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I have just replaced the top bevel gear bearing, and when the gear is placed back in the tower, the bearing housing is able to move around in the top of the tunnel, and is definitely not a snug fit. It is located over the location pin properly.

Is this movement correct, or is there a wear problem with the bearing housing or tower?

Hi,

please tell us your Ducati model.
Your bearing housing is "moving around" - radially, axially, both ways?

Hans

the Ducati vintage store sells oversize housings for the 1202 top bevel bearing

Eldert

It’s a Mototrans ts125

The bearing fits snugly in the housing and both fit snugly to the bevel gear.

When I put the bevel gear back into the tunnel housing, it is very loose in the recess at the top of the tunnel. There is a gap between the tunnel recess and the bearing housing, and subsequently the bearing housing can move.

My cylinder head is off at a machine shop having new valve guides fitted, so what I am asking is.

Should the bearing housing be loose in the recess at the top of the tunnel, and is the permanent locating of the bearing housing achieved when it is located back into the cylinder head?

I had the same problem with my Mototrans 125 and after much discussion on this forum came to the conclusion that housing is a poor design with no positive lock to head. I am having a bearing housing made with a deeper outside lip. The idea is that this lip will lock between bevel tunnel and head and instead of hoping gasket is correct thickness housing will be machined to give just a small gap to be sealed with silicone. I have not had housing back from machine shop yet and will add photo and measurements if it is successful.
There are some posts about this on my restoration viewtopic.php?f=3&t=2963

George

Are you saying that under normal circumstances, the gasket locks the bearing housing to the head?

In which case it does not matter if there is play between the bearing housing and the bevel tunnel prior to fitting back to the head, assuming all tolerances allow successful mating to the head and gasket?

From my experience with 250-450 singles, which have the same design details (it sounds like):

The bearing housing does not leave the factory with a clearence fit, rather it is a light press fit.
Clearance can develop after the bevel tube is removed and not sufficiently clamped back up to press the bearing housing to the head recess.

A suggestion is to leave out the paper gasket, which gives the tube more effective length in terms of clamping the housing.
Apply silicone sealant when assembling instead.
If the inside diameter of the head recess isn't too big, that should suffice.

If the recess has been flogged out so it's too big, that needs to be compensated for.

The Mototrans 125 has a different design to the 250. The recess in the bevel tunnel is greater than the lip on the housing and will not grip with or without gasket. I posted a sketch on my restoration posts, easier to understand if you have a look.

I see - the top bevel details are different for the smaller engines.
It's a similar issue though.

The drawings show your problem. A possible solution is to have made a new bearing steel housing, dimensioned so that the bevel tube will clamp on it?
Again, silicone could provide the seal.

I now understand that the bearing housing has a large axial play, as described in a different thread by somebody else. If the bearing housing fits snugly into it's seat in the head without radial play, there is no need to purchase or manufacture an oversize item. A simple distance ring made in proper thickness on a lathe, from steel, and placed between the bearing's outer race and the bottom of the recess in the protection tube might do the job. Finally, one has to check for the gasket's thickness with a feeler gauge and cut an appropriate one manually.

Hans