So I got my head resurfaced.. and 3 \"free\" heli-coiled exhaust stud holes

Well, I cleaned the head all up, cleaned up the valves, had it all ready to have resurfaced and the valves seated..

But I didn't think about the fact that the lower 4 exhaust studs stick out lower than the surface of the head, thus needing to be removed in order for it to be resurfaced.

So the machine shop removed them for me, and broke three of the four studs. They told me I would have broken them too.. guess I'll never know. They did totally remove and heli-coil the 3 that came out rough though "on the house". Technically a heli-coil makes it stronger than stock.. but man one of them really looks like shit, way down in there with enlarged bare alum threads all torn up.. hopefully there are enough threads down in there and it all functions as stock.

Otherwise, I'm really gonna be flipping pissed!

The valves and head do look nice though otherwise. I think they took around 4 or 5 thou off the head. Hopeing that isn't enough to effect anything like cam timing or compression too much. The block is getting resurfaced at APE when it gets bored as well..

Have you thought about drilling and retapping the holes for fatter studs?

Any word from APE on when your bore job will be done?

Man, your bike's gonna be shit hot when all this is done!

4 -5 thou should not make a significant change to cam timing or compression. On the cam timing, if you look at the geometry of the cam setup, reducing the distance between the crank gear and the cam shafts 4-5 thou will slightly retard the cam timing, maybe 1 to 2 degrees. 4- 5 thou will result in very slight compression increase but probably not any more significant than all the other factors.

Willo46 wrote:

4 -5 thou should not make a significant change to cam timing or compression. On the cam timing, if you look at the geometry of the cam setup, reducing the distance between the crank gear and the cam shafts 4-5 thou will slightly retard the cam timing, maybe 1 to 2 degrees. 4- 5 thou will result in very slight compression increase but probably not any more significant than all the other factors.

If you retard the timing on the chain you will lower the compression due to the intake valve closing later to build compression. Unless the cam is profiled to close the intake before BDC.

Must be something I'm not getting!!!!

If you're not changing the length of the cam chain and not changing the position of the cam sprockets on the cams how is the cam timing going to change when you lower the head.
As long as the relationship of the sprockets (crank and cam) don't change the cam timing should not change????
That's assuming you're using stock cam sprocket and not adjustable cam sprockets.
I'd think that raising or lowering the head in relation to the cylinder would only have an affect on the compression?

If you lower the cam sprockets realative to the crank sprocket, by shaving material off the face of the head, both cam sprockets get closer to the crank sprocket. Result, IMHO would be that the IN cam would move very slightly clockwise, looking from the right of the bike and, the EX cam would move very slightly counter clockwise.

Is this right? Anyone?

The cams would get closer to the crank but the cams won't rotate because the cam chain is still on the same teeth of the crank and the cam sprocket. The cam chain tensioner just takes up the slack in the chain.
This is assuming that the cams were reinstalled in the same position as they were before the head was milled.
Still not sure if I'm looking at the correctly.

But either way if you're looking fot a performance pickup put a set of APE slotted cam sprockets on the cams and set the cam timing at 112 EX. and 110 intake......

Yes, I agree, the tensioner at the rear of the engine would take up the extra slack but I think, based on the top cam tower sprocket remaining in a fixed position, BOTH IN & EX cams would NOW move very slightly counter clockwise?

Imagine taking say 1" off the head not 3 thou. Makes it easier to get your mind round? EX cam sprocket moves 1" closer to the crank sprocket, by "rolling" down the chain? 3 thou wouldn't be enough of a shave to allow you to move the cam sprocket to the next link on the chain?

Anyone? Thanks.

Here is how it happens. You have to visualize this. The cam chain is tight on the front side as that is the side that drives the cams. The front side of the chain will always be tight.

If you have the cams sitting a certain height from the crank, with the front of the chain tight, and you lower the cams (mill the block or head), in order to keep the front of the chain tight, you would have to rotate the cams backwards ( or rotate the crank forwards).

Jay

OK...I can't argue with Jay ( he's forgotten more about bike engines than I'll ever learn) and I see his point.
Just couldn't quite see it until the bit about the drive side of the cam chain....

Again this why there are APE slotted cam sprocket, we can set the timing where we want it....
Thanks Jay.

first off, are the APE cam gears somewhat universal? I realize they do market some for the 1000's but would the work on other cams?

Barney you got it finally there. I would have jumped in but this website never emails me when a post is made, even when I tell it to.

Anyway, yea Jay put it to a T.

I am getting the block resurfaced too though.. so I wanna say probably 10 thou total. Or more.. always look at the worst possibility

Oh and Snakebite I'm pretty sure the intake valves close before BDC. I think almost all engines have the intake valves close before BDC.. every valve opens or closes just before/after top or bottom dead center.. I think my car is like 12 or 16 degrees from center if I remeber correctly. It's not like they're dead on the money BDC and retarding the timing slightly would put them on the wrong side of the crank rotation. It will be moving it in the wrong direction for making power and being efficient though.