How to choose the right length of push rods???

[norvalwilhelm]

have never seen this topic come up. I had to go through this process this past week. I bought two sets of pushrods from Comp Cams. The high tec ones at $198 per set.
I have taken 2 pictures. Each picture has a good point and a bad point.
Can you pick them out and explain what I should be looking for in a push rod??
This is with a normal length push rod

This is with a longer push rod

 

["UNSAFE"]

Pushrod geometry

Your best bet would be a google or similar search for "pushrod geometry" to get some photos and info..

Basically ,you want the wear pattern on the valve stem to be centered.

You might try putting a piece of white paper between the rocker and the valve stem tip and then turn the motor by hand for 2 revolutions and then read the wear pattern.

You'll likely have to use solid lifters to check the geometry !

Hard to tell , but it looks a little short in the first pic.

I'm into Corvettes and Corvairs as well, here's a link with some info and pictures about pushrod geometry. It's not V8 specific, but it may be helpful

http://home.hiwaay.net/~langford/corvair/valve_geometry.html

Good Luck !
Kevin

 

[norvalwilhelm]

This post is not asking for help. I know how to set up the proper length pushrod. I was trying to get a discussion going. I wanted people who are interested in learning to step forward and I would guide the topic in what to look for. Most completely ignore push rods , install whatever and call it good.
Do any of you really know what to look for??? Do any of you really check valve train geometry? I spend a fair amount of time on this and about $400 getting it right.
Unsafe ,thank you for taking an interest. I guess we are the only ones who cares so let the post die. I don't need advice and thank you.

 

[arcticvette]

have never seen this topic come up. I had to go through this process this past week. I bought two sets of pushrods from Comp Cams. The high tec ones at $198 per set.
I have taken 2 pictures. Each picture has a good point and a bad point.
Can you pick them out and explain what I should be looking for in a push rod??
This is with a normal length push rod

This is with a longer push rod

hey norval i'll bite if you're still willing to give a lesson. hate to see a guy who's offering to share knowledge be ignored, although it maybe that there are more guys out there other than my self that might find this topic a little intimidating. if you can shed some light on the subject for us i would appreciate it, just hope I can follow along

 

[bossvette]

don't they sell a "adjustable" push rod to set legnths with?

 

[JOE BYRNE]

Sounds like a bad day for someone

 

[norvalwilhelm]

don't they sell a "adjustable" push rod to set legnths with?

Yes they do but what are you looking for when you adjust the rod?? Just making it longer, looking at it and say "Yes this is what I want"" HOw do you know that is what you want??
If you have 2 push rods , one .100 longer then the other and both look fine which do you choose??
What about having the rocker sitting in the middle or center of the valve?? True or false??
If you error on a push rod is it better to error on the short side or long side??
If you deck the block or heads, sink the valves with a new valve job, face off the valve stems? What affect does this have on push rods??
What about rocker arm slot to stud clearance??

The little things like this could destroy that expensive motor.
I lost a well built 355 in under 1000 miles because 15 were correct and one was wrong. Dropped a valve, destroyed one head and lost the block all because one valve didn't co operate.

 

[norvalwilhelm]

Sounds like a bad day for someone

Could be. It might be something you are not interested in today but down the road if you want to someday build a really screaming motor it will come up and will you know how to make a smart decision on what bush rod length to use???

 

[bossvette]

OK now I get the idea of this post and I'll take a stab at it.
first picture good point is contact area on valve stem, but hitting retainer.
the second picture has clearance on the retainer but the contact point is too far forward on the valve stem so it looks like +.050 pushrods are the way to
go.

