Valve train geometry?

[Greg Reimer 7376]

Originally Posted by buzzinhalfdozen

Ok I know this has been discussed but I'm working on my engine after having all the seats in both heads replaced. Now figuring that my stem heights, and seat depths would be moved I decided I'd better do some checking on this thing figuring my piston to valve clearence may have changed.Well when I put the rocker stand at the correct height, as per T&D's instructions which I had followed in the past I'm seeing .025 inch less lift at the valve and my roller swipe pattern on the valve tip is WIDE over .200 inch. This seemed odd to me so I put the stand back to the height I had always run it which is about .090 lower, now I'm seeing the correct lift at the valve and my swipe pattern is less than .100 wide near tip center. With the stand raised the pattern looks OK till over half lift then it start running hard to the int. side. What the heck am I seeing here and why would moving the stand lower than it should be cause this change? I'm using adjustable pushrods for this setup, maintaing 1 turn from seated on the rocker adjuster screw. What gives? Since I'm not an engine builder I need some feed back from some of the pros. Thanks for any replies. Joe

Been busy this last weekend and week with Pomona and work, etc,and had time to read your thread. Seems to me that new valve seats would raise the seat, establishing a new parameter in valve train geometry. The valve stem would not protrude out of the valve guide as far,so the rocker arm shaft would be in effect,higher than it was before,thereby altering your valve stem tip contact pattern,and causing the lift and contact pattern to change. You said that you then lowered the shaft centerline,and the valve lift and the contact pattern assumed a more favorable attitude, then your change showed that you are moving in the right direction.Can you move the rocker arm shaft lower and check it again and find some more improvement?

[buzzinhalfdozen]

Greg, yes I've been moving stand down and looking at the effects it has in lift and roller travel on the valve tip. lowering it does "fix" some of what I'm seeing wrong just didn't understand why I'm having to set it differently from where T&D wants it which is how I had always set it up. I understand that with new seats things have moved around that's why I'm double checking things versus just bolting them back on, thanks for your input I'm obviously going to put it where I have my correct lift numbers and least amount of roller travel just seemed odd that I'm having to move it this much. Based on T&Ds "tool" they send I have had to move the stand down .150 inch lower than the "gauge" shows.

[Greg Reimer 7376]

Originally Posted by buzzinhalfdozen

Greg, yes I've been moving stand down and looking at the effects it has in lift and roller travel on the valve tip. lowering it does "fix" some of what I'm seeing wrong just didn't understand why I'm having to set it differently from where T&D wants it which is how I had always set it up. I understand that with new seats things have moved around that's why I'm double checking things versus just bolting them back on, thanks for your input I'm obviously going to put it where I have my correct lift numbers and least amount of roller travel just seemed odd that I'm having to move it this much. Based on T&Ds "tool" they send I have had to move the stand down .150 inch lower than the "gauge" shows.

That's entirely possible Did they deck the heads at all? Sounds like things have stacked up to add up to several changes at once,not too unusual in a situation where major machine work has been done.