Roller Rocker geometry questions
QUOTE=skrews;1969867027]This pic should help clarify the effect of valve tip height vs rocker arm height. If the pattern is on the intake side of center you raise the shaft.If the wear pattern is on the ex side of center you lower the shaft (which us mopar guys cant do) so we use a lash cap. In the case of the OP's situation the Crane rockers are likely a bit longer than they should be (as Raymond noted) causing the scrub pattern to be out toward the exhaust side. In reality it probably would never give you any issues running the way it is, but I'd rather make it as good as I could within reason.
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Now I'm back at work and can't see your picture...lol.
But I disagree with your statement of them being too short for two reasons based on the pics from the OP I saw:
1. The path followed by the rocker tip is an arc. As a result the pattern should be centered and wider with a slight bias to the intake side of the stem. Put into motion - on the seat (valve closed, "0" lift) - the rocker tip contact should be just to the intake side of the tip of the valve stem. As it lifts the valve it should move accross the center of the tip, crossing the center and going slightly towards the exhaust side at 1/2 it's travel (mid lift) - then it moves back towads the intake side of the stem. The width of the swipe is dependent on the total lift, the rocker ratio, and the height of the valve stem tip. That pattern is narrow, telling me the rocker is not traversing the tip, but rather still moving accross the tip towards the exh side of the stem.
2. The distance between the center of the valve stem tip and the rocker shaft centerline gets narrower as the height of either of those is raised. As that pattern starts on the exhaust side, it's already too tall... meaning the rocker shaft centerline and valve stem tip are too close together because the tip is too tall.
Adjustments should be made by the valve tip unless the rocker system and heads being used have flat support blocks. Those can be safely and accurately shimmed. Shims in the rounded saddle are fine for light duty work, but IMO are not acceptable in anything that has to rev or make big power. the repair is to fix the valve job.
To the OP - Your shop may not have to cut the seats, but by placing the head in their seat machine they can measure the heights very accurately and correct the valve lengths as needed. I'm not sure on the springs you're using but if the spring seats had to be cut to get a taller installed height it's my opinion that the seats should have been cut first. I've never had to cut spring seats on RPM heads. This is why I say RPMs need to have the valve job corrected prior to use. They all always had issues if one looks hard enough.
QUOTE=skrews;1969867027]This pic should help clarify the effect of valve tip height vs rocker arm height. If the pattern is on the intake side of center you raise the shaft.If the wear pattern is on the ex side of center you lower the shaft (which us mopar guys cant do) so we use a lash cap. In the case of the OP's situation the Crane rockers are likely a bit longer than they should be (as Raymond noted) causing the scrub pattern to be out toward the exhaust side. In reality it probably would never give you any issues running the way it is, but I'd rather make it as good as I could within reason.
[/QUOTE]Now I'm back at work and can't see your picture...lol.
But I disagree with your statement of them being too short for two reasons based on the pics from the OP I saw:
1. The path followed by the rocker tip is an arc. As a result the pattern should be centered and wider with a slight bias to the intake side of the stem. Put into motion - on the seat (valve closed, "0" lift) - the rocker tip contact should be just to the intake side of the tip of the valve stem. As it lifts the valve it should move accross the center of the tip, crossing the center and going slightly towards the exhaust side at 1/2 it's travel (mid lift) - then it moves back towads the intake side of the stem. The width of the swipe is dependent on the total lift, the rocker ratio, and the height of the valve stem tip. That pattern is narrow, telling me the rocker is not traversing the tip, but rather still moving accross the tip towards the exh side of the stem.
2. The distance between the center of the valve stem tip and the rocker shaft centerline gets narrower as the height of either of those is raised. As that pattern starts on the exhaust side, it's already too tall... meaning the rocker shaft centerline and valve stem tip are too close together because the tip is too tall.
Adjustments should be made by the valve tip unless the rocker system and heads being used have flat support blocks. Those can be safely and accurately shimmed. Shims in the rounded saddle are fine for light duty work, but IMO are not acceptable in anything that has to rev or make big power. the repair is to fix the valve job.
To the OP - Your shop may not have to cut the seats, but by placing the head in their seat machine they can measure the heights very accurately and correct the valve lengths as needed. I'm not sure on the springs you're using but if the spring seats had to be cut to get a taller installed height it's my opinion that the seats should have been cut first. I've never had to cut spring seats on RPM heads. This is why I say RPMs need to have the valve job corrected prior to use. They all always had issues if one looks hard enough.