Exhaust Valve Rotator Eliminators - Team Camaro Tech
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post #1 of 16 (permalink) Old Apr 15th, 08, 11:21 AM Thread Starter
 
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Exhaust Valve Rotator Eliminators

When did chevy start putting exhaust valve rotator eliminators on the bb heads? Are they needed for all bb heads or just the vortec? I'm having a set of bare 049's done and am buying all new components and wasn't sure if I needed these?
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post #2 of 16 (permalink) Old Apr 15th, 08, 03:14 PM
 
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Re: Exhaust Valve Rotator Eliminators

I'm not sure what year GM started using rotators. I think around mid '70s when unleaded hit us hard; not sure.

Personally, I have always used spacers , and disposed of the rotators. Reason - rotator will not take higher spring pressures for solid lifter cams.
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post #3 of 16 (permalink) Old Apr 15th, 08, 04:46 PM
 
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Re: Exhaust Valve Rotator Eliminators

I think truck work engines had them moreso than regular car use engines b/c I know my good -781's have them on the exhaust side and they came off my '75 454 "TSC" P/U engine.

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post #4 of 16 (permalink) Old Apr 15th, 08, 06:30 PM
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Re: Exhaust Valve Rotator Eliminators

Quote:
Originally Posted by brew92 View Post
When did chevy start putting exhaust valve rotator eliminators on the bb heads?
Brew,
GM never put rotator "eliminators" on an engine. As far as weather you need them or not, your machine shop should be able to tell you. There are several combinations of the way the heads were machined and the types of springs used so the only way to tell what you need is to check the installed heights with the parts you are using, then go from there.

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post #5 of 16 (permalink) Old Apr 17th, 08, 08:22 AM Thread Starter
 
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Re: Exhaust Valve Rotator Eliminators

Thanks Bill,

Just so I understand, the purpose of the rotator eliminator is to keep the spring from turning and wearing out the spring seat and also to correct the spring height?

Jim
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post #6 of 16 (permalink) Old Apr 17th, 08, 08:52 AM
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Re: Exhaust Valve Rotator Eliminators

My understanding is you *want* the valve to rotate that way it gets even wear. Otherwise you risk wearing one side of the tip more than the other, then that will put more wear on the guide. All this results in needing to rebuild the head much sooner than otherwise would be necessary (since you start burning oil).

I could understand on some high rpm race motors that get rebuilt every season (or few races) you might not want them rotating but on a street motor I think you very much would.

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post #7 of 16 (permalink) Old Apr 17th, 08, 09:26 AM
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Re: Exhaust Valve Rotator Eliminators

The purpose of the rotator is to keep the exhaust valve cool by rotating it against its seat.

Haven't seen any burnt exhaust valves with rotators? Not as common as it used to be.

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post #8 of 16 (permalink) Old Apr 17th, 08, 10:54 AM
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Re: Exhaust Valve Rotator Eliminators

For one thing the BBC is common in the commercial arena where it is operated under constant load and where the exhaust rotators do their thing . Given the total number of them made only a handful ever found their way into PSGR cars. Have you ever stop at a light next to a dump truck with a BBC idling and note the driver looking around for another truck - lol

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post #9 of 16 (permalink) Old Apr 17th, 08, 11:52 AM Thread Starter
 
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Re: Exhaust Valve Rotator Eliminators

Ok, just got this off of the comp cams website:

Big Block Chevrolet Seat Spacers
Late model Big Block Chevrolet engines are originally equipped with exhaust valve rotators. Until now, the only way to make up for the rotator was to stack .300” of shims under the spring. This was not only sloppy but also did not fit as well as this new part. This will locate the spring with an outside step so the spring cannot “walk” around on the head

4779-8
Chevrolet Big Block Exhaust
Rotator Eliminator .300”

Ok, now my question is, if I'm installing new springs and don't have the rotators then I need these?
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post #10 of 16 (permalink) Old Apr 17th, 08, 12:32 PM
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Re: Exhaust Valve Rotator Eliminators

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Ok, now my question is, if I'm installing new springs and don't have the rotators then I need these?
No, you just need non-rotator length springs ...

