Rocker arm geometry problem

[fishy68]

Guys I've got a rocker arm geometry problem with my 360 and 1.5 ratio Comp Cams magnum rocker arms and I'm not sure what to do or if anything can be done so hopefully somebody here can lend a hand.

I pulled the valve covers to put in a new set of valve springs and when I took the rocker arms off and pulled out the pushrods one of the pushrod ends fell off. Thank God it didn't go down in the engine. The pushrods were new just 1,000 miles ago and Comp part # 7821 just like the paperwork that came with the rockers said to use. Well at first I thought I just got a bad one but then I got to looking closer and checking things and the first thing I noticed was I had to have the adjusters screwed in much farther than I should have according to the paperwork. It said I should have 1-2 threads left showing above the locknut but I had to screw the adjuster in where it was about 2 threads below. So apparently I needed longer pushrods. I ordered them and got them in today and installed them and adjusted them and the adjustment came out right where it said it should be. Then I thought I'd check the geometry and when the valve is seated the rocker tip is off center to the exhaust side. As I roll the engine over through the lift cycle it gets worse. At full lift it is very close to the outer edge. I can't see any way to correct this. Anybody have any ideas? Are the Comp rockers just poorly designed that it places the tip too close to the edge? That's what it appears to me.

I don't have any pictures of mine but I found a picture on Hughes Engines site that looks just like mine at zero lift to give you an idea of what it looks like.

 

[Longgone]

I`ve heard of galling problems with the Comp rockers but not anything about the geometry. It looks like you`re still not at the right length on the pushrods, Smith Bros. make a variety of pushrods to your specs, you might try them for a custom size.

 

[fishy68]

I read that article on Hughes site about the gauling too. Mine didn't show any of that. As far as not being the right length on the pushrods, I looked at it real good and if I go with any longer pushrods the crown of the pushrod cup will hit the rocker arm. The new ones I just put in are .108 longer than the ones I first had in it. I inspected the rocker arm geometry with each length pushrod and it made no difference with either one when the pre-load was set correctly to .030" so apparently pushrod length doesn't affect rocker arm geometry??

 

[Longgone]

That`s odd ,it certainly appears the longer rod would center the roller over the valve tip? You`ve got me fishy, can you shim the shafts to get the rollers centered on the valve tips and then find the proper pushrod?

 

[63dartman]

sounds like the rockers are nose up on the valve stem and walking out to the edge as they open. are you sure the rockers are for a hydraulic cam and not a solid?(not even sure if there is a difference) I'm not very familar with the comp rockers.

 

[rumblefish360]

Thats odd. The longer P rod should have centered the tip more and I thought that as the rocker push's the valve down, the tip should become more centered.
That picture, the tip looks to be in a OK, position, not the best and like I said, as it pushs the rocker doward, the rocker tip should move towards the center of the valve tip.
I have not noticed or exp. any problems with my Comp roller rockers.

 

[redfastback]

i also would have thought that 2 different length pushrods would make the change noted above. can you take pics thruout its cycle and email them to a tech at comp cams? maybe its a bad batch of rocker arms. i have installed a set on a customer's car with no problems.

 

[Longgone]

Fishy, with the valve closed you`ll want some offset of the roller on the tip of the valve and the diametric opposite with the valve at fully open.

 

[fishy68]

sounds like the rockers are nose up on the valve stem and walking out to the edge as they open. are you sure the rockers are for a hydraulic cam and not a solid?(not even sure if there is a difference) I'm not very familar with the comp rockers.

That's what it appears to me also. They say in the papers their for either a hyd. or solid cam but you have to use shorter pushrods for the hyd. I used the shorter set first and that was when I had to have the adjuster turned way in and with the shorter rods they allmost rubbed against the heads. The longer rods (the ones they say to use for a solid cam) center the rods in the heads perfectly but made no change of the geometry.

 

[416stroker]

On Mopar small blocks with a rocker shaft setup the only way to get correct rocker arm geometry is to shim the rocker shafts. Mancini Racing and a number of other distributors sell the shims. I have the shafts on my 416 shimmed .100 in order to get the correct travel of the rocker on the valve tip. Whenever you mill the heads or deck the block or cut the intake you change the relationship of the distance from the lifter to the valve and then you begin to experience the over center or under center travel on the valve tip by the rocker. There is a really good article on the web that explains this very well. Just type in Mopar valve geometry and you'll get to the site. Push rod length on a rocker shaft setup isn't going to change your geometry because that is controlled by the height of the rocker shaft on the mounting stands. When everything is a stock setup like from the factory the distance from the lifter to the valve tip on a shaft setup is known and the push rods are made to that spec to keep the rocker in contact with the valve with the correct preload.

 

[fishy68]

Rumblefish, Longone, and Redfastback. I also thought the longer pushrods would make a difference at first but they didn't. The more I look at it I can see why. With the longer pushrods you just adjust the adjuster to get the right pre-load. When the valve is closed the rocker stays in the same location on the valve tip no matter what pushrods you use.

I read on Hughes site about rocker geometry and they said the roller tip should start just off senter toward the intake valve and then roll toward the exhaust side then about half lift start rolling back toward the center. I think mine would do that if they didn't start so far off center of the wrong side of the valve tip. Funny thing is they also stated their rocker arms are designed right so they don't roll off the tip of the valve. I'm sure that's an advertising ploy but in the case of mine it might hold true. The Rockers I have are a NOS set of Comps I bought for a real cheap price. Probably the first design they made so maybe they did have a problem with geometry.

