Noise issues on 350 Scrambler engine

[Rocla]

Many thanks for your support, Bevel B, Stewartd, Graeme and Ducwiz.
I've download the guide "mesh job", that seems absolutely usefull.

I started dismounting the bevel shaft. My decision is :
- to replace the damaged nut and lower bevel gear that are both fixed on the crankshaft, to cancel the external washer (and maybe one amongst the others inside but the shim seems OK between the two lower bevel gears) to gain enough good thread on the crankshaft, and then, to check if is sufficiently tighten (if not, I would prefer 2 welding spots, that can be removed, than replacing the crankshaft, even if it is not orthodox to do so)
- not to replace the other bevel gears because they don't seems to be dented
- not to replace bearings because there is no play at all on the bevel axis
- to mesh as perfectly as possible the upper bevel gear because 1mm rotation slack is of course too much, and is the source of my so noisy engine

My only concerns are about specific tools : I've spent 1 hour to release the cam shaft bevel gear because I hadn't the right one to unscrew it... But it is possible without.

I understand the Ducwitz reaction about a probably under blowsy service of my engine, but I am really wondering if the 2 broken nuts (the one of the camshaft was dented too, when the engine was checked up 4 months ago!) are not because of the inexperience of the Ducati garage: maybe the mecanic didn't know that it was a left thread and forced a lot. When they checked up my engine, they told me that these 2 nuts were damaged and they changed the camshaft but they underestimated the problem on the crankshaft (or they forgot to fix it) I guess Ducati garages are usually not skilled for working on oldtimers bikes, even Ducati ones... Moreover, when they gave me my Scrambler back, many parts were not correctly fixed, positionned or set on the bike: carburetor, cables, tank, housings, wires... Reason why I imagine they are the ones that damaged the 2 left thread nuts. But it is impossible to get pieces of evidence... In France, it is said that efficient and serious motorbikes mechanics are less and less numerous. Is it the same in your countries?

[StewartD]

Bob, Hans,

I agree about the primary drive gear keyway and flywheel taper being very marginal design. If the taper isn't perfect and/or the flywheel is not forced onto the taper by correctly torquing up the nut, then it is very likely to come loose in service. Damage to the taper is inevitable if you do not shut off the engine straight away. The noise is fairly obvious when this happens. This happened on my Mach 1 and on my 450. On the 450 the key sheared off as well and I had to make a new key in someone's garage up country, so I could get home.
In normal engineering practice, woodruff keys are only used to maintain a location, for a timing function, for example. When torque transmission is the primary function for the key, then a square or rectangular key is normally used. Either woodruff, square or rectangular key is made of a fairly low strength steel. This is so it will shear, rather than the expensive gear or shaft, that are normally of a stronger and harder steel grade, do not become damaged. It is a designed 'weak link'.

Rocla,

I am shocked if these problems were caused by a workshop claiming Ducati expertise. I think this is typical of the trades becoming de-skilled. I think you may be better off doing the mechanical work yourself. If you want to get the crank thread welded and thread recut, I would be very careful who you send it to.

Cheers,

Stewart D

[Rocla]

Hello,

I've progressed a lot: I've moved the camshaft and its bevel gear from the head cylinder. There was no washer at all, neither on the camshaft side nor on the bevelshaft! That proves Ducati garage didn't pay attention to the huge slack when they mounted the crankshaft...
I will start adding washer by washer on each gear, and test the result up to the point there is almost no play while the gear can rotate easily...
But first of all, I'll order the washers, the nut and bottom bevel gear, and all the seals...

[Rocla]

An additionnal question: is it really mandatory to change bottom bevel gear by pair? Given it is difficult to extract the bottom vertical bevel gear (a special extractor is required), and given only the crankshaft bevel gear is dented, it could be easier for me to change only this one (that I've already dismounted)...

Is it really risky?

[Jordan]

No.

