I went out on my bike yesterday, but before I did ,I checked the electrics out ,cleaned all the terminals up and took the flywheel off and gave it a liberal spray of WD.

After 20 minutes of riding and being about a mile from my car, the bike cut out and wouldnt restart.I changed the plug but still it wouldnt start so I checked the spark.......no spark.Thoughts of what the hell have I done and why did I mess about with it if it wasnt broken were running through my mind.

I couldnt find the fault until I decided to check if I`d done anything behind the flywheel,when I took the cover off ,I could tell straight away...snapped woodruff key.The flywheel was just spinning and the nut to keep it tight was loose,I undid it by hand.

What the hell did I do wrong....I`ve taken the flywheel off and on many times to clean it ,and reassembled it in exactly the same way and never had a problem.If the key had snapped ,fair enough ,but for the nut to be loose aswel.

So,just to be sure, has anyone got a sure fire way of re-assembling the flywheel ,in case I`m not doing it right and have just been lucky the last 18 mths or so.

help is always very much appreciated.

regards

N

The true function of the woodruff key is to provide for proper alignment of the flywheel on the crankshaft taper when you slip it on. The woodruff key's function is NOT to prevent rotation of the flywheel on the crank after it is fully assembled.

The flywheel must seat fully on the taper and the nut must be properly torqued - then the mechanical "lock" of the taper resists all the normal rotational loads.

My GUESS is that this time, as you installed the flywheel, the woodruff key got bumped a bit and slid in it's groove such that the back end was "higher" than it should be - and it prevented the flywheel from seating "squarely" and completely on the taper. OR perhaps you forgot to properly torque the nut?

Anyway, I would recommend a check for damage to the taper on the crank or to the internal taper in the flywheel. If all appears to be OK - you should be able to re-install with no problems. I have spoken with folks who heat the flywheel to about 200 degrees (F) before installing the flywheel on the crank (to help insure full taper contact) - but that seems like over-kill to me, and I have never found it to be necessary. It also seems like that would lead to the need for considerably more puller force when the flywheel gets removed the next time, and I don't like that situation.

Final note: always spin the engine and watch the flywheel for wobble before installing the cover. If my guess (above) was right, you would have seen some wobble.

Ed

i have just had the same problem on my Techno, ensure all surfaces are completly smooth and no sign of the woodruff key picking up on the crank or flywheel, try fitting the flywheel onto the crank without the key in first and check you get a good fit you should have to use the puller to break the seal if it is seating ok then fit your key ensuring it is parallel to the slot.

the flywheel should be torqued to 14 KGM good luck

thanks for the advice fellas

BTW - The key sheared straight across and not angled, so I`m assuming that it was sitting level as it should be.It must`ve been that I didnt torque it off correctly and the nut worked loose.

I`ll order 5 more and when I put it back together I`ll do all the checks to make sure its fitting correctly this time. Quite annoying, not to be able to ride because of such a small cheap part.

Ahh well ....You learn by your mistakes

regards

N

If you've really scored up the shaft, you could use green loctite (wick and seal) to take up some of the space.

Good tip on watching for wobble.

One tip to add .

Slurp a little valve grinding paste on the taper/s and lap it in a bit .

Clean it up and put a light coat of grease on the mating parts , just to prevent corrosion .

Ahh well ....You learn by your mistakes 

You have no idea how rare and profound that is!

29er suggested greasing the mating parts when you reinstall the flywheel. I hope that doesn't mean the taper? Mechanical drive tapers should be assembled dry and clean ie no water-dispersant, oil or grease. You are increasing the chance of another sheared key if you put grease on the taper.

The suggestion to use lapping paste on a damaged taper can be helpful once any high spots caused by the key failure are carefully removed. If the damage has cut up the surfaces too much and key failures recur even when the flywheel is re-installed properly, loctite can be used as charliechitlins suggested but the flywheel may need heating to release the loctite next time it needs to come off.

29er suggested greasing the mating parts when you reinstall the flywheel. I hope that doesn't mean the taper?

Yep , That's what I'm sayin .

For me , it makes no sense to have any mating metal surfaces assembled dry , especially when exposed to the elements . ( I think I remember a similiar discussion on torqueing cyl . head bolts/nuts .)

I've had enough trouble removing rusted /corroded/ overtorqued flywheels and loctite would only add to the fun . A point to ponder is that magnets don't like heat .

I'm not sayin to slop a bunch a grease in between , just a lite coat , wipe off any excess , assemble , lube threads (loctite acceptable ), torque , take a short ride and then check the torque again . Works for me .

BTW , don't use any graphite type lube (i.e. anti-sieze ) anywheres near a set of contact points . It's like a sponge and water ....So I've heard

FWIW

I have used green loctite often on questionable tapers.

It should keep rust, crud, etc out, and shouldn't require heat to remove.

A couple raps with a brass hammer or drift on the shaft and/or on the face of the part being removed (as far from center as possible) will help break the seal of the loctite.

The old-timer who taught me about Indian lower ends used to put a drop of battery acid on the tapers of the crankpin, sprocket shaft and pinion shaft before assembly.

Thank God I never had to get one of those apart!