The End of the R1100RS Motor

I had only just retrieved the R1100RS from Stefan Knopf in Heidelberg on Wednesday, and then had not ridden on Thursday, as I was still recovering from jet lag and playing with my new laptop. On Friday after lunch, we rode over to Ludwigshafen to Veterama, a big vintage bike swap meet.

I managed to make contact with Anthony, one of the members of the Kradrider mailing list, and we had a pleasant chat. Sascha also met some of his local vintage biker friends. It was fun and there were a lot of things to look at, though I ended up not buying anything.

Although we had taken a bit of a roundabout route to Ludwigshafen, Sascha got us on the B9 coming back, which is direct to Karlsruhe and has a section with no speed limit. It was here, a little before sunset, that I was running along in 5th gear at about 110mph/6000rpm. I noticed that the power seemed to fall off a bit, and then that the motor wasn't holding 6000, but was going down gradually. Fortunately, there wasn't a lot of traffic, and so I rolled off the throttle some. Suddenly there was a rhythmic vibration, not severe, that lasted for about a second or so. This couldn't be good, so I pulled the clutch. All the panel lights came on and the tach dropped to zero.

The highways in europe don't generally seem to have breakdown lanes, but we were just passing an onramp at the time and so I coasted to a stop towards the end of it.. Sascha, who had been behind me, pulled in right behind. He called his Dad, to come out with a trailer and pick up the bike.

There we sat, with 182,069 on the odometer.

While waiting, Sascha and I speculated on what could be the problem, and the cause. There were no outward signs, no broken parts or leaking oil. The starter spun, but there was no compression pumping sound from the motor. The thought was perhaps a holed piston or a broken timing chain.

As we were not far from Landau, we decided that the best course of action was to drop the bike at Klaus Mayer, the local dealer. Although it was Friday night, they were conducting a customer ride, and the shop wouldn't reopen until Tuesday. Even so, Sascha said that the season had started and they were very busy. So I might not know what the problem was even then.

Tuesday came, and indeed, Uli at the shop didn't have any time for the bike, Neither was he very encouraging. But I was invited to come down and take things apart enough to find out what was needed.

The valve covers came off but nothing really obvious was visible. One possibility was eliminated, however, as the cam chains were both intact. A bad sign, however, was the presence of a few bits of aluminum, including one between a cam chain link and the sprocket on the cam shaft in the left head.

So then the heads came off. The heads themselves looked fine, and the cylinder bores looked good too, including the still-visible honing marks. But this seemingly good news was really quite bad, because it meant that whatever the problem was, it was much deeper inside. And both cylinders had a small residue of fine aluminum bits...

Uli pointed out that the right piston was not actually straight in the bore. And it wouldn't move. Releasing the cylinder from the cankcase required a mallet and a very large tire iron. The piston and the upper half of the connecting rod came with it.

Inside things were a mess. There were big and little pieces of aluminum and steel all over. The bottom half of the conrod wasn't present on the crankshaft journal, where it should have been. Later we found a part of it and the bottom conrod cap, still bolted together. Half of the piston skirt was missing, and one of the two bores in the piston for the wrist pin was cracked through. Evidence of great violence was present everywhere.

The left side came off with only a little les persuasion. Perhaps that's because BMW designed the cylinders with the inner surface projecting into the opening in the crankcase, and on this side, that projection stayed inside the crankcase. It was broken completely off the cylinder, not quite a neat circle.

Its piston also came with the cylinder, although the bottom half of the conrod and its cap were still bolted together and present on the crankshaft journal. You could reach your hand in to it and flip it around. The conrod big end bearing on this side was still ok, with no axial play.

This motor was toast.

Everything below the heads was junk.

Sascha did some calling around and a used BMW specialist a bit east of Stuttgart, Siebenrock, had a lightly used R1100RT motor for sale, only 30,000 kms (slightly less than 20,000 miles) on it, and complete except for one valve cover. The price was surprisingly reasonable, €1,500 (about $1,800). They could also do the removal and installation, which of course, would be faster and cheaper if I stripped some of the stuff off the bike.

In the actual event, we brought the bike, stripped of all plastic, including the gas tank, to Siebenrock on Wednesday afternoon, and they said it ought to be done within a week or so.

Meanwhile, I sent some photos to my friend, Brian, who was a dealership chief mechanic in a past life, and has actually worked on this bike and motor. Even before I sent him a shot of the right side piston, he speculated:

I have been thinking about it, I think you had lost a piston skirt, and it wedged itself in the bore, breaking the rod(s). The pistons had 150,000 [sic] miles on them and maybe one had a flaw. Either way, when one of those short-skirt pistons loses its skirt, it will not be happy for long. Usually it loses it just below the oil ring, and then the piston is allowed to rock in the bore, then shortly afterward, seize.

And in fact, the right piston is missing about half of its skirt. The connecting rods are from a special material; BMW casts them as one piece and then cracks them in half at the big end to create cap that mates microscopically to the connecting rod. If BMW could crack the rod in half, so could seizing the engine at 6,000 rpm under load.

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