ZeeOSix

Hi Guys .... Just joined and first post. I've lurked here awhile because of all the great and detailed info. Looking for some advice.

I'm in the middle of swapping out the stock valve springs in my '02 Z06 with PAC 1518s, and also installing the Comp Cams Trunion/Bearing Updgrade Kit.

I checked my stock pushrods for straightness by rolling them on nice flat piece of glass and a few have a slight bow to them. I used a feeler gauge between the rod and glass at the high point and the worst ones were at 0.003" air gap.

The GM service manual doesn't have any straightness spec for the pushrods, so was wondering if this slight bow was acceptable. I have a feeling they were like this all along, but wondering what others have found.

Also, would it be worth while putting in an aftermarket set of pushrods (like Comp Cams chrome-moly) while I'm in the motor .... or are the stock LS6 pushrods OK for just hard street use? I don't track this car.

If an new set of pushrods are installed, is there any concern about putting new parts in the valve train that have already wore-in to the existing pushrods? Car only has 20K miles.

Big&Tasty TA

If it was my ride and I was doing what you are doing I would invest into some aftermarket pushrods. You’re already into the motor and they aren’t that much money so you might as well. As far as the straightness spec, I am not sure if there is a spec for that.

Darkman

iTrader: (2)

Get new, hardened pushrods. Wear on companion parts is not an issue.

vettenuts

iTrader: (4)

I would upgrade pushrods as well. Stock are a little less than 5/16" OD (believe diameter might be metric) and OD is what buys stiffness, which is one of the most important requirements for a pushrod. The upgraded springs will come in at a higher seat and over the nose force and your stock pushrods will deflect more.

Note also that stock pushrods are 7.385" and not 7.400" as everyone seems to believe.

ZeeOSix

Guys - thanks for the inputs so far. So what would you recommend for aftermarket pushrods? I was looking at these form Comp Cams:

http://www.speedinc.com/cont.cfm?cid=C0000871

So looking at the lengths that the Comp Cams pushrods come in, I would assume the 7.400" length is still the one to get for drop-in OEM replacements on a stock valve train? There are none listed as 7.385" long.

Last thing I want is to mess up my valve train geometry if going with some aftermarket pushrods.

Steve01SS

iTrader: (43)

7.4 is what is used in stock sized replacement. Those Comp pushrods are good ones. I would definitely not put back in any pushrods that are bent.

crainholio

iTrader: (2)

Pushrods only measure in two categories:

1.) Straight
2.) Garbage

msydow

a push rod that is bent is weaker. a lot of vendors have their own pushrods. any will do great.

CraigS

iTrader: (6)

Measure your stock pushrods before you order. I thought the 02-04 Z's ran longer rods due to a smaller base circle of the cam, maybe its just longer valves.

crainholio

iTrader: (2)

A bent pushrod is a spring.

ZeeOSix

Funny you mentioned that, because I just measured one of the stock pushrods.

From tip-to-tip it measured 7.40". Is tip-to-tip how the aftermarket pushrods are specified/measured also?

Also estimated the wall thickness on the stock LS6 pushrod to be ~0.070".

I called Comp Cams Tech Dept this afternoon and the guy there said to install the 7.400" length ... should have no issues.

If the aftermarket pushrod was actually 0.015" longer than OEM, wouldn't that just mean the lifter plunger would be operating in a slightly different position by 0.015"?

As far as my OEM pushrods being bent or not ... I'd say that the 0.003 run-out is probably within "spec" ... if there was a spec.

vettenuts

iTrader: (4)

No, tip to tip is "Overall Length". Pushrods are generally measured using "Gauge Length" however there are some exceptions. Terry Manton prefers you provide him overall length for example. Gauge length is measured from a position on the ball where it is 0.140" in diameter (if memory serves) and an approximate gauge length can be obtained by taking overall length and subtracting 0.017". When I checked stock pushrods from two different cars I got7.385". If you take the overall length you measured and subtract 0.017" you get the same gauge length that I did within a couple of thousanths.

You could get 11/32"OD from Manton in your current stock length which "should" fit stock heads and are much stiffer or I might personally go with 7.375" gauge length which would reduce preload by 0.010".

Two other tips. One, the LS6 and LS1 pushrods are one in the same. The base circle is smaller on LS6 but the valves are taller. Second, Comp tech line is worthless based on my experience. By the way, Trend makes pushrods for Comp.

Here is a write-up I did on pushrod stiffness a while back, hopefully you will find some of the information useful. Also, Bret Bauer did some pushrod experiments with the stock LS1 and found stiffer pushrods make a difference even in a stock setup.

Link to pushrod stiffness writeup

ZeeOSix

See the attached figure to this post. I found this in the 2011 Comp Cams catalog showing the different measurements on a pushrod. Note that Comp Cams uses "gauge length".

