TurboTom wrote:
Pletchtan,
Those stands look awfully tall to get the geometry right. Am I missing something???
By the way are the stands steel or alum.?
Good looking setup though
From a previous post he said that he was going with longer valved, if they are the ones in the images I don't know. But I agree, from the images it looks like the geometry is going to be off quite a bit.
But that is one beefy setup and a beautiful head.I have a set of Harland's standard pedestal mount rockers. I had a few problems with a few (not necessarily their fault), but their support was excellent and helped me out a lot.
What are you doing for a valve cover? I know the aluminum head has a spacer built in, but will that be enough?
The valves are about .350 longer than stock. I think the spring height is .940 uncompressed. I will be able to run a .650-.700 lift without a problem. The valves in the picture are stock height. So when we get it all together , we will mill down the rocker supports to the correct height.
The valve cover is another issue, If the stock does not fit, i could use a spacer in addition to the built in spacer on the head. I also thought of fabrication something. I may have to drop the engine down for hood clearance.
Peter Lechtanski
The worlds Fastest Comanche Prroject
Plechtan wrote:The valves are about .350 longer than stock. I think the spring height is .940 uncompressed. I will be able to run a .650-.700 lift without a problem. The valves in the picture are stock height. So when we get it all together , we will mill down the rocker supports to the correct height.
The valve cover is another issue, If the stock does not fit, i could use a spacer in addition to the built in spacer on the head. I also thought of fabrication something. I may have to drop the engine down for hood clearance.
Sounds good.
What is the stand made from?
Remember, Sometimes I post after drinking!
1979 AMC Spirit
Building a Turbo 2.5
I am not very smart!
Hesco sells a valve cover spacer. And if you raise the valve cover height you will also need a thermostat housing spacer which they also sell. Not trying to push their products, but for now they are the only ones that sell them. If you are going through the effort to digitize one and machine it, make a few and you could make a nice profit selling them.
I have been away from this site for quite a while. In looking at your broken rockers they exhibit the classic fatigue break you would expect from ANY aluminum rocker. I have seen this sort of break on literally thousands of aluminum rockers. It generally originates in the root of the first or second thread of the adjuster screw hole and migrates to the housing bore. In x-ray tests we saw these fractures occur relatively early in the cycle life of a rocker. Alllthings being equal, spring pressure cam lobe etc., they will break sooner on the exhaust side because the exhaust valve opens against cylinder pressure...is it possible the intake rocker that broke was previously in an exhaust position?
The contributing factors to fatigue breakage are valve weights, high spring pressures, high cylinder pressure, aggressive cams, and high RPM's. However, even if none of these conditions are present an aluminum rocker has a cycle life. When the NASCAR teams were still using aluminum they would actually data log the RPM and time spent at it in order to predict when to pull the product from their motors.
Speaking only for our rockers, which use a small diameter shaft and have a minimum distance to the adjuster screw greater than those pictured in your post, it was not uncommon to see 25K miles in street engine with a hydraulic lifter before breakage. One way you can check the rockers, which is unfortunately not deadly accurate, is to push the bearings out and check the rocker bearing bore on a rod bore gage. We honed our rockers within .001" TIR roundness. If they came back to us in excess of .003" we knew they had reached their cycle life as the bearing bores were beginning to deform and fatigue breakage was not far behind. If you were to measure them and see in excess of .003" it would be likely they had suffered some sort of traua like over rev or piston to valve interference.
While I realize your rockers had nowhere near those kinds of miles they do use a larger bearing bore and likely have a smaller dimension between the bore and adjuster screw than our product did, which may account for the shorter mileage before fatigue
While I was screwing around at the shop I looked at the stock rockers on the 4.0 engine to see if I could easily replace the with a V8 style rocker that was semi-correct. In measuring fulcrum length, with a pair of calipers rather than a CMM or surface plate and height stand, it appears to me the stock rockers fulcrum length is significantly longer than those found on any of the V8's I looked at. They appear to be at least 1.750" fulcrum length but I would be interested in knowing if anyone knows for sure what they are.
Longer fulcrums are always an advantage as they reduce the amount of sweep across the valve tip and increase the distance from the pushrod to the fulcrum for a given ratio, which in an aluminum rocker provides a longer servic life before fatigue break. Longer fulcrums also have a less violent opening and closing action.
If one were to use a shorter fulcrum and move the rocker around so the roller tip were in the proper place on the valve it would adversely affect ratio. In other words you could end up with significantly different ratio depending on the relationship between the roller, fulcrum, and adjuster screw. To visualize this imagine a circle that a rocker would travel in around it's pivot point. All rockers are designed with those three points in a specific position to achieve a given ratio. If you move the roller down far enough and the tail up or vica versa it changes the "effective fulcrum length" and thus changes the ratio.
However if anyone is dead set on doing this I would recommend using Isky's adjustable guide plates. you can set them for the exact witdth you want and then tig weld them together....
