Shaving Heads

[Lewis Shadoff]

At 07:15 AM 2/16/02, you wrote:

><clip>The machinist is talking about taking 0.030" from the head,
><clip>
>In short, is this a safe idea at all for a mostly-street car?

The SDS Chapter of EM Section of my FSM ('97) Says that the "Resurfacing
Limit" of the cylinder head is 0.2mm (0.008 in.) Which is the "Total amount
of cylinder head resurfacing plus cylinder block resurfacing.

There must be some reason for this.  What comes to mind is:

1- The water jacket is close to the surface, and removal of too much
material seriously weakens the head/block.
2 - The timing chain cannot accommodate more than 0.008" drop in the
cylinder head (I don't really believe this.  The tensioner should be able
to handle this)
3 - Valve-to-piston clearance will be too close.

I could not find a valve-to-piston clearance in the FSM.  However JWT must
have some measurements since they designed high lift camshafts which would
produce smaller valve-to-piston clearances.

The valve-to-piston clearance is not just dependent on the valve lift.  The
cam phasing plays a role.  From http://www.laffey.co.uk/engine.htm :

"At this point the exhaust is more critical,because the exhaust valve is
opening as the piston is coming up to TDC,and the inlet is closing.You are
looking here for a minimum clearance at the tightest point of 80 thou,If
you are running tighter than this you need to take piston rock at TDC into
consideration."

Lew

Lewis Shadoff
Lake Jackson, TX
'97 200SX SE-R, Level 10 Auto, HotShot turbo
http://www.brazosport.cc.tx.us/~lshadoff/turbo/