4 replies [Last post]
conqueror
conqueror's picture
 Offline
Joined: 10/03/2008
Posts: 4

I went by my uncle's house yesterday to pick up an accordion, and we started talking about the motorcycle. He told me it was used during WW2 on the German side but was abandoned as the Germans retreated from the Russian advance. A German man found it, took it, and used for 20 something years. He sold it to another German guy who wanted to make the motorcycle faster. So he took the flywheel and, supposedly, made it thinner to cut out some weight which completely screwed up the whole engine. I don't know how, but that's wht my uncle told me. He also said that when he bought it from the guy that modified flywheel he also got the Wehrmacht license plates the motorcycle had.

So here's my question:
What would happen if you made the flywheel thinner and tried to drive the motorcycle?

schrader7032
schrader7032's picture
 Offline
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6866
New Discovery: Someone tried to make the flywheel thinner

Well, people lighten flywheels all the time, especially the /5 to /7 era bikes with the heavy flywheels. They do that to improve the engine response to revs. It might, though, allow vibrations to be felt a bit more in the drive train. The heavy mass damps that out somewhat. The heavier flywheels are also good for use with sidecars, but technically, the frame/bike wasn't designed for sidecars starting with the /5 models.

Usually lightening is done by drilling holes or cutting away portions of the flywheel while maintaining rotational balance. I've not heard anyone doing this by making it thinner. Thinner brings into question any heat dissipation issues along with changes to the clutch stackup dimensions and the ability to shift. I suppose this could be dealt with by changes in the clutch pushrod length, etc.

I can't see how a thinner clutch would "screw up" the bike in the short term but I think it presents some issues that might detract from its simplicity and long term operation.

My 0.02...Kurt in S.A.

__________________

Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Bruce Frey
Bruce Frey's picture
 Offline
VBMWMO #6316
Texas Hill Country, USA
Joined: 10/27/2006
Posts: 574
New Discovery: Someone tried to make the flywheel thinner

Depending on where the "thinning" was done, it could adversely affect the clutch operation. There is not a lot of room for variation in the clutch linkage, so some "compensation" for the thinning could be needed. I think the postwar plunger frame clutch plates are thicker, so that might be a solution if there is a problem.

It should also be easy to find a clutchplate from an M72 or similar bike.

Leszek at Oldtimer Garage coulc probably help.

http://www.oldtimergarage.szn.pl/

Bruce

conqueror
conqueror's picture
 Offline
Joined: 10/03/2008
Posts: 4
New Discovery: Someone tried to make the flywheel thinner

Thanks for the replies guys.

Sorry I didn't explain "screwed up", I'm not exactly sure what happened, but I suppose the thinning of the flywheel would mess up the torque somehow if the weight was reduced and the surface area of the fly wheel's teeth were reduced. But then again I'm not an expert and didn't do so well on my physics final exam Laughing

Bruce Frey
Bruce Frey's picture
 Offline
VBMWMO #6316
Texas Hill Country, USA
Joined: 10/27/2006
Posts: 574
New Discovery: Someone tried to make the flywheel thinner

sorry.....I meant to say flywheel instaed of clutchplate.

The easiest solution would be to find an original flywheel with the correct clutch parts. Milling the flywheel thinner could also cause damage to the taper wher it mates to to the crankshaft. Hopefully this has not happened.

Bruce

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.