Help with pushrod length and geometry
 

Hello everyone,

I am a new poster on these forums, but have used them extensively before for information. I have a 1975 Trans am that I am knee deep in building a 465ci stroker motor for and I have a question about pushrod length. My usual method to determine pushrod length is the contact area on the valve stem, and trying to get it exactly centered. I looked up the correct way to do it with a roller cam, and I did the valve geometry method, where you find half lift and get the valve and rocker at a 90 degree angle. However, both of these methods have resulted badly. The contact area method landed me with a 9.5 in pushrod and horrible geometry, and I had no thread left on my poly locks. The half lift method resulted in a 9.1 in pushrod and a contact area (see pic attached) on the intake side and wider than I want. I have 1.5 ratio Comp rockers, and comp evo hyd roller lifters. Am I doing something wrong or can I just run it with the 9.1 in pushrods? I have ample thread with those (around 6 turns to tighten on poly locks. Also my poly locks are too long and hitting my OEM chrome valve covers, can I shave them down to get rid of 3/8 of thread so I can use my stock valve covers? Sorry I know this is a long post but I know somebody had probably had my same problem before. Thanks.

Let’s forget about the poly lock issue just for now.

With any of the push rod lengths you have tried how close have you come to the amount of lift you should have in regards to contact patches one way or the other?

Contact traces that are towards the intake port side of the head mean your push rod is too short , if it’s the other way and on the exh side of the stem then there too long.

Make sure that if your using roller rockers that the rocker body is not touching the retainer.

As the ratio of the rocker goes up above 1.5 the push rods static position gets drawn closer to the rocker stud.

Do not minus your cams recommend lash out of your checks your making .

In general you want the narrowest patch you can achieve while being within .040” or so of the valve stem center while getting within .012” to .015” of the lift you should have.

If I get the contact patch in the middle of the valve stem, the pushrod is 9.5in and i run out of thread on my rocker studs. It’s not hitting the valve retainer anywhere. Currently with the 9.1in pushrods, The path is .030 away from the center of the valve stem but I am only getting .375 in of valve lift while I should be getting .521. Should I get 1.65 ratio rockers instead of the 1.5s that I have now?

What!?
Are these fully roller rockers?

If so do you have the rocker trunon facing the wrong way with the flat side facing the poly lock?

Yes they are roller rockers, and the flat side of the trunion is facing the polylock.

FWIW Once you get your geometry set you should be able to fit under stockers, I have all this going on and they fit with 2 VC gaskets

I measured again and I do in fact have the correct amount of valve lift. I am just going to run it. I attached a pic of the wear pattern. I am going to order a slightly shorter polylock and with thick valve cover gaskets the covers do fit! So problem solved. Thanks guys for the input.

NO! You do NOT have the problem solved!

Your issue is the way your positioning the flat side of the trunion facing the poly lock.

The side of the trunion with circular depression in it is where the poly lock goes into.

The proper ploy locks will fit in that depression.

Is the plunger in the hydraulic lifter at the bottom or is the clearance reduced when checking the push rod length?

Just to say, and I know how many feel about this, but the half-lift method is the 'proper' way to achieve proper geometry/pushrod length.

https://www.youtube.com/watch?v=o5is9BsH5OU

You don't have to use 2 VC gaskets, just get the double thick ones if you need more room. No mess gluing them together, etc.

Double check trunnion orientation.



.

Yes I have the polylocks sitting in the circular depression, I thought that was what you meant by “flat side”. I have some thick cork gaskets that I will use on my vc and they fit good.

I had to get longer Rocker studs for my #64 heads. I belive I have 9.4 or 9.5" pushrods as well. Valves are longer. Dave at SD Perf installed longer valves for greater lift. Thus requiring longer pushrods and rocker studs. ARP sells them in all sorts of lengths. I found my pushrod length using the half lift method, then seen how short my studs were. Then ordered of ARP the ones that would ensure they worked with the polylocks

The lifter is pumped up and has some springiness to it. I checked the pushrod length using the geometry method and came up with 5.21 turns on the polylock and got a length of 9.1 in for my pushrods.

My contact patch was much larger when I got the contact area in the middle with a 9.5in adjustable pushrod. I really don’t want to have longer rocker studs because that would mean tall valve covers and thus modifications to my a/c bracket and power brake booster.

It seems that the overall reach of the rocker arms is not optimal for the geometry of Pontiac heads. I looked in the instruction manual for these rockers from Comp and they only list Chevy and ford applications, no Pontiac engines. However, they were provided to me by butler and there are obviously others who have had success with these. There are a million factors that can determine these things I guess.

They are probably 1.6 Ford rockers .

There is no right or wrong rocker geometry. The narrow-est mark in the centre of the valve tip is very popular but it takes no account of what is happening on the prod side. What happens on the valve side in terms of lift & area under the curve ...... is times one. On the prod side it is times 1.5 [ for a 1.5 rocker ]. David Vizard's BB Chev book has a chart of various rockers he tested. Lift at TDC & max lift was tested as well as the overall ratio. The numbers are all over the place & show you can spend a lot of time to gain nothing except a warm & fuzzy feeling.

Put a .050 lash cap on and try it again. You have the right retainers

This is not true, there is definitely a right & wrong. There may be a little wiggle room due to the fact that pushrods generally come in .5 increments, but if you're more outside of that, it's 'wrong'. Or at least not 'optimum'.

The problem with the Comp roller tip arms is really more about the varying ratio than the usual regurgitated rocker ball issue, which some say they have corrected (to a degree, pun intended).

Just because Butler offers them they may not be 'optimum' for YOUR engine. Lower lift cams and less aggressive profiles won't be impacted as much as the opposite. So what 'works' on one engine may not work with another. And vendors may offer 'budget' alternatives to not chase customers away.

Do it right, do it once.

These would be a much better option, and still on the 'budget' side:

https://butlerperformance.com/i-3164...tegory:1459691

Get what you pay for.

Been there done that, but never tried those Butler stainless ones. I only buy one now, they last forever, and there's no question:

https://butlerperformance.com/i-2445...tegory:1459691

.

.

As a test, check patterns on ALL the rockers. Then you will see how far out of whack (or not) they are.

Also, it is possible the intakes may require a diff length of rod than the exhausts, which is basically a factor of valve availability and the fact that some exhaust seats may have had to be cut diff due to valve recession.



.