250 N/C Bevel Gear Replacement

[Octane]

So I started pulling my N/C Scrambler motor down to install the new Electrix alternator, and I thought I'd also whip all the engine covers off and check clearances etc, as the motor only has ~200kms on it since being build (I purchased the bike with 0kms on it)

Unfortunately it looks like the bevel gear clearances weren't set correctly when the engine was built (among all the other things wrong with this bike when I bought it :-/ ) and the gears have chipped. I also found some fresh metal shavings in behind the bevel gear cover.

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I've managed to source some NOS bevel gears which should arrive this week. I'm a competent (qualified) mechanic, but it'll be my first time pulling the head of one of these motors, and first time replacing the bevel gears. Anything I need to look out for? Or any special tools I need?

[Bevel bob]

Wonder what got in there?,bits of follower?, where did the bits of gear go?,into the bevel shaft bearings?, You will need a cam holding tool to get the LH? threaded nut off,and a set of shims and a mike. Is there a lot of clearance between the gears or none at all,if so why? I think they have run very loose at some time. Check the Angular contact bearings carefully. Interesting! ,let us know what you find.

[ducwiz]

Hi Octane,

http://renato2.bplaced.net/DUCATI/DucatiCamDriveGear.pdf is a description for the lower gear set. For the top pair, work is basically identical. In addition to the tools mentioned, you need a centering bush for the bevel shaft, which prevents tilting of the gear/shaft in it's swivel bearing. This bush has to fit snugly between the bevel shaft's lower end and the outer sleeve (aluminum). Afaik it is depicted in one of the workshop manuals.

Hans

[Bevel bob]

For a centering bush I used a socket from my tool kit with some tape round it to fit the tower.

[double diamond]

Note the two oil drain holes outside the upper bevel bearing sleeve. Debris from the bevel gear destruction likely made its way through these drain holes, down the bevel tube and into the lower bearing cartridge

You can remove the cam nut before removing the head and avoid the need for the cam holding tool. Left hand thread! If you have an impact wrench, it will be easy to remove. Otherwise, you need to prevent the crankshaft from rotating.

Matt

[Bevel bob]

Its possible to do what Matt says but if the nut is very tight then the forces are carried by the camdrive gears, I would prefer not to do this. It may have been this action that strained and weakened the gear teeth ,possibly in the factory .Who knows.