mistermog

Hey everyone,

Well, in the process of finishing up the parts and tools for the head/cam swap and have a question regarding checking pushrod length.

I am getting a custom cam made and milling the heads 20, and it was suggested by the shop that this would put me right around .080" preload using the stock 7.8" pushrod but they STRONGLY recommended I check myself as they cant guarantee because of gasket and yada yada... totally understandable.

The question is, what pushrod tool do I get? most people are recommending on here the 6.8-7.8" comp cams tool. This does't make sense to me. If the lifter is drained of oil it would be longer the the 7.8" of the stock rod and would be flopping around when the rockers tightened and the lifter drained and compressed.

Comp does have a 7.5-8.7" pushrod checker, that seems like it would be the best option but it doesn't have the line marker nor can I find out what 1 turn equals on the threads.

Am I wrong here? Getting all my learning reading the interwebs can be dangerous. What have you guys used that have done the empty lifter method, not the shim method?

Mark2009

The lifter has a spring inside.

mistermog

Hence saying and compressed... meaning compressing the spring to get the full travel length+pushrod length, then subtract for preload.

Maybe I'm wrong in how I'm assuming this works...

briancb1

I usually do the mockup bolting the head on the old head gasket while using an old lifter I filled with epoxy to ensure it stays up.

Comp has a variety of gauged pushrods checkers and one of them will work.

If you end up needing 7.8" pushrods, PM me as I have a set of 7.8", .120" wall Manton 3 piece 4130 pushrods on hand I'm selling.

mistermog

I don't have a spare lifter and my stock pushrods are 7.8" i believe.

If I do a mock bolt up with the old gasket, wouldnt that regunk the deck with that crap on the gasket that im going to have to scrape off? without the heads being torqued down wouldnt that change it a tad bit too?

custom cam and stock heads milled .020 i think i should still be ok with stock rods but i want to make sure.

Or has anyone done the "check using a stock pushrod and counting the turns of the rocker bolt from snug to 22ft/lbs"? Apparently 1.7 turns would be .08 preload if I read that method right. And doesn't need a checker.

Mark2009

I think so

Set the pushrod length checker to a length shorter than you think you'll need. Slide it into the pushrod hole, install and tighten rocker arm (making sure that pushrod length checker remains loose when the rocker bolt is snug.).

Remove rocker arm and lengthen pushrod checker a little bit. Reinstall pushrod length checker and rocker arm.

Rinse and repeat until pushrod checker becomes ever so slightly snug when rocker arm is torqued down (the first few tries you don't need to torque it, but you should for the final check). Make sure the lifter end of the pushrod is indeed sitting in the lifter cup. This is your zero preload pushrod length. Add whatever preload you want to that length (say, .080). Then that is your desired pushrod length.

If you've got tiny fingers maybe you can unscrew the pushrod length checker until it is snug when it is installed in the head. I didn't have any luck with that, but I didn't really try that hard. Get the one with the markings on it.

Also see http://www.compcams.com/Products/CC-...rods%27-0.aspx

No. That would be .140 or better (based on info posted by John_G in his thread).

Your stock pushrods will be too long... they give a ton of preload -- .130 or so in my case, with stock heads.
.

mistermog

Youch... I was way off then.

I was told that the stock rods give about .050? Sheesh... ok so basically and bear with me here...

Make the rod much smaller, and torque the rocker down to 22... then extend it so theres no wiggle room in the rocker.

Does this compress the lifter spring at all? If not then I know what to do, and if it does ALL the way I know what to do, but what about if its just somewhere in the middle... ?

I'm confused now, can't I just use pretzel sticks?

Mark2009

Correct.

No. Unless you've got the length checker too long. To be on the safe side leave just a tad of wiggle... that will probably be just a few thousandths (.002), close enough for Government (Motors) work

You'll have the lifters out of the car anyway, so play with trying to push the cup into the lifter and you'll see how strong the spring is.

One of the most important things is to make sure the pushrod end is in the lifter cup. I'm not sure how easy it is to miss the mark in an LS7 (in the ooooold engines it was reeeeeal easy).

Also, don't try to shortcut by measuring the checker with a dial caliper. For reasons known only to pushrod makers, they use a different dimension called a 'gauge' length (so if you measure a 7.800" pushrod with a dial caliper, you'll get something like 7.950" or some such). The pushrod checker with the marks on it should give the correct number.

mistermog

Ah I havent tried seeing how stiff the spring in the lifter is.

I DO know however that the lifter cup is almost impossible to miss with the plastic lifter tray in place.

Are pushrods messured inside or outside of the ball ends? I've seen reference to both. ?

Mark2009

Neither, it seems. LOL. Go back and check that Comp Cams link I posted earlier... it's got pictures

mistermog

Yeah I looked at it, but I wish I didnt.

