View Full Version : RS50 Runs Great, Can't Shift

08-02-2015, 10:37 PM
Hi Gurus,

I'm Kent Larson in Minneapolis. I've owned a 2001 RS50 since 2002 and put many miles on it before the wrist-pin retainer came loose and pushed past the piston-ring and bounced around the combustion chamber before disappearing down past the rings again. That gave me an excuse to put on a 86cc kit and big carburetor and I was back with a 85 mph top speed for 23 more miles.

Then the transmission locked up in 5th gear. Apparently I didn't get all the debris out of the bottom end and something got jammed up down there.

5 years later, I'm determined to get the bike back on the road. I guess I'm about to take out the engine and crack it open unless someone wants to suggest a different way to go. Currently, after messing with the clutch and shifter a bit, the bike now seems to be in neutral or (bump the shifter a bit) in some gear that locks up the back wheel with the clutch not allowing the lock up to spin.

So, I'll crack the case in a few weeks and let you know what I find, unless someone else has a better suggestion. (electric motor to replace? wrecked bike with good engine for swap?).

About me: I road raced for 10 years (amateur), been riding for 30 years, wrote a book that has a great chapter on suspension setup (https://books.google.com/books?id=gg1LM967OhMC&pg=PA118&hl=en#v=onepage&q&f=false) that you should not buy--I'll give you one for free instead if we ever meet.

Kent Larson

08-03-2015, 06:16 AM
Hello Kent,

I recently rebuilt an AM6, splitting the cases n all at and it went back together and shifted beautifully.

I took the shift drum and the forks and i took some emory to take off any sharp edges and high spots and it shifted so much better when I was done. Also I made sure that I set the clearance side to side play according to the manual. When I received the bike it wasn't shimmed to spec and it shifted horribly.

I think you have chosen the correct way to go. Remove the engine, pull the top end, split the cases. I made a case splitter out of a piece of 1/4" steel plate with a bunch of holes to bolt to the side and press the crankshaft out. The transmission does not press in, once the crank is pressed apart from the main bearings the cases split perfectly easily. It is akin to a typical dirt bike two stroke engine.

some things that may help.. although you're much more experienced than me..

1) I slip fit the crankshaft to 'slide' on to the main bearings. This puts the cases together and apart much easier. If you beat the hell out of these little bikes they will come apart much easier and according to the karting guys, the cranks and bearings even manage to last longer as a result. Your mileage may vary but I use some emory cloth and I resize the crankshaft to be approximately 0.0004" smaller diameter than the main bearings. That is plenty of clearance.. the bearing will slip right on to the crankshaft and she will go together and come apart wonderfully. When I purchased the doppler endurance racing crank, it was actually oversized on the bearings such that it was an interference fit of about 0.0003". So I took a total of 0.0007" off of the crank to go from a press fit to a slip fit, and the thing goes together so much easier and it seems like it is aligned better as well.

2) The manual states to heat the cases up to install the bearings n all at and i think 250F is what I set it to in the oven for about 45 minutes. it is well worth it. whole damn thing goes together so much easier this way.

Good luck, if you don't have the manual I can throw it up on google docs get you going

08-04-2015, 07:57 AM
Thanks for the advice and info. Please don't assume I have any bike wrenching experience. I ride every day but have not done much wrenching other than the superficial oil, tires, chain/sprockets, etc. This will be my first time splitting an engine and having an engine I can pickup with one hand seems a good place to start.

The manual I have seems pretty thin. Only about 50 pages and not as detailed as I'd like. I would love having access to the manual you used but don't want to put you out. If it's easy to get it to google docs, please let me have a look at it.

Thanks for the help. PM me your address and I'll send you a copy of my book (if you want one).

08-08-2015, 02:25 AM
I pm'ed ya, I have the engine service manual and can email it to you, it's small enough

08-08-2015, 06:18 AM
Hey Matt if you get a chance you should try and make that a stickey for that manual. Seems all the links online are dead anyways. The slip fit is the way to go. At least on my old banshee motor.