Mutha Thumpr with stock rockers?
May 25th, 2019, 05:51 PM
#1
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Join Date: Feb 2019
Posts: 115
***** Thumpr with stock rockers?
Will the ***** Thumpr work with stock rockers and .020” taken off the heads? Not familiar with non adjustable rockers.
Whats the process to go about things, adjustable pushrods and non-stock length pushrods or can I shim anything?
Cam is:
.500/.486
234/249
107
Whats the process to go about things, adjustable pushrods and non-stock length pushrods or can I shim anything?
Cam is:
.500/.486
234/249
107
May 25th, 2019, 11:29 PM
#2
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Join Date: Mar 2011
Posts: 558
it should. My cam is .504 on both. Stock pushrods worked fine.
May 26th, 2019, 05:41 AM
#5
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Join Date: Mar 2008
Posts: 3,847
ideally you will choose pushrod lengths to give about .020" preload on the lifters. The rocker slots should be long enough for the lift of your cam. With significantly higher lifts, you would have to elongate the slots in the rockers.
May 26th, 2019, 07:47 AM
#7
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Join Date: Sep 2017
Location: St. Paul Minnesota
Posts: 4,047
1. A simple answer to shimming rocker arm stands is yes. Your cam lift isn't much more than an Oldsmobile cam. Milling .020" from the heads isn't much either. You probably had more than enough lifter preload before.
2. As Run to Rund implied, check the rocker arm slots and enlarge them if needed.
3. Ironically, "back in the day" when NHRA stock required "stock" valve gear, shimming rocker arm stands was standard practice. In fact, Oldsmobile suggested (shim difference from one side of the stand to the other) is no more than 1/32" (.031"). Some racers replaced the "paper clip" wire valve lifter disk retainers with internal snap rings.
.....Just my two cents worth.
If you would like more info, PM me.
2. As Run to Rund implied, check the rocker arm slots and enlarge them if needed.
3. Ironically, "back in the day" when NHRA stock required "stock" valve gear, shimming rocker arm stands was standard practice. In fact, Oldsmobile suggested (shim difference from one side of the stand to the other) is no more than 1/32" (.031"). Some racers replaced the "paper clip" wire valve lifter disk retainers with internal snap rings.
.....Just my two cents worth.
If you would like more info, PM me.
Last edited by OLDSter Ralph; May 26th, 2019 at 08:03 AM. Reason: Additional info
May 26th, 2019, 10:50 AM
#8
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Join Date: Feb 2019
Posts: 115
Ok, so sounds like I’m just overthinking. It just seemed to push the plunger down a good bit when I tightened #1 valves. Yes they are both on base circle. I’ll shim as necessary if it seems like I think it may be excessive.
May 26th, 2019, 02:37 PM
#9
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Join Date: Mar 2011
Posts: 558
Mark the pushrod with a permanent marker at the push rod hole on the bottom of the head. Then tighten down the rocker pedestal. You will then see how far you have compressed the lifter. You can use a feeler gauge at that point to measure the gap between the bottom of the head and your mark.
The spec is 20 to 60 thou of preload.
The spec is 20 to 60 thou of preload.
May 26th, 2019, 03:16 PM
#10
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Join Date: Sep 2006
Location: Utah
Posts: 147
I believe it’s highly recommended to use adjustable valve train on anything above .500 lift, I’m 485/490 and I’m still going to adjustable, takes all the guess work out of shimming to get the correct valve adjustment
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