Push rod length has me wondering
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TECH Apprentice
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From: Clearwater, FL
Push rod length has me wondering Ok so I got my new heads bolted on and checked my pushrod length today. I have a 98 TA and I have a set of Patriot Stage 2 243's. They are milled to 62cc and I am running the GMPP ASA Cam. I checked PTV with the stock graphite gasket and I was tighter then I should be so I went with the MLS gasket. I have LS7 lifters and my calculations are telling me with a .050 preload I should run 7.3 pushrods. This seems off to me. I have read that the ASA has a .025 smaller base Circle and I figure my heads have about .035 off of them. I am not seeing where the pushrods would be .100 different in size.
I used COMPS 6.80 adjustable pushrod and got 9 turns so
6.800 + 9 x .050 = 7.25 + .050 = 7.3
If anyone can help me understand the why this would be I would appreciate it.
I used COMPS 6.80 adjustable pushrod and got 9 turns so
6.800 + 9 x .050 = 7.25 + .050 = 7.3
If anyone can help me understand the why this would be I would appreciate it.
Last edited by THE CHOP SHOP; Jan 28, 2008 at 10:05 PM.
Stock preload is around 0.080" - 0.100". The only stock setup I measured was at 0.100". Also, I believe the stock pushrods are actually 7.385 in gauge length which is what you are measuring with the adjustable pushrod. I think this makes sense since everyone quotes them as 7.400" and the difference between gauge length and overall length is about 0.017".
When I was doing my swap a couple of weeks ago I searched the boards and asked around and was told/read that the LS7 lifter needs to be between .080 and .100 of preload. I measured and factored in .100 and have not had any issues.
My pushrod length is 7.350. Same math as yours only .100 added instead of your .050.
R/
Frat
My pushrod length is 7.350. Same math as yours only .100 added instead of your .050.
R/
Frat
My question is how are you measuring preload with a hydraulic lifter? I have found that if you get to zero preload, where all slack is taken up(which this is easier to do with checker springs) then within 3/4 of turn I reach 22lbs works awesome for us. I personally like a little lighter preload of a 1/2 turn. Seems to wind up so much easier and too higher rpms with out any valve train bounce or float. I have had to long of pushrods/too much preload and my engines would have horrible valvetrain dynamics at rpms as soon as 6,000 and would bounce, not float(power cuts in and out). Getting pushrod length right is very helpful with checker springs. It has taken me some pistons, and valves to figure this out.
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Its based upon the type of lifters and your measured PR length. If your lifters need between .080 and .100 of preload, you measure your PR length and then factor in your desired preload and that is your total length.
I did not "measure" preload. I asked my vendor what the recommemended preload for my lifters is and added that to my measured PR length.
R/
Frat
I did not "measure" preload. I asked my vendor what the recommemended preload for my lifters is and added that to my measured PR length.
R/
Frat
Its based upon the type of lifters and your measured PR length. If your lifters need between .080 and .100 of preload, you measure your PR length and then factor in your desired preload and that is your total length.
I did not "measure" preload. I asked my vendor what the recommemended preload for my lifters is and added that to my measured PR length.
R/
Frat
I did not "measure" preload. I asked my vendor what the recommemended preload for my lifters is and added that to my measured PR length.
R/
Frat
Sounds about right. I measured mine with stock heads, smaller than stock base cam circle and went with .080 preload on stock lifter and came out with 7.450. I double checked with the wipe method and all seems fine though i have not started the engine yet.
Thread Starter
TECH Apprentice
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From: Clearwater, FL
I am under the impression that if I was to run to long of a pushrod it could possibly keep the valve open longer then expected thus tightening PTV clearance. If I am wrong let me know but it makes sense.
Too long could hold it open or possibly pump up. I know Roger Vinci actually likes to set them a little deeper and my last setup with stock lifters I was set deep at 0.125". I can't run the Morel's like that though. The 0.050" preload may be very loud, especially as the block grows during the heat up.
Please explain....
I have been under the impression that since our valve trains are non-adjustable, lifter pre-load is a function of PR length.
Are you saying when one goes to measure length, use a solid lifter to measure base PR length and then add your desired pre-load?
If so... I am following ya....
R/
Frat
I have been under the impression that since our valve trains are non-adjustable, lifter pre-load is a function of PR length.
Are you saying when one goes to measure length, use a solid lifter to measure base PR length and then add your desired pre-load?
If so... I am following ya....
R/
Frat
Please explain....
I have been under the impression that since our valve trains are non-adjustable, lifter pre-load is a function of PR length.
Are you saying when one goes to measure length, use a solid lifter to measure base PR length and then add your desired pre-load?
If so... I am following ya....
R/
Frat
I have been under the impression that since our valve trains are non-adjustable, lifter pre-load is a function of PR length.
Are you saying when one goes to measure length, use a solid lifter to measure base PR length and then add your desired pre-load?
If so... I am following ya....
R/
Frat
Order of setup:
1. Obtain correct wipe pattern (may require shimming of rocker)
2. Measure for pushrod length to obtain zero lash
3. Add lifter preload to zero lash pushrod length to get final pushrod length
1. Obtain correct wipe pattern (may require shimming of rocker)
2. Measure for pushrod length to obtain zero lash
3. Add lifter preload to zero lash pushrod length to get final pushrod length
I agree with fossil .050" preload, which is about 1 turn from zero lash to 22ft lb. With your heads at 62cc I think 7.35" would be the correct push rod, but check it with an adjustable PR to make sure. I think .125" preload for OEM, LS7,Caddy, or Comp 850 is WAY too much, bad reccomendation.