I've posted this over on HTT, but I though I'd put it here as well as some may find it intersting.

 

I'm getting close to my rebuild using WFO Larry's 2+ heads and Tman 625 Cams.
I want to keep my fairly new 95 10.25 cast pistons, but will there be any problems
opening up the vale reliefs ?

Is their plenty of material in the piston to work with ?
Should the stock relief be deep enough and just need to be wider ?
I had planned on doing it with them still in the motor using a die grinder. 

If I were to replace them, I would go to a 98 forged piston.
What piston could I use to give me similar comp to the 8cc (measured) dome on the cast piston ?
I'm aiming for 10.4:1 with 84cc heads and 30 thou' gasket.

Any hints on clearancing the Cam chest ?
Should I just buy the proper Tool ?

Cheers

 

I'm a big fan of cast pistons for the street as well.
Paul Hallam, who did a great job and custom bored the cylinders to suit the pistons also agree's Cast is more street'able.
And your probably right, better off to pull them to resize the valve relief's.
I really hate those piston circlips though.
At least I wont have to run in the bike again !!
The Georges Cam chest tool is around $130, so even if i sold it for half price afterwards, it's probably worth it.

Clay the pistons first before you start taking material from the valve pockets. I done my cast 103 pistons in the cylinders with a dremel tool with no problems. I ran masking tape around the piston and cylinder so nothing could get into the bore and then covered the piston with grease to catch what was flying around. I done 10.000 K with the cast slugs and then replaced with a set of forged CP 103's.

Claying the Pistons first appears to be a little tricky.
As I can't just turn the motor over by hand, I would need to replace the Valve springs with lighter springs,
and manually operate the valves to the correct lift with the piston at TDC.
As I know with the larger Valves, decked heads and TDC lift, it will need the reliefs to be enlarged, so thinking I would cut them first, then mock it up with two head gaskets and then check with Clay with all valve gear installed.

Any thoughts ?

If you strip the valve springs and place the heads on at TDC and drop the valves onto the clay on the pistons that will tell you where you need to remove material. If they hit on the eyebrow then relive there to standard depth in the valve pocket.  When finished I would clay the motor again and turn over slowly by hand and then masure thinkness of the clay to see how much you have .60 Is what most shoot for.

 

http://harleytechtalk.org/htt/index.php/topic,3747.msg35187.html#msg35187

Thanks for all the input.
I do remember reading that HTT post, but good to have a refresh.
One hint I picked up was to practice first on an old Piston !
When I get around to doing it, I will post a few pics of the process.
It will save me a few $ by modifying and re-using my cast pistons (and there only about 6k old).

Cheers

 when i do  valve relief's i check the top ring depth + the valve relief depth &  how far  back & down from the back of the top ring grove , then measure from the bottom inside of the piston to under the crown  etc  for how much you can take off & depth  , on the inside bottom of the valve relief radius you will want about 2.5 m.m  min thickness too the inside back of the top ring gland either way,  can squeese too 2 .m.m ,                                                 do a valve too piston dummy run check 1st ,  ,  i radius the valve reliefs & polish the crown just because i can  +  looks the goods 

daddyR , do you do them by hand, or in a Mill ?

 i do them by hand with the 1/4 "  chuck  porting tool,  different shape bit's  finish with sandpaper scrolls   then too fine finish with wax  then pioish , when porting stop & measure  4 time's  you  can take metal off but you can not put it back on a piston