Pushrod length measuring and zero lash? What lifter preload?

[Mark Myles]

Originally Posted by CamaroSpike23

Very informative thread. Thanks danhr and SC2150

Yes, thank you both and the op for starting it. This is a nice thread that one can sink their teeth into, great information.

Although having said that, I personally have no idea what the hell you guys are talking about......but I'm sure others do..lol.

M

[robertway]

Originally Posted by CamaroSpike23

Very informative thread. Thanks danhr and SC2150

Yes, a big thanks to danhr and SC2150 from me as well. I have gone ahead and videotaped myself going through the entire pushrod measuring procedure that has been discussed here so hopefully others can take advantage of it as well. Should have it posted up in a little while once I edit all the "dead air" time out of it and mis-speaks when I step on my own tongue

I went back in and switched the pushrod checker to have it set at 7.375 and that has given me right at about 1 turn on the four different rockers (intake/exhaust on driver and passenger side) so I think I can rest assured that I have chosen the correct pushrod length.

[CamaroSpike23]

Originally Posted by robertway

Yes, a big thanks to danhr and SC2150 from me as well. I have gone ahead and videotaped myself going through the entire pushrod measuring procedure that has been discussed here so hopefully others can take advantage of it as well. Should have it posted up in a little while once I edit all the "dead air" time out of it and mis-speaks when I step on my own tongue

sounds good.

[robertway]

After going back through the steps I took I realized that one turn on the pedestal bolts really on;y gives me 0.050 (0.047 to be exact) preload as danhr stated above each turn is 0.047 and I even got out my digital caliper and verified it. So to get to my 0.075 preload I would need 1.5 turns of the pedestal bolt. I went back and started from scratch and this time I torqued down a rocker on either side of the cylinder I was working with to make sure there was absolutely no play in the rocker seat bracket as before I only had it hand tightened down at the two far ends.

With the rocker seat firmly in place I went ahead and ran the zero lash at factory torque measurement and got 7.325 on the pushrod length checker, adding my 0.075 preload gave me a 7.400 inch pushrod length. I adjusted the length checker to 7.400 (6.800 base plus 12 turns), hand tightened down the pedestal bolt until there was zero lash, and them proceeded to get almost dead on 1.5 turns out of the pedestal bolt on all four of the rockers I checked which confirms the 0.075 preload added to the length checker.

This actually makes more sense because as I had said at the beginning of the thread, I had measured the base circle of the stock cam to be about 0.035 (0.033 to be exact) larger than the new cam and since the stock pushrods measure to 7.375 the 7.400 pushrod just about makes up for the base circle difference. Even though the actual stock preload that was in there before I tore everything apart is unknown, the measurements and results make a lot more sense now so I am more confident that 7.400 is the length I am going with.

Here is the video I did that shows the entire process I went through, you can enlarge it to 480p if it only starts out at 360p. I'll be including this video and probably a reference to this thread in the full cam swap write-up I'll be doing in a couple of weeks (once my pushrods and trunion upgrade kit show up and I can finish)...

[Mikes2nd]

I would need to do this for stock setups?

my father seems to think i need to adjust the lash on a l99 engine

[Nitroman28]

I know this is an old thread but 7.4 is the stick length correct?

[litle88]

Yes it is.

[shiftkit]

My checker measured at 7.2875" and I am planning on ordering 7.350" pushrod length (about 0.062" pre-load), but looking at the stock pushrods, they measure about 7.370". Does this sound right (same cam as Robert's, stock heads, gaskets, rockers, etc.)?

[rvadim76]

Old reply but yes that sounds right (to shifttkit)

[christianchevell]

Since I am the old man On here I have kept many old threads this one showing what was the go too Robert Way; and his thread installing his own cam was the one many used installing theirs as he did a big DIY which was nice but he was confused in his own ways during the process. I put this out there what I have learned over the years on here, .070 is the preload for the ls7 which uses a higher preload with a higher rev limit and this is all in my opinion from reading so much over the years.

The lower preload amount he referred too is .060 the ls3 preload average which actually can be noisier and some do go lower to .040 range as the more preload makes more noise in typewriter sound, and different varied lifters such as Johnsons or Morels will have different varied preloads recommended.

I bring this zombie thread back from the dead so some may learn if only it is alive, to get the correct lash you go to zero which for most being that they have a new base circle for the cam being smaller stock pushrods that 7.375 area and 7.4 its I think different ls3 to l99 IMO...... and can vary and most have to add some length for the loss of base circle to be added to the stock pushrod length for the correct geometry ideally.

IMO Robert got lost with not knowing that yes the Threads are .047 thread pitch on the bolt for the rocker but when you tighten the bolt down from zero lash you are tightening on a fulcrum that the rocker is, thus one turn on the bolt/(nut on stud for those with studs and that thread pitch), is .077; as 1.7 rocker ratio x .047 = .077 thus why most tighten in the 2/3 to 3/4 turn area from zero lash to get into " the Range" as .060 the average lash being on the ls3 from people tearing it down to lows of .045 area....

As you can read if you read this thread is that Robert over tightened his preload which would make the engine a little more noisy and well also bottom out the pushrods into the lifters internals as he was way over the preload needed and would of course still run being roller lifters and a strong engine.....

The problem with over tight preload is it grenades the engine eating the roller and cam with to much pressure so it basically trashes the top and it takes time being that its a roller cam.....Pushrods do bend and do cause cups to go into the lifters too far making things really hard on the engine to just stay alive. Just a thought I have had for a long time and seeing this old thread I thought I would share, maybe BO has a opinion on this also he's done more cams than anyone else here...LOL ' he's as addicted to change as I wish I could be.....and used to be with a fleet of old chevys.

