KTM 420 piston to cylinder clearance

[Bill Campbell]

Can anybody please tell me the piston to cylinder clearance when you rebore a 420 barrel. I need the specks for a Mahle piston not a Wiseco one as I have been told that they expand at different rates.

Cheers Bill

[G Ellis]

Bill .0025 to .003 thousands Later Gary

[rob w]

Nah, can't be so.
3 mm = .118 "

[Larry Perkins]

Me thinks Gary meant .025-.030".

Larry P

[rob w]

You mean .0025" to .003" (per side)  [?]

[Larry Perkins]

Yes thousandths.  Poor math skills it said on my report card.  We probably have poor Bill all cornfused now.

Larry P

[454MRW]

My 1980 KTM owners manual which oddly lists the clearance for a 400? as 3.0-3.5 thousanths, which would be total clearance, not per side, but doesn't list a 420, which began in late 79. I would think it would be similar. Depending on how you ride the bike at first during break in and how much time you put on it before racing, I would prefer the tighter range for longevity. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
75 Can Am 175 TNT & 77 250 Black Widow
1976-78 RM & 77-79 PE Suzuki's
74 CR250M 07 CR125R & CR150R

[Larry Perkins]

I was meaning total clearance but it is from memory.

Larry P

[Bill Campbell]

Thanks guys. I was a little confused but I finally made up my mind to go with .003".

Keep up the good work.

Cheers Bill