FYI > Did some measuring of drivetrain parts > What we found
02-04-2003, 08:40 PM
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FYI > Did some measuring of drivetrain parts > What we found We did some measuring with a micrometer on my car's stock vs Thunder Racing cam and the pushrod length while I had my engine apart (head/cam/header change). Here is some info that I will pass on to you for what it's worth:
Stock LS1 Base Circle is 1.552” across the lobe. That equals a 0.776” centerline to heel distance.
TR-220 Base Circle is 1.502” across the lobe. That equals a 0.751” centerline to heel distance.
Thats exactly .025” less than stock (if your concerned with lifter preload).
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Also, be advised that after measuring the the stock length Thunder Racing 7.40" hardened pushrods against a stock LS1 rod, the TRs are exactly .016" longer.
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Also measured the factory spec preload on a my stock LS1 engine.
It took anywhere between 1 3/4 to 2 turns of the rocker bolt to tighten from "zero preload" to 22 Ft Lbs torque.
Here is an explanation of preload if anyone may want to know:
1. Turning the engine, bring the EXHAUST valve on one of the cylinders down until it is at peak lift (valve fully open). The pushrod will be pushed all the way down and the valve spring will be compressed.
2. Now, fully loosen the rocker arm bolt on the INTAKE of that cyl. (this valve will be fully closed).
3. Then turn that INTAKE rocker arm bolt down until the lifter is at "zero lash". You will be able to tell it is at zero lash when the rocker bolt gets very hard to turn. It gets hard to turn because the valve spring starts to compress. Again, stop turning the bolt as soon as you feel resistance to turning.
4. Mark the bolt with a marker.
5. Now count how many turns it takes to completely tighten the rocker bolt to 22 FT/LB.
The bolt should have turned between 1 3/4 to 2 turns for the acceptable GM lifter peload.
If you don't get the 1 3/4 to 2 bolt turns of preload, you need a different length pushrod. (IE: longer rod if it takes much more than 2 turns, and a shorter rod if it takes much less than 1 3/4 turns).
NOTE: You really only need to do this on one cylinder. The rest will be the same.
NOTE: If you have aftermarket Comp Cams “Type R” lifters, I understand that those like less preload than stock lifters. Instead of 1 3/4 to 2 full turns as indicated above, 1 to 1 1/4 turn may be more acceptable. I guess you would need to talk to the manufacturer.
Ron,
<small>[ February 04, 2003, 08:42 PM: Message edited by: Kimchee and Rice ]</small>
Stock LS1 Base Circle is 1.552” across the lobe. That equals a 0.776” centerline to heel distance.
TR-220 Base Circle is 1.502” across the lobe. That equals a 0.751” centerline to heel distance.
Thats exactly .025” less than stock (if your concerned with lifter preload).
_______________________________________________
Also, be advised that after measuring the the stock length Thunder Racing 7.40" hardened pushrods against a stock LS1 rod, the TRs are exactly .016" longer.
_______________________________________________
Also measured the factory spec preload on a my stock LS1 engine.
It took anywhere between 1 3/4 to 2 turns of the rocker bolt to tighten from "zero preload" to 22 Ft Lbs torque.
Here is an explanation of preload if anyone may want to know:
1. Turning the engine, bring the EXHAUST valve on one of the cylinders down until it is at peak lift (valve fully open). The pushrod will be pushed all the way down and the valve spring will be compressed.
2. Now, fully loosen the rocker arm bolt on the INTAKE of that cyl. (this valve will be fully closed).
3. Then turn that INTAKE rocker arm bolt down until the lifter is at "zero lash". You will be able to tell it is at zero lash when the rocker bolt gets very hard to turn. It gets hard to turn because the valve spring starts to compress. Again, stop turning the bolt as soon as you feel resistance to turning.
4. Mark the bolt with a marker.
5. Now count how many turns it takes to completely tighten the rocker bolt to 22 FT/LB.
The bolt should have turned between 1 3/4 to 2 turns for the acceptable GM lifter peload.
If you don't get the 1 3/4 to 2 bolt turns of preload, you need a different length pushrod. (IE: longer rod if it takes much more than 2 turns, and a shorter rod if it takes much less than 1 3/4 turns).
NOTE: You really only need to do this on one cylinder. The rest will be the same.
NOTE: If you have aftermarket Comp Cams “Type R” lifters, I understand that those like less preload than stock lifters. Instead of 1 3/4 to 2 full turns as indicated above, 1 to 1 1/4 turn may be more acceptable. I guess you would need to talk to the manufacturer.
Ron,
<small>[ February 04, 2003, 08:42 PM: Message edited by: Kimchee and Rice ]</small>
