Machining plated barrel-gasket surfaces

SFO

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#1
I am setting the squish on my 426 by clipping the base gasket surface off.
I would also like the face the topside off just to assure perpendicularity.
When I did this on my 501 I ended up flaking some of the coating material off of the top of the bore.
Is there a way to face this off without chipping the plating? Or, am I just dreaming, and should leave it alone?
 

SFO

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#3
Good one...

Thats one I didn't think of...
Using a Dumore toolpost grinder to deck the cylinder. Wonder what wheel wouldn't load up on the Al?
 
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#4
a wheel made for stainless or non ferrous materials. never ground aluminum i looked in the MSC catalog and didnt come up with much.norton SG series wheels and a ceramic bond type wheel from a no name co.thats made in the USA. hope this helps a little.
 
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EricGorr

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#5
Hi Bill,
The top radius of the cylinder was machined prior to plating so if you deck the top of the cylinder it could chip easily. Sometimes I turn the cylinders on a lathe using an expanding mandrel. We went overbored on Rich's YZ444 setting the squish clearance at .025in. but then again consider the guy whose riding it! Big pressure big boom!
 

SFO

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#6
Old habits die hard...

Eric, thanks for the heads-up.
I am used to clipping the gasket surfaces in one chucking to create parallelism.
Machining it true to assure squareness.(Like your mandrel)
Upon assmbly I found the squish to be allready at .045" w/gasket.
Didn't leave me room to fuss around but I spun it and checked the barrel with indicators and it looked good.
I cut 40 grams out of the 97mm piston and pin.
Before assembly I checked the cyl/piston clearance and came up with .0033"
clearance.
I misplaced the suggested clearance #'s for this set-up and am wondering if the piston closed up or grew via the lightening process.
I think that three and a half sounds right for this bore, and am not worried.
You sure got a staight hone job in it. Straight and round within .0002"!
 

EricGorr

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#7
Hi Bill,
Measuring the piston and setting the clearance on 4-stroke thumper pistons can be a bit tricky, every company seems to have some idea on how to do it. J&E says to measure the edge of the slipper skirt and set the bore size to the same dimension, assuming that the skirt will collapse .002in. upon start-up. I set the bore size to 97.01mm to account for slight differences in pistons, the model you have should measure 96.950 out of the box. You're still safe with .0033in. clearance.
Its amazing that you removed 40 grams from that piston, thats a ton when you spin it to 12 grand!
Regarding the honing accuracy, US Chrome uses a CNC honing machine with all-abrasive anti-rollover mandrels. That set up is really beneficial for large 4-stroke cylinder bores. Most of the other plating vendors are using horizontal hand-feed single-row stone honing machines. I use that same set up for my 58mm and smaller 2-stroke cylinders too. Its very tooling and skill dependent to get any decent result, but its also easy to change surface finishes for various degrees of plateau finish.
The modern lightweight slipper piston on the big thumpers require a very round bore to take advantage of the piston's unique shape.
Keep us updated on how your YZF performs with your lightening mods on the piston.
Thanks, Eric

P.S. What do you think about counter-boring the top of the cylinder to fit a ring of copper-berylium as a heat sink and anti-detonation gaurd? Thats starting to become common on plated NASCAR blocks.
 

SFO

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#8
Berylium copper

P.S. What do you think about counter-boring the top of the cylinder to fit a ring of copper-berylium as a heat sink and anti-detonation gaurd? Thats starting to become common on plated NASCAR blocks.

I would like to know more about this anti-detonation ring stuff.
I first saw it on my friends rs125.
He says you have to send it back to the japanese company that installs them for replating.
I would be interested in the process of doing it.
I think ampco45 would be a better choice than berylium copper.
Berylium copper valve seats and valve guides seemed to be more of a mystery metal selling point than anything I have seen proven.
The 15% nickel in ampco 45 is tougher than berylium and less toxic to machine.
Those Hendricks are on the leading edge as usual...