Crankshaft/ alternator/ keyway/ Very worrisome! Please help

Pasophisto · Post by **Pasophisto** » Wed Apr 01, 2009 10:08 pm

Reassurance needed- Help!
In my hour of need, I hope someone can help me out:
1970 450 Scrambler.

The crankshaft has a Woodruff key for the primary pinion gear. Given.
The alternator rotor is brass, heavy (flywheel function?) and sits behind the primary pinion.
The crankshaft is not tapered under the alternator rotor, but has a shoulder inboard of the alternator rotor that stops the rotor from hitting the stator.
There is a locking washer and a nut that holds the primary pinion and the alternator rotor on.

The nut was loose, the pinion and the alternator were loose from the crankshaft when I got in there.

When I first removed the pinion gear, the Woodruff key was mangled with a portion of it sheared off in the pinion keyway. I cleared that out and ordered a new key (not here yet). The keyway for the pinion Woodruff key in the crankshaft was clear.

When I pulled the alternator off with a puller, the keyway in the alternator (***NOTE the diagrams in several books show no keyway in the alternator rotor- is it possible that the ones in the diagram are taper fit but mine is not?***) was occupied by a clean slice of key- flush with the keyway. On the crankshaft corresponding with the alternator key location was the outline of a keyway- but filled in. I assumed (?!) the occupant of the alternator rotor keyway was a piece of a sheared off Woodruff key (though narrower at 3mm than the pinion key at 4mm) and the outline on the crankshaft under the alternator rotor was the remains of the other part of the sheared off Woodruff key. As a result, I ordered a 3mm key and tried to punch, then auger the crankshaft "keyway" out. Its been hard work. It does appear that the metal in the "keyway" is softer than the surrounding crank material- but I am not certain. The keyway has resisted clearing to the point that I wonder if the keyway was filled by design and the alternator rotor filled with a piece of key by design and the rotor works by pressure fit between the torqued bolt holding the pinion gear and the shoulder on the inboard end of the alternator rotor. I am having doubts about continuing to carve out the "keyway." Can anyone help with info?

Is there or is there not supposed to be a key between the alternator rotor and the crankshaft? If not, what was the outline in the crankshaft?

Is there or is there not suposed to be a keyway in the alternator rotor? If not, why does mine have one?

Thank you,

Sheldon

bobnorton · Post by **bobnorton** » Thu Apr 02, 2009 12:06 am

On the narrowcase the flywheel is on a taper only and fits tight, sounds like yours has been modded, i would lap the tapers and refit with new key in the pinion and use locktite on the nut also tab washer,, important to hold crank to get tight, if you have mag ignition flywheel position important. what ignitoin do you have?

bobnorton · Post by **bobnorton** » Thu Apr 02, 2009 1:00 am

Reading your post more carefully, if there is no taper on the shaft then the key is needed and you will have to clear out the keyway, the flywheel wont stay put otherwise. Do you have points? are you going to ride on the road?, are you going to need indicators? My feeling is that its best to dump the mag system (if thats what you have) and fit battery, coil, indicators 12v control , may need to modify stator also, I dont know your model so get other opinions.

Pasophisto · Post by **Pasophisto** » Thu Apr 02, 2009 10:15 am

Thanks for that reply-
Its a 1970 450 Scrambler widecase with 6v battery and lights but no signals. Coil, points and condenser, not electronic ignition or magneto. The shaft has no taper, but a shoulder inboard of the alternator rotor, and the rotor has a keyway. My search on exploded diagrams does not show that keyway on most of the alternator diagrams. Also most of the exploded diagrams show only one Woodruff key on the left side of the crankshaft (for the pinion gear).

I am still unsure of what to do.
Sheldon

bobnorton · Post by **bobnorton** » Fri Apr 03, 2009 12:45 am

Hi sheldon, patience is a virtue, when in doubt do nothing,someone will come up with the goods, certanly the flywheel will need more than just clamping force,get a magnifying glass on the shaft , you may have to drill out part of the old key to weaken it or to tap a small thread into it to force it out. A plea to Eldert may produce information.

Pasophisto · Post by **Pasophisto** » Fri Apr 03, 2009 8:42 am

Eldert?

bobnorton · Post by **bobnorton** » Fri Apr 03, 2009 10:02 am

Eldert, member no14, font of all knowledge , very usefull guy.

Eldert · Post by **Eldert** » Fri Apr 03, 2009 11:45 am

Hi Sheldon
sorry for the late reply , but only the primary gear has a keyway ( 4 mm woodruffkey ) the alternator rotor has a taper something like 6 degrees
so it looks like someone modified your crank .
a picture would be helpfull to see what could be done to save your crankshaft

Regards Eldert

Pasophisto · Post by **Pasophisto** » Fri Apr 03, 2009 12:37 pm

Hi Eldert.

Thanks for your comment. There does not appear to be a taper on the shaft- nothing I can see, and of course it is difficult to get in there with a mic to confirm (though I will now try) absent removing the thing. There is a keyway in the alternator rotor though. What's with that?

Thanks

SMS

Lumpy · Post by **Lumpy** » Fri Apr 03, 2009 2:28 pm

I have seen what you speak of Sheldon, however it was on a TT500 Yamaha of mine. I put the points plate in wrongly then tried to kick her over. She bit back and damn near broke my leg. I realised my mistake, put points in right but then she would start, idle beautifully but die with throttle. After much horsing around, and I mean much much much, i finally pulled off the ignition stator. The woodruff key had sheared when she backfired and digging the sheared portion from the crank was a nightmare. The shear was also so very clean you would have thought it was made for it.
I would possibly take some very very fine grit emery and lightly rub at the key/crank. If it`s just a mark from the keyway in the rotor it should polish off, if not and an outline is left the keys in there.

Eldert · Post by **Eldert** » Sat Apr 04, 2009 12:46 am

Pasophisto wrote:Hi Eldert.

There is a keyway in the alternator rotor though. What's with that?

Thanks

SMS

Hi Sheldon
keyway in the rotor is not original . and on a original crankshaft the
taper is clearly to see . no need for calipers

Eldert

bobnorton · Post by **bobnorton** » Sat Apr 04, 2009 12:08 pm

Sounds very much like you have a modified setup, you have nothing to loose by clearing out the keyway in the crank and refitting with new keys locktite and doing up tight, I would consider the posibility of lightly countersinking the back of the pinion so that the rivets on the flywheel lock into the back of the pinion ( if you have this detail) The pinion would also need to be able to move inboard a little, if it doesent work you will end up replacing shaft and flywheel with a complete engine strip.

bobnorton · Post by **bobnorton** » Sat Apr 25, 2009 10:09 pm

Hi Sheldon, any progress??, unless you can get it to work with new keys and locktite you will end up replacing all the modified parts, I have always thought that the detail is the wrong way round, alternators generally have the key and drive sprockets have a taper , dont know why Ducati had to be different,but without a taper in the mix i think its a bad job. find a spare motor??

<-=- Club Bevel Heaven -=->

Crankshaft/ alternator/ keyway/ Very worrisome! Please help

Crankshaft/ alternator/ keyway/ Very worrisome! Please help

Its a widecase

Thanks Bob

More Keyway

sheared key

Re: More Keyway