Head Milling

How far can I mill the head down on a 750-four? How far is too far for stock pistons?

Jimi

Hey jimikz-Stay under 30 thou to play it safe.
Here is an interesting link that might give you some more info to help you decide.

members.tripod.com/gpz_rider/technical/FAQ2000.htm

You might also want to search the Kzr archives on head gasket choices as there has been some discussion there on using the 750 Turbo head gasket instead of the Kz or Gpz normally aspirated gasket to play with compression.

Cheers-Colin Firth -Ontario Canada

1977Kz 650 Custom-Brought back from the dead after 12 years of neglect. Rebuilt, Restored or Replaced every nut and bolt on the bike with about 1000 into the project (o.k. I went overboard but what the hay!)

Post edited by: reborn650, at: 2006/01/13 20:34

You need to measure the valve to piston clearance before milling it to determine how much can be milled. A safe rule of thumb is at least .100 clearance on the exhaust and .080 on the intake valves. And then you will need to slot the cam sprockets to get the cams back in time.
.030 would "probably" be safe.

why are you milling your head down?

wireman wrote:

why are you milling your head down?

My guess is it has something to do with this thread
kzrider.com/index.php?option=com_joomlab...tid=2&id=15988#15988

ok,now i remember!did you check the cylinder to make sure it was flat?

No, the bike's still in one piece. At last discussion we suspected the addition of a Zephyr oil-cooler as having oil-starved the head thus causing it to spring a leak and possibly warp. I'm still not 100% on this cause but will remove the cooler when I do the head just to eliminate that variable. I'm also looking into the crankcase breather valve causing high pressure and then blowing the gasket or even oil-pump and oil-bypass valve failure, though the engine shows no other signs of oil-starvation after 5000 miles with the suspect oil-cooler set-up.

jimi

If it was suffering oil starvation to the head it would have destroyed the cam bearing surfaces long before it would overheat.

among other parts!i think that motor wouldve been doing a lot of hammering if it was starving for oil,but we shall see! goodluck,happy wrenching!

That's exactly what I think but some others felt since the incidences of head gasket failure coincide with the fitting of the oil-cooler then it is suspect. Do you have any ideas why the gasket keeps blowing? And yes I have done everything by the book and was extreamly careful and clean.

jimi

As long as the cylinder block and the cylinder head surfaces are smooth and parallel, and the proper clamping force is applied, the head gasket will not blow, so one of those three is not correct.