long story...short version follows:

bought rebuilt long block...mech. installed as i had a lack of time...ran ok but over about 2-4k miles, got rough running. discovered a cam lone worn...busted push rod..replaced cam, rods and lifters...4-5k, same problem, had a "friend" replace heads, cam and lifters...4-5k, same problem, broken pushrod, VERY worn cam lobes and lifters...

Removed heads myself, found that piston #2 had a broken lip, 2 inches long and about 1/4 inch deep or so, (pics avail next week). No scratches or damage in the cylinder at all, gasket fine, heads fine, here is my theory:

criminally clever rebuilder drops piston and breaks lip, installs it in anyway, figuring he is selling it to a schmuck who wont discover this for awhile anyway, take money and run sort of thing..."friend" who replaced heads either doesnt notice, or pretends not to notice so he doesnt have to breakdown the whole engine, which is what he would have to do if i found out about it.

NOW:

the wear on the lobes and lifters, etc. would be caused by the lower compression of that one cylinder, vis a vis all the others, causing an imbalance that threw the whole engine off, chewing up the cams.

we are checking the block to make sure nothing else is F@d but would appreciate hearing if you all think this is probably what happend

 

where the valves bent on the cylinder with a broken piston? Chances are, the piston hit the valve(s) and, bent the push rod, and jamed the lifter and worn the cam down....

 

No..., no valves bent etc. on #2. all/most wear is down the line... broken push rods and worn lifters/lobes were from other parts of the engine, ie, broken piston #2, broken push rods were on #5 and #6, at various times. no metal fragments or damage anywhere. As my buddy just took the engine apart, we havnt looked at the cam yet. but we can see its worn like hell. we are surprised it would even run.

 

Is this engine a 383 that was rebuilt by a local machine shop?

 

Not enough information but I'd say you have a bad clearance problem. Any number of things can be wrong with the valve train causing belt pushrods and wiped out cam lobes.

Was the pushrod geometry checked?
Are the heads modified to accept the amount of lift the cam is doing (valve guide to retainer distance etc)?
Are the valve springs matched for the cam that was used?
Are the rockers designed for the amount of lift? Stock rockers don't like high lift.
Piston to valve clearance checked?
Deck height of the piston?

Unless you have the block machined by a known machine shop, you can't even guess if it's been machined properly.

Unless you're buying an engine with a warranty, don't expect it to be assembled properly. You get what you pay for.

One cylinder with low compression, blow by past the rings, won't wear out a cam lobe. Cam lobes normally get worn out from too much pressure on the lobe from the lifter and the rest of the valve train, a stuck or collapsed lifter not rotating or a lack of oil. A broken ring land on a piston isn't going to bend pushrods but valves hitting the piston will bend pushrods and damage the piston.

You've either got a serious valve train clearance problem or a poorly assembled engine.

 

No way. That's not possible.

I'd be more inclined to suspect that the valve springs aren't set up properly or aren't the right ones for the cam, or that proper cam breakin procedures weren't followed.

That other didn't happen like that.

 

thanks to all for the responses. . . so much for my theory. the engine builder was not local, no recourse to me, and though professional mechanics worked on it, I blame myself for buying it as i did. we are rebuilding it and checking for all issues.

 

That's really about all you can do at this point....

My advice would be, to get your block back from the machine shop with NO PLUGS and NO CAN BEARINGS, and take it to the quarter car wash, and use several cans of diesel fuel in a spray can typ engine cleaner and rifle brushes, and brush EVERY SINGLE PASSAGE in it; then take it back to the shop, and get the cam bearings and plugs installed.

The vat doesn't dissolve metal shavings, which the motor is now full of, from the rolled lobes. Doing as I describe will dramatically improve the odds of a successful rebuild, without near as much risk of mystery bearing destruction.

 

I agree, go get some kerosene or diesel fuel (I use JP-8...the additives in military jet fuel work wonders )and use that to clean EVERYTHING out, make sure you get all the passages and oil galleys W/ a rifle bore brush

 

good idea on the cleaning. ill make sure this is done. thanx.

 

Does you broken piston look like this?



If so, that's either detonation or inadequate top ring gap that cases that.

You mention there was no damage to the heads or cylinder. But do you have little aluminum flecks on the piston face, valve faces and combustion chamber? If so, that's definitely the problem. You might think a chunk like that would tear up the motor pretty bad, and it doesd sometimes, but about half the time the aluminum chunks just fly right out the exhaust on the next stroke. Ask me how I know.

If you'd like to know more about that type of damage you can read about it here:

http://kb-silvolite.com/clearance_pop.php

 

What kind of cam is it?