New member with bevel gear size questions

[Fpicabia]

Hello All,

New member here and very grateful that this forum was set up. First off, I hope I’m posting this in the right spot. I’ve got a stock 450 wide case engine that I’m rebuilding and possibly modifying. I did a search here looking for the answers to my questions but didn’t seem to find what I was looking for. Forgive me if I’ve missed answers to these questions.

I’m familiar with a number of Italian bikes and their engines but this is my first Ducati Single. Also please pardon some of my wording as I’m not familiar with this engine just yet. I do have both the Ducati Singles Restoration book by Mick Walker and the Ducati MkIII and Desmo Singles Haynes manual. Haven’t been able to find the answers in those books yet either…

Bought a non runner-as is and when I opened up the bevel gear cover I found that the bevel gears on the gear that connects to the cam shaft were pretty chewed up. Apparently the coupling that engages the rev counter dislodged and rattled around inside there. Oddly, the gears on the “head” that’s connected to the shaft that passes through the tube down to the bottom end are hardly damaged at all.

I’ve found a few sources that are selling some second hand and some NOS parts but they aren’t mechanics. What I’m getting at here is, are there easily understood locations to pull dimensions on the upper bevel gear as well as the “shaft” bevel gear that I can measure on my damaged parts that I can then pass on to the seller so that we’re both sure that I’m buying the right sized replacement parts?

Given that I already found this issue, I have a feeling there will be many more, ahem, situations I’ve yet to uncover.

Also considering a 12 volt conversion…only because it’d be nice to run brighter head/tail lights. Any thoughts on that subject would also be very well received.

All my best and thanks in advance,
Fpicabia

[bendik]

Hello
I am also pretty new to this and have been thru kinda the same process on my 250. It's my understanding that it would be better to hunt down a pair of used bevel gears that are matced as they would grind a mark on the gears in the factory that You use when shimming the bevels. From my experience I would also check previous shimming both on the head and the lower bevels for peace of mind..

[Fpicabia]

Hello @bendik
Thank you for the response. This all makes sense. I’m also hoping to determine measuring points to determine the sizing (length?) of the lower bevel shaft and possibly thickness variations of the upper bevel gear from engine to engine. I suspect that there are some differences between the 250, the 350 and the 450 dimensions. Differences in lengths and possibly thicknesses of the upper “cam shaft” bevel. I’m close to having the parts removed from the engine and will be able to measure the parts easily but I’m not sure where to pull the dimensions from to pass on to sellers to make sure we’re talking about the correct replacement parts. Hopefully someone in this collective pool of knowledge knows the answers.
All my best,
Fpicabia

[Eldert]

on a 450 bevelshaft if you measure from under the gear to the bottom of the coupling its 192 mm long

Eldert

[Fpicabia]

Hello @Eldert,

THANK YOU! This is extremely helpful. Thanks for taking the time to share your experience and knowledge. Once I get the parts removed, I hope it’ll be obvious regarding what you mean by the “bottom of the coupling.” I suspect that the 192mm measurement will clarify where you’re referring to. Thanks. Might you know if the upper bevel gear connected to the cam shaft is the same size/dimension/thickness on all the 250, 350 and the 450 engines? This question might be moot because I do understand that I’m supposed to swap out both the shaft bevel gear along with the upper “cam shaft” gear. Fingers crossed the sellers I’ve found have a matching set that doesn’t break the bank. Ha.

Best wishes,
Fpicabia

[ml83136]

I'm pretty new to bevel-drive Ducatis, too, but I believe that the upper bevel (vertical) shaft that's "waisted" (narrowed center section) is the one that all 250s use, so if it's not waisted it will be wrong. Hopefully someone else will confirm this.
I just measured the upper vertical bevel gear on my stripped-down 250 head and I get a shade under 37mm across the widest part and it has 20 teeth.
The camshaft bevel is on the order of 50 or 51mm diameter and has 28 teeth.

[ml83136]

But I should add to my reply that it appears that not all 250s use the same gears!
See the bottom of page 17 here: file:///E:/Dropbox/.Vehicle%20Images/.Bikes/My%20Bikes/1964%20Ducati%20250%20Monza/Ducati%20250%20Tech/DucatiNC-250_Parts_1965.pdf

[ml83136]

Sorry -- that link is bad. See the bottom of page 17 in the 250 parts catalog in Motoscrubs' reference links.

[Fpicabia]

Thank you @ml83136. I appreciate the response. Thank you for the clarification regarding the “waist” on the 250 bevel gear shafts and the dimension of the upper gear as well. For clarity, I have a 450 wide case single and, if I understand you correctly, the bevel gear shafts that have a waist will not work in my 450 engine.
Best wishes,
Fpicabia

[blethermaskite]

Search 'bevel shafts length' in the search box above.......there is a shaft length list form a member on here....Jordan... in a reply to me. Cheers George