{"id":5527,"date":"2025-11-14T09:06:42","date_gmt":"2025-11-14T13:06:42","guid":{"rendered":"https:\/\/kgworks.ca\/?p=5527"},"modified":"2025-11-14T09:06:42","modified_gmt":"2025-11-14T13:06:42","slug":"head-scratching","status":"publish","type":"post","link":"https:\/\/kgworks.ca\/?p=5527","title":{"rendered":"Head scratching"},"content":{"rendered":"\n
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I’m exchanging the original crack prone heads from the L48 for a set from a GM crate motor #83417369. The Internet AI info about these heads is as follows- <\/p>\n\n\n\n

“The GM 83417369 is a cast-iron cylinder head with a 76cc combustion chamber and 1.94-inch intake\/1.50-inch exhaust valves<\/mark>. These were basic, non-performance heads from the “smog era” often found on Goodwrench crate motors. For a performance upgrade, they are often paired with an RV cam, a dual-plane intake manifold, and a 600-650 CFM carburetor to improve low-end torque. “<\/p>\n\n\n\n

And that is about what I’m going to do with a Stage 1 cam, flat top pistons, high rise intake and the standard Qudrajet 4 bbl.<\/p>\n\n\n\n

The valves and heads are in good shape so I can use them as is with a bit of work. First I’ll clean them up and then cc the combustion chambers to see how even they are. I’m not trying to do an expert blue printing job. I have done this in the past and feel that it is good to get the heads even and also same with the piston and rod weight. The closer I get the smoother the engine will run. The last engine I did this on was a Studebaker 259 R1 (stage one cam from factory) and the engine is very smooth with just a light lope at idle.<\/p>\n\n\n\n

Here I’m cleaning up the combustion chambers with a brass wire wheel so as to not damage the valve contact surfaces. There wasn’t much carbon residue.<\/p>\n\n\n\n

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After cleaning the combustion chambers, including the valve openings, I cleaned up each of the valves on a wire wheel – being careful not to hit the valve\/head contact surface. the exhaust valves were fairly clean, but the intakes had significant carbon deposits. May have been the result of poor valve seals on the intakes.<\/p>\n\n\n\n

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With the valves in place I went on to blocking the spark plug hole with a blob of dum-dum – carefully flattened to the head casting surface.<\/p>\n\n\n\n

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I used this plastic plate for earlier cc jobs – ignore the hole at the side. The two smaller holes at the top are the important ones. The head is tilted slightly so the to holes are a little up. The plate is sealed to the head with a smear of vaseline around the combustion chamber edge.<\/p>\n\n\n\n

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I picked up a pipette from Amazon some years back. It is marked off in ccs. I fill it to the top (0 cc) and then fill the combustion chamber. I fill it until the two holes are filled to the top and all the air is out of the chamber. I’m looking for an even combustion chamber volume. t The little extra water in the two fill holes will give me a slightly higher reading, but it will be the same for all cylinders. The final number may be a bit off, but they will all be the same and it’s the evenness that counts.<\/p>\n\n\n\n

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This particular cylinder is showing about 73.7cc The range of volumes is between 72.0 cc and 75.0cc. So I will need to open up all combustion chambers to about 75.0 ccs. From what I have read it’s best to get them within 1cc of the largest chamber. The heads are rated at 76cc.<\/p>\n\n\n\n

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There will be very little extra volume in the plug area so I’ll just go with 75 cc heads in my compression ration calculations. In truth it will be a fraction less because of the two holes in the plastic cover plate.<\/p>\n\n\n\n

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#2 cylinder was the smallest at 72.0cc. I used a small ball grinding bit on my dremel tool to scrape a small amount from the chamber surface and remove some of the shrouding around the valves. The amount removed from each cylinder varied. Final result was all cylinders within 1 cc of 75 cc. <\/p>\n\n\n\n

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Took a moment to clean out the plug holes after removing the dum-dum used to seal them off while I did the cc work.<\/p>\n\n\n\n

Next : More heads than one<\/p>\n","protected":false},"excerpt":{"rendered":"

I’m exchanging the original crack prone heads from the L48 for a set from a GM crate motor #83417369. The Internet AI info about these heads is as follows- “The GM 83417369 is a cast-iron cylinder head with a 76cc combustion chamber and 1.94-inch intake\/1.50-inch exhaust valves. These were basic, non-performance heads from the “smog … <\/p>\n

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