Bought a 72 Commando with a 304 that's hitting on 5. :eek:
Took off the heads and found three of the exhaust valves (two on one head, one on the other) bad. Looks like the valve seats have gone bye-bye and the valve is sitting down about 1/8 inch inside the head. The others all look good(well, reasonably ok). It almost looks like someone machined the seats too deep but I know that's not the case.

My question is, what could cause this? Maybe running unleaded gas in an older engine, designed for leaded fuel?? Running it hot?? Any ideas?? Can I get these fixed or should I be looking for some new heads?? :)

Hhhmmmn

Not an AMC expert but an engine off that vintage could NOT have hardened valve seats. Which would let the valves slowly eat down into the head. I know they make extra tall seats that can fix hogged out valve seats but I don’t know what the spec is for “beyond repair”. Looks like a trip to the machine shop will get your answer

FYI.. I have seen vales eat down into the head enough to go through the walls and into a cooling passage
:eek:

:eek: Yikes!!! So, what is it that causes this to happen?? I understand the 'non-hardened' seats but I'm just curious as to why only three valves were affected. Could it be type of fuel or perhaps running the engine hott???

Thanks for the input.... :D:D:D

If I had to guess, I would say a vacuum leak caused the those cylinders to run Cherry hot… in turn burning out the valve and guides… then the worn guides let the valve wreak havoc on the seats….and possibly rockers….

Or an oiling problem to same effect…. The motor should be able to “tell its story” if you inspect it thoroughly:D

what valves in particular had this problem? all at the back or front would seem to indicate to me a mixture problem, if they are random it could just be a fluke. also check to see which ones feed off what side of the carb as it may have run a vacum leak on one half.
I would ask a machine shop on the new heads question, and look around for another set to get a price comparison, if you can find a set noone wants cheap (like a blown bottom end) it may be cheaper.

Originally posted by mytzlflick
what valves in particular had this problem? all at the back or front would seem to indicate to me a mixture problem, if they are random it could just be a fluke. also check to see which ones feed off what side of the carb as it may have run a vacum leak on one half.
I would ask a machine shop on the new heads question, and look around for another set to get a price comparison, if you can find a set noone wants cheap (like a blown bottom end) it may be cheaper.

They were all exhaust valves. Two in the middle on the right side (looking at the engine from the tranny), one middle valve on the left side (third one back). All the others 'appear' to have no visible wear and have good compression. :confused: I'm off to Roseville machine shop in a day or two to have them take a look. Tks for the inputs... :beer: :D:D:D