M8 x 1.25 is metric, each thread is 1.25mm apart, like the image. 1.25mm to inches is 0.0492126in. So, one turn will move the bolt down one thread, or 0.0492126 inches.

 

With my math, assuming its correct I have 0.13678175 preload with 7.350" pushrods, or 1 3/4 turn on the bolt. So that's 7.21321825" before any preload, so my measurements from the beginning where correct. With 7.300" pushrods ill have 0.80" preload on the high end. I say on the high end, because I may have begun the counting with a slight amount of preload, and it was just a hair over 1 1/4 turns, 1.8 turns would be my guess.

 

From RBO4Av's post I thought you were looking for 1 1/4 turn pre-load, that how I came up with .062. I would check with the company that you bought the lifters from and ask them the recommended pre-load. On my BTR LS7 lifters I was told that the preload should be between .075-.100" from what I remember I came in at .085" with 7.400" pushrods with my LQ9 head gaskets, LS3 heads, cleaned up block deck.
Sorry LS9 headgaskets. Gen 3 LQ4 block.

 

Ohh, sorry. Thats on me. Yes, for 1 1/4 turn would be that. Thanks for the advice!

 

For anyone looking at this thread for help in the future, this will only work for 1.7 rocker arms, here is how I did it:

To find the lifter preload with a known length pushrod, find zero lash, then count the turns of the rocker bolt it takes to get to 22 ftlb, then multiply the turns by 0.078161". That will give you the preload with the pushrod. Take that number and subtract it from the pushrod length you used, and it will give you the pushrod length before preload. Then add the recommended preload for your lifters, and you have your pushrod length.

I recommend not rounding any numbers until you go to buy pushrods, you'll lose a few thou, and that's not ideal. And when it comes to buying the X.400" vs the X.390" you want the closest you can find.


Here is a drawing I made of the rocker arm, as the rocker arm is a ratio, the exact lengths of both sides do not matter.

 

How about a good visual representation?

 

I had seen this video in another post, it's great, I just wasn't able to find it again. Thanks!

 

No problem! I have never purchased from them but they have a good explanation on there web page.
https://gwatneyperformance.com/lifte...ont-hurt-will/

That being said, Strictly my opinion, but I have noticed more valve train noise on the LS7 lifters the more preload they have. I shoot for about .060 myself.

 

Ill see how it is, if I get sick of it, I can always go for a lower preload later on.
I may get a small cam in a few months too, so I might have to get new pushrods anyway.

 

I agree-PR checker is dead nuts when used properly. If people must use bolt turns, keep in mind that roughly the last 1/8 turn makes no difference in preload. In fact, after the rocker arm trunnion is bottomed into the mounting scallop, all you're doing is stretching the bolt, NOT adding preload. This is why I use a pushrod checker. No guesswork, period. Virtually the cheapest component of any engine build....

 

I third the pushrod checker, the bolt turn method should only be used in a pinch, or to verify the measurements. But id argue that it's even less than 1/8 turn that takes up slack, my guess is a 1/16 turn. Either way, it would only throw off the measurement by less than 10 thou. It's not worth even measuring that.

 

Rounding to .001" or even .002" on lifter preload isn't going to make or break your build. When dealing with lifter preload, and you want to get let's say within .040" of "ideal" (½ of .200" = .100", we'd like to be, let's say, between .070" and .100", more or less), .001" here or there isn't a deal breaker. If you can get within .010" you're PLENTY close enough, considering that unless you're willing to $$$bite off$$$ on abuncha $$$$custom PRs$$$$, that's as close as you can buy, anyway. See "muda" https://en.wikipedia.org/wiki/Muda_(Japanese_term), in particular the 6th instance. While not everyone subscribes to this system as some kind of absolute, even for those who don't, the idea of "overprocessing" including too much precision for the situation you're dealing with, is illustrative. "Perfection" sometimes is the enemy of "get the job done and ship the damn product".

Like, if I'm putting up a wall and I ask my assistant to hand me a 8' (96") stud, I don't expect him to expect me to buy him a micrometer that can measure to the nearest .0005" of a 96" object, and reject every 2×4 that's outside of the range of 95-63/64" and 96-1/64". Unless I tell him so. Otherwise I can accept studs within 1/8" or whatever. Capische?

"Measure with micrometer, mark with chalk, cut with axe."

