Rob's Bike

Rob's bike, an R1100RS, failed on our ride home, following our 50CC, on Thursday, 12 Oct 2000.

We had just fueled at exit 138, Natchitoches, LA. Rob is running the new Bridgestone 020's and they seemed to be holding up very well, when compared to my BT-50's. We decided to swap bikes a while so I could get at least some feel of the new tires.

11 miles north, running about 75 MPH under even throttle, his bike dropped power suddenly and appeared to be running on one cylinder. I immediately hauled in the clutch and killed the engine to prevent further damage, coasting to a stop on the shoulder. It didn't take long to find the right plug had been struck with something and the gap closed. Further testing revealed no compression on the right side.

We got the bike off the highway at exit 155. I rode on to look for the nearest place to park his bike safely while we waited at the local Holiday Inn for "The Woman" to drag a trailer over from Clovis, NM to get the bike back, so he could open it up and see what broke.

Rob finally got the head off today, 16 Oct 2000 and posted this update on the failure to me.

"Just pulled the right head off my RS.  The failure was immediately
obvious...

The piston crown between the piston surface and the first compression ring
under the lower exhaust valve failed.  There is a piece of piston roughly 1
3/8" long x 1/4-5/16" thick that separated from the crown around the
perimeter of the crown under the lower exhaust valve (that part is missing
and assumed to have broken up, lodged in the muffler, or blown out when I
cranked the bike with the plug out in LA).  There is NO hole in the piston,
but compression is lost straight through the 1st compression ring groove.
The cylinder is NOT scored.  Original cross-hatch is still there after 111K.
There is evidence of this broken part rattling around in the chamber, which
explains the Autolite 3923 plug ground electrode being hammered onto the
center electrode.  Valves "look" good, though I'm going to specify that Iron
Horse replace at least all four exhaust valves.  There is virtually little
to no carbon buildup.

In addition to head work, I will replace BOTH pistons and ring sets, plus
all gaskets and other seals, of course.  Head work and parts permitting, I
will soon be back to riding.

I suspect my early experimentation with a smaller FRAM fuel filter, which
plugged quickly, may have caused unduly lean mixtures and overheating of the
pistons (latent damage).  Even with the larger Deutsch filter I now use, I
will be looking for an even larger one to avoid loss of fuel pressure.
Paul:  What is the large filter you are now using on Voni's bike?

Rob

Aikens Comments about possible cause