Picked up a 72 Pontiac 400 for my 54, and started to break it down today. The number 3 exhaust valve, and numbers 4 and 6 have cracks in them. The bores look good, and everything else looks normal. Could this be from over heating? I'll try to upload pictures of the two heads, and was just wondering if anyone has seen this before. Thanks
Would you believe those are very rare self seat cutting valves. They have rotators for the valve spring retainer like a big block Chevrolet, and as the valves rotate, they keep a constant fresh seat angle cut.
I actually seen this on a used race motor I had bought. Valves were discolored and one had a crack like yours. As 73RR said be sure to have those heads checked real good.
Burned valves have been around for a long time..... I have seen three on one engine before, a 53 buick 322 V8.
My 330 Ford truck engine had three like that, but worse. I chucked the heads for 352 car heads and manifolds. Like they say, check those heads real close before you spend any cash on rebuilding them. Cracks, warping, all that fun stuff is a possible byproduct of that much heat.
I've seen those! They were on the same Pontiac factory spec sheet as the dual overhead cam turn signals!
Wow, yeah. Simple burnt valves, like others have said check out those heads before re-building!! Doc.
Actually there are cases of minute spot welds being formed on exhaust valves that will cut the seat area. No bull, a friends shop had a contract to supply the GSA with rebuilt heads and short blocks at the Nevada test site,many of the heads he got back as exchanges or cores had the seats receded into the head as much as 3/16". It was being caused long periods of idling by security vehicles using unleaded fuel. On close inspection with a magnifying lens ,one could see the small weld spots and as the rotators did their job, the seats were eroded !
To answer the OP's question, this don't neccesarily mean overheating as in water boiling. This is hot in the combustion chamber, maybe from too lean or retarded timing. A 1972 engine is already a smogger, I would have thought this would have better material for valves to withstand the abuse that the 70's gave. Retarded timing and really lean mixes. Another thing to consider, I had a 235 Chevy that was an oil burner, and it was pretty happy except for the smoke. Back in the early 90's they added the MTBE here and the first tank of that shit, the combustion chambers got so hot, all the oil crud burned off, went out thru the exhaust valves and screwed up the seats so there was 0 compression. Towed her home.
------------------------- Ha! Big deal! Henway had both those features long before Pontiac! Those thieving, 'Johnny-come-lately', so-called 'engineers' at Pontiac stole both of those innovations - the 'self seat-cutting valves' and the 'dual overhead cam turn signals' from Henway Motors....as well as a bunch of other great Henway automotive firsts too! At Henway Motors Corporation, we've always prided ourselves on our use of the very latest advances in the fields of 'alchemy', 'crypto-technology', 'pseudo-science' and 'advanced metaphysics', to constantly push the envelope of modern automobile design and provide our customers with the most technologically complex and mechanically contumacious vehicles possible! Not only did HMC engineers invent 'self-seat-cutting valves' and 'dual overhead cam turn signals' - we've had both of those features on all of our cars, going back as far as 1949 ....way, way before Pontiac ever had them! And that's not all either! Beginning with the 1950 models even - and continuing right through to all of our current 2011 production models too - all Henways come with several other unique and even more complex, cutting-edge innovations....and all as standard equipment too! Things like, self-aligning, high-speed, 'muffler bearings', innovative, cross-compound-coupled 'flux capacitors', special, hammer-forged 'thorndykes', made from rare, imported, extra-stellar-sourced, dilithium-plated kryptonite(!)eek - and even 'far beyond state of the art', ultra-high-efficiency, sodium-cooled 'frazzle shafts' with 'rich Corinthian leather-lined' gimbal locks(!!)eek:) - all Henway firsts by the way, and things that Pontiac, even at their supposed 'innovative height' during the so-called 'Muscle Car-era' of the 1960's', never ever had! Mart3406 ('Official Henway Motors Corporate Historian and Archivist') ============================
The " self seat cutting valves " were a extremely rare option on the RAM AIR MACH 5 Cylinder heads. The set you have were the rarest, they had only one cutter groove and were very unbalanced causing excesive valve guide side loading and wear as they roated. This of course prevented " concentric " valve seat cuttage. The RAM AIR MACH 5.2 had two cutter grooves spaced 180 degrees apart to eliminate the unbalance during rotation, and premature valve guide wear, therefor allowing for a concentric seat cut. Ive been told, the SERDI Corporation bought the technology from Pontiac Motor Division, and soon thereafter the company began to manufacture thier own line of valve seat cutting machines. Rumour has it that some of the original MACH 5 heads went to Japan in the mid 1960's, and were used in a experimental type race car to be featured in a new television series. BDM
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