Saturday, April 24, 2010

Still Trying to fix the Derbi.

So I pulled apart the derbi case and discovered that yes indeed, the engine seizure was due to a bearing on the crankshaft freezing up. Why would that happen, I wonder? I suppose it could be due to lack of lubrication, though the unburnt oil from the 50:1 should be lubing it, or it could be that this is a 31 year old bearing and at some point it's going to say NO MORE.

Since I had borrowed a bearing puller from Naz I decided to rebuild one of my puch motors while I was at it. While I was working on this I had a realization:
Almost everyone I know pulls the rubber seals off the bearings when they install them on the crank. But those seals are to protect the bearing from contamination such as bits of metal getting mixed in with the bearing when you seize your cylinder. Does it make more sense to keep the rubber on? Is there a possibility of the rubber melting within the crankcase?

Here is a picture of the E50 I rebuilt:

This motor will go very fast, it was ripping before but it wouldn't idle very well which I discovered was due to the crank bearings being totally shot.
-port-matched case
-70cc Athena Piston port kit
-19mm intake
-20mm PHBG
-3 shoe clutch

Ok, back to the derbi. As it turns out, the flat reed bearing sizes were different than a variant. Here are the bearings that I pulled out of my piston port case:
-6303 (this is the one that seized) on one side of the crank
-6302 (other side of the crankshaft)
-6203 (though this one actually just says "203", I'm assuming that it is the same as a 6203)

And in case anyone else is rebuilding a piston port variant from 1979, here are the seals:
-17.28.6 x 2
-16.24.4 x 2 for the pedal shaft

In other news I just sold old Orange and Black Maxi. That bike has been with me for a long time in various incarnations and I was a little sad to see it go. The orange and black front end was one of the first things powdercoated by Mike Rafter and the Motomatic Team and after sending everything to me he said, "I will NEVER powdercoat EBR's again." Also, this bike took second place in the Latebirds Invitational Club Relay Race. And considering first place was this bike which won the Polini Cup, that's pretty decent. But, it's departure means more money for moped parts and it went to a good home so I'm sure it will continue to rip around Seattle for many more years.

The last few moments of me and Ol' Orange and Black:

Whenever I see a picture of myself standing next to one of my mopeds I am struck with how little mopeds are. Or I am a giant. Could be both.

Gotta peel off the Mosquito Fleet badging.

That's all for now, peds are gonna roll!


  1. did that maxi really take 2nd place with a bing and a boss? or did you swap those back on to sell. also about the bearings...i always remove the rubber shield on the outer side in order to allow the bearings to be lubricated by fuel mixture, and if you kept both of them on i'd think it would seal that out. a solution or best of both worlds situation may be to use bearings with the metal shields that have small slits al the way around...they're available for electric motors, like if you got skf's you would find your bearing under SKF 6303JEM. hope that helps!

  2. No, it was the motor up there ^ that I just rebuilt that won 2nd.

  3. thanks for the seal sizes! i'm going to rebuild the piston port motor i just got pretty soon. what puller did you end up needing for your flywheel? and was it a motoplat flywheel? my piston port came right off with the bosch flywheel puller, so it had me mystified even more of your problem.

  4. I ended up using a three jaw puller, I don't know what the deal is with the flywheel. It IS a motoplat but none of the pullers I borrowed worked, Naz said that there is another Minarelli puller that may be the right size.

  5. What tools did you end up using in the end? anything weird or unusual? i am just starting a rebuild on my piston port.

  6. You need a hobbit puller for the clutch, I used a three jaw on the flywheel but apparently treats has a bosch puller that works for puch and derbi, and of course you should have a piston stop and some bearing pullers.

  7. i have that treats puller for the flywheel. what did you use to stop the rear variator?

  8. seth, i used my cordless impact wrench (best tool i've ever owned). but a pair of chain vise grips or belt/strap wrench works. you might be able to lock up the rear variator enough just by wrapping the belt around it, cinching it up and using regular vise grips to lock the belt down.