lapping flywheels

[270YAM]

EML-
I have spent much of the day slowly lapping the tapers to match as best I can. I say that because it is one hell of a mess after chopping several woodruff keys off over the years and there is a complete circle of meat missing around the middle so therefore I have essentially two tapers with a gap in the middle-

I think the 2 tapers with a gap in the middle is normal

[tony27]

Not on that crank though, you can still see the machining mark from when it was made in the step

[EML]

Ours has a gap about 1/2 of that so I dare say that it has had a full lapping in the past but that it has had a key spin on it at some stage.
Since it is only a baby motor it will not be having the full job done, not this time anyway.

There is probably a few motors out there that will do the job that are lighter but they would be two strokes. And we run pre 85 not friggin' dinosaurs.

[270YAM]

What other choices are there in pre 85 ? Weslake  perhaps ?

Ok, I'll add another Couple.
Affordable And readily available


EML which dinosaur where u referring to?

[EML]

knowing what we know now any of the big 2 strokes would have done/will do.
Maico, Yamaha SC500 et al, much lighter and same HP/torque available power to weight ratio wise.
and any thing pre 75 is a dinosaur

[pancho]

In the 60's I built a road racing 500 out of an R50 BMW. 
 These used a taper drive muff coupling from the drive shaft to the final drive pinion shaft..
 A few laps 'round Oran park on full song saw it it split the muff coupling along the keyway as the result of a wheel standing upshift.
 On research I found that the R69 [sports 600] deleted the keway and relied on the lapped taper. I copied that and no more trouble.
 On the same day [I think] a rider on a new Bultaco 250 production racer had the flywheel come loose by not only shearing the key, but it ripped a big half moon chunk out of the crank shaft.
 If I could delete the key on my RT1 flywheel I would but since it's needed for timing I use a soft aluminium key. cheers pancho.
 On my XT500 points model engine I have deleted the key and rely on the lapped fit, no probs.
 

[EML]

Thanks to all for input.
Flywheel finally lapped in and fitted. On this model the taper is female (I thought that when I first saw it ) that is the thread is inside and not male with the thread outside. Therefore there is a bolt that goes into it and it has been tapped as a metric 1.25. I would have thought metric 1 to 1 would have had more chance of staying put and it should be left hand thread as the way it stands it is throwing itself off with the vibration and centrifugal force. Not too bright on someones point.