250 Monza top bevel bearing loose.

[el_guru]

Hi Guys, I finally pulled out my so called "restored" Monza 250 out of the back of the garage as it was rather rattly top end and I didn't have time to investigate it....

Anyway I pulled the head off and found the upper bevel drive self aligning bearing carrier has been spinning in the head. See pictures.

Is there a common/recommended fix for this or does someone in the US know of an engineering company that can machine the head or make an oversize carrier.?

Thanks..
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[Jordan]

I never had this problem on my bikes, but I've heard of others that had.
Depending on how much free play due to wear there is, maybe there's a Loctite product that can take up the play?
If it's only a few thousandths of an inch, copper plating the outside of the bearing sleeve could work? It's a good way to make good sloppy valve guides, so might do this job too.
If all else fails, the head can be rebored for a new, oversized bearing sleeve.

[ducwiz]

The bearing bush must have a tight fit in it's bore, otherwise it is a source of clanking noise, and may increase wear on the bevel gears. In axial direction, it has to be slightly pressed against the head-bore's shoulder. This can be accomplished with a gasket of appropriate thickness between the head and the bevel shaft's outer sleeve (use sealing compound). Instead, shim(s) can be placed between the bearing's outer race and the pedestal on the sleeve's upper face (stick in place with some grease).
In case of considerable radial play, an oversized bush imho is mandatory.

cheers Hans

[el_guru]

Danke Hans,

I do have a spare head fortunately so I can spend some time correcting this problem properly. I have taken the rest of the head apart and one of the cam bearings is a bit rough so will change it.

Does anyone know of the specification for the upper bevel bearing specifications and will it be made to an interference fit or should it just be "snug"..?

Thanks.

[ducwiz]

Read this: http://renato2.bplaced.net/DUCATI/dioc40_12-14.pdf

I adjust them in a "snug" way, so that you just see a drop of oil dispensed between the teeth in contact beeing squeezed slightly, when you work one gear against the other. But no real backlash should be sensible, or even audible. During the procedure, the centering bush between the bevel shaft and the protection sleeve should be mounted. This prevents the bevel shaft from svivelling sidewards thus tampering the measurement.

Hans

[el_guru]

Thanks again..... I was referring to the actual specification/drawing of the bevel self aligning bearing carrier. ( Ducati classic cycles do make an 0.005 oversize one for £17)

I found the previous owner had doubled up on the top bevel tube gasket so there was no way that the tube was supporting the bearing carrier which allowed it to move and spin.. Lesson learnt.

With judicious use of grey bearing lock from Loctite and correct gasket it should all be ok now...???

[Bevel bob]

I'm pretty sure you can't rely on the bevel tube to support anything as it just hangs---. why did you need to use 2 gaskets?.

[Eldert]

the Ducati vintage store sells oversize bearing carriers in ( std is 39 mm ) 39.05 and 39.10 oversize

what i do is mount the beveltube with the bearing carrier without a gasket . then measure the space left in between the cilinderhead and beveltube with a feeler gauze and cut a gasket in paper the size needed .

another thing you can do to prevent the bearing housing from spinning in the cilinderhead is put a little blob of weld on the outside of the bearing carrier and line this blob up with the oildrain cutout . i know its a low tech fix but it works

Eldert

[el_guru]

BevelBob I didn't use 2 gaskets, the previous owner did for some reason which allowed the carrier to drop a bit and spin. As Ducwiz explained that the tube actually supports the bearing carrier when nipped up.
Eldert.... very clever work around. Thanks.

All seems good now I appreciate all of the advice.

[BDang]

This is a case of someone (previous worker) didn't understand how the bearing/carrier works, and perhaps in an attempt to fix a small oil leak through the gasket he added a second gasket. This bearing carrier (called bushing by book) needs to be clamped down by the vertical tube and the head by the two hex screws. Too thick a gasket will not allow the carrier to be clamped. This is the same situation as the lower bevel bearing carrier, and the best way is to use "Toyota form a gasket" sealer instead of looking for the perfect thickness gasket.

Regards,
Brian