As I rebuild the heads on my '62,should I go with valve seats for unleaded fuel?
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Re: Unleaded Heads
Heads will last quite long without hardened valve seats provided the engine sees little wide-open-throttle or extreme prolonged performance duty. Even then only the exhaust side need benifit from hardened seats. I've never used them on the street with unleaded fuel and rather brisk operation. I've noted very little valve seat recession upon rebuilds.
Varooom!
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Re: Unleaded Heads
Dave, something I've been doing for years to keep my exhaust valves and seats up is installing rotators on the valves like a diesel engine has. It speaks for its self and keeps the valve seat and mating surfaces evenly worn.grr#33570Comment
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Re: Unleaded Heads
Hey grr! How about discribing these rotators and tell us how they work.
Varooom!
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Re: Unleaded Heads
Are these valve rotators readily available for my valves?Comment
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Re: Unleaded Heads
Dave:
Absolutely!! You don't want to use lead additive, do you?
All you need to do is have hardened EXHAUST seats inserted. Invest in a good 3 angle valve job, as this gives the best bang for the buck to improve flow. Also, make sure the valve springs are replaced and the spring heights are set up properly. I don't recommend letting just anyone do the head work - try to find a good shop that specializes in heads.
By the way, I have a pair of 461 heads dated G93 and G123. These have the 1.94" intakes used on the earlier 327 motors, and are in good shape.
Good luck.
JoeComment
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Valve rotators
"Rotator assemblies" on the exhaust side are called out in the parts manual for all 73 to 78 Corvette 350s, 6263794, and 330848 for 73-74 454s. I believe they replace the conventional retainer, but I actually don't recall ever seeing a rotator. Maybe someone with a service manual from this era can post additional details.
DukeComment
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Re: Unleaded Heads
Dale------
Rotators were used on the exhaust valves of many Chevrolet (and other) engines beginning in about 1973, but they may have been used as early as 1971 on some engines. The rotator replaces the valve spring cap (a.k.a. retainer). It is a factory-sealed unit which contains sort of a simplified "sprag clutch" assembly which induces the valve to rotate a little bit during each cycle of the valve. However, the rotator assembly is considerably thicker than a normal valve spring cap and other accomodations have to be made in order to use them.
During the early use of rotators on small blocks, the valve spring pockets of the cylinder head were configured exactly like earlier heads which didn't use rotators. In this configuration, both intake and exhaust valve spring pockets are machined to the same depth. When used on these heads a special length valve spring has to be used on the exhaust side in order to compensate for the extra thickness of the rotator. If this is not done, and VERY FEW folks know about this including many automotive machinists, the exhaust valve will have significantly increased spring pressure due to, effectively, shimming the valve spring by about 1/4". The spring required, which, to my knowledge, is ONLY available from GM, is GM #6263796. This spring is about 1/4" shorter than the standard GM #3911068 spring and produces equal pressure when used with a rotator. After about 1977, the cylinder heads were machined with different depths for intake and exhaust so that the rotators could be used on the exhaust side while using the same GM #3911068 spring for BOTH intake and exhaust. However, if rotators are used on any head of approximately pre-1977 vintage, then the GM #6263796 valve spring MUST be used on the exhaust side. Any attempt to machine the exhaust valve spring pockets of these heads by the required compensatory amount, will usually result in "break-through" to the water jacket.
The initial rotators used for small block engines were GM #6263794. These rotators proved to be problematic and were replaced about 1985 by GM #14042575 which used an improved internal design. Externally, they are virtually identical, however. GM stopped using rotators in 1987 for Corvette and certain other V-8 engines.
Except, possibly, if they were used during the 1971-72 period, rotators were always used with cylinder heads which also had induction-hardened valve seats. Personally, I am not a big fan of the use of rotators.In Appreciation of John HinckleyComment
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Re: Unleaded Heads
Hey Joe Lucia, THANKS for the tutorial! I learn something new every day. Being one of those who never ventured out of the straight axle era I was not aware of these rotators. Thanks agin.
Varooom!
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Re: Unleaded Heads
Hardened exhaust valve seats are ABSOLUTELY NOT NECESSARY for Corvettes driven on the street using unleaded gas.
Varooom
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Re: Unleaded Heads
Joe,plan to use the original heads,but thanks.Comment
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Re: Unleaded Heads
Dale:
This may be true. But since the heads are already out, and need rebuild, it would be foolish to skip this upgrade considering the relatively small investment involved.
JoeComment
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Re: Unleaded Heads
It is written, (by Smokey Yunick), that thy shalt not fix what ain't #&*%ing broke!
Varooom!
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Re: Unleaded Heads
HEY DAVE:
You aren't using Discussion Board to sell parts are you?
That will piss off a lot of people, TRUST ME! I've been there.
Varooom!
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Re: Unleaded Heads-exh/valve rotators
Joe explains the theory of the rotators function well.I first had some installed on a 70 LT1 when I bought a set of new HP/SB 202 64cc heads otc at my local chevy dealership. The heads came with hardened seats screw in studs, guide plates etc.from the factory. I had the local cyclinder head shop install the whole new valve train assy. w/rotators. I never had any problems with the valves until I broke my timing chain shifting into 3rd at 6500 rpm. No bearing damage,(use synthetic) but bent the life out of several valves. I would recommend calling your local cylinder head shops and ask their opinions on rotators. I thank Joe again for his input.But to make a long story short, do what you want as I really didn't need the rotators but didn't know where I could find food (leaded fuel)at that time for the engine other than the strip. That's when I found out about Stone oil lead Supreme 130 (muscle car magizine)which the engine was fed and consumed happily. Kemco sells the same product as they provided Stone products which was out of GA. but no longer in service.grr#33570Comment
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