[Gregdownunder]

Ok, so we are putting in an XE 256 cam into an internally stock 318.
I'm told however we need to shim the rockers as the new cam does not have the same clearance.
I'm hoping someone can explain this in layman's terms as I'm struggling to get my head around it.
So the rockers on a 318 are shaft mounted and non-adjustable, I understand that.
The new cam lobe  lifts the lifter/rod and hence the valve open further/longer that the stock cam, I get that.
But how then, assuming the rear of the lobe is the same as the stock one, should anything change requiring shimming?


Thanks,

Greg.

 

[ToxicDoc]

Whomever told you about shimming doesn't know your engine. Don't listen to them anymore. You will have to check pushrod length. To fit a larger lobe, the base circle of the cam is made smaller. This allows a taller lobe to fit through the cam journals. Smaller base circle often requires a slightly longer pushrod to make up the difference. You will need to get an adjustable measuring pushrod and measuring lifter to check.

 

[Gregdownunder]

Right, I think I'm with you, smaller base circle increases lash?
Wondering then how shimming (raising)the rocker shaft would help, wouldn't that increase lash too?
Unless he is talking about shimming somewhere else.

Longer rods make more sense to me thinking about it.


Thanks,

Greg.

 

[ToxicDoc]

Right, I think I'm with you, smaller base circle increases lash?
Wondering then how shimming (raising)the rocker shaft would help, wouldn't that increase lash too?
Unless he is talking about shimming somewhere else.

Longer rods make more sense to me thinking about it.

Thanks,

Greg.

Correct on all counts. He probably doesn't know about or understand your shaft-mounted set up and maybe thinks it's individual stud-mounted rockers.