Pushrod/Preload question
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
If you want 0.050" lifter pre-load, then you need pushrods that are 7.275 + 0.050 = 7.325".
FYI ... putting 7.350" pushrods in will be around 0.100" pre-load.
I'm about ready to say screw this method. I don't have a caliper that goes past 6", so I can't do the feeler gauge method. I also don't have a torque wrench that goes below 25ft/lbs, so I can't do that method. Looks like I'll have to buy some tools or find a happy medium within my measurements.
Last edited by ZeeOSix; Feb 21, 2012 at 08:47 PM.
Thread Starter
Le Mans Master
Joined: Jul 2005
Posts: 7,121
Likes: 3
From: Shreveport/Bossier Louisiana
St. Jude Donor '08
Here is what I got...
6.8 + (9.5 x 0.05)
6.8 + 0.475 = 7.275"
Add 0.050 preload = 7.325
Then, add the 0.015 to cover the tip-to-tip length unless I get some that are actually measured/advertised in gauge length = 7.340"
Is this right?
6.8 + (9.5 x 0.05)
6.8 + 0.475 = 7.275"
Add 0.050 preload = 7.325
Then, add the 0.015 to cover the tip-to-tip length unless I get some that are actually measured/advertised in gauge length = 7.340"
Is this right?
Drifting
Joined: Sep 2008
Posts: 1,389
Likes: 3
From: somewhere shooting my assault rifles
I have never read or talked to anyone that adds anything more in calculation like "to cover the tip-to-tip length" you mentioned above. I think what you order size wise is number you get above via calculation.
Thread Starter
Le Mans Master
Joined: Jul 2005
Posts: 7,121
Likes: 3
From: Shreveport/Bossier Louisiana
St. Jude Donor '08
True. I know comp sizes theirs in gauge length. Other manufacturers may size theirs in actual length. It depends on which brand is purchased.
Drifting
Joined: Sep 2008
Posts: 1,389
Likes: 3
From: somewhere shooting my assault rifles
.015 isnt gonna really make any noticeable difference adding it in anyway. Ive known guys that run as little as .040 and as much as .130 preload with no noticeable noise differences or problems with LS7 lifters as they have a huge range of good to use preload numbers low to high. GM charts seem to say that .082 is the sweet spot. I think you are using LS7 lifters right? Once engine is at operating temps the measured cold preload is gonna loosen up .010-.015 as well. One week I threw in 3 sets of different PR lengths making my preload .050, .075 and .125 and saw no noise difference and no performance differences. The high and low ends got more noise when cold but once warmed up both .050 and .125 were quiet but the .075 was the best sounding when cold. I then settled on wanting a .100 for cold measurement as when hot its about .085-.090 and thats where I wanted to be altho I honestly dont think it really matters where it is between .040 and .125.
Last edited by Z06supercharged; Feb 23, 2012 at 12:28 AM.
Thread Starter
Le Mans Master
Joined: Jul 2005
Posts: 7,121
Likes: 3
From: Shreveport/Bossier Louisiana
St. Jude Donor '08
.015 isnt gonna really make any noticeable difference adding it in anyway. Ive known guys that run as little as .040 and as much as .130 preload with no noticeable noise differences or problems with LS7 lifters as they have a huge range of good to use preload numbers low to high. GM charts seem to say that .082 is the sweet spot. I think you are using LS7 lifters right? Once engine is at operating temps the measured cold preload is gonna loosen up .010-.015 as well. One week I threw in 3 sets of different PR lengths making my preload .050, .075 and .125 and saw no noise difference and no performance differences. The high and low ends got more noise when cold but once warmed up both .050 and .125 were quiet but the .075 was the best sounding when cold. I then settled on wanting a .100 for cold measurement as when hot its about .085-.090 and thats where I wanted to be altho I honestly dont think it really matters where it is between .040 and .125.
Safety Car
Joined: Aug 2011
Posts: 4,442
Likes: 408
From: Portland OR
.015 isnt gonna really make any noticeable difference adding it in anyway. Ive known guys that run as little as .040 and as much as .130 preload with no noticeable noise differences or problems with LS7 lifters as they have a huge range of good to use preload numbers low to high. GM charts seem to say that .082 is the sweet spot. I think you are using LS7 lifters right? Once engine is at operating temps the measured cold preload is gonna loosen up .010-.015 as well. One week I threw in 3 sets of different PR lengths making my preload .050, .075 and .125 and saw no noise difference and no performance differences. The high and low ends got more noise when cold but once warmed up both .050 and .125 were quiet but the .075 was the best sounding when cold. I then settled on wanting a .100 for cold measurement as when hot its about .085-.090 and thats where I wanted to be altho I honestly dont think it really matters where it is between .040 and .125.
Someone finally said it!!!!!
Ron
Thread Starter
Le Mans Master
Joined: Jul 2005
Posts: 7,121
Likes: 3
From: Shreveport/Bossier Louisiana
St. Jude Donor '08
I measured another way and feel more comfortable with my measurements.
