Questions regarding lightweight flywheel on R69S

[malmac]

Here are some pics of two flywheels I have that are different but both look genuine and not obviously or significetly modified.

The way the timing marks are stamped looks very much the same and yet the outside diameters are very different.

In regard to the hard starts, I would first check that the OT mark is right on Top Dead Center. If the flywheel has moved on the crank then it would be easy to have the engine timing incorrect.

Maybe the smaller flywheel is from a 250 because I can't even remember where I picked it up.

I have added a screen dump from Mark Huggetts online shop showing the two different part numbers for the flywheels R60 vs R69s.
Well I have learnt something today.

Mal

[mcsherry1328]

I have some current experience with many of the things you're describing. I recently finished cleaning the slingers on an R69S engine that I put in my R67/2 frame. This engine has a Bowman flywheel and starts on first or second kick every time. I also have an R69s with a stock flywheel that is on my sidecar rig. Starts the same with one or two kicks. I wanted the stock flywheel to use with the sidecar. Although, I feel that gearing is more critical than flywheel inertia. My sidecar has a 27/7 gearing which I feel is perfect for this set up. It walks away just off idle with no problem and can cruise easily at 60 mph. For the record the common 26/6 gear set is too low. This was made for an R60 with less power than the R69S. Your starting issue sounds like the timing is incorrect. I bought a magneto buzz light from Vech and it works perfectly. Be sure and set the magneto body in the center only, set the point gap and adjust timing with point plate. Hot starting problems are nearly always a coil issue. I use the Emerald Isle coil (also from Vech) and they work perfect. Both engines have been converted to 12 volt. I would recommend this upgrade as well. Having spent many of my younger years racing moto cross and enduros, your R69S is never going to hurt your ankle starting it. Lots of good replies and ideas from the group, hope this helps. Feel free to contact me with any further questions. Michael

[schrader7032]

Doesn't having a non-solo transmission play into how a sidecar rig performs? It should have a lower first gear, but after that the gearing is the same as the solo bikes.

[jtaylor]

Thanks for more of these insights, everyone...much appreciated.

[Daves79x]

Actually, the claim from BMW is that the R50 and R69S both require the 26/6 gearing for the sidecar. The theory is that with the lack of low-end power and the higher rev capability of the R69S, the 26/6 is correct. Guys that have used this set-up may have other real-world impressions. The only final drive shown as BMW-approved for the R60 is the 27/7. I think if you have a genuine sidecar transmission (standard of the early R69 and R50 models, maybe the first R60 also), the need for alternate final drives may be diminished. Guys with experience may comment differently.

Dave