cam dowel pin free play

[5axis]

Wayne. I am installing some elgin SC330 grinds and I am having trouble with getting the spec that I got from Stephen at IA.
I am fighting with the free play in the dowel pin fit. I set the spec and try to tighten and of course it slips. It slips enough to be out of my range. When I first dial the crank into position I am dead center on a hole, and the pin falls in. I tried the adjacent holes and they are out. My toolmaker fingers tell me I got at least a thou per side. Is it supposed to be that loose. Perhaps a PO/mech polished them down. I ordered a couple of new ones from you, just in case. If nothing else I could grind my own custom pins -.0002-5" for a very nice slip fit.

The other possibility is that it's fine and I need a helper when doing the tightening and the sprocket will stay centered?
I miss the slotted sprockets on my GSXR.


regards
david

[Doug Zielke]

David,
I don't know if this helps you, but when I did my motor recently, the original pins did seem a bit worn (loose?). I bought some new ones and they did fit with much less slop.

[ChrisBennet]

That's normal. Think of them as very small slots. The "slop" will allow you to get the cams perfectly even.
-Chris

[Wayne 962]

Right - you need to adjust for the backlash in the pin. High lift cams are notoriously difficult in this aspect - that's why I separated them in the procedure in the book. You must hold the cam steady when you tighten the 46mm nut (or bolt), keeping your eye on the dial gauge at all times). You do really need about 3 hands to do this right, but with a few tries, you should be able to get it right by yourself...

-Wayne

[5axis]

Reporting success! Doug, I did notice a slight improvement with the new pins. The procedure I used was still the low lift method. The SC330's are a mid range turbo grind. I ended up "pre loading" the lift #'s such that the cams came back right on spec as I set the torque.
Thanks to the pelicans and the big bird (Wayne)
David 89 turbo cab

[Doug Zielke]

Originally posted by 5axis
I ended up "pre loading" the lift #'s such that the cams came back right on spec as I set the torque.

Good!
I used this method as well.
It's a bit of trial and error, but once you determine how much to compensate for the tightening torque, you can get the reading spot on.

[snowman]

I found thats its really really necessary to maintain tension on the chains during the entire process. On the one side the tensioner can be used, on the other a pair of vice grips will hold the tensioner taut while the pin is installed. Unfortunately this tensioner must be removed to install the cam nut.