Super Rat Model 98 Modification

[JackM]

Dirty-rat,
That's probably what I'll end up doing. I'll see what my buddy at the motorcycle shop has to say. What I can't figure out is why this cylinder only measures 55.7mm when it is supposed to be 56mm if it is a stock super combat cylinder. My buddy insisted that it had definitely been chrome plated, so maybe that accounts for it being smaller than 56mm. (chrome plating)?? He told me that back in the day they used to chrome plate the cylinders on motocross bikes. You may not be able to see it in the photos, but some of it has chipped/flaked off near the bottom. I won't try to convert it back to 100cc. That's out of the question now. Thanks for your input. Jack

[Hydraulic Jack]

It is hard to see from the photos whether or not there is plating metal in the bore, but I don't think it matters at this point. It needs to be bored so whatever might be in there will be machined away in any event.

The chips and gouges I see appear to be from a piston failure. It died hard. As far as not getting the measurement you would expect for a stock bore, this may be due to the tool you are using. Calipers won't give you a reliable reading on the inside of the bore simply because they rarely have a fine enough edge not to stand off of the inner curve of the bore just a bit, and it is nearly impossible to tell when the caliper jaws are actually on opposite sides of the bore. Your measurement is close enough that I would think it is the best you can get with calipers. A machinist won't use calipers to measure your bore diameter because they won't give an honest or repeatable answer. I would definitely not draw conclusions about chrome plating based on the measurement. Besides, any plate job has to have the correct bore or the piston won't fit, so the bore would never be undersized simply due to plating. Undersized is undersized. The bore would have to be clearanced against a piston, so if stock, it is going to be 56mm plus or minus up to perhaps 2 or 3 thousandths of an inch. Even a factory bore isn't necessarily exactly 56mm.

Take the cylinder to a competent repair facility (some motorcycle shops do their own work, some always contract this out to a machinist - ask your local bike shop which it is in their case). If the bike shop doesn't do their own bore work, and if they are not the ones disassembling and reassembling your engine, I would bypass the bike shop and go straight to their machine shop.

Or, you can contact one of the Hodaka repair guys here and have them do it or send it out. They will know who to trust with this job.

You will need a new piston and rings, and if the engine quit under the circumstances reflected in the photos, I would figure on bearings, seals, and a crank inspection. It may not need any of this and you could get away with just having a new bore job and piston, but I would not be surprised to find that a lot of the shrapnel that dinged your head and took chunks out of the bore also ended up down in the crankcase and ran around for a bit inside your bearings. My guess is this one was not running when it was taken apart.