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Valve Stem Wear Pattern
I installed a set of roller rockers and it was brought to my attention that centering the rocker over the valve stem can result in the valve stem not rotaing - thus causing a wear pattern to develop on the valve stem that can be seen where the roller contacts the stem. This seems to have occurred with me. The instruction sheet that came with the roller rockers is specific about rocker position with regard to certain installations. The reason I centered the rollers was to prevent the pushrods from contacting the manifold. Can anyone comment on this?
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For the valve stem to rotate, I believe everything else would have to rotate too. Spring...spring retainer ?
I dont think those parts were meant to rotate at least not in a performance application anyways. The car company's did use valve rotating devices back in the old days when there was leaded gas but when the no-lead showed up they stopped using them. Without lead in the gas there wasn't enough lubrication between the valve seat and the valve face to prevent scuffing and with the rotaters still in there it caused severe valve seat erosion. Leave your rockers centered, I'm sure your valve guides will be happier. :D Dale |
Dale- thanks for your input. I believe you are correct about centering rockers over valves - makes no sense not too. Besides in all the info I've read, good contact is the accepted method. I am having pushrod clearance problems on my intake manifold and centering the rockers results in much better clearance. The source I was quoting said I should not be shimming the rockers away from the stand. This would result in less clearance. I am using a 6005 Edel. head fitted to a MR tunnel wedge manifold. This doesn't create a port mismatch problem but does cause a valve center to manifold hole center problem. I will have to do more grinding on the manifold and stay with 5/16" pushrods.
Paul |
Hi Paul Your roller rockers are centered for the pushrod and not off centered, that has an intake rocker and exhaust rocker. If you put white grease on the top of your valves the roller should stay in the center of the stem if the geometry is correct. You may have to oblong the holes in your intake for proper clearance of the pushrod through the intake. Go to the book stroe and find a blueprint book of engines and check out this part. You can due this yourself. Take the intake off before you due any grinding of the manifold I dermial tool will work great for what you have to do. Mark the spots to be removed with felt pen. When finished clean the intake real good and air dry to get any metal chips out of the intake runners or holes. Reassemble, set valve lash depending on lifters, rotate engine 4 turns and check for clearance area in manifold. Good luck take your time, ONLY TAKE ENOUGHT metal to clear the pushrod under full movement in slot. Rick Lake
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Rick- Thanks for your advice. I do not have the larger valves in these Edelbrock heads. They are SCJ valves. Edelbrock however says they moved the intake valve 0.060" away from the center of the bore. This results in more clearance for the intake pushrods and less rubs but the exhaust valves all seem to contact the lower inside edge of the manifold. I am convinced that if my heads had the larger diameter valves (spaced further apart) I would have very little if any problems. The manifold is a high rpm med. riser tunnel wedge which no doubt was cast for the med riser 427 heads with the larger valves. I will proceed to do my clearancing to the manifold. Thanks again.
Paul |
Hi Paul,
Valve rotators are for high mileage type engines, non-performance. These add a whole bunch of weight to the valvetrain, so this is diffenetly out in a performance application. If the rocker is not centered on the valve tip, then you start side loading the guide and it wears out quite quickly.Your centering is exactly what you want on your motor. The wear can come from, now get this, either not enough, or too much valve spring pressure! If you have a fairly big cam, and are reving it high, if you dont have enough pressure, your valve will bouce on the seat, there by hammering the valve tip against the rocker. Similarly, if you have too much pressure, especially open pressure, it can cause scrubing on the valve tip if there's not enough oil getting to the valve train at high RPMS. Hope this helps!! Tom, FE Specialties. |
Thanks for your wisdom on this matter. I will certainly center the rockers on the valves.
Paul:) |
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