I'm going to rebuild my 302 head. Machine shop said it maged ok, but it most likely will need guides and valves. It's the D shaped head. My question is will Chevy v-8 valves work, or a good place to buy GMC valves. I believe my other head on my 270 has v-8 valves and I believe its an H head. Jay D.
Last edited by Gdads51; 09/24/20241:48 AM. Reason: fixed typo in title/added detail to title
Jay D - What year 302 do you have? Just asking to see if it helps find some answers to your questions.
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i'm guessing early to mid 50's.i think all these big port heads were the same except for the 270 H head mine is the standard 302 D shape combustion chamber. Jay D.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
I don't have the head here right now its at the machine shop 100 miles away. i was with the thought that the valves on the big port heads were all the same??? Jay D.
It's possible for a good machinist to alter either/or both the stem length and head diameter on a valve that's close to the dimensions of an original equipment item. If the stem is shortened and new keeper grooves are machined, use a hardened steel lash cap to prevent wear to the top of the stem. Jerry
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I used to build a lot of GMC heads. As far as I know casting number 2193983 is the only one that fits a 302. They can either have rotating or non rotating valves. We used rotating valves 60 something years ago when we still worked GMC engines. But I see no reason for rotating valves in an engine that is built today. Adjusting them is very critical. I still have the tool to adjust the rotating valves, but I will probably never use it because I just don't see the reason for rotating valves. GMC 302 valves used to be everywhere because the government had so many spare parts for their 302 engines. There may still be some on eBay. I always pressed in cast iron guides and then reamed them to fit. I always reamed them to the maximum clearance number. Most machine shops are afraid to press guides out and back in. They use bronze. But again I would use caution to make sure that they give the stems enough clearance. You must remember that this family of engines was engineered 85 years ago and the 302 was introduced over 70 years ago. And those engines required wider clearances than modern engines. I have seen so many newly built engines fail because they didn't have enough stem clearance. I still have a bunch of valves, but none of them are boxed. I have always just matched like for like
It's possible for a good machinist to alter either/or both the stem length and head diameter on a valve that's close to the dimensions of an original equipment item. If the stem is shortened and new keeper grooves are machined, use a hardened steel lash cap to prevent wear to the top of the stem. Jerry
YEP, talked to the machine shop and they are up to speed on useing the chevy v8 valves thanks! Jay D.
I used to build a lot of GMC heads. As far as I know casting number 2193983 is the only one that fits a 302. They can either have rotating or non rotating valves. We used rotating valves 60 something years ago when we still worked GMC engines. But I see no reason for rotating valves in an engine that is built today. Adjusting them is very critical. I still have the tool to adjust the rotating valves, but I will probably never use it because I just don't see the reason for rotating valves. GMC 302 valves used to be everywhere because the government had so many spare parts for their 302 engines. There may still be some on eBay. I always pressed in cast iron guides and then reamed them to fit. I always reamed them to the maximum clearance number. Most machine shops are afraid to press guides out and back in. They use bronze. But again I would use caution to make sure that they give the stems enough clearance. You must remember that this family of engines was engineered 85 years ago and the 302 was introduced over 70 years ago. And those engines required wider clearances than modern engines. I have seen so many newly built engines fail because they didn't have enough stem clearance. I still have a bunch of valves, but none of them are boxed. I have always just matched like for like
what was the difference in the 302 and 270H head, just combustion chamber size? i believe the 270 H had a flat top piston and the d shape 302 had a pop up style piston. i'm going to put this 302 head on a 270 with the stock pistons, W/slight dish ( for now) thus my compression ratio is going to be low. i haven't had a chance to get all the parts together to check the CR yet. low compression it going to work for me as i'm going to turbo this engine. Jay D. .
The H head was very rare. It came out when the government wanted more horsepower and GMC built the H head in 51 and 52 while they were developing the 302. I have in my notes that the H head was casting number was 2193417. But I am not real sure about that. I think the H head still used a domed piston. I know it had the large intake ports that used a single barrel carburetor. A 302 manifold would fit but it used a 2 barrel carburetor. In civilian use it used a 3 bolt Holley and government applications used a 4 bolt that accepts a WW Stromberg. The correct manifold for an H head is a single barrel carburetor. If I remember correctly GMC did not change pistons for the H head. The H head raised the compression for the old dome pistons and used larger intake and intake ports. 2136477 and 6107412 castings were for the domed 228, 2194819 were for the flat piston 228, 248 and 270, 2193417 were for the H Head and is for all 302 engines. All of the GMC heads use the same bolt pattern, but the ones for domed pistons have to have domed pistons or you will have hardly any compression. The ones for flat pistons need flat pistons because the domes will hit them. See what the casting numbers are on the heads you have. I only had one H head in my lifetime and it stayed on the engine until the vehicle was stolen. So I really don't have first hand knowledge if the 270 with the H head had a flat or domed piston. But i remember correctly everyone was looking for H heads 60 to 70 years ago to get more power out of their 228 and 248 engines . Post some photos of the casting numbers and the shape of the combustion chambers. The combustion chambers are drastically different for domed pistons and flat pistons.
