Im setting up my valve train, and right now Im trying to determine the correct length pushrod for my combo (XE270 retro-roller/isky lifters/trickflow heads). Im curious what everyones thoughts are before I order pushrods

Ive heard a lot of opionions as to what the correct wear pattern is. Some people seem to say to go with the length of pushrod that will result in the smallest wear pattern, but on my combo, this puts the tip of the rocker way out toward the edge of the edge of the valve stem. After some tinkering, I managed to pull the wear pattern in a bit with a 7.200" pushrod lenth. Obviously this increases the sweaped area of the rocker tip, but near max lift, the rocker tip travel seems minimal (in the below photo, the cleanly polished area near the edge of the wear pattern is the travel above 2/3 lift). To me, this seems to be the best comprimise as the tip travel will be the least when the spring pressure is the greatest. Does this seem reasonable?

 

It doesn't matter where the contact is, as long as it's the smallest area.

 

The smallest wear pattern puts the tip right next to the edge of teh valve stem with the parts in use. Is that safe? The valves im testing on could be the best case scenario. Im just afraid that one of the roller tips could take an off-road excursion and cause some serious damage if one of the tips falls closer to the edge.

To play devil's advocate for a bit, I was playing around with the length of the pushrod a bit more. I can get to a point where the rocker tip has almost no travel at all for the last 1/3 of the lift. This length is a bit too short as I dont have enough stud left for the 1/4 turn preload, but in theory, might this be more preferable? It seems that the least contact method has more travel near max lift where the spring pressure is greatest.

Im just sort of confused as to whats best. Some say 1/2 lift, 2/3 lift method, least contact, centered... Too many methods with no true clear cut answer.

 

Ok, so I decided to stop reading all the stuff on the internet and put a few minutes thought and some mspaint skills to work (see below). Before thinking about it, I agree that the smallest area method seems to be the best approach, but one thing about the smallest area method is that at 1/2 lift, the rocker will be essentially perpendicular to the valve steam, which means that during the last half of the valve lift cycle, the rocker tip will have to come back across the face of the valve steam when the spring pressure is greatest.

With the factory settings (using near stock length pushrods), there is much less movement near max lift where the spring pressure is the greatest. Theoretically, this will result in less wear and tear as the tip is nearly stationary during the point when the force is greatest.

Would everyone agree that its better to defer to the GM settings rather than whats recommended by the aftermarket guys? Im probably (more like definitely) over-analyzing this, but I figure its better to work it out now when its easy.

 

I set mine up like the factory does. The rocker tip hits the "inflection point" at about 2/3 of max lift. I'm in the minority on this, though.

The factory does it for the reason you describe- reduced wear/friction. Using the 1/2 lift method probably gets the valve off it's seat a little faster, though (I'm not good enough at geometry to figure out the comaprison between the two methods at various lift points).

 

Over analyzing? I'm not sure that's possible. There is only over reacting.

Generally, the "smallest pattern" method is in line with the theory that the rocker should be approximately perpendicular to the stud at about 1/3 of total lift. Theoretically, that would put the starting point of the rocker tip somewhat outboard of the valve stem center so that at peak lift (and peak spring pressure) the rocker tip will be at the strongest part of the valve stem, or just slightly inboard of it, and will be imparting no side-loading of the valve at peak pressure.

 

Well... Im not exactly to the point of loosing sleep over it

This is just my first time setting up a valve train. All my other setups used stock type flat tappets and factory heads and lifters, so the setup was limited to tossing in some 7.800" pushrods and forgetting about it. When you read the manuals and liturature that comes from the aftermarket guys, they make it sound like all doom and gloom will happen if you dont set it to what they specify. I guess in reality with roller rockers, the valves probably could care less which method is used.

The thing that concerned me the most with the 1/2 lift method and the parts in use is that it put the rocker tip right next to the edge of the valve stem face, which to me, could mushroom the valve stem. The factory method at least has it kind of centered on the valve stem.