Flywheel Key Failure

robinh44 · Post by **robinh44** » 18 Jun 2007 08:35

Hi,

Has anyone had a problem with the key or woodruff key that locates onto the flywheel and crankshaft failing ie shearing off, during a test run my key appears to have sheared off flush to the crankshaft and the flywheel nut exited through the flywheel cover leaving a large exit hole!!. Is it possible the nut if it becomes loose could cause this failure mode or could it have started with the key failing?, any help advice much appreciated. Fortunately not to much damage, stator coils, flywheel and crankshaft end intact. Need to order new key, spring washer and M14 nut. Pictures to follow. Also had a pleasant 2 mile push home during which time it started raining....nice end to fathers day.

Regards

Robin

huub · Post by **huub** » 18 Jun 2007 12:04

the key should only locate the parts , so the original failure was the nut coming undone.
you need the spring washer under the nut, or it will undo itself.
i am not sure you should use locktite, the flywheel can be a pain to remove, even without the locktite...

cheers,
Hubert

EVguru · Post by **EVguru** » 18 Jun 2007 13:27

The flywheel is held on and driven by the taper. The key is just there so the timing marks stay in the same place.

In theory you should be able to torque the nut up and then remove it. The taper should then hold. The nut is there to stop the flwheel running amok if it does come off the taper for any reason.

Both the mating tapers MUST be burr free and perfectly clean. I think the manual recommends washing down with MEK.

If you draw lines down the taper with a soft pencil and turn the flywheel on the crank (without the key of course) you should see the lines smeared where you have good contact. If you don't properly sort the fit of the flywheel on the crank you'll always have problems.

It's not a troublesome design, but careless owners get dirt in the taper or tighten the flywheel nut with the key in the wrong place, damaging the taper, which then doesn't hold. If the taper breaks loose it either shears the key, or even worse it wallows in the keyway. In either case you have to clear up the dammage PROPERLY so the taper will hold once again.

robinh44 · Post by **robinh44** » 18 Jun 2007 14:36

Hi,

Thanks for the help guys, yes this definitely looks like an own goal. Well I will wait for NLM to open tommorrow and order up the key, nut and washer. Luckily the damage is limited and repairable, the key sheared clean and the keyway appears undamaged. Shame because otherwise it was running ok. I will also check the taper contact with the flywheel.

Regards

Robin

huub · Post by **huub** » 18 Jun 2007 17:08

you can use valve grinding paste to seat the taper, but usually a spring washer, en serious torque is enough to keep the flywheel in place..

if you use grinding paste, dont forget to grease the taper before reinstalling the flywheel .
i have had a flywheel corroding into place solid, after i had repaired the taper.
removing the flywheel on that one was a pain..

hubert

robinh44 · Post by **robinh44** » 18 Jun 2007 20:38

Huub

Yes I will check the taper seating with soft pencil as already advised and then may apply some fine grinding paste just to ensure a good fit. Regarding torque the manual specifies 6.5 mkg which on my torque wrench equates to 63 nm or 47 ft/lb's, does not seem particularly massive torque. I assume it is sufficient with the spring washer assisting to hold?, does anyone know of any different information?

Regards

Robin

EVguru · Post by **EVguru** » 18 Jun 2007 21:41

I think grinding paste is not a good idea. It sounds like storing up trouble for the future. Tapers should never be greased, it would defeat the purpose of them gripping by friction. I suppose if you polished the taper afterwards it might be OK.

I had to clean up a flywheel taper on a Dart engine and did so with a triangular scraper to remove high spots and also burrs along the keyway.

If you get the flywheel seating well enough that it takes a fair bit of tension on the puller before it pops off, you should be fine.

claymore · Post by **claymore** » 19 Jun 2007 02:41

robinh44 wrote:yes this definitely looks like an own goal.Robin

Own Goal....Funny but in reality, a real Bummer.

Can't wait to see your bike in all its glory, Could that be it in your avitar?

robinh44 · Post by **robinh44** » 19 Jun 2007 08:20

Claymore

Yes unfortunately experience is where you get the test before the lesson. So guess who won't get a flywheel coming off again!! even if I have to weld the b*stard on!!. Parts due tommorrow so should have the bike back on the road tommorrow evening. Yes the avatar is a sneak peek, but my camera gave out so I want to get some decent pictures before I post. Out of interest the picture below shows casing damage and the broken woodruff key:-

I have already repaired the casing with JB Weld, I cover the hole on the outside with tape then fill from the inside with JB weld. Leave overnight and instant casing repair, just need to sand and paint.

Regards

Robin

jb666 · Post by **jb666** » 19 Jun 2007 13:54

I can concur with all the advice given!! The same happened to me in France though without the cover damage. One for the reference book - some things you never forget - French for woodruff key la clavette. Also the one I repaired my failure with came from a chainsaw.

John.

robinh44 · Post by **robinh44** » 19 Jun 2007 14:07

John

I was lucky, if you can call this luck!, I was only 2 miles from home, unfortunately this was the bikes maiden run. So the stats so far are ridden 2 miles, pushed 2 miles. Still I have to say it is a nice bike to push, although would not recommend doing an initial test run on a Sunday evening at 2200 shortly before it starts raining. My wife agree's.... now that she is speaking to me again.

Regards

Robin

moriniuk · Post by **moriniuk** » 19 Jun 2007 19:55

I'd recommend the lapping in of the flywheel rotor to the crank using grinding paste. It worked for me. My flywheel fell off once while I was leading the sighting laps at the Morini track day. This was a correctly torqued nut on clean tapers and using the correct washer. Luckily it was at the end of the last lap just at the top of the mountain, so not too far to push it and no damage done. A trip to Louth for some paste and the kind donation of a new key and I was back on the track within the hour.
This was the only breakdown I have ever had on my race bike, and luckily it wasn't during a race.

robinh44 · Post by **robinh44** » 19 Jun 2007 20:30

Hi,

I have just finished doing just that, started with coarse and finished off with fine and checked using tip from Paul regarding pencil lines. Initially lines left at the front of the taper, now smudging all of them. So taper good just need to wait for parts tommorrow, then torque up. Is the service manual torque of 6.5mkg/65nm sufficient?

Regards

Robin

robinh44 · Post by **robinh44** » 20 Jun 2007 21:42

Hi,

Parts arrived today, just finished off making a flywheel tool from an immersion heater spanner. As my strap wrench method not satisfactory. Finished off casing repair just need to repaint, picture below:-

Regards

Robin

huub · Post by **huub** » 21 Jun 2007 06:44

the repair on the side cover looks nice..
With just the tip of the taper making contact the flywheel has probably been rocking on its shaft, and loosened up .
apparently the taper had already been damaged before you got it.
now with the freshly ground taper the recommended 6.4 kgm should be enough.

cheers,
Hubert