 

[fishy68]

On Mopar small blocks with a rocker shaft setup the only way to get correct rocker arm geometry is to shim the rocker shafts. Mancini Racing and a number of other distributors sell the shims. I have the shafts on my 416 shimmed .100 in order to get the correct travel of the rocker on the valve tip. Whenever you mill the heads or deck the block or cut the intake you change the relationship of the distance from the lifter to the valve and then you begin to experience the over center or under center travel on the valve tip by the rocker. There is a really good article on the web that explains this very well. Just type in Mopar valve geometry and you'll get to the site. Push rod length on a rocker shaft setup isn't going to change your geometry because that is controlled by the height of the rocker shaft on the mounting stands. When everything is a stock setup like from the factory the distance from the lifter to the valve tip on a shaft setup is known and the push rods are made to that spec to keep the rocker in contact with the valve with the correct preload.

Thanks 416. I was thinking the only way to get it right is to shim it but I've read where some engine builders say you shouldn't shim them. Why I don't know?? They never went into an explanation. I'll do a search on rocker arm geometry and see what I come up with.

Longone I see you mentioned shimming them above also, Thanks.

 

[416stroker]

Fishy is right! The rocker arm position is constant on the rocker shaft. It moves in an arc out and back. The valve height and the shaft centerline are constant and the only way to change that is to raise or lower the shaft.
Check out FBO's website for a real good explanation on the subject. When you run a rocker stud setup like on a chevy or some Fords the push rod length comes into play when dealing with correct geometry.

 

[rumblefish360]

Ahhh, thus it is exposed. I'm wrapping the LA and MAgnum parts and problems together. Thats where I think I got it from.

Good job fellas!

 

[Longgone]

Thanks 416. I was thinking the only way to get it right is to shim it but I've read where some engine builders say you shouldn't shim them. Why I don't know?? They never went into an explanation. I'll do a search on rocker arm geometry and see what I come up with.

Longone I see you mentioned shimming them above also, Thanks.

That`s the only other thing I could think of. Give it a go, it sounds logical and with what 416`s saying, using shims, you should be able to put those rockers right where they need to be and smile again. :grin:

 

[416stroker]

Fishy, When I had the issue with my valve geometry, I called Dave Hughes at Hughes Engines because he built my engine. I was concerned about the shimming part of it and he told me not to worry as it is a common fix and that his hardcore racing customers with big cams and tall valves do this all the time with no problems. He said you can shim as much as .120 if you had to without worry or until you run out of threads on the rocker bolt. I was worried about the stability of the shaft and he assured me not to worry because the rocker is the only thing that is moving and that the shaft is held in postion by the stands and is bolted in place.To this day I haven't had any problems with having my shafts shimmed up.

 

[fishy68]

That's a real good explanation Don has on his tech page. I forgot all about his tech page until 416 mentioned it.

Thanks alot to everybody that replied. Looks like I just need to get some shims.

 

[daredevil]

im with 416 as when i installed my indy heads i shimmed .050 to center roller on top of the valve then measured pushrods.

 

[jaxle]

i wish i knew about shims about four months ago! i have a set of crane rollers sitting in my garage right now cause of the same problem. i got a set of comp steel rollers to replace them on my edelbrock heads and they had no offset problems. every one i talked to said nothing about shimming; not even comp when i called their tech line.

 

[Longgone]

i wish i knew about shims about four months ago! i have a set of crane rollers sitting in my garage right now cause of the same problem. i got a set of comp steel rollers to replace them on my edelbrock heads and they had no offset problems. every one i talked to said nothing about shimming; not even comp when i called their tech line.

Chalk one up for FABO!

 

[416stroker]

Amen to that!!!!1

 

[moper]

It looks to me that the arms are too high in that pic. (i know, not your heads...). That is the result of the wrong valve hieght, as was stated. You dont fix that with shims. You use a new valve (valve jobs tend to make them shorter effectively) or you can sink the seat a little, or remove the rocker stands and use blocks. In any case, pushrod length doesnt directly affect the sweep. Only the shaft height, valve tip hieght, and rocker design.

 

[fishy68]

It looks to me that the arms are too high in that pic. (i know, not your heads...). That is the result of the wrong valve hieght, as was stated. You dont fix that with shims. You use a new valve (valve jobs tend to make them shorter effectively) or you can sink the seat a little, or remove the rocker stands and use blocks. In any case, pushrod length doesnt directly affect the sweep. Only the shaft height, valve tip hieght, and rocker design.

Actually they are brand new valves. Their stainless valves from REV Industries and are stock length. All the exhaust seats are new also. Intake seats aren't new but the shop that did my head work said they were fine (not sunk bad). Note they didn't assemble the heads. I did that so I'm the one to blame for not correcting the final valve stem height. Although I did try to find out the installed height but couldn't seem to come up with a figure anywhere in any of my books so I just assembled them as they were hoping everything would be ok since they were new valves and good seats.

Since I have allready ordered a shim package from Mancini's I'll see what happens when I put shims under the rocker shafts. At this point I'm going to give it a try and see what happens before I go yanking it all back apart again. If it has a negative affect then I'll pull the heads and go through them again.

Does anybody know what the valve stem installed height is supposed to be?

 

[moper]

The distances are not very large. If the seats are new, maybe they didnt cut them deepengouh, or he was carefult to leave the intake seats up in teh chamber, but ddint realize the issue created. No problem so long as you're looking. That's the good part of this. But if your rocker looks like that one, the shaft effectively is too high already.

 

[fishy68]

Thanks for the reply Moper. I see what your saying. Next week when I get a chance again I'll mess with it some more and see if I can do anything with it.

Everybody have a nice thanksgiving.