Hello Chevy family . i have an 84 Monte t top that came with a 305 originally . So i purchased a 305 from a 78 camaro already tore down to go back in it . The guy i bought it from said his buddy had it bored and the crank ground and sold it to him after it blew a head gasket a litte while after the rebuild , and after he bought he decided to go 350. Now after research I've come to the understanding that my cranks mains are .010 under and rods are .020 under from the stamping on the back of the bearings and some measuring myself . My pistons have 40 stamped on the top and bores read 3.776 ish so i am at a .040 over bore . Now while doing research on everthing i came to the understanding the having an engine bored over you cant just order a gasket set and put them head gaskets on , that you need to order seperate / new head gaskets that are .030-.060 bigger than your new bore size , and using the head gaskets for stock bore size in the fel - pro gasket set is why they blew , so am i correct ? and with my new bore size being 3.776 that means i will need 3.806-3.836 head gaskets . the only one ive found is from Cometic its a 3.800 and .036 mls . will these work and should i go with .040 thickness or will the .036 work . i have sbc 601 heads and i see no signs of deck work . and does anybody sell a full gasket set to where i can just let them know what size head gasket to add with the rest of the set? thanks

 

Without personally witnessing the history of the engine from build to failure, one can only rely on the honesty and transparency of the person you got the engine from – kinda like relying on your lover fully disclosing his/her previous sexual partners. In other words, assume you're not getting the whole story.

With that said, there are many different causes for gasket failure. Faulty gasket manufacture is, of course, possible. Improper machining by the machine shop – as little as 0.001in. off compounded on each surface would contribute to failure. Improper installation/torqueing. Engine overheating. If you don't have machining measuring tools and micrometers, you may want to take your block and heads to a few (for comparison) engine machine shops to have them measure surfaces and angles against reference points to verify if everything is in spec or not. Or, you could always just slap the engine together, roll the dice and cross your fingers.

As for gasket size, from my 40+ years of experience, I've always used stock size FelPro gaskets on bored out blocks without problems. If you're building a precision, high RMP circle track runner or 1/4-mile screamer, head gasket size may play a role.

Keep us informed.

 

The most burtally honest response I think Ive ever seen on a forum. Well said!