[Mad Maggot]

People have told me that using billet main caps on a SBC block is a bad idea, regardless of the fact that they are stronger. Something about the expansion rate of the metal being different from the block material throwing the crank journals out of round. Can someone enlighten me on whether or not this is true?

[NorthStar]

Thats a bunch of bull.

You will need to have the caps fit to the block and align bored though.

[k-star]

The person that told you that is technically correct, but i am sure they don't know why. The coefficient of thermal expansion is different for cast iron and steel depending what material the steel cap is made of. There is a chart that shows this. Some of the steel crosses the cast iron for rates, meaning it has the same expansion rate. All that being said the difference is so small that i hardly doubt you could measeure it in a main bearing cap application. There are thousands of small chevys running with steel caps and have no issues at all......none!!!!

So to answer your question they are fine to run......


Keith

[tresi]

I'm sure that is true to a point but an iron block and cap won't expand at the same rate either. The block has more heat put into it and heat doesn't transfer across the part line as fast as it transfers through solid iron. I really don't believe that the difference would be enough to matter.
Look at the expansion rates of steel and aluminum. A steel cap works OK on an aluminum block.

[camaroman7d]

I have been running billet steel caps for a few years now. I have yet to see a problem. The guys above have given very good explanations. Just to add to that, these caps aren't carved out in some guys back yard, lots of engineering goes into most auto parts. The engineers usually take into account the different expansion rates and make the needed adjustments.

Royce

[NAIRB]

That is an untruth. If that argument held any water, then aluminum blocks with steel caps wouldn't work either

They are ran every day.

[Mad Maggot]

guess I'll be the next guy to use them then. I have a bone to pick with the guy that was B.S.-ing me...

[k-star]

mad maggot, I think you should go talk to him...

One thing with the after-market caps is the quality of the caps being used, as well as the style of cap. Some of the caps use the stock register to locate from, With others you need to mill the block to fit the cap. This is the style that i have found works the best. They have alot of contact area at the split, plus you can make the interference fit as tight as you want and are not locked into what is already there...

I have seen conversions from other shops and the workmanship has been awful. So like everything else people will make assumptions that it was the caps fault when it was actually the way it was installed.

Keith