I am about to rebuild a 350. If I compession test and all is good does the pistons and block need to be touch or can i just rebuild top end such as cam, lifter, rockers, timing chain, etc. what size cam is good ?:beers:

If the engine is out and the bores are good then might as well replace the rings/bearings too. if it test good and is in the car then a top end swap is good too. Cam choice depends on what you want out of the engine and the rest of the combo.

I did a head swap, intake and carb upgrade, and cam install a year and a half ago on the stock '74 chev 4 bolt 350 that was in my car when I bought it.

The motor had 150-155 lbs in every cylinder prior to tear down.:thumbsup:
When I pulled the heads there was very little ring groove and .030 4valve relief flat tops looking at me. I figured I was good to go ahead with the upper end stuff.

I put it all back together with the upgrades and at the same time installed a set of gauges. Cam break in went well, the motor ran fine, but...

I found out that what I hadn't counted on was... I had only 5lbs of oil pressure at idle and 35 at cruising speed.:(

I pushed my luck and ran it like that for a year including 3 Test and Tune days with no issues.

When I pulled the motor for a thorough upgrade last winter I found that all the low end bearings were worn down to the copper, thus my low oil pressure.

I guess what I'm saying is... you might get away with a top end upgrade... but I agree with badrad that you might as well pull it the rest of the way down and then you'll know exactly what you are dealing with. :yes:
If you stick to fairly basic components and machine work, you really aren't looking at very much additional money.

Good luck!

Can't go wrong w/ an old-school 268/270/272 cam in a stock 350 by me.

BUT right, we need to know a bunch more info to help you pick a good one for your application.

pdq67

FYI,you can have acceptable compression if the compression rings are still in good enough cond but then still have a situation where the oil rings are worn enough to use considerable oil.

Thats where just going by a comp test doesnt tell it all,even a leakdown wont always tell the complete story either.

If the motor has plenty of miles on it,has considerable blowby, and is currently using a fair amount of oil and or smokes when you push it hard it likely needs re-ring too & not just a top end rbld.

Scott

the engine is going up on the stand this weekend and after a comp test i was going to pull the heads just to see the pistons and walls to make sure the walls are not scratched because i was told the motor was bored .10 so the machine shop told me to make sure the pistons are .10 and not the originals with oversized rings. but i might as well go a little further and change the rings. is that what your saying

I wouldn't put it back together without rings, bearings, and a new oil pump at the bare minimum... but that's just my opinion.
While it's this far now would be the time to upgrade pistons "if" they aren't what you want.

what Buick Special Greg said 2x

Screw the new oil pump if it is the old-fashioned h-d casting instead of onna the light-weight jobbers that tend ta break off nowadays!

pdq67