Can't say I've seen one ported like this previously [?]
http://www.ebay.com/itm/PENTON-SACHS-CYLINDER-JUG-1974-125-SIX-DAY-OEM-VINTAGE-AHRMA-54ZN5W1-/161459572397?pt=Motorcycles_Parts_Accessories&hash=item2597bd8ead&vxp=mtr
PENTON 1974 125 OEM CYLINDER
THIS OEM CYLINDER IS IN USED CONDITION. NO CRACKED OR BROKEN COOLING FINS. SURFACE HAS BEEN SANDBLASTED CLEAN. CYLINDER WALLS ARE STILL VERY SMOOTH WITH THE EXCEPTION OF SOME KIND OF PORTING DONE TO THE SLEEVE. WE ARE NOT SURE THE PURPOSE OF THIS PORTING, IF IT IS EVEN BENEFICIAL OR RUNNABLE BUT IT IS BELOW WHERE THE RINGS WOULD SIT. WE BELIEVE ITS FOR EXTRA LUBRICATION. CHECK OUT THE PHOTOS TO SEE.
ALL THREADS ARE STILL USABLE AND THE BORE SIZE MEASURES 54.50 MAKING THIS .50 OR 2ND OVERSIZE.
Dale Fisher
Penton Owners Group - Memberships
Mudlark Registry
Facebook - Cheney Twinshock Racing Group - Administrator
'70 Six-Day 125 - V2017
'71 Six-Day 125 (Dave Fisher's) - V5553
'72 Mudlark - W257
'73 Jackpiner - 175 21159727
'74 Berkshire 100 - 40171056
And some silly other bikes...