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Old 09-16-2010, 02:35 PM
v8hed's Avatar
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Spring installed height issue with Dart Pro-1 heads

I've got all the parts to assemble my heads and, on the advice of folks on here, I decided to get +.100 longer valves. Now I've got hold of a valve spring mic, I've discovered the longer valves put my installed height at 1.88", meaning I'd need .130" of shims to get to Comp's recommended height of 1.75" with the 986-16 springs! So, question is this... should I see if I can return the longer valves and get them swapped for stock length valves which would leave me needing just a single .030" shim under each spring, or can I keep my longer valves and install x2 .060" shims under each spring? This would still leave me .010" out, but I think that would be acceptable(?) Returning my springs will be a real PITA as I'm in the UK and the valves were purchased from a vendor in the States.

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Old 09-16-2010, 03:20 PM
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Kind of a shame this wasn't sufficiently researched to determine the right valve length- I would have been on the phone or website to Dart and asked them. I'm not knocking you- just sayin' is all... but as long as the shims do not bring the bottom of the spring above the machined spring "cup" in the head, you should be OK. If, however, the spring cup isn't deep enough to still have some cup left to it after adding the 0.120" of shims, you will need to use taller springs or shorter valves.

Another option is to use -0.060" locks that absorb some height. This will mean just one 0.060" shim needed in order to have the correct installed height.

Yet another option is to use a "valve spring locator" that captures the spring by its ID, not the OD like a spring cup. This part would supply 0.062" of thickness, so would sit atop a 0.060" shim. You would select the correct part by your spring's ID. Unfortunately, the "VSL's" shown in the Competition Products catalog (NOT Comp Cams) does not show any that match your spring's OD or ID. Other manufacturers may have something that will fit.

BTW, don't worry if you are +/- 0.010" on the installed height.

Last edited by cobalt327; 09-16-2010 at 03:25 PM.
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Old 09-16-2010, 05:23 PM
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I should've mentioned... I've got a set of .060 ID locators, so I guess one of those + a .060 shim under each locator should do the trick.

Just hope the valve train geometry will check-out using stock length push rods and that I don't end-up needing shorter than stock length.

Thanks.
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Old 09-16-2010, 05:31 PM
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Quote:
Originally Posted by cobalt327
Yet another option is to use a "valve spring locator" that captures the spring by its ID, not the OD like a spring cup. This part would supply 0.062" of thickness, so would sit atop a 0.060" shim. You would select the correct part by your spring's ID. Unfortunately, the "VSL's" shown in the Competition Products catalog (NOT Comp Cams) does not show any that match your spring's OD or ID. Other manufacturers may have something that will fit.
Yea, I've got a set of Comp 4771-16, which do fit the 986-16 spring (.690" inner spring ID).
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Old 09-16-2010, 06:06 PM
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longer valves requires longer pushrods.

Higher lift cam requires longer pushrods.

Most high performance heads require longer pushrods.

But, some rocker arms require shorter pushrods, so its always best to mock-up your assembly and determine correct pushrod length.
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Old 09-16-2010, 06:22 PM
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Quote:
Originally Posted by lmsport
longer valves requires longer pushrods.

Higher lift cam requires longer pushrods.

Most high performance heads require longer pushrods.

But, some rocker arms require shorter pushrods, so its always best to mock-up your assembly and determine correct pushrod length.
Absolutely, gonna mock-up using checking springs and check the geometry with a set of +.100 moly push rods I've got laying around. Hopefully, they'll give me good geometry, otherwise I'll be shopping for new push rods.
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Old 09-16-2010, 06:29 PM
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With the .060" locator, I'd use a set of -.050/.060" locks and then fine tune with .010/.015/.020" shims to get where I want it to be. The "-" locks will also help insure you have no retainer to rocker body interference situation arise because they move the retainer down the stem away from the rocker.
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