Cutting Pistons for Valve Pockets...

[leec]

I am fairly certain my next motor will need valve pockets cut in to the pistons due to high compression ratio and 48x40 comp eliminators.
My question is how do you know where and how much to cut? Can someone explain the process to me please!

Thanks,
Lee

[Erlend / bug66]

You need to center punch the pistons with the center of the valves. Remove valves and use a milled, sharp valve to center punch both exhaust and intake valve.

Then you can find the angle of the valves at the pistons (is it 7 or 9 degrees?). Cut the pockets big enough in size (for example use 42mm for exhaust and 50mm for intake).

Depth you need to find by figuring out the smallest distance the valve is from the piston. I think I ended up with 2mm on inake and 3mm on exhaust after cutting valve pockets.

[NoBars]

Everything needs to be mocked up as close as possible, including deck height and cam degree. Center punch at TDC.

When you put it all together I highly recommend claying your valve clearances to make sure you have enough side clearance between the edge of the valve and the pocket. That stuff moves around a lot at high RPM. A millimeter on the radius as suggested sounds good.

Unless you have a piston vise you will probably have someone do this for you.

[RMS Boxer Service]

Then you can find the angle of the valves at the pistons (is it 7 or 9 degrees?).

9.5 degrees for type 1 heads. (or more scientific correct: 9 degrees and 30 min)

/Rolf

[MeXX]

My question is how do you know where and how much to cut? Can someone explain the process to me please!

Lee

Hi Lee

Check out how I did it :

http://cal-look.no/lounge/index.php/topic,20436.30.html

MeXX

[dangerous]

Depending on your camshaft and dialled-in position,
I have found the closest point of the piston to valve is normally
10 to 12 degrees AFTER TDC for the inlet,
and 10 to 12 degrees BEFORE TDC for the exhaust.
This is around the overlap period, using a very light valve spring, and thumb pressure to determine the space you have to the piston.

I determine the exact position using a dial indicator and degree wheel,
FOR EVERY VALVE,
and then remove the head and valves,
replace it with no valves,
and mark the piston through the valve guide,
with the same crank angle that I found to be the closest.

The next step will be to set up the piston in a milling machine at the correct angle,
and set the spindle in line with your marks.

https://www.facebook.com/photo.php?fbid=10150163142188270&set=a.391462693269.171369.792373269&type=3&theater

https://www.facebook.com/photo.php?fbid=10150163142003270&set=a.391462693269.171369.792373269&type=3&theater