POROSITY PROBLEMS
Frank’s porous head casting on his oilburning Smokey Joe T160 is a fault I’d often heard of on old motorcycles but never experienced… until recently. Despite a total engine rebuild, my newly acquired 1964 New Bullet 350 (the enlarged Crusader) expelled embarrassing quantities of oil when the engine became hot on longer rides. It was oil-tight on shorter rides. Riding it with the right-hand cover removed, I was surprised to see oil oozing from a breather at the top of the gearbox cover, while the engine oil level in a separate reservoir in the crankcase fell alarmingly on the dipstick.
With no other logical explanation, I concluded that engine oil was transferring into the gearbox, probably assisted by crankcase pressure, through a porous portion of the casting when hot. Perhaps this mystery explained the number of previous owners (at least eight according to the accompanying paperwork) and their butchery marks left inside such a low mileage engine!
It’s common to find yellow sealing paint applied inside Royal Enfield castings at the factory, but it certainly wasn’t a treatment given to all Crusaders and was absent on my 350. A soul-destroying second strip-down of an engine which was otherwise running so sweetly took me several weeks, allowing access to degrease and paint inside every corner of the crankcase halves with Glyptal 1201, an industrial high temperature paint for sealing crankcases.
My story has a happy ending. The Bullet no longer spews oil and consequently has been ridden for more miles than in the previous thirty years. I was surprised to learn that porosity still poses a problem in modern casting processes in the motor industry, requiring testing and correction techniques which haven’t changed so much.
Oily Boot Bob, member
The fix on my old T160 involved shot peening the combustion chambers and rocker box floors. And it worked!