Soo.... I had my comp pushrod checker bend on me, after hammering it 99% straight again and using vettenuts method. I had 13 turns to close it, adding in .080 preload for LS7 lifters. It came up with a 7.637. WRONG. Did it twice. made sure I had oil in the lifters and they werent dry.... So then I tried the Shane from Thunder Racing method. I had a 7.500 pushrod and snugged it down to zero lash. I knew when I was there.. did that 5 times just to make sure. Got the old torque wrench out set to 22 lbs. Took 2 and just short 1/4 turns to click it to 22 ft lbs. That meant I needed a pushrod roughly .025 shorter than the 7.500 I was using. So a TFS 59 cc head with a 7.475. I ended up with 2 extremes when everyone say I should be somewhere between 7.500 and 7.550. What the hell am I doing wrong here??? I have brand new HS rockers.

 

For starters, using a measurement tool that was hammered back into shape. Get a new one for christ's sake.

 

Yeah thanks smart azz. It was slightly bent... cant handle that much spring pressure obviously. Guess I shouldnt have used my remote starter with the adjustable pushrod installed.... The other method came out to roughly 7.475. Could that be OK?? Since TFS recommends 7.500 and my heads are 59cc so .025 shorter doesnt sound too out of question? Although researching I still find 7.500 - 7.550 on milled TFS heads and a comp cam ( smaller base circle)... hmmm i dunno

 

Post this on the LS1Tech forum.

 

If you arent using lite cam checking springs on your heads your numbers are going to be all over your compressing the lifter

 

Refer to the word "Never"......


http://www.jesel.com/Instructions/Tools/INS-29425v2.pdf

 

Make sure your on the base circle................
Also the lifter is "pumped" up just sitting there with no pressure against the plunger. There is a spring inside the lifter that pushes up on the plunger. So the easiest method is to get a pushrod checker, collapse it all the way, put cam on base circle, tighten rockers all the way down to 22ft lbs then slowly lengthen the expandable pushrod until you have zero lash but not puting any pressure on the lifter. Pull that back apart and measure the pushrod. The length you get is the length you would need for 0 preload. Add .050" to that and you have your preload.

the pushrod is just a function of proper preload on the lifter. The rocker is a fixed fulcrom in correlation to the vavle tip.


Thanks............

 

If you use Shane's method, you have to make two corrections when moving off of his one turn number. First, correct for rocker ratio and second correct for the number of turns from the rocker bottoming until full torque is achieved. On my motor with the YT rockers, I found the latter to be 1/3 turn. If I use your 2-1/4 turns and my correction and "assume" a rocker ratio of 1.7 (this may in fact be different on the seat) I get a preload of 0.150" noting that this method is approximate. I spent some time reviewing his method when I did my tapered pushrod swap and when corrected his method and measurements were within a few thousandths but it is also subject to operator error. The best way to measure it to put a dial indicator on the rocker and measure the preload but not sure if you have a dial indicator.

When you are using the adjustable, are you lifting the rocker tip or turning the pushrod to feel for zero lash. Sometimes its helpful to leave a little lifter tick to ensure there is no load on the lifter cup and measure between the rocker tip and the valve stem with a feeler gauge to double check the zero lash number. Whatever you measure you then divide by the rocker ratio to get the amount you need to add to the adjustable pushrod length to obtain the zero lash value.

Were the estimates you have for pushrod length inclusive of the HS rockers and any milling of the head or thinner head gasket (if you used one)?

With this big of a difference, I suspect the adjustable pushrod measurement may be in error and would focus attention on obtaining zero lash.

 

Read my sig.below; I went with factory preload after there was much debate about the preload and pushrod length with LS7 lifters when they first came out. 7.4's were too tall/tight/noisy. John (deceased) from ECS did an excellent preload measurement and we discarded the 7.4's for 7.35's. 20K miles now, runs great and quiet, no problems.

 

Vettenuts I always read your posts but sometimes find I get lost technically. LOL.. I did like Shane's method better and I did achieve some credible results. For the record. MLS GM gaskets. 1.7 Harland Sharp non adjustable rockers. TFS 215 heads measure at 59.7 cc. Stock LS6 block and deck. I dont understand what needs revision on Shanes method? Could you explain it in laymans terms please? I got 3/4 of a turn on an intake... and 1 1/2 turns on the same cylinders exhaust valve. So if this is true: I need a 7.525 on the intake and the 7.500 is bang on for the exhaust of this 1 particular cylinder.... Im using a pair of 7.500 pushrods doing this. BTW I dont have a dial indicator and wouldnt have the first idea how to use it.Im a handy turn bolt and assemble kind of guy. Not good with blueprinting tools. LOL

 

No counting turns, just a simple direct method of getting the preload right!

Ron

 

I thought you got more turns using Shane's method. In a nutshell, if you think about what is happening when you tighten the bolt. The rocker tip is on the valve stem and the other end is on the pushrod. As you tighten the bolt, the rocker moves downward pivoting on the valve stem (the valve may open a bit while you tighten but ignore this as the lifter will eventually bleed down). So as you tighten the bolt, the pushrod end moves downward more than the bolt by an amount related to the rocker ratio on the seat. Shane has posted he found that 1 turn of the bolt results in approximately 0.049" of preload (can't remember his exact numbers). However, if you find that the bolt takes more or less turns, then the rocker ratio must be used to correct for how much the pushrod end will move.

The second thing is as you tighten the rocker down, the rocker moves downward into the stand and when it seats in the stand you are still tightening the bolt. However, once the rocker seats further turning of the bolt is not actually providing more preload but rather it is preloading the bolt. This portion of the turn counting must be removed from any calculations because it isn't preloading the lifter. On my motor with my rockers, I found this to be 1/3 turn. It may be different on other motor/rocker setups. When I subtracted this from the turns I was counting using Shanes method, I got within a few thousandths of of the measurement I was taking with a dial indicator.

So using Shane's number for one turn, and subtracting the 1/3 turn that I found my motor required to preload the bolt, I would only get 2/3 turn where the lifter is actually being preloaded. In 2/3 turns, the bolt will move (2.3) X 1.25/25.4 = 0.0328 inches. Since the rocker pivots on the valve stem and the ratio is assumed to be 1.7 on the seat (the stock rocker is actually less, not sure on the HS you are using), the distance from the valve stem to the pushrod in relation to the distance from the valve stem to the bolt is (2.7/1.7) = 1.588. This is then used to correct how much the pushrod end of the rocker moves such that in the example 0.0328" X 1.588 = 0.052", which is pretty close to Shane's value considering counting bolt turns itself is subject to error. The nice thing is that the lifters are somewhat forgiving in that the preload doesn't have to be within a couple of thousandths of an inch to work correctly.

Hope this makes sense.

Also, since you see a large difference between intake and exhaust, I would check another cylinder or two to make sure you get consistent measurements. I would also go with larger OD pushrods than 5/16". I believe later TFS heads will accept 3/8" OD pushrods but would verify with Brian Tooley first. This would provide a much stiffer valve train noting that the pushrods act as springs and you want them to be as stiff as possible.