I had a simular case on my old Yellow Truck it is pretty much a mild build I needed early style heads to match my TPI baseplate and used a set of 305 heads that I bought on Ebay some time ago with 1.94 intakes. Bought some pretty blue Aluminum roller rockers and some of them would bind on the pedastal. Tried several sets of pushrods with the same results, took them to work and measured the legnth with a height gage and they were all the same :W (Stock, Comp Cams , Summit and Ebay ones).
Stock rockers worked fine with no binding, but they would not stay on the valve stem; the pushrod holes were round instead of oval. The machine shop I used suggested "self aligning rockers" which I used and they didn't bind and stayed on the valve stem.
Its a mild 305 TPI that I doubt will see much over 3500-4000 but now after seeing Norvals post I have to look at it a little closer. I hope I dont have to change anything but the way this whole project has gone I probably will.
Craig sr

PS I also didn't see any nuts on the head stud in the first pic :L

 

[jdp6000]

I have no idea which one is right. But its something i will be doing this summer. if I had to guess I would say the second picture...more coverage and better clearence over the spring.

Jim

 

[norvalwilhelm]

Your right about analzying both the pictures.
One thing to try with your rockers and push rods is take the nut off and with the cam on it's heal/ where you would set lash push down on the push rod end and try lifting the end with the roller over the valve stem. You should be able to lift this end a 1/4 inch or more. If you feel it is a little tight it means the slot is not long enough to the back. Simple work with a die grinder quickly opens the slot up so it is not touching the stud.
Again without a nut on the rocker push down on the push rod end and left up on the valve stem end. This is making sure the slot is ok on the rocker. At least at rest it is ok.
Next push rods should be a short as possible NOT long.
Got to go

 

[glen242]

Norval:

To really check my pushrod length I would think I would have to use blue dye or a Sharpie over the valve tip. And since I am using hydraulic lifters, should I have a slid lifter to install for the test? If so, what length and where do I get a solid lifter that will match the hydraulic lifter when it is running @ its proper setting? Thy hydraulic lifters are the CC ones that came with the XE 274 cam.

HELP!

 

[norvalwilhelm]

Norval:

To really check my pushrod length I would think I would have to use blue dye or a Sharpie over the valve tip. And since I am using hydraulic lifters, should I have a slid lifter to install for the test? If so, what length and where do I get a solid lifter that will match the hydraulic lifter when it is running @ its proper setting? Thy hydraulic lifters are the CC ones that came with the XE 274 cam.

HELP!

Glen242 I don't know if the hydraulic installed height is the same as a solid or not. I always always run solid cams so I haven't had to deal with a hydraulic. As for borrowing a lifter to check I thought most speed shops would have them laying around.
As for dye that is a good ideal but I have used my digital camera in most cases and took pictures and later studied them.

 

[norvalwilhelm]

The first thing I look at is retainer to rocker arm clearance, you definitely need clearance but how much?? The second is where the point contact on the valve head starts and finishes.
The rocker sweeps outward/ towards the exhuast manifolds as the valve is compressed so you want to start this sweep on the side of the valve stem closest to the intake or inside of the valve.
The rocker sweeps about 1/3 of the valve.
Lets divide the valve into 6 parts, not 3 but 6 parts and have the rocker sweep 2/6ths. We also heard that the rocker should push on the center of the valve to prevent side loading. This is not possible since the contact point is moving.
If we start in the middle like the 2nd picture, remember is clears the retainer put starts in the middle of the valve. So we start of 3/6th and sweep 2/6ths and that leave 1/6th from the outer edge.
This means at full lift the roller of the rocker is only 1/6th from the outer edge of the valve, certainly not near the center at the time when maximum load in on the valve.
The longer the push rod the further out the roller on the rocker starts.
If we have the ideal pushrod the roller starts say at 2/6th from the inside, sweeps another 4/6th or ends up 2/6th from the edge of the valve or only slight past center under full load/lift.
This is ideal When maximum load is reached the contact tip is only slightly past center.
So the first picture shows the proper contact spot but contact between the retain and rocker and the second picture with a pushrod .080 longer then the first is starting in the center/ something we do not want.
I used the first push rod, the one touching the retainer.
I used Lash caps. Lash caps are little caps that go over the top of the valve, protect the valve for the action of the rocker , can be replaced very easily but most of all they gave me more retainer to rocker clearance and moved the contact point even more towards the inside.
I now have my retainer to rocker clearance, my contact point is behind center and my valve is protect.
You do need special retainers for lash caps but I always run them anyway.
Be sure to check slot clearnace on the rocker to stud and also that the bottom of the rocker isn't riding on the stud socket head or it will grind into the bottom of the rocker.
I hope this gives you some insight into what to look for. I know it in my mind but have problems sometimes getting it into words.
If you ever loose a motor over something like this you will have it ingrained into you for life.

