need engine help...

[69Elky]

ok my buddy has a 61 corvette motor in his 3/4 ton lwb gmc nd we got the motor together dropped it in now we have been putting it together a week ago it started pulling out a rocker stud(think thats right) well we replaced it with a screw in and then it started doing the same thing to 2 more...



heres the engine specs

283 bored .60 over
flattop pistons
stock fuelie type heads
roller tipped rockers(he wanted em)
comp cam power max some thing like 463 ands 481 lift like 280 duration think thats right
and he put stock valve springs in-.-


now we ran a compression test one 2 had ok comp like 120 then the other had a very low # dun member what it was now could the valve springs not have enough force to shut the valves and compression leaks out? lso once in awhile we get a backfire timing everything else is deadon


sry about any spelling errors etc im tired....would appreiciate if someone would take they're time to answer this....

[Eddie H.]

It sounds like the camshaft you're using may have too much lift for the stock heads. The technical term is called "coil bind" where the springs are being compressed farther than their design limits.
The end result will be pulled out rocker studs, bent push rods, etc.
Also , too much lift can cause interference between the piston and the valves, causing bent valves, loss of compression and all kinds of other expensive noises.

[Eddie H.]

It sounds like the camshaft you're using may have too much lift for the stock heads. The technical term is called "coil bind" where the springs are being compressed farther than their design limits.
The end result will be pulled out rocker studs, bent push rods, etc.
Also , too much lift can cause interference between the piston and the valves, bent valves, loss of compression and all kinds of other expensive noises.

[Kid]

I think you nailed it Eddie. With that much cam lift (and apropiate spring pressure) , even without coil bind, I think the studs would start working their way out unless they were pinned

[GloryHound]

another thing to look into is the rocker ratio if he changed to roller they might be the 1.6 ratio instead of the 1.5. ending up with the same result as an oversized cam. Also you could call the cam manufacturer and they are normally more than willing to help you choose a cam, rockers, and springs to match your engine!

[69Elky]

they're 1.5 already went through the 1.6 deal:P we're going to order or locate a set of matching valvesprings for it then change to all screw in studs


thanks alot guys...

[bigjimzlll]

if your going to use screw in studs that have a jam nut..the rocker bosses will have to be machine down .3 or so. Also your cranking Compression will be low(with that much duration) with a mini-mouse