I just went & dug up my Base Circle measurements. I did these with my Digital Calipers, probably should have used a Mic in hindsight.

It's surprising the range from lobe to lobe, subjective being I was using Calipers. They are good Calipers so I'm comfortable with go...no go numbers.

Vettenuts have you ever measured the Base Circle lobe to lobe?

You combine an error on the Base Circle with how a valve is seated? You wonder how any of it can work Then the push rod length & rocker arm & how the head was milled were the rocker shaft seats...OMG

 

I recently did a valve spring swap in my stock 2002 Z06, and while at it put in some stout Manton pushrods ... ordered to the same OEM length of 7.400" from end ball flat-to-flat. I also put the Comp Cams Trunnion Kit in while in there.

When I installed the rocker arms, I made note of how many turns it took on each one to go from zero lash to 22 ft-lbs (avg was 1-1/4 turns). Converting that to a lifter pre-load, the total range variance from least to greatest pre-load distance was only 0.012". Tells me all the valve stem heights and cam lobes/base circles were pretty darn consistent.

My valve train is probably as quiet as they get in the LS6. With the hood closed, you can't really hear much at all. Have to put your ears down a foot above the rocker covers to hear some slight sewing machine noise. My lifters are pretty much pre-loaded to the mid range of their travel (~0.060" for my stock LS6 lifters) ... just like they came from the factory.

 

The heads are 100% stock, '02 Z06. I took them apart, cleaned them and lapped the exhaust valves, but other than that they haven't been touched. My cam/lifters went south a couple of months ago, hence the new cam and lifters. Reassembled with GM MLS head gaskets and ARP studs. I bought the car in 2004 with 26k miles on it, now has just over 120k miles. Daily driver.

Looking forward to your input!

 

I'll be happy when it sings like a Singer!

When I installed the new rods the valvetrain got quieter overall, but there were new sounds. After a couple of days I started realising they were not normal sounds and were beyond the typical big cam LS1 sewing machine.

 

Well, the last thing I want to do is get into custon length pushrods! That sounds like a huge PITA, not to mention the $$$.

Your preload calculations agree with mine. I agree, with the 7.425" rods there were several lifters operating with far too little headroom.

Something is not adding up, maybe the cam is out as you say.

 

FYI, everything I've read says the stock rods are 7.385". Going with that you've got 0.015" extra preload.

Good to hear about the consistent numbers. Mine are varying over 3X that much.

 

My thoughts exactly.

 

Well, I now have the stock 7.385" pushrods in, and the 7.425" rods installed on just #3 and #7 exhausts. It is the quietest it's been since doing the cam. Valvetrain noise is still audible, with several valves seeming to "stand out" compared to others, but the noise is now more of a "chatter" than a "clatter" like it was before. I'm not too happy with this arrangement, but it seems to be the best compromise for now.

I may remove the rocker stands and measure the individual trunion mounts just to see what kind of variation lives there, if any. That's the only other thing I can think of beyone the base circles being out of whack on the camshaft.

I can't see the rocker stand bosses being machined different from each other since they likely all get machined by the same machine set to one height, and this would happen after the bottom surface of the head was finished. I doubt there's many issues with the head itself.

I would accept that maybe the cam bearings could have been bored off center, but that would show up as all measurements for one head being higher than the other and that's not the case here.

Everything seems to point to the cam, and d@mmit that's the one thing I can't measure since it's in the block already. I wonder how LPE would feel about getting one of these cams off the shelf and measuring all of the base circles for me... right.

 

Some builders are very comfortable using different push rod lengths, exhaust to intake. I would not have a problem either knowing what I've learned this last cam go around. I did not compare the Intake error to the exhaust error, maybe a good exercise. Two different lengths.

A little wiser each time.

My current push rods are Manton 11/32 thick wall. We had a good conversation on the phone verifying what I had measured. Interesting stuff. They are very approachable people.

I've been chasing a power issue, thats brought on my little chase the tail syndrome.

 

I found this thread a very interesting read. Tried to learn something but way over my head.

 

Actually, my OEM pushrods, and the custom Manton pushrods (per my build request) are the exact same length. They are 7.385 "gauge" length, or 7.400 "flat-to-flat" as defined by a 0.140" dia plane through the end ball.

To clarify, there are a couple of different ways to measure pushrods. I've learned a lot about them since I've done my mini valve train upgrade on my '02 Zee. See this thread - particularly post #13 and #24 and the attachments in those posts.

http://ls1tech.com/forums/generation...ness-spec.html

The OEM pushrod with a 5/16" dia ball end will have a "gauge length" of 7.385" and a "flat-to-flat" length of 7.400". This is where the trickiness comes into understanding pushrods. The basic key is to know how the length has been defined.

BTW, the custom pushrods I had built by Manton were only $10 each.

 

I think your lifter pre-load was just too much ... way past the mid-point of the lifter's plunger travel. GM sets up the lifter pre-load at almost exactly travel mid-point as you've seen in that table you reference a while back in Post #31.

And those LS7 lifters have a relatively huge travel range - 0.166" compared to my OEM LS6 lifters which only have 0.126" travel. The setup is even more critical on the LS6 lifers since there is 25% less travel range to play with.