 

[glen242]

Norval:

Thanks for your reply. My present set up is ok, but, as a safety margin, I want to install springs with a larger coil bind. I am using TF 23* heads and I am going to call TF to see what various parts they recommend for their stiffer springs. Installed height for the stiffer springs is larger than my stock springs, and I wondered how that would be accomplished? Will I need different retainers/locks for the new springs as the spring pockets will be the same as stock?

Am I over analyzing this?

 

[norvalwilhelm]

glen242 you should run the lightest springs you can get away with, Stiff springs are harder on lifters rockers and valve stems and guides. I wouldn't up the pressure just for insurance.
For long installed height you need a different retainer and different keepers. EAch can be had with about ,050 increase in installed height. That is .100 max. Only other way is longer springs and that gets too expensive,

 

["UNSAFE"]

You must use solid lifters to get the right length pushrod. Hydraulics can't be used because the lifter collapses.
All lifters are not the same, you must measure the the height of the lifter at the pushrod contact point and compensate for any difference in height with the hydraulic lifters you are using. Put a ball bearing in the lifter dimple and then measure height with a micrometer or calipers. Remember it will probably be preloaded about .010. or more when lash is adjusted.
The adjustable pushrods are only for determining the correct length and NOT for use in a running motor. Usually you have to use a very soft spring in place of the valve spring to prevent deflection or even breaking of the adjustable pushrod.
If you change rocker arm ratios, you also change the rocker geometry.
Kinda hard to imagine a major engine problem in less than 1000 miles just because a pushrod was a little too long or short, it would have to be so far off that it should've been obvious at the rocker stud threads and very noisy.
Usually it just increases the side load at the valve guide and the guide wears out prematurely.
Extreme cases will usually have a lot of noise in the upper end.
Pushrod length is not quite as important with stock type rockers because the rockers can slide on the ball.
On roller rockers, the rockers do not slide.
Valve jobs,different head gaskets,milling the block/heads, changing rocker arms, etc. can all effect pushrod length.
Hard at it today, finishing up the install of my new crate ZZ383/425hp motor and TCI streetfighter tranny with a 2400 rpm converter and 3.70 gears. I am also installing a new set of hooker 1 7/8 SS headers and sidepipes with STS baffles.
I would've had it running already, but the dang torque converter wouldn't fit the 153 tooth flexplate of the ZZ383 so I had to get a 168 tooth flexplate. Luckily my starter will fit either.
Can we post pics here, and if so ,how ?
Kevin, "UNSAFE"

 

[glen242]

glen242 you should run the lightest springs you can get away with, Stiff springs are harder on lifters rockers and valve stems and guides. I wouldn't up the pressure just for insurance.
For long installed height you need a different retainer and different keepers. EAch can be had with about ,050 increase in installed height. That is .100 max. Only other way is longer springs and that gets too expensive,

You are correct regarding pressure. I am looking for a spring with about the same seat pressures but more maximum lift before coil bind. I may be close to the maximum valve lift with my present springs. I have a +/- 5 year old set of TF 23* heads. When I bought them, TFs specs were 0.520 maximum lift. I saw their specs for their latest 23* heads, and they have lowered their maximum lift spec to 0.480. I am running 0.501 maximum lift with my present cam, and I am a little worried.

I called TF about this, and they said they reduced the maximum lift spec, on their regular springs, because of the radical ramps on the newer cams - CC XE and Lunati Voodo. I am running a CC XE 274.

New stroker only has about easy 500 miles on it and I want to be safe when I beat on it this spring.