I feel really stupid but I am missing something when it comes to cam timing.

Trouble is I'm using a cam designed for a low capacity engine at high revs in a large capacity engine at lower revs and need to change the cam timing. Theory of what to change it to is OK its the practice that gets me.

I have a cloys chainset with a 20 tooth crank sprocket and three keyways giving plus or minus 4 degrees.

Fine but what if you want to change it by more than 4 degrees?

Moving one tooth gives 18 degrees and backing off the keyway takes off 4 degrees giving 14 degrees.

Seems I can have standard, 4deg, 14deg, 18 deg etc but not much inbetween.

How do I get a finer adjustment?

Cheers

vernier cam pulley ?

I've had the keyway on the cam sprocket recut in the past, when a vernier was not available.

Turn the sprocket 180degrees from normal, get the cam where you want it, mark new key position, then recut the keyway.

Cheers,
Nev.

Excellent I can get a few cut on the cam sprocket just like the crank sprocket - now why don't the manufacturers think of that!

I'm a bit iffy on vernier cam sprockets I read somewhere they are prone to slippage.

Ta for the advice chaps

It is really the overlap period when both valves are open at the same time at the end of the exhaust stroke that determines the shape of the power curve.

On an engine where both the inlets and exhaust valves are operated by a single camshaft you can't change the the overlap. On twin camshaft engines like the Rover K16 or Silvertop you can tailor the shape of the power curve quite a bit by adavancing the inlet and retarding the exhaust and vice versa.

[Edited on 12/7/08 by britishtrident]