OTOH, failing to understand the physical reality of how things move with respect to each other, like ignoring the fact that the rocker is a LEVER and taking into account how it multiplies or divides one motion with respect to another, WILL result in ... unexpected consequences.

That said, I don't use the "turns on the bolt" deal, myself. I'm not smart enough to use that effectively. I ONLY use an adjustable push rod. I've been using the same one now for around 40 yrs on all sorts of motors, LS types included. You look for different things on motors with different designs of their valve trains, butt in the end, thousandths of an inch are thousandths of an inch, always. Metal is metal. Butt as some point it ultimately comes down to a question of HOW MANY thousandths of an inch ACTUALLY make any kind of a difference, or can you ACTUALLY buy the "perfect" parts that you're "measuring", or will the lifter's inherent cushion and self-adjustability take it up and render it meaningless. Be reasonable. Understand what you're doing, and what REALLY matters, rather than bowing down to some kind of dogma you watched or read from some guru (or yutz) on the Internet.

 

You may be right on 1/16th turn, rather than my 1/8 turn. Don't know for sure, because I never do PR length checking with bolt turns. But my point is after the bolt head nests the rocker fulcrum in the pedestal at zero lash, that's that. You can turn it 'til it strips the threads, and the zero lash figure wont change, whether its 1/8, 1/16th, or 1 full turn. But if you don't know what the Hell you're doing, you're required PR length will be off. Best to always use a checker, and use it CORRECTLY......

 

Now your just taking the fun out of everything...

 

^^^ This ^^^

I see people on here get all wound up over "22 lb-ft" of torque. As in, I torqued my bolts to exactly that, at such-and-such crank locations. BULLPLOP. The valve springs, even if they're 400 lbs/in, make less than 1 lb-ft of bolt torque difference; it DOESN'T MATTER where the crank is. Besides, the bolts are METRIC, and the actual spec is METRIC as well. The actual # is 30 N-m. This converts to 21.7 lb-ft. OTOH, note that 30 N-m is precise (not the same thing as "accurate"; "precise" means, EXPRESSED to some level of fineness of detail, which is different from "accurate", which means MEASURED as such) to ONE decimal place. The reason is, it's the standard torque for that size hardware. That's IT. No magic "perfect" tightness. No more, no less. The factory used automatic tightening equipment, and they had to set it to SOMETHING because it's not bright enough to make that decision on its own, and those settings are the numbers that ultimately make it to the service manual, in the sense of duplicating the factory's processes, as opposed to some random concept of "perfect". Understanding when those torque specs and the like are CRITICAL, like when they compress some malleable object like a head gasket vs when they merely call for a bolt to be tightened "enough" but not "too much", is important. It's beyond SILLY to take a number with ONE decimal place of precision, and "convert" it to a number with MORE decimal places of precision. You see it all the time: in the Ukraine some missile has a "range of between 18.64 and 21.75 miles", when what the general REALLY said was, "we can count on usually hitting what we're aiming at if it's within about 30 or 35 km". BIG difference.

"Measure with micrometer, mark with chalk, cut with axe."

Sorry, my education was as a mathematician and physicist, in the days of the Apollo program, even though that ceased to be a marketable skill as I got going in my "career". For all these decades in between I usually functioned as an industrial, electronic, or electrical engineer, and later after I got a MBA, as a technogeek. We didn't have pocket calculators and supercomputers back then. We used slide rules and log tables for most things. (ever heard of Benford's Law?) We had to concentrate our very limited computational resources where they MATTERED, because they were EXPENSIVE; and therefore the first thing we had to figure out was, what MATTERED and what DIDN'T.

As grinder pointed out, the rocker bolts tighten abuncha stuff metal-to-metal. Nothing compresses, nothing deforms, nothing changes once the bolt is "tight enough". The spec is merely what the factory set their automatic machinery to, because being automatic, they had to set it to SOMETHING, so they chose the standard torque for that size of hardware. It's not like if the torque is 5% or even 50% off there's going to be a problem, unless it's not "tight enough" (backs off during operation) or is "too tight" (strips threads, breaks bolts, distorts parts permanently).

Be all that as it may, I've never been a fan of the "turns on the bolt" method in a non-adjustable valve train. For one thing, I'm not smart enough to use it effectively; and for another, there's too much variation in the parts to allow it to be accurate. So I just stick with my trusty Comp 7702 that's coming up on a half-century old.