Arnel, your PM box is full so if you see this, it looks like the pushrods you offered to send are going to be too long to even start with.
I hope you didn't ship them yet, but if you did, I can send them back. Thanks so much for the offer!!
Arnel, your PM box is full so if you see this, it looks like the pushrods you offered to send are going to be too long to even start with.
I hope you didn't ship them yet, but if you did, I can send them back. Thanks so much for the offer!!
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Burning Brakes
Joined: Feb 2004
Posts: 1,069
Likes: 8
From: Sanford NC
Z06 Supercharged. How many turns past 0 lash are you getting for .080" pre-load till the bolts are torqued. I am sitting at 1 1/2 to 1 3/4 turns after 0 lash and the math for 1 turn is .047 supposedly. So that puts me at .083" theoreticaly. Is that what you found? I just went from a .060 stock gasket to a .040 Cometic and milled the heads .015. So that tells me that I need a .035" shorter push rod to get back to where I was stock. Should I just leave well enough alone?
Drifting
Joined: Sep 2008
Posts: 1,389
Likes: 3
From: somewhere shooting my assault rifles
Z06 Supercharged. How many turns past 0 lash are you getting for .080" pre-load till the bolts are torqued. I am sitting at 1 1/2 to 1 3/4 turns after 0 lash and the math for 1 turn is .047 supposedly. So that puts me at .083" theoreticaly. Is that what you found? I just went from a .060 stock gasket to a .040 Cometic and milled the heads .015. So that tells me that I need a .035" shorter push rod to get back to where I was stock. Should I just leave well enough alone?
I'm gonna pull a cylinders i/e rockers and recheck my pushrod length this weekend.
Last edited by Z06supercharged; Feb 23, 2012 at 07:18 PM.
Burning Brakes
Joined: Feb 2004
Posts: 1,069
Likes: 8
From: Sanford NC
When I had .075 ish~ preload I had 1-3/4 turns. I wouldn't worry about it but this sort of things bugs the hell out of many people. There is some argument exactly how much a turn actually is.
I'm gonna pull a cylinders i/e rockers and recheck my pushrod length this weekend.
I'm gonna pull a cylinders i/e rockers and recheck my pushrod length this weekend.
Safety Car
Joined: Aug 2011
Posts: 4,442
Likes: 408
From: Portland OR
I have a Trick Flow adjustable pushrod. I measure it to be .035" per turn.
I'm not sure why the torque of the bolt that holds the rocker in place is being mentioned. It doesn't add to the equation. It just holds it there and should be torqued to spec.
This process seems like it should be simple.
Get the cam on the base circle. However you like. TDC method, EOIC method or dial indicate it.
Set the lash to 0.
Remove the pushrod and measure. Flat to flat is the only accurate measurement you can make. You need 8" calipers.
Add the desired preload to the measurement and order.
This assumes you aren't dealing with a high lift cam that requires adjustment to the height of the rocker arm to get the swipe on the valve tip correct. That get's a little trickier.
Ron
I'm not sure why the torque of the bolt that holds the rocker in place is being mentioned. It doesn't add to the equation. It just holds it there and should be torqued to spec.
This process seems like it should be simple.
Get the cam on the base circle. However you like. TDC method, EOIC method or dial indicate it.
Set the lash to 0.
Remove the pushrod and measure. Flat to flat is the only accurate measurement you can make. You need 8" calipers.
Add the desired preload to the measurement and order.
This assumes you aren't dealing with a high lift cam that requires adjustment to the height of the rocker arm to get the swipe on the valve tip correct. That get's a little trickier.
Ron
Drifting
Joined: Sep 2008
Posts: 1,389
Likes: 3
From: somewhere shooting my assault rifles
Its not the final torque of the bolt but how many turns from 0 lash to the final torque of bolt thats being calculated. Its a quick way to figure approx preload is using the existing pushrods you have in there and not knowing exactly what their measurement is (for people that dont have large enough caliper)..
Last edited by Z06supercharged; Feb 24, 2012 at 11:43 AM.
Burning Brakes
Joined: Feb 2004
Posts: 1,069
Likes: 8
From: Sanford NC
You have to calculate it since this is a non adjustable system. The bolt has to be torqed to spec then set the push rod to 0 lash for you method to work. I am just reverse engineering your process. I count the revolutions from 0 lash to bottoming out the bolt and measure the distance the bolt travels with a dial indicator and viola, you have the pre-load. Seems pretty simple to me. If we come up with a solid rotation to distance number then it can be put out and a lot more guys can do at home cam swaps and not need a lot of tools or math to set the pre-load correctly.
Besides, I believe over 550 lift the stock valve trane geometry is jack up anyway. It puts undue stress on the side of the valve and wears out valve guids. Every time I use aftermarket rocker arms I have to shim them more than what people think to get the correct wipe pattern. To bad you can't get a good wipe pattern with the stock rocker arms. Shimming the stock rockers may be benificial now that I think about it. It would compensate for the extra lift going from say .500 to .550 lift of the stock cams to over .600 like most of us run. I am going to look into that. Has any one researched this?