Jordan

[Bevel bob]

It is possible to remove the bottom bevel assembly without any tools, It can be tapped upwards and levered out after clip removed , a bit of a fiddle.However if the bottom bevels can be mated and shimmed it is likely that it has not been out before ,it would be a shame to loose the basic shim settings and make more work.It is most likely that you will find all manor of mistakes and nothing can now be trusted.As you have no experience of these motors it will be much more difficult for you to spot the missing/wrong parts . I had to get parts made /donated by friends ,Good luck!.

[Rocla]

Hello,

Given that the shim setting is perfect on the bottom bevel gear, I won't change anything except for the crankshaft bevel gear that is dented. Reason why I've asked if it was mandatory to change bevel gears by pairs. As I see it, I can change the only dented and if the new one fits like the previous, I don't modify the number of shims. Do you confirm that I can change only 1 out of 2 gears on the bottom side?

For the top bevel gears, I've understood that if I add a washer above the bearing, I have to substract it below. I've already seen that there is no washer on the camshaft bevel gear, that is absolutely not normal, given the huge play. I've ordered the related washers and I will adjust washer by washer on each gear given the meshdepth is correct but not the backlash. I will do that as long as the backlash is too big, and up to the point the backlash is Ok while the gears can still rotate easily. Of course, I am not experienced with these motors, but what would you say about the Ducati garage? And the big difference between them and I, is about motivation: I want to make my engine reliable. They don't mind... To the contrary, all my skills are mobilized

[Bevel bob]

Hi, you seem to have a good grasp of whats needed,But if you fit a new gear its likely the shims will be wrong. I would happily use non matched gears as long as they mesh well and close with no tight spots, For long life the gear teeth need to meet correctly and they can be "blued" up and the meeting areas seen and adjusted, Roy Creasy did a usefull article on this many years ago, its on the webb somewhere.A good selection of shims, a mike and notepad and lots of time will sort it.IF there is crank end float then your time will be wasted.Make sure that the bottom bevel bearings/steel bushing/ bevel gear cannot be tapped up and down after the alloy housing has been fitted, as it will move in service and mess up the shimming you spent so long setting up., This is not easy to spot,and is controlled by a large shim/gasket thickness that can go missing.Ask yourself what happened to the swarf/chips from the gears,and which bearings did it go through?.

[Rocla]

I'll use colored ink to check if the bevel gears are working correctly !

Of course, thanks to this very fruitful forum, thinks seems managable. I am not anxious any more for meshing the bevel gears.

But another tricky step is ahead: to set up the ignition timing. I will read all the related documents. If there is a very simple guide for that, I am interested in, of course... Anyway, I've download the manual from a previous ducwiz's post (many thanks!)

[Rocla]

Hello everybody,

I've meshed the top bevel gear and it was not as much tricky as I feared, of course, it takes time but it is not out of reach.

The choise of the shims is so wide (when you order a complete set, you get 10 washers of 0,1, 10 of 0,2, 10 of 0,5 and 10 of 1,0) that it is possible to choose exactly the relative position of each pinion. For the top bevel gear, there were no shims at all (such Ducati service!) but now, I've added 1,7mm shims behind the camshaft pinion and 0,7mm below the vertical pinion... The longer was to find the perfect balance between play (the bevel gear rotate freely) and the noise (the play is so limited that it is impossible to ear the pinions when you quickly rotate them manually in one direction then in the other) and it requires evry time to validate in mounting the head cylinder on the engine. But now, I am sure that my engine won't be noisy any more...

ScrBevel9.jpg

For the bottom bevel gear, I've disccoverd that the vertical pinion is dented too. And badly positionned relatively to the crankshaft pinion. That means I am forced to remove the complete bevel gear. I didn't succeed to remove it without any extractor. I hope I'll borrow one next week. It is the only job to achieve before remounting the engine (I've already replaced the camshaft bearings and the dented rocker)...

I've relized that single Ducati are specific and need a very accurate setting up. I think such bikes cannot be repaired and checked everywhere, certainly not in Ducati garages... It requires specialists, or motivated owners...

I would like to emphasize how interesting and profitable a forum like this one is!