pushrod length/preload help + how much advance?
08-04-2010, 11:10 AM
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pushrod length/preload help + how much advance? 1. i measured for pushrods, but the length checker i got didnt come with instructions, so im not sure how far it travels per turn. the length checker i have is the comp cams 7702-1. i had a total of 10 turns to get 0 lash.
2. how much preload should i have? theyre ls7 lifters, xfi lobes if that matters. and 6800 rpm redline
3.also i am installing the cam into the shortblock, it is a 347, 12:1, 248/254, 622/622 113+3. my question is, how much should i advance it? i have a billet timing set that i can go +2, +4, +6. motor will be on a 175 shot.
thanks in advance!!!
2. how much preload should i have? theyre ls7 lifters, xfi lobes if that matters. and 6800 rpm redline
3.also i am installing the cam into the shortblock, it is a 347, 12:1, 248/254, 622/622 113+3. my question is, how much should i advance it? i have a billet timing set that i can go +2, +4, +6. motor will be on a 175 shot.
thanks in advance!!!
Last edited by Bobsmyuncle; 08-04-2010 at 11:32 AM.
08-04-2010, 11:18 AM
#2
If you are measuring for pushrod length, then you need something that actually measures length, i.e. a caliper. We're talking thousandths of an inch, so don't guess. Buy/borrow a caliper and actually measure the length of the pushrod checker at zero lash and then add in the amount of pre-load you want, and that's the pushrods to buy.
As for how much advance, no clue, but I sure hope you have some valve releifs in your pistons with that large of a cam.
As for how much advance, no clue, but I sure hope you have some valve releifs in your pistons with that large of a cam.
08-04-2010, 11:26 AM
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If you are measuring for pushrod length, then you need something that actually measures length, i.e. a caliper. We're talking thousandths of an inch, so don't guess. Buy/borrow a caliper and actually measure the length of the pushrod checker at zero lash and then add in the amount of pre-load you want, and that's the pushrods to buy.
As for how much advance, no clue, but I sure hope you have some valve releifs in your pistons with that large of a cam.
As for how much advance, no clue, but I sure hope you have some valve releifs in your pistons with that large of a cam.
08-04-2010, 11:31 AM
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From Shane at Thunder Racing:
FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
08-04-2010, 11:33 AM
#6
The comp cam checker is .050 per turn. Get as close to zero lash as possible with the PR checker and the count the turns to 22ftlb. You want to be in the 1 1/4-1 3/4 turns to 22ftlbs. If your right with the ten turns of the checker than your in the ball park of 7.3. I would check with the torque wrench to be sure.
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08-04-2010, 11:45 AM
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The comp cam checker is .050 per turn. Get as close to zero lash as possible with the PR checker and the count the turns to 22ftlb. You want to be in the 1 1/4-1 3/4 turns to 22ftlbs. If your right with the ten turns of the checker than your in the ball park of 7.3. I would check with the torque wrench to be sure.
is there any advantage to running more or less preload when running higher rpms? motor could see 7200 rpm occasionally
08-04-2010, 12:34 PM
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I would measure total pushrod length, even if the instructions say that it's .050 per turn.
I can't remember the brand I used at the moment, but mine was advertised as .050 per rev. Measurements and verified with calculations show that it was actually .0417 per full revolution.
While not enough difference to cause any major issues, it could sway your decision in choosing one length over another.
I can't remember the brand I used at the moment, but mine was advertised as .050 per rev. Measurements and verified with calculations show that it was actually .0417 per full revolution.
While not enough difference to cause any major issues, it could sway your decision in choosing one length over another.
08-04-2010, 01:23 PM
#10
Again, if you're going to go through the process of measuring it correctly, don't resort to using internet math to guess how long it is, measure to be accurate. Fortunately, you have a good amount of room to be off considering the lifters have approximately 0.150 of plunger travel.
08-04-2010, 03:47 PM
#11
The adjustable pushrod is 0.050" per turn. If you count turns, you will get gauge length. If you measure with a caliper, you will get overall length. The two measurements differ by approximately 0.017" so if you measure with a caliper subtract 0.017" if you are buying something like Comp or Trend pushrods that use gauge length. If you are buying Mantons, then he requires the overall length.
Either way is more accurate then counting turns on the rocker bolt, especially if you have valve springs in place and are using an adjustable pushrod. That may be a decent way to do things without the adjustable pushrod, but you have the tool so use it correctly.
Either way is more accurate then counting turns on the rocker bolt, especially if you have valve springs in place and are using an adjustable pushrod. That may be a decent way to do things without the adjustable pushrod, but you have the tool so use it correctly.
08-04-2010, 06:08 PM
#12
The adjustable pushrod is 0.050" per turn. If you count turns, you will get gauge length. If you measure with a caliper, you will get overall length. The two measurements differ by approximately 0.017" so if you measure with a caliper subtract 0.017" if you are buying something like Comp or Trend pushrods that use gauge length. If you are buying Mantons, then he requires the overall length.
Either way is more accurate then counting turns on the rocker bolt, especially if you have valve springs in place and are using an adjustable pushrod. That may be a decent way to do things without the adjustable pushrod, but you have the tool so use it correctly.
Either way is more accurate then counting turns on the rocker bolt, especially if you have valve springs in place and are using an adjustable pushrod. That may be a decent way to do things without the adjustable pushrod, but you have the tool so use it correctly.
08-04-2010, 07:39 PM
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so this is what i got:
with length checker at 10 turns, i have zero lash
i removed the rocker, and added 1 turn for preload(1 turn=.050)
with the beginning length of 6.800, and .050 for each turn, thats 6.800+.050x11
and i get 7.350.
all this look correct? when i tightened up the rocker the final time, it was like 1 1/4 turns preload
with length checker at 10 turns, i have zero lash
i removed the rocker, and added 1 turn for preload(1 turn=.050)
with the beginning length of 6.800, and .050 for each turn, thats 6.800+.050x11
and i get 7.350.
all this look correct? when i tightened up the rocker the final time, it was like 1 1/4 turns preload
08-04-2010, 07:58 PM
#14
Is sounds just about right. The 7.35 is guage length (Comp push rod) and 7.350 + 0.017 if you order from Manton. The only thing that is a little off is that I would thought that adding the one turn, which is roughly the 0.050 for pre-load, would have resulted in a One-turn to torque instead of the 1 1/4 you report. But that difference may not matter with your particular lifter.
08-04-2010, 08:31 PM
#15
Is sounds just about right. The 7.35 is guage length (Comp push rod) and 7.350 + 0.017 if you order from Manton. The only thing that is a little off is that I would thought that adding the one turn, which is roughly the 0.050 for pre-load, would have resulted in a One-turn to torque instead of the 1 1/4 you report. But that difference may not matter with your particular lifter.
08-04-2010, 08:47 PM
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and it makes pretty good sense, the gaskets are .045 and heads are milled to 58cc. .050 shorter than the factory pushrod. .007 difference in gasket and head are milled a little over .040
