Little introduction, questions, about an old school ride

[ezdubbin97]

Let me start off by saying hi, I have been off of bikes for about 16 years, with that being said, I have decided to bring out my super crusty 1981 KDX 175 out of storage and get the ol' girl running again...sentimental thing.

The bike was "bored" or more probable "stroked" to a 200cc (said by previous owner to a then 13 year old me). Bike ran fine for quite a while, then poof, the flywheel flew off (for lack of better words). The culprit, a home made aluminum woodruff key that sheared. The flywheel's magnets were busted and the bike never ran again. My interests turned to girls, cars, family, etc. I sourced a new flywheel several years back, but never tore in to it.

Questions I have:

Has anyone heard of someone changing the crank to up the displacement in these bikes?
The woodruff key for the crank that is in there is wider than the 175 flywheel notch (my reasoning behind thinking the 200cc was achieved in part by changing out the crank).

The flywheel had ruptured one of the coils in the stator, where is a good source for a new coil/stator assembly?

Any good recommendations of where I should start on reviving a bike that has sat for 16 years?

Any inputs will be helpful...first time for me tearing into a two-stroke...wish me luck!!

[KarlP]

Can you have the notch in the flywheel widened to match the crank?

I believe there is a fella on this site that rewinds coils......

Did that bike have a CDI, or was it a points type system? CDI, I'm sure

It sounds like if you could get the coil(s) straightened out and the flywheel back on you could turn the clock back 16 years.

[canyncarvr]

Ask RickyStator. As long as the core plates are salvageable, they rewind 'stuff'.

An aluminum key...wonder what kind of brain dead boob figured that one out. I guess aluminum is a lot easier to 'fit' than a tool-steel woodruff key that's got a Rockwell reading of a brazillion (that's only an estimate).

If the rotor got loose enough to take out a coil, I'd be concerned about the crank, too. Any scratches/dings on it? That's not as big a worry as the runout. I'd suggest checking that before you sink too much into it. If the crank got wobbly in the process (maybe why the rotor came off in the first place...maybe the same guy with the 'Let's use aluminum for a crank key!' is the guy that 'rebuilt' the crank.

Of course...now someone like fuzzy (that races karts that turn to 25KRPM) will say, 'I use aluminum keys all the time! As long as the rotor is tight and the crank ain't wobbly... they work just fine.'

It could happen!

Oh...GOOD LUCK!

[ezdubbin97]

Thanks for the replies...I'm not sure of the crank condition as of yet, still waiting to get it out of storage, rain has kept us from getting a trailer to the barn. I am looking into buying another crank for those reasons, as well as to return it to stock. The aluminum key might have held up had he not put a mechanical notch in it by stepping it down to fit the FW. I'll look into Ricky stator

[canyncarvr]

I was too mouthy about the brain dead part.......

If nothing else is wrong (crank out of true, damaged taper etc.) I suppose an aluminum key would work.

Considering it's a tapered fit..fastened to 65-70ft/lbs, it's going to take a LOT of force, force that shouldn't be there in the first place, to shear a key.

Maybe it simply was not torqued properly from the git-go.

KarlP's idea (widening the slot in the rotor) sounds like a good idea..if you keep your stroker.

Funny thing about stroking a 2T..lots of things change that may have not been considered...like port time. There's a lot more to increasing the stroke than just making the piston go up-and-down farther.

No, I'm not saying I know anything about it..I don't. But that it sure would change 'stuff'.

BTW..it is rickystator-dot-com. There's a link there you can use to contact their tech folks.

[ezdubbin97]

I called RickyStator and they confirmed that the $39 coils they advertise on their website for the KDX200 will work for mine...so that's good news. I agree with you on the stroke...and my two-stroke knowledge is limited, but it makes absolute sense.

[fuzzy]

Yeah, I'm betting something else happened. A rotor should hold with no key in it at all...Especially if lapped on to ensure perfect fit...Key is really there for alignment during assembly on a tapered shaft such as this, not strength. Just spinning a rotor unlike the other side. Heck on my kart, like cc mentioned, I'll run a key on the rotor side (again, for alignment), but the OUTPUT side I run a taper-fit belt driver, and put nothing in the keyway, and this is the PTO driving the whole vehicle.

[canyncarvr]

My rotor shifted without a key. The key slipped out of the slot (I didn't check for it to be in AFTER I put the rotor on) and lodged behind the rotor.

It took a day of riding..but man did I have fits getting up some pretty basic stuff. Timing was WAY retarded!

No..I did not lap-fit it. Yes...it was torqued to spec.

Maybe the KDX rotor/crank isn't the best fit in the world......

Still..fuzzy's right. That key isn't there to HOLD anything.

The proof of the pudding is in the eating, though! Obviously something is wrong with the setup. If the crank is true, I'd start with a 'real' key and make it fit one way or another.

[ezdubbin97]

yeah, I think you guys might be on to something for sure...I'm going to acquire a stock crank assembly. If for no other reason than the fact I did a little research on the parts diagrams for my bike, as well as the KDX200/250 of the same vintage (1980-1986) and every single one calls for the same woodruff key (#92038-001). Makes me really suspicious as to what crank is in there. I wish the rain would let up here so I can retrieve it from storage. I'm ready to get into it again. The mailman delivered my service manual today, so at least now I can do a little testing/measuring and know where I'm at on things.