have you ever shimmed the stock rocker stands?
09-06-2012, 07:33 PM
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have you ever shimmed the stock rocker stands? Title has it. I'm new to the gen 3/4 and I've come across something I haven't read about.
I'm putting together an iron 408 with ls3 heads, prc springs, stock rockers with the comp cams trunion kit.
When I bolted everything down and checked the swipe of the rocker arm across the valve stem, I found that the pattern was very close to the inside edge of the stem. The only way to center it was to raise the rocker stand about .060. with a washer under the stand.
Anyone else see this? Are there dedicated shims availible to raise the stand?
I can't explain the fact that the pattern is way off. I did have a valve job done and that may have sunk the valves a bit. And the comp cams trunion might lower the rocker a bit.
Any ideas?
I'm putting together an iron 408 with ls3 heads, prc springs, stock rockers with the comp cams trunion kit.
When I bolted everything down and checked the swipe of the rocker arm across the valve stem, I found that the pattern was very close to the inside edge of the stem. The only way to center it was to raise the rocker stand about .060. with a washer under the stand.
Anyone else see this? Are there dedicated shims availible to raise the stand?
I can't explain the fact that the pattern is way off. I did have a valve job done and that may have sunk the valves a bit. And the comp cams trunion might lower the rocker a bit.
Any ideas?
09-06-2012, 08:11 PM
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Yeh, longer pushrods are a given. I never expected to use the stock Length anyhow. High lift cam ensured new pushrods.
Having said that though..... Pushrod length should not affect the swipe pattern on the valve stem.
Clark
Having said that though..... Pushrod length should not affect the swipe pattern on the valve stem.
Clark
09-08-2012, 08:32 PM
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Hey, I want to post a follow up and explain a mistake I made.
When I originally put this thing together and checked the rocker arm swipe at the valve, I did so with a lifter that had no oil in it. As such, this lifter compressed when lifting the valve and altered the swipe pattern on the valve stem. At that time the pattern was centered very close to the inside edge of the valve stem. This led me to believe that the rocker arm should be shimmed up to move the swipe pattern to the center of the stem.
Today I re- did the same check but I used an adjustable length pushrod set at a length that preloads the lifter at full compressed travel. Now the swipe pattern starts at the inside edge of the stem and travels all the way across to just short of the far edge. Basically my .621 lift cam with stock style rockers creates a wide swipe pattern across the valve stem BUT the stock rocker stands un-shimmed seems to keep it centered on the stem.
Just wanted to pass this along.
Clark
When I originally put this thing together and checked the rocker arm swipe at the valve, I did so with a lifter that had no oil in it. As such, this lifter compressed when lifting the valve and altered the swipe pattern on the valve stem. At that time the pattern was centered very close to the inside edge of the valve stem. This led me to believe that the rocker arm should be shimmed up to move the swipe pattern to the center of the stem.
Today I re- did the same check but I used an adjustable length pushrod set at a length that preloads the lifter at full compressed travel. Now the swipe pattern starts at the inside edge of the stem and travels all the way across to just short of the far edge. Basically my .621 lift cam with stock style rockers creates a wide swipe pattern across the valve stem BUT the stock rocker stands un-shimmed seems to keep it centered on the stem.
Just wanted to pass this along.
Clark
09-09-2012, 08:10 PM
#5
So you fully compressed the lifter and you have a correct wipe?
What happens when you get oil in the lifter? Now your back to square 1.
Best way to do this is to take the lifter apart and shim it up solid, set your wipe pattern with an adjustable push rod, then add in your lifter pre load when ordering your push rods
What happens when you get oil in the lifter? Now your back to square 1.
Best way to do this is to take the lifter apart and shim it up solid, set your wipe pattern with an adjustable push rod, then add in your lifter pre load when ordering your push rods
09-09-2012, 08:47 PM
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No
While it is true that I used a compressed lifter, that change in dimension was corrected by using a longer pushrod. I simulated the geometry that the valve train will have when running.
My first attempt at measuring the swipe pattern suffered from the failure You describe. The total lift was reduced due to lifter compession. This created a narrow swipe pattern that was close to the inside edge of the valve stem. This led me to believe that a shim under the rocker was warranted.
The second attempt at measuring the swipe I used a longer pushrod that fully compressed the lifter while the valve was closed. The valve and lifter then saw the full lift of the cam. This created a pattern that started close to the inside edge of the stem but traveled much further across the stem. With the end result being it was basically centered.
A .624 lift cam with stock rockers creates a very wide swipe pattern on the valve stem, it is almost edge to edge.
Clark
While it is true that I used a compressed lifter, that change in dimension was corrected by using a longer pushrod. I simulated the geometry that the valve train will have when running.
My first attempt at measuring the swipe pattern suffered from the failure You describe. The total lift was reduced due to lifter compession. This created a narrow swipe pattern that was close to the inside edge of the valve stem. This led me to believe that a shim under the rocker was warranted.
The second attempt at measuring the swipe I used a longer pushrod that fully compressed the lifter while the valve was closed. The valve and lifter then saw the full lift of the cam. This created a pattern that started close to the inside edge of the stem but traveled much further across the stem. With the end result being it was basically centered.
A .624 lift cam with stock rockers creates a very wide swipe pattern on the valve stem, it is almost edge to edge.
Clark
Last edited by mallder; 09-09-2012 at 08:53 PM.
