I am starting to research motor building and am wondering what the purpose of a block guard is? Seems to me it may block some coolant flow? Does it help the cylinder walls from caving outward or something?

Links would be great too!

 

its supposed to provide some cylinder support... but most people agree its useless. the point it supports is at the top of the cylinder, but the rod angle is most severe when it attacks the middle of the cylinder. where the block gaurd provides support the piston is happily travelling exactly up and down...

 

Agreed. Most are poorly crafted and can "egg" your sleeves.

 

thats why you should only use it when you are having the cylinders re-bored and honed. The blockguard doesn't necessarily have to go right at the top either.