notch the cam for midrange torque?

[79XS11F]

34 teeth on my 1978 XS1100E back up / hopup engine intake cam sprocket. I have them out of the engine and just counted them so the guessing can be put to rest.
So that's 10.58 degrees per tooth.
Rob

[Geezer]

Remember the cam turns 1/2 engine speed so be sure and add this into your calculations. It's too late in the evening for me to comment further on this. I can't do math when I'm tired...

This is an old and well accepted way of engine tuning. I don't have the tools to properly slot the sprocket holes or I'd have done it to the Mongrel already.

Back in the bad old days slotted cam sprockets were an off the shelf hot up item and probably still are for the newer bikes.

Geezer

[79XS11F]

Originally posted by 79XS11F
34 teeth on my 1978 XS1100E back up / hopup engine intake cam sprocket. I have them out of the engine and just counted them so the guessing can be put to rest.
So that's 10.58 degrees per tooth.
Rob

The above is 10.58 degrees of cam MOVEMENT not 10.58 degrees of timing.
Rob

[LoserShoes]

It's probably crank degress, which would be 2.5 degress of cam rotation. It's easier to measure the bigger number accurately.

The way the big guys do it is with a dial inidicator on the camlobe, or rocker arm( we don't have rockers) and a degree wheel on the crank. And they don't start counting til around 2 - 3 thou of lift.

Steve

[79XS11F]

That makes more sense to me as well. There is no advantage to having the larger intake valve open before the piston hits DTC because doing so would add unwanted pressure to the intake tract. There is a fraction of time lost at TDC while the piston changes direction and the intake valve can open as soon as the piston is no longer exhausting or perhaps "ever" so slightly before because exhausting gas will help draw in the new charge.
Rob

[trbig]

Now I'm lost. The cam is moving DOUBLE the speed of the crank... so crank at 5 degrees would put the cam at 10... not 2.5, right? So one tooth would be pretty close at 5.29 degrees. 360/34/2.


Tod

[79XS11F]

No Tod the cams are in deed smaller by they are driven by their sprockets which are bigger so every full rotation of the crank is 1/2 rotation of the cam. They spin at 1/2 the speed.
I believe this is correct.
Rob

[skids]

The first time you check valve clearances, you will find that to be true. Two rotations of the crank for one rotation of the cam lobe.

Originally posted by 79XS11F
No Tod the cams are in deed smaller by they are driven by their sprockets which are bigger so every full rotation of the crank is 1/2 rotation of the cam. They spin at 1/2 the speed.
I believe this is correct.
Rob

[trbig]

So then basically.... 2 teeth on the cam would be abourt right if you were going by the timing ?? Man, something just doesn't seem right. I don't believe I wanna be the guinea pig on this one... lol. it has to be talking about just advancing the cam 5 degrees.

Tod

[79XS11F]

NO .. 5 degrees at the CRANK will be about 1/2 a tooth at the cam. This valve timing change is to be made at the CRANK.
Rob

[randy]

Are we having fun yet?

[turbopete]

When setting up/degreeing/timing cams the degree wheel is fixed to the crankshaft end, and any references to degrees of adjustment are ALWAYS degrees of rotation of the crankshaft, not the camshaft. This is because the valve opening/closing times are quoted as degrees before/after top dead centre of the piston, which is of course connected to the crankshaft.