The 914 head can be shaved .090" to have the same compression ratio as the 848, but the intake valves must be recessed into the head the same distance to avoid valve to piston interference. Drop me a PM if you would like some more specific details on how that modification is done. It was a pretty common mod before the 848 head was available. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I am wondering if the lack of any depression in the combustion chamber near the intake valve has caused the problem of that area to cook, as well as cooking the valves. I do have two 1954 heads (913) which I believe are unmolested and there is a significant depression near the intake valve which my '56 (848) head is lacking. I am going to take those to the machine shop tomorrow so that he can measure the height of these to compare to the height of the '56 head to determine how much has been removed from it over the years.
I'm struggling to picture the depression Carl is talking about, and to understand how it relates head-shaving. Could someone explain or even better, post a picture?
Normally, there is a small step in the combustion chamber that slightly shrouds the intake valve. When the head is milled, unless the valve is recessed the same distance, the step goes away and exposes the edge of the valve to the flame front as the fuel burns. Obviously, the alleged "machinist" didn't know to move the valves back after the milling was done. That's another reason to find a different metal butcher! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I just purchased a set of carbide-blade hand turned cutters from an Ebay seller that can be used for the recessing operation. Each one of the different size and angle cutter heads also has a set of blades on the back side that are usually used to narrow the valve seating area from the top. For instance:
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I went to the machine shop with a '54 235 head so that the height of that head could be compared to the height of the head in question. My '56 848 head measured .050" less than than the '54 head. We don't know if the '54 head has ever been shaved, so that .050" difference may indeed be more than .050". This has lead to an elevated compression ratio on a head which is already the highest compression ratio head available. Add to this, the lack of compression chamber volume near the intake valve, things are going to get hot and valves are going to cook. Jethro from Virginia has graciously offered me a 848 head from his inventory. I have dropped off the '54 213 head at the machine shop to be built, but I may take up Jethro's generous offer on his 848 head.
I would not give up on that head if, as you say it's not cracked. They usually crack between the exhaust port and the intake port up the side of the combustion chamber. I have an 848 head that's been milled a moderate amount to make sure it's flat and the quench area around the intake valve is noticeably diminished. The head is on a 261 which should give 9.2:1 + a little from milling. It runs fine on regular gas. I have a hotter than stock cam and checked the intake valve clearance to be 0.050 at minimum. I don't think your blueing is caused by high compression ratio. Probably lean mixture is the culprit. Cut the valve seats back enough to protect the intake valve and set the seat contact at the outer edge. That helps keep the edges cool. Also make sure the intake valves aren't too thin at the edges. I have cut the edges back a little to eliminate thin edges on motorcycle racing engines with no shrouding and had them survive a whole season's racing.
Measure your valve clearance with one cylinder assembled on a used head gasket. If you get 0.050 I'd say you're good to go.
1951 3800 1-ton '62 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971. In the DITY Gallery
I would not give up on that head if, as you say it's not cracked. They usually crack between the exhaust port and the intake port up the side of the combustion chamber. I have an 848 head that's been milled a moderate amount to make sure it's flat and the quench area around the intake valve is noticeably diminished. The head is on a 261 which should give 9.2:1 + a little from milling. It runs fine on regular gas. I have a hotter than stock cam and checked the intake valve clearance to be 0.050 at minimum. I don't think your blueing is caused by high compression ratio. Probably lean mixture is the culprit. Cut the valve seats back enough to protect the intake valve and set the seat contact at the outer edge. That helps keep the edges cool. Also make sure the intake valves aren't too thin at the edges. I have cut the edges back a little to eliminate thin edges on motorcycle racing engines with no shrouding and had them survive a whole season's racing.
Measure your valve clearance with one cylinder assembled on a used head gasket. If you get 0.050 I'd say you're good to go.
You may well be correct about not giving up on the head, but it needs new valve guides and new valves, and who knows what all that heat did to the head. I have a couple three extra heads to choose from to put back on this engine. I would rather go that route since my out of pocket expense will be the same whether I have the current head redone or one of three others I have to choose from.
