My gearbox is fried...fix or replace?

Long time, no post...picked up a 4-stroke kit (one of these, by the looks of it) from an eBay seller (no, not he-who-shall-not-be-named, but another one based in California) last summer, put it on a bike, and got maybe 100 miles out of it before the gearbox started acting up. The clutch would grab at idle while stopped, which would either stall the engine or make it bog badly. When I popped it open, the clutch bell was a bit "wobbly" and the gear on it showed signs of accelerated wear. I tightened things up a bit more, threw in some grease, and put it back together. I got a few more miles out of it (maybe up to 120) before it went back to its misbehaving ways.

I parked it in the garage last August or September and didn't get back to it until this evening. I had to pull on the starter forever to get it running, but the engine still seems to be good. The clutch almost seemed better for a bit, until I took a quick trip around the parking lot.

I've spent a few hours catching up on the past few months' posts, figuring out which way to go next. I had some crazy ideas about hanging a Delco 10SI (the alternator you'll find under the hood of most '70s and early-'80s GM vehicles, available everywhere dirt cheap) off of the engine and going to a series-hybrid configuration, but with only 2 hp on tap, I'd think it would be better to avoid as many energy-conversion steps as possible.

One possibility, if someone sells the parts, would be to fix the gearbox I already have, but everything I've seen about the three (?) gearboxes available for 4-stroke bike kits suggests that I ended up with the weakest model. I think I'd end up tearing into the gearbox more than I'd really like. There's also the small matter of not having found somebody who sells the parts.

The other possibility is a replacement. eBay only seems to have rack-mount GEBE kits and frame-mount kits from he-who-shall-not-be-named, but there seem to be a few more vendors in the business now than there were a few months ago. In particular, this looks interesting. The gears (especially the one attached to the clutch bell) look more substantial and look like they ought not wear out as fast. The whole unit looks like it's a bit longer than what I have right now, but that's nothing that a chain breaker can't fix. Other people's feedback indicates that it holds up a bit better, and is also a bit more quiet once it's been broken in.

According to this, it should work. Has anyone else switched gearboxes on a 4-stroke yet? I'm a bit bummed at the prospect of shelling out more money, but if it'll get my bike running again for less than the cost of replacing both the engine and the gearbox, I might just bite the bullet and go for it.

I also "had" the kit from that seller in California! I also came to the same conclusion as you, NO PARTS. I did look at the kits by Grube, but decided on a Staton chain & gear kit. Mostly because I caught a bargain on ebay, but also because of the "heavy-duty,,parts available aspect.

My suggestion would to be, dump the "JL" style box, Keep the rest and just get the gearbox from a Grube distributor. YES, I would avoid the other ebay seller you mentioned at all costs! The seller bicycle-engines, seems like a better choice. Their site shows that have parts also. Hope this helps.

Papa

I can't say for sure that it would work with your engine, but a Grubee gearbox is available here: http://www.bicycle-engines.com/complete-gearbox-assembley-p-104.html

The only thing about whether it would work that I can see is the output shaft of your engine and the mounting bolt pattern. However, the Grubee website you linked has the dimensions and if the measurements line up, it should work. Maybe you can talk to the vendor directly with your measurements in had to make sure. One of the nice things about this gearbox (I have one) is that parts are available- but i have not needed any yet.

Just a note on the Grubee. I had around 2,000 mile when my clutch spring broke when I went to replace it I noticed the bushing in the bell housing was worn I took one from another gearbox and it was too small for the shaft. I machined it out to fit and have put another 1,000 miles on it so far. I talked with bicycle-engines and found Grubee was having parts machined at a different shop. Mine may be a rare instance, don't know. From what I know there are 3 co. in China that make these knock offs of the Honda 50. I believe they all have the same out put shafts and bolt pattern. You can get a Grubee gearbox for around a hundred, the clutch should fit your shaft, check length may be different. The company's that import from Grubee only one I know of (and I have tried to contact them all) will answer questions and carries parts that is bicycle-engines.com.