Decking the Head
- Thread starter 200cifox
- Start date
The only way to know for sure is to mock up the assembly with modelling clay, put it all together and turn the engine over by hand and pull the head, cut through the clay and measure how deep the valves are in the clay and how much room between bottom of indentation and the piston surface.
Its going to vary from engine to engine.
IIRC you can mill the heads up to .080" and many people shave .040" to .060" to raise compression back up for use with the modern composite head gaskets.
Its going to vary from engine to engine.
IIRC you can mill the heads up to .080" and many people shave .040" to .060" to raise compression back up for use with the modern composite head gaskets.
200cifox":2tob0wft said:
With machine shop access, you can maximize the potential.
With machine shop access, as well as Shaving the head for overall CR adjustment, CC'ing each combustion chamber for similar volume and Relieving to "balance" each cylinder, larger valves, intake runner mods, port divider and all kinds of radical mods are possible. Posts on Decking the 200 block include letting piston protrude a few .00X's before valve interference.
The Falcon Six Performance Handbook and lots of posts on each subject are handy to work out a buid plan.
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Howdy,
You said "I have 3 stock 200 heads and wanted to play around with them a bit. I also have full access to a machine shop. Does anyone know how far you can deck the head on a stock 200 before you run into valve clearance problems?"
I'll be a Smart Alec and answer, "It depends"... Seriously. You need to tell us the casting number on each head. It will be like C9DE-6090 AA. The "C" means 1960. The "9" means 9th year... so a 1969. The casting numbers are on the firewall side on top of the log.
A 1967 head will have fewer cc's (higher compression) than a D4 (1974) head.
More is not always better, and bigger is not always better. (unless it is Dolly Parton.)
We have NEVER had Valve clearance problems.
I have ANGLED milled a 1974 62 cc head .110" with a .025 gasket to go on a 144ci block. Would I recommend that much... NO ! ! ! but I don't mind breaking a few parts to find out what works. You need to leave at LEAST .100" thickness on the gasket surface in the head. With a virgin head you can USUALLY safely go .090" with a .045 composite head gasket.
USUALLY, if you took the head off the engine, and it had a steel shim head gasket, then the head is PROBABLY stock and has not been previously milled. If it had a composite head gasket, then it has been off previously and has POSSIBLY already been milled a bit to get a flat gasket surface.
If the heads were given to you already off, the only way to know is to "cc" the chambers and see where they are at. Probably a GOOD IDEA even if you think they are virgins. The rule of thumb is that every .010" that you mill reduces the combustion chamber approximately 2 cc's down to where the combustion chamer turns into just a "D".
Go to the url link in my signature, then to the "Compression Calulator" is the left sidebar. Play with the number of cc's and watch the compression ration change.
Good luck
Dennis
You said "I have 3 stock 200 heads and wanted to play around with them a bit. I also have full access to a machine shop. Does anyone know how far you can deck the head on a stock 200 before you run into valve clearance problems?"
I'll be a Smart Alec and answer, "It depends"... Seriously. You need to tell us the casting number on each head. It will be like C9DE-6090 AA. The "C" means 1960. The "9" means 9th year... so a 1969. The casting numbers are on the firewall side on top of the log.
A 1967 head will have fewer cc's (higher compression) than a D4 (1974) head.
More is not always better, and bigger is not always better. (unless it is Dolly Parton.)
We have NEVER had Valve clearance problems.
I have ANGLED milled a 1974 62 cc head .110" with a .025 gasket to go on a 144ci block. Would I recommend that much... NO ! ! ! but I don't mind breaking a few parts to find out what works. You need to leave at LEAST .100" thickness on the gasket surface in the head. With a virgin head you can USUALLY safely go .090" with a .045 composite head gasket.
USUALLY, if you took the head off the engine, and it had a steel shim head gasket, then the head is PROBABLY stock and has not been previously milled. If it had a composite head gasket, then it has been off previously and has POSSIBLY already been milled a bit to get a flat gasket surface.
If the heads were given to you already off, the only way to know is to "cc" the chambers and see where they are at. Probably a GOOD IDEA even if you think they are virgins. The rule of thumb is that every .010" that you mill reduces the combustion chamber approximately 2 cc's down to where the combustion chamer turns into just a "D".
Go to the url link in my signature, then to the "Compression Calulator" is the left sidebar. Play with the number of cc's and watch the compression ration change.
Good luck
Dennis
kirkallen143
Famous Member
I have just milled my D5** head down 0.090" brining it to @ 47cc combustion chambers. We were close and almost got into the water jackets but didn't.
Kirk
ps. if you do go that far don't forget to massage out the oil passage at the back of the head.
Kirk
ps. if you do go that far don't forget to massage out the oil passage at the back of the head.
