Closed head /v Open head
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Freshman User
Joined: Jul 2003
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Closed head /v Open head
Ok, I just picked up a 300 i6 for $100.00 and it has a closed head with it, cuz the head on it is cracked, and the motor looks a bit worn.
What should I do, take the time to rebuild this motor ( take me 2 years or more) or do I rework the closed head and replace the open head on my truck now??
I just put new rod, and main barrings in the motor that is in my truck now, had the crank tanked and polished, but I will rebuild the second motor it will just take time
What should I do, take the time to rebuild this motor ( take me 2 years or more) or do I rework the closed head and replace the open head on my truck now??
I just put new rod, and main barrings in the motor that is in my truck now, had the crank tanked and polished, but I will rebuild the second motor it will just take time
Post Fiend
Joined: Jan 2000
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From: Metro Detroit (Redford)
Closed head /v Open head
Not sure what you mean by "closed head" and "open head." Something to do with the combustion chamber maybe? Would you mind defining these terms as I have never heard them before.
Posting Guru
Joined: May 2003
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From: South Dakota
Closed head /v Open head
Typically 'closed' head and 'open' head refered to open chambers and closed chambers. With open being the larger in CCs.
If a motor came with 'open' chambers or larger combustion chambers, then putting on 'closed' combustion chambers would in all likelyhood result in damage from the valves impacting the piston tops.
However one way to check for this is to put modleing clay on top of the piston(dust the piston top and chambers with baby powder to ease removal of the clay), put the head on the block without plugs, timing gear installed, snug down with bolts and slowly rotate the crank BY HAND a couple of times. Making sure to do this slowly in case the clearance is so tight the valves are going to impact the piston. Then remove the head and check the thickness of the clay where the valves squeezed it the thinnest. Do this by using a sharp knife and slice lengthwise thru both valve depressions in the clay. Then measure the thickness.
Even if there is enough clearance by putting on 'closed' heads this could raise your compression level to the point of requiring premium gas use all the time. And to use this head you may need to replace the pistons with the correct ones for this head.
If a motor came with 'open' chambers or larger combustion chambers, then putting on 'closed' combustion chambers would in all likelyhood result in damage from the valves impacting the piston tops.
However one way to check for this is to put modleing clay on top of the piston(dust the piston top and chambers with baby powder to ease removal of the clay), put the head on the block without plugs, timing gear installed, snug down with bolts and slowly rotate the crank BY HAND a couple of times. Making sure to do this slowly in case the clearance is so tight the valves are going to impact the piston. Then remove the head and check the thickness of the clay where the valves squeezed it the thinnest. Do this by using a sharp knife and slice lengthwise thru both valve depressions in the clay. Then measure the thickness.
Even if there is enough clearance by putting on 'closed' heads this could raise your compression level to the point of requiring premium gas use all the time. And to use this head you may need to replace the pistons with the correct ones for this head.
Senior User
Joined: Sep 2003
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Closed head /v Open head
I don't see any way that piston contacting valve is related to Cyl. head CC shape. Everything is in the same place, the CC is just smaller. You have, however described the procedure that should be used EVERY TIME AN ENGINE IS CHANGED INTERNALLY. New cam, new heads, new valves, new pistons.....
Basically, an open chamber head has portions of the CC extending to the full bore of the Cyl. "D" CC's are open chamber. Peanut shaped are closed.
Basically, an open chamber head has portions of the CC extending to the full bore of the Cyl. "D" CC's are open chamber. Peanut shaped are closed.
Posting Guru
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From: South Dakota
Closed head /v Open head
I am not talking about shape of the chamber, rather the size of the chamber ie CC or cubic centmeters. An open chamber head has more room and or height therefore the valves are usually farther away from the piston. Therefore the piston could be closer to the top of the block. With a closed chamber the valves are usually closer to the piston due to a less taller chamber. So if the piston is to close to the top of the block for the closed chamber head, the vavles can impact the piston top. By changing the pistons or rods to effectively lower the piston, this would keep the valves from contacting the tops. The only sure way of determining this is as I said. Use modeling clay. Even when purchasing different pistons or heads it is a good idea to check this, even if they were recommended for that motor. If the deck has been milled and or the head(s) milled this can bring the vavles to close to the pistons. If the clearance is a little on the tight side a person can use a thicker head gasket to add some clearance. That is why some pistons come with valve notches cut in them, to add clearance for the valves while retaining compression ratio.
Posting Guru
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From: South Dakota
Closed head /v Open head
Unfortunately incorrect. Hopefully this does not lead to broken pistons or valves.
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New User
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Closed head /v Open head
Pistons and valves can occupy the same space, just not at the same time. It's called an interference engine and a lot of cars are set up like that. Just don't screw the timing up or you will have lots of bent valves.
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Closed head /v Open head
The closed head is made for the 300 i6 so there should be no problems with the Pistons and Valves, as for the timing it will be set the same as it would be with the open head.
The only thing that will be changed is the compresion, from around 8.1 to 9.5 give or take a little, the only differance between the open and closed heads are that open heads have an oval and the closed are more of a peanut shape, there for less air space, and more compresion
The only thing that will be changed is the compresion, from around 8.1 to 9.5 give or take a little, the only differance between the open and closed heads are that open heads have an oval and the closed are more of a peanut shape, there for less air space, and more compresion
Post Fiend
Joined: Jan 2000
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From: Metro Detroit (Redford)
Closed head /v Open head
Someone once posted photographs of the heads for both carburated and EFI 300 I6's. From memory it would appear the carb version was open head and the EFI closed.
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