Little oil leak on the top bevel shaft housing

[Rocla]

Hello everybody,

My Scrambler works very well, everything is ok except for a little and boring detail: there is a sort of oil leak on the very top of tbe bevel shaft housing. If I run 30 km after an engine wash, some oil spray appear arounf the seal. It is as much amazing as:
- there is no leak elsewhere in the engine and its cylindrer head (it is totally clear and dry!)
- the seal is new (and mounted with a special paste)

When I remounted the engine, I was surprised because of the free space between the top of the bevel shaft housing and the matching part of head cylinder. I am sure it was possible to mount 2 seals on the top of the bevel shaft housing.

Did seomebody have the same surprise and mounted 2 seals insteed 1?

[Bevel bob]

The gasket needs to be compressed. If too thin you will distort the parts. Its possible to seal the parts with a silicone ( and spacers ) but I would not be happy with that.You may have to make your own gasket.I have a friend with a lazer cutter ,if I do this job again i'll get him to make me an alloy spacer / gasket of the right thickness and fit it with a thin coat of sealer.

[double diamond]

The upper bevel shaft bearing fits in a sleeve that in turn fits in the head. This sleeve is held in place by a raised lip on the gasket surface of the bevel shaft tube. Consequently, when compressed, the bevel tube gasket needs to be as thick as the raised lip. If this junction is leaking, either the gasket is too thin or there is an issue with the bearing sleeve not seating properly. Improper seating of the sleeve could be caused by a compromised bore for the sleeve in the head, foreign material preventing the sleeve from seating properly or incorrect upper bevel shimming. Adding gaskets to address the oil leak may lower the bevel gear and introduce excess backlash at the bevel shaft/cam gear mesh if the compressed gasket thickness is greater than the height of the raised lip that pre-loads the bearing sleeve. You should determine that the bearing sleeve is seated properly, that bevel gear mesh is correct and that the gasket is the proper thickness. The gasket should be slightly thicker than the height of the lip on the bevel tube gasket surface.

[Rocla]

Thanks for your replies, double diamond and bevel bob,

But I am atonished with your answer, bevel bob, because, for me, the position of the bevel shaft tube is independ from the bevel gears position. Their position is determined thanks to the shims and circlips. The bevel shaft tube is straight fixed on the head cylinder, whatever the position of the gears and the shaft...

Here below the picture that (for me) shows that:

Distribution1.jpg

It is the reason why either there is a pb with the metal, or the gasket is too hard... Isn't-it?

[Jordan]

The tube locks the bearing/sleeve assembly in position, so in that sense the bevel gear location is not independent of it. Adjustment of the gear is however by means of shims and circlip.
It's important to have the gasket thickness just right. Maybe some non-standard, thinner one is causing the problem?
If the flange is warped, it will need to be flattened by machining I think. And then, a gasket thickness will definitely need to be carefully chosen.
Maybe the flange had already been modified?

[Rocla]

Hello Jordan,

It is right the bevel shaft tube is fixed both on the head cylinder and on the bearing housing. Here below the zoom on this part. It is bizarre, but that confirms you are right, consequently, the gasket has to be with the right thickness. For sure it is a too thin gasket. Mono Ducati are very sophisticated engines! This gasket comes from Amicci dello Scrambler, and maybe, as I felt when I've remounted it, it requires 2 gaskets. Or better than that, a thick but very soft one... I don't know where it is possible to find thicker gaskets...

Distribution4.jpg

[Bevel bob]

for sure these engines are not as simple as they seem. There are a few pits ready and waiting for the unwary to fall into. If you could see the bumps on my head!.

[double diamond]

Actually, my recall of the upper bevel shaft bearing retention was a bit inaccurate. As one can see in the attached drawing of the upper bevel gear assembly, it is not the bearing sleeve (referred to as a “bushing” in the drawing) that is retained by the lip on the bevel tube. It is the outer race of the bearing itself that is loaded in compression by the bevel tube. The sleeve is retained in the head by both the outer race of the bearing and by the flange on the bevel tube. If the gasket is too thick such that there is clearance between the lip on the bevel tube and the outer race of the bearing, the bearing may recede in the sleeve. If this happens, the bevel shaft gear will develop more backlash, assuming it was properly shimmed without a gasket in place. This is just a cautionary note that, if the gasket stack ends up being too thick to allow the lip on the bevel tube to seat against the outer bearing race, installing additional gaskets to address your oil leak may prevent the bevel tube from seating against the upper bevel bearing and allow excessive backlash to develop. You can determine the required gasket thickness by removing the gasket and attaching the bevel tube on the head. Then, measure the gap between the head and the bevel tube flange with feeler gauges. Add a little to this measurement to allow the gasket to compress and you should have a good approximation of the correct gasket thickness. Of course, there should be no damage to the gasket seating surfaces. Perhaps Nigel Lacey has individual gaskets of the correct thickness? I also understand that Elring makes gasket paper in different thicknesses and you may be able to find a supplier in France.

[Rocla]

Thanks! Of course the Ducati mono is very very complex

You are right, the best way is to measure without he gasket, and to add a little proportion for compression. The best decision is probably to built up a gasket on my own. Unless here are some different thickness gaskets available. For sure it doesn't exist in Amicci dello scrambler, the biggest in italy. I will check with the other suppliers (Lacey, etc...)

[Bevel bob]

My understanding is that Nigel builds his race motors with no gasket at this point. You can see why I am thinking of making up something myself.