6 replies to this topic

[ozz1]

Whats the 'proper' way? Des Hamil mentions turning down pushrods in his tunning book but not shimming the rockers.

My block has been resurfaced (I will need to check with the machinist but for arguments sake - say 0.005") and the head has been skimmed by 0.040''. So I would need a 0.045'' shim or the same removed from the push rod - typically what is the largest amount you can skim before you can no longer compensate for lack of cylinder head thickness through valve clearance adjustment?

 

Cheers, Oscar

 

 

[nicklouse]

It depends. As the cam production can also effect the stack up.

[carbon]

Chances are that with 45 thou total skim you can just take this up with the rocker adjusters, and should not need to shorten the pushrods.

 

You only put shims under the rockers if the rocker geometry needs altered, and this is not affected by skimming the lower face of the head or skimming the block.

 

As Nick says, it all depends. I've used small bore heads with almost 80 thou skimmed off and has worked OK with standard rockers and standard cam. But if you change to a higher lift cam then chances are the base circle will be less, and the pushrods will sit slightly lower anyway.

[Spider]

Considering the adjustment in isolation, as Carbon has said, you'll most likely get that on the adjusting screw alone, however, given by the sounds of this that it's a performance build, what should be looked at (regardless of any skimming in fact) is the geometry of the set up as fitted as you could well be loosing or at least not optimising the lift that the cam has to offer and you could be cutting yourself well short.

[ozz1]

Considering the adjustment in isolation, as Carbon has said, you'll most likely get that on the adjusting screw alone, however, given by the sounds of this that it's a performance build, what should be looked at (regardless of any skimming in fact) is the geometry of the set up as fitted as you could well be loosing or at least not optimising the lift that the cam has to offer and you could be cutting yourself well short.

thanks for the advice - when refering to rocker geometry is it just a case of ensuring the tip of the rocker is dead in the centre of the valve stem when it's fully compressed? 

[Spider]

 

Considering the adjustment in isolation, as Carbon has said, you'll most likely get that on the adjusting screw alone, however, given by the sounds of this that it's a performance build, what should be looked at (regardless of any skimming in fact) is the geometry of the set up as fitted as you could well be loosing or at least not optimising the lift that the cam has to offer and you could be cutting yourself well short.

thanks for the advice - when refering to rocker geometry is it just a case of ensuring the tip of the rocker is dead in the centre of the valve stem when it's fully compressed? 

 

 

Actually, no.

 

What I was banging in about was where the ball centre of the tappet adjusting screw ends up in relation to the shaft centre and the Valve Tip.

 

But the point you've raised is also important.

[ozz1]

 

 

Considering the adjustment in isolation, as Carbon has said, you'll most likely get that on the adjusting screw alone, however, given by the sounds of this that it's a performance build, what should be looked at (regardless of any skimming in fact) is the geometry of the set up as fitted as you could well be loosing or at least not optimising the lift that the cam has to offer and you could be cutting yourself well short.

thanks for the advice - when refering to rocker geometry is it just a case of ensuring the tip of the rocker is dead in the centre of the valve stem when it's fully compressed? 

 

 

Actually, no.

 

What I was banging in about was where the ball centre of the tappet adjusting screw ends up in relation to the shaft centre and the Valve Tip.

 

But the point you've raised is also important.

 

ahh, got it!