Bevel drive nasty!

[blethermaskite]

So as Bill had said earlier, there is a lot of tiny metallic shards in your timing case (as a result of your gear destruction) and these will of course have 'got everywhere' in your motor, i'm sure you don't want to take the whole bl**dy engine to bits to clean it out, but at least if you remove the primary drive side cover (which is easy) and remove the clutch (easy) and alternator flywheel (which needs an extractor) you will then get better access to your 'other' main bearing (you already have access to the timing side bearing) you can then wash out both bearings with a solvent to get rid of the oil which will allow you better to determine crankshaft end float. Ideally if you have (or can get a hold of) a dial test indicator mounting it on a temporary bit of sturdy steel plate bolted to the crankcase face you then can properly measure the crankshaft end float. If you do get a DTI, set it up to measure the crankshaft run out which if excessive will make setting up your 'new' bevels problematic and could also be the culprit for your current damage?
The more 'bits' you can get off the crankcases the more chance you have of getting the debris out with a really good wash. and when you rebuild make sure to fit a magnet onto the oil filler dipstick which should catch any 'floating stuff'. If you decide to take the head and barrel off then get the crankshaft sludge trap screw out and get the cavity cleaned out too.
There are so many reasons that could be responsible for your damage your best way forward is to assume nothing is correct and as much as possible start from scratch again........crank endfloat first.
Cheers,
George

[Hiya9612]

[quote="blethermaskite"]So as Bill had said earlier, there is a lot of tiny metallic shards in your timing case (as a result of your gear destruction) and these will of course have 'got everywhere' in your motor, i'm sure you don't want to take the whole bl**dy engine to bits to clean it out, but at least if you remove the primary drive side cover (which is easy) and remove the clutch (easy) and alternator flywheel ...

Hi George. Although you would expect there to be a lot of metal inside the engine, pretty well nothing came out with the oil. I purposely drained it all into a completely clean container then dredged a strong magnet through it.
Then transferred it to an old coke bottle (yup, I realise it should have been more liquid than two litres.... another black mark against the previous "mechanic"). I left the bottle on it's side for a couple of days so any metal should have sunk to the bottom. Again, the magnet sliding along the bottom of the bottle picked up nothing.
After doing some more work today, It seems to me that the damage was likely caused by a ham fisted dolt not shimming the pinion gear (at all) and by tightening it, broke the tooth.
Realising that replacement parts would cost £250 or more, and that the engine would run, even with the damaged pinion, they decided to move it on. As the oil was completely clean when I took delivery (even if there wasn't enough of it), did that person wash it all out first
I shall take the advice and check the crank float..... I just hope the same bodger didn't split the cases.
Oh, and can anyone advise me approximately what the (missing) pinion shim stack thickness is likely to be? I'll obviously have to get a mixture of shims to achieve a reasonable mesh, are the same sized shims used with any other components?

[blethermaskite]

Well at least that's pretty good news on the 'bits' in the oil.......you will have to excuse my pessimism on these things, slightly over 50 years of working on Ducati singles has made me like that actually the centrifugal sludge trap in the crankshaft is pretty efficient at catching stuff that shouldn't be in the oil so hopefully it has caught the majority in your case. As an aside most owners never bother to clean out this trap and it can really surprise just how much cr*p is in there, of course once the trap is full it can no longer work as a centrifuge and becomes useless.
Cheers,
George

[Bevel bob]

In an Ideal situation you would obtain a set of gears that have been matched and had a ground off area accross the gears to show when the best tooth engagement is obtained. In reality you will probably get a set of gears that need to be "blued" and shimmed to ensure the gear teeth flanks meet properly and some time will need to be spent going back and forth with different shim combinations to get both the mesh depth and minimal backlash at the same time.Once the ideal situation is found then the gears can have a grinder run accross the faces so that its easy to reproduce the setting in the future. This is what the factory did ( hopefully !

[Duccout]

Hi Phil,

Lacey Ducati sells a selection of 28 bevel shims for £10.50; get those, they will do for all of your shimming requirements. Try to use the largest shim possible rather than lots of thinner ones.