Besides, I believe over 550 lift the stock valve trane geometry is jack up anyway. It puts undue stress on the side of the valve and wears out valve guids. Every time I use aftermarket rocker arms I have to shim them more than what people think to get the correct wipe pattern. To bad you can't get a good wipe pattern with the stock rocker arms. Shimming the stock rockers may be benificial now that I think about it. It would compensate for the extra lift going from say .500 to .550 lift of the stock cams to over .600 like most of us run. I am going to look into that. Has any one researched this?
Burning Brakes
Joined: Feb 2004
Posts: 1,069
Likes: 8
From: Sanford NC
I agree. I have only used Comp 850's in all my builds and set them at a 1/4 to 1/2 turn. Don't remember the exact preload but I think it was in the .030" range. I can tell you that the motor has never been more smooth or quiet in its whole life. So I guess it likes around .080". What do you think about my shimming idea for the rocker. Any validity to that thought process.
Here is what I don't get. Does the lifter work correctly, i.e. giving you full lift and duration no matter where the plunger is set to? It would seem that the less pre-load the more oil in and taller the lifter acts. Therefore the more lift and duration you get. I am probably not understanding correctly. I know my machinist runs a shim in his race motors that leaves only about .010 travel and routinely revs them past 8,000. I guess it effectivly turns it into a solid lifter. The stuff they do to these things to keep in the rules but still run bottom 10's is insane. I want to apply a lot of it to my next street motor. I think I could pick up at least 20rw over a normal build and still maintain all of its manors.
Here is what I don't get. Does the lifter work correctly, i.e. giving you full lift and duration no matter where the plunger is set to? It would seem that the less pre-load the more oil in and taller the lifter acts. Therefore the more lift and duration you get. I am probably not understanding correctly. I know my machinist runs a shim in his race motors that leaves only about .010 travel and routinely revs them past 8,000. I guess it effectivly turns it into a solid lifter. The stuff they do to these things to keep in the rules but still run bottom 10's is insane. I want to apply a lot of it to my next street motor. I think I could pick up at least 20rw over a normal build and still maintain all of its manors.
Safety Car
Joined: Aug 2011
Posts: 4,442
Likes: 408
From: Portland OR
Its not the final torque of the bolt but how many turns from 0 lash to the final torque of bolt thats being calculated. Its a quick way to figure approx preload is using the existing pushrods you have in there and not knowing exactly what their measurement is (for people that dont have large enough caliper)..
Ron
Safety Car
Joined: Aug 2011
Posts: 4,442
Likes: 408
From: Portland OR
Here is what I don't get. Does the lifter work correctly, i.e. giving you full lift and duration no matter where the plunger is set to? It would seem that the less pre-load the more oil in and taller the lifter acts. Therefore the more lift and duration you get. I am probably not understanding correctly. I know my machinist runs a shim in his race motors that leaves only about .010 travel and routinely revs them past 8,000. I guess it effectivly turns it into a solid lifter. The stuff they do to these things to keep in the rules but still run bottom 10's is insane. I want to apply a lot of it to my next street motor. I think I could pick up at least 20rw over a normal build and still maintain all of its manors.
Your machinest uses the trick he does in order to limit lifter "pump up" in the event of valve float.
Think of it this way. When the valve floats, the lifter looses contact with the nose of the cam. The lifter being hydraulic, (think of a hydraulic jack) pumps up to remove the clearance, and this keeps the valve open when it shouldn't be and the valve could hit the piston. Especially if the valve to piston clearance is set real tight.
Ron
Drifting
Joined: Sep 2008
Posts: 1,389
Likes: 3
From: somewhere shooting my assault rifles
Here is a pretty good read on this subject of preload checking:
http://ls1tech.com/forums/generation...questions.html
http://ls1tech.com/forums/generation...questions.html
Burning Brakes
Joined: Feb 2004
Posts: 1,069
Likes: 8
From: Sanford NC
The position of the plunger (amount of pre-load) has no bearing on the lift.
Your machinest uses the trick he does in order to limit lifter "pump up" in the event of valve float.
Think of it this way. When the valve floats, the lifter looses contact with the nose of the cam. The lifter being hydraulic, (think of a hydraulic jack) pumps up to remove the clearance, and this keeps the valve open when it shouldn't be and the valve could hit the piston. Especially if the valve to piston clearance is set real tight.
Ron
Your machinest uses the trick he does in order to limit lifter "pump up" in the event of valve float.
Think of it this way. When the valve floats, the lifter looses contact with the nose of the cam. The lifter being hydraulic, (think of a hydraulic jack) pumps up to remove the clearance, and this keeps the valve open when it shouldn't be and the valve could hit the piston. Especially if the valve to piston clearance is set real tight.
Ron