Valve Spring Installed height
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Intermediate
Joined: Apr 2007
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Valve Spring Installed height
I have a late 1986 vette with the 128 aluminum heads. I replaced the valve springs before putting 1.6 roller rockers on. I was going to take the exaust valve rotators off and put retainers on. The book i had said to add .12" shims to compensate.
The manual says the installed spring height should be 1.7188 on intake and 1.5938 on exaust. When i measured i got from 1.718 to 1.741 on the intake and 1.7 to 1.724 on the exaust. I never changed any of the shims around when i did the springs. I dont understand how the exaust valve height could be so far off. The shims on it now all look about the same for intake and exaust. I can see that the exaust spring surface is machined down at least .1 lower than the intake. Has anybody else checked their installed hieght. If i took the exaust valve rotator off i dont know if i should just do a .12" shim to compensate for that or use at least .25" to make it what it is supposedly supposed to be.
The manual says the installed spring height should be 1.7188 on intake and 1.5938 on exaust. When i measured i got from 1.718 to 1.741 on the intake and 1.7 to 1.724 on the exaust. I never changed any of the shims around when i did the springs. I dont understand how the exaust valve height could be so far off. The shims on it now all look about the same for intake and exaust. I can see that the exaust spring surface is machined down at least .1 lower than the intake. Has anybody else checked their installed hieght. If i took the exaust valve rotator off i dont know if i should just do a .12" shim to compensate for that or use at least .25" to make it what it is supposedly supposed to be.
Burning Brakes
Joined: Aug 2006
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From: Seattle WA
I'm confused - for the exhaust hgt measurements you stated, were those with the rotators and without the .12 shims? Or were they with neither? If neither, you should be right in the ballpark with the .12 shims added at 1.58-1.60.
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The exaust measurement was with the rotator and without a .12 shim. I would need a .12 shim just to make it the right height with the rotators and then another .12 shim to compensate for taking the rotators off(about .25 total)
I am just questioning the accuracy of the manual on the exaust installed height. The spec says for 1984 to 1996 in the haynes manual. What has anyone else seen on their car?
I am just questioning the accuracy of the manual on the exaust installed height. The spec says for 1984 to 1996 in the haynes manual. What has anyone else seen on their car?
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The installed spring height specs are the stock specs. I am just using stock springs.
Is that normal though that the exaust valves have worn in about 1/8 inch, and should i just shim it to bring it back in spec?
Is that normal though that the exaust valves have worn in about 1/8 inch, and should i just shim it to bring it back in spec?
Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
My factory manual says there are different installed heights for intake and exhaust.
1 23/32" intake
1 19/32" exhaust
Edit: I see now you already know there is a difference. I would install what ever shims are required to get each spring to it's correct installed height. I tossed all the rotators and shields, went with LT4 springs and shimmed as required.
1 23/32" intake
1 19/32" exhaust
Edit: I see now you already know there is a difference. I would install what ever shims are required to get each spring to it's correct installed height. I tossed all the rotators and shields, went with LT4 springs and shimmed as required.
Last edited by AGENT 86; Jan 22, 2008 at 09:58 AM.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
The installed spring height specs are the stock specs. I am just using stock springs.
The RRs give steeper slopes to the valve movement which requires more spring force to properly control the valve.
When I installed RRs on my #113 heads I used Comp Cams #981 springs, shimmed for a little more seat force as well as more over the nose.
Remember that our L98s are not designed to rev much over 4,500rpm so the stock springs are rather weak, around 80lbs on seat if memory serves.
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Thread Starter
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Does anybody know where i can get about a .300 thick valve spring seat for the exaust springs. I seen they sell them for the BB chevy engine at Jegs for eliminating the exaust valve rotators, but not for the SB Chevy. Other wise i would need to add 4 .06 shims under the stock .05 spring seat and im not sure if that is a good idea.
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Any help would be appreciated.
I was going to run it on the dyno as soon as I get it back together and post the results.
I was the one that posted the results of all the bolt ons.
I was going to run it on the dyno as soon as I get it back together and post the results.
I was the one that posted the results of all the bolt ons.
Last edited by 86vettez51; Jan 27, 2008 at 05:38 PM.
Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
Try your local machine shop that rebuilds heads etc. I'm using the L98 base with the LT4 base and shims in between the two.(LT4 springs)
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I get to a .300 exaust spring seat by .125 to compensate for removing the exaust valve rotator + .125 to get the installed height back in spec from about 1.72 to 1.59 + .05 which is the original thickness of the spring seat.
.125+.125+.05 = .300
I found them for the BB chevy but not SB chevy.
Any sources?
.125+.125+.05 = .300
I found them for the BB chevy but not SB chevy.
Any sources?