If you are thinking of new bevel gears, have a look at www.widecase.com, they had some last time I looked, or if not their Italian supplier Vintage Ducati has them for €185 + VAT + postage, which I think will work out at about £230. Used ones are not easy to find, for obvious reasons.

Cheers,

Colin

[themoudie]

Morning Colin and Phil,

Just clicked on your link Colin and read this notice, mid screen on the "Widecase Ducati parts and services" website?

Closing down sale! From 25% to 50% off
Sale ends 14th November 2023.

I know nothing more!

Maybe worth enquiring further before placing an order?

Good health, Bill

[Duccout]

I knew that the business was for sale, so it appears that there were no takers. He is still listing bottom bevels, so maybe a bargain to be had?


Colin

[LaceyDucati]

Hi All

Sorry to be the bearer of bad news.....You do have to strip the bottom end to remove the lower bevel shaft. The gear head is greater than the lower bevel housing bore and the gear will not come out the bottom as the crank is in the way.

The only difference in w/c and n/c lower bevels is with regard to the later widecases with the larger bearing on the timing side. The bevels used in these had the head of the shaft gear reduced in diameter to avoid contact with the casing changes. The earlier shaft gears can be used on these later engines by having the gear O/D ground down to 50mm. So if you are struggling to find a later type this could be an option.

Be aware some new gears are not great and all I have seen do not have any ground surfaces to aid setting up. You will therefore, without the grinding marks, be in the same situation as trying to match odd used gears.This involves using micrometer blue to set the contact area. If trying to use unmatched gears be aware not all gears match each other as over the years there have been different manufacturers and I suspect helix angle variations. Clearly some gears will never sit together. Some of this may stem from mixing some era's of Italian and Spanish gears. Basically they need to mesh snugly together and show some indication of "mutual contact". If they whirr, whine or grind to any extent when being turned they are not meshed and will probably expire in quick time.

If you want to take a chance and avoid stripping the bottom end with a secondhand crank gear there is one on Ebay below, good luck. Before going down this route you will have to ensure the crank is shimmed correctly as is the bevel shaft and it's housing. Play in either of these will just lead to more wear and probably failure. Side play on the crankshaft will mean stripping the casings anyway.

https://www.ebay.co.uk/itm/324497308193

Lastly, please don't believe all you read on Forums as 70Nm is NOT the correct torque for the bevel gear thread and tightening it to this will damage the nut and quite possibly the crank. For the bevel gear nuts I use 35 ftlb, which is about 47Nm.

Hope this helps

Regards Nigel

[themoudie]

Aye Nigel,

Nigel, thank you for the informative resume and update on the state of play for these helical bevels. May I ask if there is a preference for either helical or straight cut bevel gears in the drive train to the cam? Just in case!

Thank you.

Good health, Bill

[LaceyDucati]

Bill

Straight cut bevels are easier to manufacture than Spiral (with helical teeth). Spiral gears should in theory be lapped as pairs and always run as pairs....however I am not convinced that this was the case with all Ducati bevels. Certainly some sets fit together much better than others.

Spiral bevels will run smoother and quieter than straight cuts. Straight cuts are said to be stronger, which is why factory racers are said to have used them. However I'm not sure if that is significant or true. Certainly for small production runs straight cuts are cheaper and can be cut on conventional machinery. Spiral bevels require very specific machinery for their manufacturer and don't suit small batch manufacture, hence limited availability.

I've never fitted or used a set of straight cut bevels myself and never really experienced any failures with spiral bevel even in race use. The only failure I have ever found in an engine I built was a set of later type widecase bevels where a tooth had come off the crank gear. It was found during a routine strip down and fortunately not caused any other damage.

I believe the factory "improved" the crank bearing by fitting the larger bearing on the timing side and subsequently weakened the bevel gear by having to reduce the effective tooth width. Bearing in mind I have never experienced a main bearing failure on the early widecase singles with the small bearing It seems to be a bit of a home goal! I have heard of other failures with these later type bevels, but it is of course difficult to separate the narrower tooth and just poor assembly. I would add I've used many other sets of the later types without an issue.

Regards Nigel