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  #1  
Old 12-01-2001, 12:00 AM
BigEdsGarage BigEdsGarage is offline
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Question 340 racers, rocker arm/shaft question

Did anyone have to machine thier rocker shaft to move them in closer to the intake manifold side? How about shimming the shaft .060 for proper geometry? I am running a 68 340, x-heads milled .015, Hughes solid 554/285 107 centerline, comp cams aluminum 1.5 roller rockers. When I put the setup together the roller tip was closer to the exhaust side of the head, called Hughes, was told this was a common problem on small blocks, sent heads and rocker to them, machined shafts and stands to center roller, used thier pushrods,cam and lifters, checked everything at 1/2 cam lift per thier instructions, they had me place a .060 shim between shaft stand and shaft in order to get proper geometry. This seems like an awful lot of work to get a set of rockers to work. The car was running 12.90-13.20 times with a 484 hyd cam and stamped rockers, all this work and it runs the same times. Do you guys think the rockers were wrong and this was a poor way of making it work. I checked roker arm to spring retainer clearance before shimming the shaft, it was fine.I think Im going to put in a 509/292 cam with 273 style adjustable rockers if I cant figure this out. Any help is appreciated!
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Old 12-02-2001, 11:13 AM
sanborn sanborn is offline
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Shaft rockers are a very good design. They keep the rockers more stable while in operation but are more expensive to manufacture. They are also easy to setup and maintain when using the camshaft/ lifters they were designed for. They become more difficult when setting up for a high performance/racing application.

One of the problems encountered when using stock type rockers with a high lift camshaft is the amount of sideways force exerted on the valves stem as the valve is depressed. High pressure springs make this problem even more acute. This can lead to a very short valve stem life. Hence, roller tip rockers came into being. It drastically reduces the sideways force on the valve stem; but, the roller tip requires much more precise assembly. Why? Because the poller tip only contacts the valve stem on a very small area. If you are off too much, the roller tip can actually run off the valve tip. If that happens, it gets nasty. 3/8" stems give you some clearance, it gets closer with 11/32" stems, it gets real precise with 5/16" stems. Lash caps can help, but aren't used in racing applications much.

It is not unusual to shim rocker stands after every valve/seat reface. Usually the adjustment on the rocker arm can take up the slack required.
After 2-3 reface jobs the pushrods may require changing.

On our race engines(.700" lift, 5/16" stems) we sit down with dial indicators to measure how much the roller tip moves across the valve head. Less is better. We try to get our shims close enough to allow only .015-.020" sideways movement across the valve head. This is extreme for a non race engine. But it shows you how much work can be involved. We have made shims as thin as .005"

Hope that helped to explain the reason.
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Old 12-02-2001, 10:43 PM
BigEdsGarage BigEdsGarage is offline
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I understand the critical alignment, I'm sure that is why Hughes had me do all the work. I still wonder why I haven't heard of others having this problem. I can see shiming the shaft, but what about machining it to drop it back towards the intake. Everything looks real good when you turn it over, no noticable movement on roller tip, straight across tip of valve.I wonder how the iron 273 rockers would work without allthis machining and shimming.I know guys who run A body cars deep into the 11 sec range and have used them with good results. I'm new tothe forum here Sanborn, was wondering how much experience you have with racing. I would like to give someone a breakdown of the cars setup and see what they think. I still feel it should be running at least a sec faster than it is.
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Old 12-02-2001, 11:12 PM
451Mopar 451Mopar is offline
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My 360 with the 1.6:1 ratio Crane Aluminum roller rocker arms also had the same problem. I just shimmed the rocker shaft up with the tapered shims ftom Hughes. This also helped with my pushrod length, as the Crane pushrods were a tad long. The pushrod problem was likely from the result of milling the block and heads.
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Old 12-03-2001, 11:24 AM
sanborn sanborn is offline
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Big Ed, it just dawned on me what your real question is about. If you look at your rocker arm stands you will notice the mounting points are perpendicular to the cylinder bore. But your valves are 18 degrees off perpendicular and are tilted toward the intake. So as your valves get longer or are sunk further up into the valve seat the tip actually moves toward the intake manifold. Said another way, your rocker tip would move closer to the exhaust side.

This problem is common. For example when using .300" longer valves in W2 heads, you use offset stands to move the rocker shaft toward the intake manifold. Mopar offers the stands and the offset machined shafts. I seem to remember the tip moved .137" with .300" longer valves. Its been a long time since I worked with W2s with stock type rocker shafts.

The reason many people don't encounter this problem is they don't realize it's happening. The problem isn't bad with lower lift cams(.550" and below) but begins to show up quick at higher lifts(and/or longer valves).

Hope this helps to explain. By the way, you asked how much racing experience I have; been at this for over 40 years(I would be rich if I hadn't gotten involved but far poorer because of what I would have missed), drag raced in the early years, got to the finals at Indy in 68(A/D), went to Army (you know, draft, Vietnam era-didn't go thank goodness, jumped out of perfectly good airplanes, etc.), got out in one piece, been going around in circles ever since. So I am a bald headed old geezer, my wife says I'm semi retired-I'm really an under employed engineer-tired of running all over the country and the world. Got one wife, one son and three dogs(the dogs are really good). The son races, the wife is his biggest fan, I go along for the ride. I try to help when I can and occasionally butte in when I see questions like yours.
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Old 12-03-2001, 12:57 PM
Jims451 Jims451 is offline
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sanborn is right.
Don't let the Chevy guys tell you that the rocker tip to valve alignment is determined by the pushrod length, this is only true with the stud mounted "floating" rocker arms.

Mopars shaft mounted rocker arms ensures the rocker arms piviot point never changes, reguardless of pushrod length.
To get the rocker arm tip centered over the valve stem, you can either vary the valve stem length, or move the position of the rocker shaft (shims.)

The pushrod length will determine the misalignment angle between the pushrod end (usually a cup end) and the rockerarms adjuster (usually the ball end.) I like my pushrod length to be set so the adjuster and pushrod are in alignment at about 3/4 valve lift (not 1/2 lift.) My reason is the spring pressure is greater at the higher lifts, so there is less stress and deflection on the pushrod at the higher lifts because the pushrod is in better alignment.
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Old 12-03-2001, 11:45 PM
BigEdsGarage BigEdsGarage is offline
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Thanks guys! I was told by others that the machining wasn't neccessary but had to trust the guys at Hughes, since they do it for a living. Sanborn, your description of 18 deg valve angle shed some light on how alignment was thrown off by milling, valve jobs and higher lift cam with stiffer springs. I also used the pushrods they reccomended for the cam. Still think another cam will improve et's though. I feel better knowing I didn't waste my time paying close attention to the valvetrain and setting it up per Hughes specs. Gotta ask people to see what everyone knows!
Thanks agian. I would really like to see some 12 teen timeslips this year.
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