlargement. It would be difficult to determine and would result in potentially catastrophic results.

Having said all of this, I feel confident that Graham was probably thinking along the lines of a stock or mild rebuild. Considering what you are doing, this bit of info probably doesn't have much value to you, except for the larger main bolts/studs.

[flyin ryan]

Originally Posted by A26B

He also went on to say that he was opposed to increasing the main bolt dia because of the possibility of encountering casting porosity during the bolt thread enlargement. It would be difficult to determine and would result in potentially catastrophic results.

I agree, need to have the meat in the casting first. If the surrounding material isn't there...

[tpepmeie]

Originally Posted by Polo-1

Sent you a pm

Kevin, thanks.

[rkreigh]

Originally Posted by A26B

Todd,
I had this very discussion with Graham last year at BG. You were there too, sure wish you had been there for the talk-about.

Summary: Torque to yield doesn't actually mean the bolt exceeded yield strength and suffered permenant deformation which would occur if yield had been exceeded. The differential thermal expansion rates of steel & aluminum would however, place additional longitudinal stress on the bolts, for which no empirical data was ever obtained. It could be calculated but would probably assume "0" deformation under the bolt head or through the thread engagement.

Bottom line: Graham didn't think there would be any adverse results from reusing them. FWIW, this same line of thinking also applied to the head bolts.

He also went on to say that he was opposed to increasing the main bolt dia because of the possibility of encountering casting porosity during the bolt thread enlargement. It would be difficult to determine and would result in potentially catastrophic results.

Having said all of this, I feel confident that Graham was probably thinking along the lines of a stock or mild rebuild. Considering what you are doing, this bit of info probably doesn't have much value to you, except for the larger main bolts/studs.

I was there and overheard this discuss at JVDs. graham is the man. he also didn't think studs were all that hot either as the bottom end is plenty beefy.

you can magnaflux the bolts, but I would chase the threads, lube em up and reused them. you should be fine.

[Polo-1]

Originally Posted by A26B

He also went on to say that he was opposed to increasing the main bolt dia because of the possibility of encountering casting porosity during the bolt thread enlargement. It would be difficult to determine and would result in potentially catastrophic results.

Originally Posted by flyin ryan

I agree, need to have the meat in the casting first. If the surrounding material isn't there...

Also these are " formed " or " rolled " threads NOT cut threads. The blocks are threaded to the bottom of the holes.

So how many folks have done a rebuild with old bolts and how many folks with new bolts only? I have never had issues in the past with SBC or BBC rebuilds using the old bolts.