Discussion
Dear Speed Six owners,
From my reading over the past few days, it would seem that the two largest problems within the range of Speed Six engines are related to either:
1.) a lean condition in the #6 cylinder (or is it 4,5, and 6 to varying degrees?) and
2.) the cam followers excessively loading the valve stems through their arcing motion.
Having spoken with my brother who has great experience making things blow up, I’ve learned his opinion on the “valve stretch” encountered by some of you. He feels that if the exhaust valve heats up too much because of a lean condition, the valve head will mushroom thus giving the impression of the valve stem stretching.
If most of you are seeing this “valve stretch” in the rear three cylinders or mostly on #6, this would lend credence to his opinion.
The piston skirt wear some of you wrote about can also be caused by “pinking” as this moves the pressure center to the point of pre-ignition and rocks the piston on the wrist-pin.
If the three companies that are working on revised inlet manifolds have succeeded in their work, your problems should be greatly reduced.
My thought regarding the side loading of the valve stems is that if finger followers could be made with roller tips, this would go a long way toward reducing the side loading on the valve stem as the tip of the follower would no longer drag across the valve tip. Is there space to do this? I cannot tell from the pictures that are posted. Another thing that comes to mind regarding the “flawed” valvetrain geometry is that the pivot point for the followers might be more easily modified than the location of the cams but to equal or greater effect.
I don’t mean to rub salt into open wounds, just trying to help with an outsider’s perspective and hoping you will all be able to make your cars live longer.
OK, START
ing me now!
From my reading over the past few days, it would seem that the two largest problems within the range of Speed Six engines are related to either:
1.) a lean condition in the #6 cylinder (or is it 4,5, and 6 to varying degrees?) and
2.) the cam followers excessively loading the valve stems through their arcing motion.
Having spoken with my brother who has great experience making things blow up, I’ve learned his opinion on the “valve stretch” encountered by some of you. He feels that if the exhaust valve heats up too much because of a lean condition, the valve head will mushroom thus giving the impression of the valve stem stretching.
If most of you are seeing this “valve stretch” in the rear three cylinders or mostly on #6, this would lend credence to his opinion.
The piston skirt wear some of you wrote about can also be caused by “pinking” as this moves the pressure center to the point of pre-ignition and rocks the piston on the wrist-pin.
If the three companies that are working on revised inlet manifolds have succeeded in their work, your problems should be greatly reduced.
My thought regarding the side loading of the valve stems is that if finger followers could be made with roller tips, this would go a long way toward reducing the side loading on the valve stem as the tip of the follower would no longer drag across the valve tip. Is there space to do this? I cannot tell from the pictures that are posted. Another thing that comes to mind regarding the “flawed” valvetrain geometry is that the pivot point for the followers might be more easily modified than the location of the cams but to equal or greater effect.
I don’t mean to rub salt into open wounds, just trying to help with an outsider’s perspective and hoping you will all be able to make your cars live longer.
OK, START
ing me now!Shooting You..................Not At All.
The Roller Rocker (Roller Finger Follower) is a totally sound Idea. I just don't know if there is physically the space to build this into a finger follower. When you think of the old BMC A & B Series Engines that were used in racing, they used to knock out there valve guides in a few hundred miles due to the extreme lift on racing cams and the angles that this caused between the rockers and valves, causing heavy loads to be put on the valve stem and valve guides. Then a few companies brought out the Roller Rockers which prolong the life of racing engine valve guides almost indefinately, due to reducing the side loads on the valves and valve guides. Anyone who's read David Vizard books will see that he was a great supporter of the Roller Rocker. The roller obviously causes much less side loadings when opening the valves that a rocker or finger follower acting directly (metal to metal) in friction.
Your also quite right when you refer to the valve head distorting due to higher than expected tempretures in the combustion chambers (Due to lean running) and the effect on the head of the valve and not necessarily the valve stem, due to the additional extreme heat.
Basically we all know it's a sound design, but with components that are not correctly spec'd.
The Roller Rocker (Roller Finger Follower) is a totally sound Idea. I just don't know if there is physically the space to build this into a finger follower. When you think of the old BMC A & B Series Engines that were used in racing, they used to knock out there valve guides in a few hundred miles due to the extreme lift on racing cams and the angles that this caused between the rockers and valves, causing heavy loads to be put on the valve stem and valve guides. Then a few companies brought out the Roller Rockers which prolong the life of racing engine valve guides almost indefinately, due to reducing the side loads on the valves and valve guides. Anyone who's read David Vizard books will see that he was a great supporter of the Roller Rocker. The roller obviously causes much less side loadings when opening the valves that a rocker or finger follower acting directly (metal to metal) in friction.
Your also quite right when you refer to the valve head distorting due to higher than expected tempretures in the combustion chambers (Due to lean running) and the effect on the head of the valve and not necessarily the valve stem, due to the additional extreme heat.
Basically we all know it's a sound design, but with components that are not correctly spec'd.
Edited by Jim Green on Sunday 12th October 01:26
Edited by Jim Green on Sunday 12th October 01:29
Edited by Jim Green on Sunday 12th October 01:45
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