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post #11 of 16 (permalink) Old Apr 17th, 08, 04:37 PM
 
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Re: Exhaust Valve Rotator Eliminators

And remember, there are two stock BB head spring install heights!Earlier, 1.88" and later at 1.80" so make DARN sure you have the right springs and retainers so you hit either like need's to be done!I've been all through this crap!And if your spring is some too stout on the seat or over the nose, you can use a different height retainer and/OR .050" +/- locks to adjust this too!pdq67PS., spring rate is figured this way! Pounds at lift - pounds on the seat/ Seat height - lift height!To figure pounds at lift, you do it this way. Pounds at seat + rate x lift!Hope this helps.



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post #12 of 16 (permalink) Old Apr 17th, 08, 06:15 PM
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Re: Exhaust Valve Rotator Eliminators

Jim,
No matter what any one else says .... the only way to know which springs you need are to measure your particular heads to see what the installed heights are, period.

There are big block heads with no rotators.
There are big block heads with exhaust rotators and two different length springs.
There are big block heads with exhaust rotators and all of the springs the same
There are Big Block heads with Exhaust and Intake valve rotators.
There are probably big block heads with some other combination I have not seen too

Anyone who really works in a machine shop on a daily basis has learned that GM (and all of the others) have used so many different combinations of springs/rotators/ etc that the ONLY way to know is to measure. Period !!!!!

As far as the reason for the eliminators .... I cannot swear to it, but most performance applications do not need a crazy rotator under the spring, which is moving around too much anyway. The rotators are actually designed to keep the valve from wearing the seat in high load situations. Every time the exhaust valve closes, if it is red hot, it tends to "micro weld" itself to the seat. If you did not rotate it, eventually it would weld it self and come loose in the same spot so many times that it starts to erode the seat and the valve sinks into the head. The rotation itself is probably better for a mild engine, but once you start getting higher spring loads, and much higher rpm, spring stability is more important so the rotators should be removed.

Hope this helps,

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post #13 of 16 (permalink) Old Apr 17th, 08, 06:53 PM
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Re: Exhaust Valve Rotator Eliminators

Comp Cams have BBC Seat Spacers .300" thick PN 4779-8 which I believe are made by CRANE named BBC Exhaust Rotator Eliminators - I don't see the Crane PN now but I used them on many BBC heads.

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post #14 of 16 (permalink) Old Apr 18th, 08, 09:23 AM
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Thumbs up Re: Exhaust Valve Rotator Eliminators

Quote:
Originally Posted by BillK View Post
Jim,
...
There are big block heads with no rotators.
There are big block heads with exhaust rotators and two different length springs.
There are big block heads with exhaust rotators and all of the springs the same
There are Big Block heads with Exhaust and Intake valve rotators.
There are probably big block heads with some other combination I have not seen too

... the ONLY way to know is to measure. Period !!!!!


Hope this helps,
The only BB head I've never seen with rotators are the Rectangular Port type - as Bill said, all the others have varing combinations of rotators on both the Exhaust and Intakes to meet the service-life needs of the original application.

Since you will need to replace the original springs in almost all head applications that had rotators to use them in performance applications, you might as well just buy the proper length springs and not woory about "adapters" to replace the rotators.
GM/Chevy makes several great replacement performance spring combinations in both double and double w/damper styles
These are available in various seat pressures, open pressures, srping rates and stack heights - so replacing the originals with good factory parts is not hard or that expensive.
Aftermarket stuff is very good in many cases also and their prices can be attractive for certain parts.
You and/or your machinist can look at your application and needs and find a suitable replace system quite easily.

Any performance modification to the valve spring sytem should be done using carefull measure measurement of installed and compressed hieghts, as well as the spring pressures in those conditions to assure the system will perform correctly - period, as Bill also stated

A little time and money properly spent in this area will give youa a great performing and trouble free engine

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Last edited by Vintage 68; Apr 18th, 08 at 09:35 AM.
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post #15 of 16 (permalink) Old Apr 18th, 08, 11:12 AM
 
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Re: Exhaust Valve Rotator Eliminators

My good -781's off my '75, 454 P/U engine had them on the exhaust valves!

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