Turns out the hole in the bottom of the TM motor is supposed to be there. It’s a drain hole of some sort. Right there in the bottom of the motor. Whod’a thunk? Glad to hear that. Now it’s off to the post office.
I had a bit of a disappointment tonight as I was cleaning up the little Suzuki motor to ship off to the engine builder. Upon turning it upside down to clean the gunk I discovered a hole along the centerline of the engine cases. “Uh oh, this can’t be good.” It’s an odd little hole, sort of square. It’s located in a place where someone may have tried to pry the cases apart with a screw driver, but it’s not broken like that would be. There’s a bigger picture here. The bike wasn’t leaking gear oil, and it wasn’t empty because I drained several hundred CCs out of it before I pulled it from the frame. That means it must be under the crankshaft – which could explain why the engine ran so poorly, but the cylinder shows no sign of sucking dirt. It’s weird. But anytime there is a hole in the motor it means my repair bill could be significantly higher. We’ll just have to see.
For my New Year’s Eve and Day I celebrated by starting the tear-down on my little 1975 Suzuki TM100M. I bought this little guy a couple of years ago from a kid in FL. It’s been taking up space in my garage ever since. But since AHRMA is running a 100cc class this year I’ve decided to at least start on the rebuild. My first step was to pull the top-end and see what sort of shape the motor was in. The bike ran when I got it, though not real well.
I was pleasantly surprised. The motor could easily have been ragged completely out but it was a nice, clean bore only 0.5mm over stock (1st over) and the cylinder wall is in good shape. Even better, someone took the time to do a respectable blueprint and polish job on the cylinder. As you can see in the photo the intake port has been cleaned and matched but the surface has been roughed up to improve air/fuel mixture. The port bridge has been smoothed and knife-edged per standard late-’70s practice. Overall it’s quite nice. Here are a few more pics of the porting work if you like that sort of thing.
I took it all over to John Astleford this afternoon. John runs an industrial machine shop but has been making vintage parts for almost two decades. I don’t have micrometers or anything and I wanted to see if the bore was straight, etc. The cylinder also had a bolt broken off in one of the exhaust flange holes. So John mic’d the cylinder out for me and said it was in good shape. He also drilled out the broken bolt and Heli-Coiled the hole.
The next step is to get in touch with a top-notch engine builder. I want to have this motor gone through by someone who really knows their business and really cares about what they’re building. Once the motor is out the rolling chassis will go back in the shed until such time as the motor is ready to go, whenever that may be. The bike needs both wheels rebuilt, the tank de-rusted or replaced, and various odds and ends. But one step at a time.