I see where you are coming from now. The confusing thing is that Comp Cams shows the 7.400" long pushrods as the "Standard Length" for the Gen III, LS1/LS2/LS6 engines (Comp Cams p/n 7955-16) throughout their catalog. See 2nd attached pic.

My guess is they specify the 7.400" because the next shortest pushrod they make is the 7.375" (p/n 7795-16).


Yeah, not sure what to do at this point. I need to get some pushrods on order as I've decided to replace the OEM pushrods since I'm into the engine now.

Seems a lot of people just put in the 7.400" pushrods and don't seem to have an issue ... and Comp Cams recommends 7.400" as the standard replacement instead of the 7.375". One would think Comp Cams has decided on 7.400" instead of 7.375" for some good reason.

Good info ... thanks for the link.

ZeeOSix

Forgot to ask. What is the total travel distance of the hydraulic lifter plunger?

Let's say with the stock pushrods that the lifter's plunger is right in the middle of the travel range. If 7.400" gauge length pushrods were installed, then the plunger would be ~0.015" closer to the bottom of its travel range (0.015" more pre-load). If 7.375" gauge length pushrods were installed, then the plunger would be ~0.010" closer to the top of its travel range (0.010" less pre-load).

If the total plunger travel range is say 0.250", then would 0.010" or 0.015" from center really matter that much?

vettenuts

iTrader: (4)

I seem to recall total travel to be about 0.150" but am not positive on that value. Most stock setups I have measured come in close to 0.100" preload. The 7.400" would put you at approximately 0.115" assuming you have 0.100" and the 7.375" would put you at 0.090". That's why I though the shorter might be a better choice. Having said all that, you might want to contact Terry Manton and order custom length from him as they are not much more money and Terry bangs them out very quickly. You would likely have themat your door in a few days.

Comp shouldn't advertise 7.400" as stock length. It is the nominal replacement length for aftermarket cams with a smaller base circle.

ZeeOSix

So apparently the pre-load of the lifter doesn't necessarily put it in the mid point of its total travel range. I'd go with the 7.375" if I knew for sure it would be better than using the 7.400". It might be better to not pre-load the lifter as much with the shorter pushrod to put the lifter closer to the mid-point of preload? ... or is it necessary to have more preload towards the bottom end of the lifter for some reason as you've indicated above?

How do I contact Terry Manton?

Techs at Comp Cams claim they have sold thousands of the 7.400 pushrods to Gen III guys with stock cams and have never had any issues. He also said that using the 7.375" would probably be OK too, but had no technical data to support that.

Thanks for all your help with this vettenuts.

vettenuts

iTrader: (4)

Here is the link to Manton Pushrods: Manton Pushrods

When I called them, Terry actually called me back from his car and spent quite a bit of time with me on the phone. He made me a special pushrod that I could use to make adjustments, i.e., one of the end fittings was loose so I could cut the pushrod if I wanted. He is great to work with and can produce the stock length for you as that seems to be where you feel most comfortable. Trend can do the same thing if you want. I would call Terry and speak with him, since you have the overall length, you can discuss your requirements. I wouldn't be surprised if he can get them to you by the middle of next week. A lot of guys have turned to him for pushrods, and many have increased the OD to 11/32". With the stock cam, you can go with the 5/16" OD, thicker wall and stock length. Sort of like having your cake and eating it too. Plus he makes them right in his own shop

joecar

The lifter full travel depends on the lifter, see attached (copied from CF)...


Edit: ah, I then saw the OP's other thread: https://ls1tech.com/forums/generatio...questions.html

vettenuts

iTrader: (4)

Actually, I believe the original post with that table on CF was from "Eric D", who works for GM.

ZeeOSix

Well, after doing some measurements and some scaled layouts from the OEM pushrods, I called Manton and talked to them. They recommended their Series 3, 11/32" tube with 0.120" wall with 5/16" ball ends of course. Might as well go a little "overkill" vs. not.

Turns out Manson specs their overall pushrod length from flat-to-flat on the ends of the *****. Their ball end flat diameter is basically the same diameter as the OEM pushrod at 0.110~0.115" which means the overall length of 7.400" in the Manson should match the OEM within a couple thousands. The OEM measured out at 7.400" from flat-to-flat. After all the analysis, it all boiled down to a no-brainer.

The Manson pushrods have a 0.063" dia oil hole instead of the 0.100" dia oil hole in the OEM pushrod, but I doubt that will make any real difference to oil flow to the heads.

I was ready to pull the trigger on the Comp Cams 7955 Chrome-Moly pushrods (7.400"), but I liked the design of the Manton better which uses a machined ball end instead of forming the end from the tube material like Comp Cams does.