 

I guess I could have been a bit more clear. I would definitely be comfortable using different pushrod lengths as long as that was a DESIGN requirement (like different intake and exhaust lobes, as you mention). What I'm not terribly comfortable with is having change two pushrods out of a set of 16 to compensate for what is looking to be sloppy cam grinding.

At the end of the day, as long as each pushrod is keeping its respective lifter happy that's all that matters. In my case there's so much variation I'm wondering if the cam lobes are even ground properly and I'm getting the intended valve lift? What about the delicate closing ramp geometry? Maybe this is why I still have some valves that are louder than others?

These are questions I wasn't planning to ask...

 

Here is a suggestion, looks like your exhaust range is .625 & the intake range .250. Take the highest & lowest of your intake & exhaust, recheck those which I'm sure you have already done. Then verify your findings by doing a turn check, from zero preload to 22ftlbs. Looks like you would have a different length push rod for your exhaust vales & intakes valves, I should guess .025 based on your post measurements.

As mentioned previously there are builders that are fussy doing this, I would not hesitate to do this. Maybe one day if I can get my other haunting issue's squared away I would go back & do it just for the education & who knows, a quieter valve train. I would even do a before & after dyno.

 

I guess if you've never looked into it before, pushrod length and lifter preload could seem complicated, but do yourself a favor and figure it out before diving into a project like this. It will be well worth your time and will give you the power to determine things for yourself. Once you see how it all works it's really pretty simple.

I really hope this information helps someone out!

 

Good to know! I knew that pushrods weren't usually measured by overall length, but didn't k ow exactly how they were measured.

Custom Mantons for $10 each? That sounds too good to pass up! When I go to roller rockers I will be sure to call them. Their product looks far superior to the Comps I'm using now, and not much more money.

 

Per Manton's catalog, they actually define their pushrod length from tip-to-tip ... not "gauge" length like Comp Cams does.

The OEM LS1/LS6 pushrods are 7.400" between the flats from tip-to-tip, which corresponds to a "gauge" length of 7.385" as I detailed in my thread on LS1Tech.com.

I don't know for sure ... but I'm assuming the (Comp Cams?) adjustable pushrod you used is designed to measure the required pushrod "gauge" length? If not, and it gives you overall length, then there could be about a 0.015" difference going on between what you measure and what you use. You have to be careful to know which length measurement system is being used.

What's weird about Comp Cams is they list a "7.400" inch long pushrod as the LS1/LS6 OEM. Well, if Comp Cams defines their pushrod length by gauge length, then are they 7.385 gauge length, or 7.400 gauge length ... which would actually be about 0.015" longer than the OEM pushrods. See what I'm getting at?

 

Interesting... you'd think there would be some sort of "standard" among the parts manufacturers. I bet this has lead to some errors before!

I went and checked how the checker works. It's PN 7022 from Comp. Measuring one of the stock pushrods with the checker gives me approximately 11.5 turns, which works out to 7.375" (there's a very good chance I'm off by that 0.010" - this was far from a lab-grade measurement ). This would suggest the checker is providing gauge length, which is what I would expect since it should corelate to Comp's products.

That said, it is a pretty crude measurement and 0.025" error is possible. I went out to the garage armed with my nice Mitutoyo caliper determined to get an accurate measurement only to find once I got there that the caliper only measures to 6".

I'm sure Comp made a decision not to make 7.385" pushrods since they already make pushrods in .025" increments. A .015" longer pushrod would serve well as a stock replacement as well as offer a little more preload over a stock rod for someone who has installed a higher lift cam in an otherwise stock engine. As soon as one gets into radical cams, new lifters, milled or aftermarket heads, the protocol would be to measure for the new required pushrod length and round up or down to the nearest available size.

The confusion with measurement techniques seems to stem from two sources:

1. Manton uses an overall length spec (which, in my opinion, doesn't make sense since the overall length can vary depending on the size of the oil hole in the end of the ball... bigger hole, longer rod!)

2. Comp specifies 7.400" pushrods as stock replacements without a footnote detailing that they are actually 0.015" longer. Dumb, but probably avoids scaring people off who don't know their lifters have a "range" to work in.

 

Yep, It sounds like the adjustable pushrod from Comp is designed to give the gauge length. Makes sense because that's how Comp defines their pushrod lengths.


The flat across the end of the Manton pushrod is basically the same diameter as the flat across the OEM pushrods ... which is 0.110~0.112". It's just that Manton uses a 0.065" oiling hole instead of a 0.100" oiling hole like in the OEM pushrod. Manton says that at high RPM the stock pushrods over-flood the valve covers with oil, so they use a smaller oiling hole.

 

Interesting... so the Mantons actually have a flat machined into the base of the ball end and then have a hole drilled that is smaller? I guess this is necessary if he is supplying them based on overall length instead of gauge length.

Less oil into the heads at high RPM sounds like a good idea. GM has had oil starvation issues with cars on the track; long, high-G turns don't allow oil to flow back down into the crank case from the cylinder head, so putting less oil up htere in the first place could help that situation. Pretty simple.

Though if it was that simple, and less oil was required in the heads, it begs the question "Why didn't GM just do that in the first place?". Maybe the extra oil is needed at high RPM to keep the valve springs cool or something? Quite often things like this are not understood before a change is made.