ANYWAY IT SOUNDS LIKE TO ME ROBERT WAY HAD THE RIGHT LENGTH OF PUSHRODS BUT OVERTIGHTENED HIS PRELOAD WITH 1.5 TURNS TWICE THE NEEDED TO GET TO A PRELOAD RANGE HE AIMED FOR WHICH WAS HIGHER THAN EVEN THE LS7 AT .070 SO THE PLUNGER ON ALL HISE LIFTERS WAS GOING INTO THE BOTTOM OF HIS LIFTERS AND THUS MAYBE WHY HE DISAPPEARED OVER TIME...... AS 1.5 TURNS = .385+.077= .1155 PRELOAD NOT A HAPPY RANGE.....

JUST THROWING IT OUT THERE STUFF IMO THAT A LS ENGINE WOULD SURVIVE FOR WHILE BEING THAT ITS SO STRONG BUT THEN IT WOULD EAT THE TOP END MAYBE EVEN BREAK A SPRING/ PUSHROD. AND OF COURSE LIFTERS....ANYWAY THATS MY RAMBLE FOR THE DAY FROM THE OLD FART..

[1Camaro2SS]

Originally Posted by christianchevell

Since I am the old man On here I have kept many old threads this one showing what was the go too Robert Way; and his thread installing his own cam was the one many used installing theirs as he did a big DIY which was nice but he was confused in his own ways during the process. I put this out there what I have learned over the years on here, .070 is the preload for the ls7 which uses a higher preload with a higher rev limit and this is all in my opinion from reading so much over the years.

The lower preload amount he referred too is .060 the ls3 preload average which actually can be noisier and some do go lower to .040 range as the more preload makes more noise in typewriter sound, and different varied lifters such as Johnsons or Morels will have different varied preloads recommended.

I bring this zombie thread back from the dead so some may learn if only it is alive, to get the correct lash you go to zero which for most being that they have a new base circle for the cam being smaller stock pushrods that 7.375 area and 7.4 its I think different ls3 to l99 IMO...... and can vary and most have to add some length for the loss of base circle to be added to the stock pushrod length for the correct geometry ideally.

IMO Robert got lost with not knowing that yes the Threads are .047 thread pitch on the bolt for the rocker but when you tighten the bolt down from zero lash you are tightening on a fulcrum that the rocker is, thus one turn on the bolt/(nut on stud for those with studs and that thread pitch), is .077; as 1.7 rocker ratio x .047 = .077 thus why most tighten in the 2/3 to 3/4 turn area from zero lash to get into " the Range" as .060 the average lash being on the ls3 from people tearing it down to lows of .045 area....

As you can read if you read this thread is that Robert over tightened his preload which would make the engine a little more noisy and well also bottom out the pushrods into the lifters internals as he was way over the preload needed and would of course still run being roller lifters and a strong engine.....

The problem with over tight preload is it grenades the engine eating the roller and cam with to much pressure so it basically trashes the top and it takes time being that its a roller cam.....Pushrods do bend and do cause cups to go into the lifters too far making things really hard on the engine to just stay alive. Just a thought I have had for a long time and seeing this old thread I thought I would share, maybe BO has a opinion on this also he's done more cams than anyone else here...LOL ' he's as addicted to change as I wish I could be.....and used to be with a fleet of old chevys.

ANYWAY IT SOUNDS LIKE TO ME ROBERT WAY HAD THE RIGHT LENGTH OF PUSHRODS BUT OVERTIGHTENED HIS PRELOAD WITH 1.5 TURNS TWICE THE NEEDED TO GET TO A PRELOAD RANGE HE AIMED FOR WHICH WAS HIGHER THAN EVEN THE LS7 AT .070 SO THE PLUNGER ON ALL HISE LIFTERS WAS GOING INTO THE BOTTOM OF HIS LIFTERS AND THUS MAYBE WHY HE DISAPPEARED OVER TIME...... AS 1.5 TURNS = .385+.077= .1155 PRELOAD NOT A HAPPY RANGE.....

JUST THROWING IT OUT THERE STUFF IMO THAT A LS ENGINE WOULD SURVIVE FOR WHILE BEING THAT ITS SO STRONG BUT THEN IT WOULD EAT THE TOP END MAYBE EVEN BREAK A SPRING/ PUSHROD. AND OF COURSE LIFTERS....ANYWAY THATS MY RAMBLE FOR THE DAY FROM THE OLD FART..

When I swapped out my cam, I made 1.5 turns as Robert suggested. It's been 5 years since but the car has only been driven 6K miles since. Made few passes at the drag strip and drove the car pretty hard on the street at times. So far no issues.

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[Russell James]

If using rocker nut turns, you're doing it wrong. That will put you in a guesstimated preload.

To get it exact, you contact the cam maker and the lifter maker. Come to a conclusion on what preload should be used for that cam and that lifter. Then you use a PR measuring tool to establish that exact preload. Reading the directions on your PR length checker tool...it'll tell how to tell from the turns of the tool exactly what length PR to buy.

I've dug into several engines that were set up using rocker nut turns. They were way off. But...if using stock long travel lifters, stock base circle cam, and lots of PTV clearance... being way off often will work just fine. Get into short travel lifters, close PTV, dimensions changed from machining... just my opinion, I'd measure the right way.

[christianchevell]

6k miles is my daily driving in a year..I would worry....

[1Camaro2SS]

Originally Posted by christianchevell

6k miles is my daily driving in a year..I would worry....

Nothing to worry about. Has plenty of piston to valve clearance. 7.4" push rods on these engines is common with stock lifters. Comp Cams also recommend this length.

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