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Old 04-05-2003, 03:51 PM   #1
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I'm changing valve stem seals on a 88 GTA 5.7L & decided to install a little better valve spring at the same time. The springs I got were from competitioin products & were stated to be Z28 springs. They also came with retainers. Their installed height are to be 1.700". BTW, I'm doing this in-vehicle. Well, if you remove the exhaust rotator & replace it with the supplied retainer, the installed height is 1.860" which will set the preload too low. The installed height WITH the rotator is 1.685, which is right for the new spring. I'm thinking the lock groove on the exhaust valves are cut higher for applications running valve rotators. I guess my question is, how do you replace the rotator with a plain spring retainer and maintain your 1.700" installed height. I'm .160" off. Am I missing something here in my thought process? A final question, do factory Z28 sbc use rotators on the exhaust valve? I'm in the middle of this right now, so if anyone can quicly reply, it would be helpful.
Thanks, FJK
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Old 04-05-2003, 04:12 PM   #2
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If I'm correct, the springs you have are the old version LT1 springs from the early '70s. Those engines didn't use rotators on the exhaust valves. The spring pockets were also not machined as deeply as what you have in your heads. The options you have now are to stack two or three 0.060" spring shims under each exhaust valve and use real retainers (trash the rotators) or manufacture a single spacer from a hardened material. If you use shims, I'd suggest two, and leave the spring just a little loose (taller). The reduced mass from the lack of a rotator coupled with the slightly better springs (120# @ 1.70" vs. 85# @1.70") should allow good control of the valve with the slightly reduced seat pressure.
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Old 04-05-2003, 05:56 PM   #3
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You'll need 1 .060 shim, 1 .030" shim and 1 .015" for each of the eight exhaust spring seats. (.105" total)
You can get them From local Automotive machine shops, some performance shops and from Competition Products.
When you install this combined with the factory valve spring oil shield (.030") and a stock retainer, you'll be good to go with the Z28 springs.

the exhaust spring seat is machined deeper in these heads

Last edited by F-BIRD'88; 04-05-2003 at 06:00 PM.
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Old 04-09-2003, 12:39 AM   #4
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Try offset locks, they make them in .030 so you can get away with only two shims. Good luck!
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Old 04-10-2003, 01:46 PM   #5
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Been there, done that many times. Your heads have the exhaust spring pocket milled slightly deeper than the intakes to compensate for the thicker exhaust rotator/retainer. They take exactly the same spring as the intake side if you keep the rotator/retainer in place.

Otherwise, if you ditch the rotator/retainer and go with standard retainers on the ehxaust side you'll have to shim the spring up as stated in above posts.

The exhaust valve lock groove is in the same place on the valve stem regardless of whether you use standard retainers or rotator/retainers.
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