big block chevy heads

[smokeyco75]

Ok folks, I was tinkering on the hot rod today and decided to pop of the valve covers to findicate out the casting numbers of the heads. They turned out to be 336781 which I hear are good heads to work with. I also discovered a broken pushrod. The cause could be one of a few things but since I know nothing about this engine I am assuming the worst at this point. That being a sticking valve as the culprit. With that being said it would mean a rebuild of the heads are in order. Do you folks think they are worth rebuilding or should I shop for aftermarket replacements? I wouldn't be going crazy with them, just a basic rebuild including valves, guides, springs, etc. I was going to replace the springs and seals when I swapped cams anyway. What say you?

 

[smokeyco75]

Wow just looked at the price of new heads. I think a rebuild is more in my budget lol.

 

[fletcherson]

Wow just looked at the price of new heads. I think a rebuild is more in my budget lol.

A broken push rod could indicate a collision between a piston and valve. You really need to do some detective work to learn the full story before shopping for parts. Just my thoughts.

 

[smokeyco75]

That is another thing I will be checking. The timing cove has been off before so perhaps the re was an issue with the timing chain at one time. Definitely a thorough check of things is in order before I commit to using this engine.

 

[fletcherson]

That is another thing I will be checking. The timing cove has been off before so perhaps the re was an issue with the timing chain at one time. Definitely a thorough check of things is in order before I commit to using this engine.

That's the risk with an engine that you can't hear run. I used to replace engines in my shop and I have had guys buy their own replacements and pay me to swap me and several were worse than the ones being replaced. I told them up front that I get paid either way, let me make sure it's good before buying it. It may just be valve damage if the engine wasn't really cranking when it broke. If it was a timing related issue, it likely has a good deal of miles and wear on it. I hope you get lucky on it!

 

[smokeyco75]

Thanks me too. I can always fall back to a small block if this one is hurt too bad.

 

[T-Test]

A broken push rod could indicate a collision between a piston and valve. You really need to do some detective work to learn the full story before shopping for parts. Just my thoughts.

Don't think a BB Chevy is a clearance engine. Have to have broken a valve for it to hit a piston, or the push rod jammed in some way to hold the valve further open than normal.

Best advice is to remove heads and have a look see, go from there. JMO

 

[smokeyco75]

A friend is coming over with a scope so I can have a look see in the cylinders without removing the head. The valve moves freely and seems to be trouble free so if the piston checks out okay I will drop the pan and check the rod and main bearings. If those check out I will put in a fresh oil pump, change the cam bearings, cam, lifters, springs, gear drive and cross my fingers when it comes time to light it off.

 

[SRM1952]

A friend is coming over with a scope so I can have a look see in the cylinders without removing the head. The valve moves freely and seems to be trouble free so if the piston checks out okay I will drop the pan and check the rod and main bearings. If those check out I will put in a fresh oil pump, change the cam bearings, cam, lifters, springs, gear drive and cross my fingers when it comes time to light it off.

At that point all you are saving is a set of head gasket----job would be much easier with heads off and you check out your combustion chamber and valves ?????????????

 

[smokeyco75]

I heard big block chevy had issues with the head bolt threads in the block. That is why I was avoiding removing the heads. I have changed valve springs without removing the heads before. I'm kind of a "if it ain't broke don't fix it" kind of guy. I'm on a tight budget so avoiding unnecessary machine work is in my best interest.

 

[Mike]

If those check out I will put in a fresh oil pump, change the cam bearings, cam, lifters, springs, gear drive and cross my fingers when it comes time to light it off.

Not really too sure how you will knock in a new set of cam bearings, with the crank in the block, as you won't be able to verify alignment of the oil galley holes with the corresponding holes in the bearings. The only way to see that is to look through the main webs.

I heard big block chevy had issues with the head bolt threads in the block.

I've never seen this be a problem with BBC, any more so than any other cast block.

 

[smokeyco75]

Mike, if the thread is no more an issue than any other cast block then that's cool. I won't sweat it then. On cam bearing alignment you are correct based on what I have found as well. I debated this with my uncle who swears he knows a way. I am skeptical but if he can convince me it will work and it saves me from pulling apart a perfectly good bottom end then I will allow him to make his case. I haven't even checked the integrity of the rod and main bearings yet so this may all be for nothing. Perhaps I should replace that one pushrod and do a compression check on all the cylinders before I tear into it at all.

 

[2old2fast]

why not do a leakdown test , it,ll tell you whether or not you have bent or burned valve as well as the condition of the rings...... you'll not be able to see thier condition.
dave
bbc are hard on timing chains &gears

 

[smokeyco75]

Well I just took the intake manifold off. Looks like the pushrod broke clean. Doesn't appear to be any debris in the valley. inside is sludge free. Bad news is there is rust in two intake ports. Cylinders are dry. No water or rust on the plugs. I think a complete teardown is in order at this point. Looks like I was violated with a sandpaper condom on this deal. Wait till I see this guy again. Carma sucks.

 

[smokeyco75]

 

[smokeyco75]

 

[smokeyco75]

 

[fletcherson]

Water in the combustion chamber could account for a bent push rod. Ouch! It must have been hot. You better check everything.

 

[smokeyco75]

Bad news. Took the heads off today. Found two cylinders side by side that had water in them at some point. Now I have to ponder wether or not to save this engine or build a smallblock.

 

[fletcherson]

Bad news. Took the heads off today. Found two cylinders side by side that had water in them at some point. Now I have to ponder wether or not to save this engine or build a smallblock.

Ouch! That's ugly. I would say that engine was overheated and ran till it died, jmo. That would explain the push rod issue. Same cylinder? Not only was it likely overheated, it was left to die with water in the cylinders. You should go through it and check all castings, surfaces, for cracks and warps. It will likely require a complete overhaul. I have seen many engines that were overheated and the outcome is not usually good. Heat and water in the wrong place are about the worst enemies.