Seems that the gauge length is what comp uses which is built into their checker. I wonder if anyone knows if the 7.8" length is the same as the stock rod?

I know people have the 7.8" checker from comp and stock rods laying around.

Comparison?

Michael_D

One thing to keep in mind with regards to LS heads in general, is that they have pretty high cover rails that shroud the area where you will need to reach into to “twist” the adjustable pushrod. It’s a bitch getting my fingers in there….. Then add a little oil on the rod and that makes it a frustrating thing to do. Having said that, make sure that the adjustable rod is knurled above and below the split line.

Don’t concern yourself with oil in the lifter. The spring tension is quite high. Try to compress it by hand if you don’t believe me. The only time I worry about this is when checking piston to valve contact and not using low tension springs. Sometimes it’s easier to modify a hydraulic lifter (make is solid with washers) than to swap springs when you want to check several cylinders.

Another way to figure out rod length is to use a dial. Make sure the lifter is on the cam lobe’s base circle. Use the stock rod. Seat it into the lifter cup and set the rocker onto it. Thread the rocker bolt with your finger, lifting up on it to check rocker to tip contact. When you reach zero lash, put a dial on the rocker tip. Make sure the dial is positioned in line with the rod (straight line) and you have about .100” or more tension on the dial anvil. Zero the dial. Then tighten the rocker until it is completely seated onto the pedestal. Read the dial to see just how much preload you have on the lifter. Do the math and figure out how much longer or shorter the rod needs to be to obtain your desired preload. The general rule of thumb with hydraulic lifters is to set preload at 50% lifter plunger travel. Make sure you check both intake and exhaust.

Checking lifter plunger travel is a trial and error thing. You’ll need to get creative with this. I use an old rod bolt stretch gauge I have. I can turn a set screw that will compress the lifter while observing a dial. You’ll want to check several and get an average. They will not all be exactly the same. Or I should say they have not been when I’ve checked them…..

mistermog

I do like the idea of not having to deal with the lifter but I can't make it solid, once I torque the head down on the new gasket I don't want to deal with taking it off AGAIN to unshim it.

I want a pop it all toether, stretch the rod and then add preload.

Darn it!

Michael_D

Shim? I don't follow you. No need for a solid lifter unless you are using your normal springs to check piston to valve clearence. And if you are checking ptv, the head must come off anyway.

mistermog

Referring to the 2 ways to check the lifters.. one is drain the oil and compress the spring, the other is to shim them and make them solid.

Was just saying I dont want to R/R the heads twice for this.

briancb1

No it's fine. It's the proper thickness and you don't care that its done for after you lift the head back off.

You aren't putting in new lifters? They are like $125 and cheap insurance IMO.

What preload do you want? You can have as little as .030" to about .080" on the LS7 lifters and be fine. I personally went with .060" but that's just me.

mistermog

No, my lifters looked great when I checked them though i didnt check the inside goodies yet but I only have 11,000 miles on them.

I would be shooting for .075-.080 preload.

Michael_D

Lifter preload is kind of a personal preference thing. I know builders that run it as light as they can, whereas others like it towards to max plunger travel end. My thought process is to set them near the 50% plunger travel range. It's for that reason that I like to find total travel, then set preload from that. I'm also very annal when it comes to engine building, more so than most - but time is not a concern for me.

If you run it too low, you will have some clatter, more when the engine is cold. Run it too high, you may end up with the valves not seating. With these LS7 lifters, I think anything between .050 and .100 would be OK. You do not need to disassemble or modify any to figure out what rod length you will need. Just make sure that they have had plenty of time to drain. When they are drained, they will find their neutral position. You can then use your dial to find out exactly what you have with the head torqued down. Or you can fiddle with an adjustable push rod. I prefer to use a dial, but again, I'm fussy. You will want to check both intake and exhaust, as I have seen variances with many aftermarket camshafts. Some more than others. In many cases, I've ran different length rods on the intake and exhaust.

I would highly encourage you to buy new lifters. It is impossible to inspect lifters with the naked eye. Yes, you can re-use yours. Should you though?? I would not, but again, I'm fussy.

mistermog

I would be shooting for right about .080 based on what Jason said.

I have no idea if I should replace them, but I don't want to keep spending 100s of dollars just because. I don't think I had anything going on before, and the rollers look good. How do you know if you need new ones?

briancb1

I understand you want to be financially conservative, but just getting to the lifters is an expensive and laborsome ordeal in itself.

If you find one that has a busted looking wheels are bad feeling bearing, you caught a widow maker and were lucky. Me, personally, I would do it because I don't want to have to get in there ever again just in case. If its like a AC belt or exhaust gasket, yea fvk it replace it as needed but this is a little harder to access.

Let me know if you need 7.8's