Remove the bevelshaft without dismounting the crankshaft?

[LaceyDucati]

Least said about your the mod...........

The only possible way to match unmatched bevels is with engineers blue (absolute minimum) and look at the contact patch. Then all you need is a lot of time! It should be noted that matched pairs when correctly meshed to the grinding marks don't always line up to any other edges. So I would not attempt to line up any edges on Ducati gears.

Also BEWARE with mismatches, Italian and spanish bevels seem to have a different helix angle so bugger all chance of matching them!

Aside all the possible alloy swarf, I would stop using that brand of paper towel as there is an awful lot of fibres around your gears. These engines live or die on cleanliness!

Nigel

[Paddy]

The only possible way to match unmatched bevels is with engineers blue (absolute minimum) and look at the contact patch.
Nigel

Smells nice too

[StewartD]

Kev,

My last post may not have been that clear. I was trying to point out that the gear tooth geometry is quite sophisticated to achieve the the smooth transmission of rotation from one shaft to the next. The diagram and text I hope gave an appreciation of the problems in designing this geometry. If this is appreciated, I think it will counter any 'rough enough's good enough' attitude.

I do agree with Nigel about the engineers blue, though I've never had to do this. I've always had matched gears with the ground surfaces luckily. I am amazed that the Italian and Spanish machines had different helix angles for their bevel gears.

Cheers,

Stewart D

[Rocla]

Hello everybody,

Thanks for your comments but I am a little bit surprised: how could you assess gears matching just thanks to photos?

Even if the theoritical approach is usefull, matching bevel gears is mainly pragmatism. You have to arbitrate between the play and the noise. You have to position each gear perfectly in front of its counterpart, while you have to minimise the play for a bevel gear free rotation.

About your remarks between Mototrans and Ducati, the top bevel gear is the genuine one. It was not dented, so I kept it, but I've meshed it because before, there was 1mm play on the rotation, the play was huge, there was no shimm at all (we can applaude the Ducati garage mechanics)! On the bottom bevel gear, it is a brand new one, from Amici delo Scrambler in Italy (100% Ducati). May be the approach is different for meshing a Mototrans or a Ducati bevel gear. But my approach was very pragmatic: it consisted in insuring the play was at the minimum acceptable while keeping a free rotation, with teeth perfectly opposite. If you were in front of my engine, you could check that. As I see it, on pictures, it is less easy. For instance, on the bottom bevel gear picture, it seems the vertical one should be pushed a little bit (in cancelling a 0,1mm shimm), but if you check inside the gears, you can see that the teeth of the crankshaft gear are exactly in front of the bevelshaft gear. And when I removed a 0,1 mm shim, there was no play any more. In fact, the lengh of the bevelshaft gear teeth is a little bit longer thant the crankshaft one. You can see that if you have a bevelshaft gear apart at you home.
About the dirt, do you really think I've remounted the housing without cleaning the gears tooth by tooth and the housing itself ? I didn't take photos at each step of my work, it is tricky enough to setup everything
The next step will be to try the bike (once the ignition will be OK). But before, I want to insure that the oil pump is working (when you remount the right housing, it is not obvious to match the oil pump with is counterpart in the housing (between the crankshaft and the ignition pinion)... So far, with the kick, it is not enough to push the oil up to the headcylinder. I will add oil in the bevelshaft pipe to initiate the pump. Normally, can you initiate with the kick only?

[Jordan]

It's clear from the photo that the outer conical edges were not matching. You've told us it was an early photo, not the final arrangement.
Having them perfectly matching doesn't confirm perfect mesh, but the ones I've seen were much closer than in your first photo.

Stewart and Nigel have advised that a new set ought to be fitted properly by bluing and shimming, and I'm sure that's right. I confess however to never having done that. On one or two occasions when I had to use unmatched gears, there have been no obvious troubles with it. But maybe the gears could have been quieter?

Stewart's description of why bluing is theoretically preferable makes sense to me, if I understand it correctly.
I think the gears can be shimmed so that there is free movement and no linear play (along the shafts), but still have some rotational play?
Imagine a ridiculously extreme case where the thick outer edges of the gear teeth of one gear is engaging with the thin inner edges of the other gear, yet they are shimmed for free movement with no axial play. The difference in tooth thickness would result in rotational backlash.
So, one aim of shimming is to have the varying tooth thickness corrected so they are matched for both gears. At any point along the teeth, the tooth thickness should be the same where they touch the other gear, to eliminate backlash.
Am I on the right track?

Jordan

[LaceyDucati]

The reason for needing blue is that the teeth are curved, cupped as such. The convex side of one tooth needs to sit in the concaved side of the other, small sideways movement away from alignment will mean the teeth will drive on one edge, increasing load. When meshed correctly you will get a wide contact patch in the middle of the tooth. Small misalignments will probably bed (wear) in and not come to much harm, but greater misalignments will probably result in broken teeth. When meshed correctly the gears will not only sound smoother they will also feel smoother, although this is more of an arbitrary thing. Anyone who has worked on drive boxes and differentials will understand the principles of bevel gears as its the same. Look in a Guzzi workshop manual as the description of setting up the drive box shows the principles well. All very tedious, which is why matched bevels make life a lot easier!

On the different helix angle / tooth form if anyone has a few sets of bevels to hand especially Spanish and Italian, mixing up pairs will soon show you what I mean. There is no way on earth some gears will fit together, if they won't sit together in your hands then there is no amount of shimming will sort that!

All this said, all is generally not perfection in Ducati bevels at the best of times, as the gears are not often perfectly concentric. I've looked at hundreds of gears and believe me it's not wear as it is found on NOS gears as well. Count yourselves lucky you have a single, as some of the squarecase bevel twin gears have got to be seen to be believed . At the tightest spot I go for no perceptible play with no rough or tight feeling. Anything else in the way of play I live with and I've not experienced any breakages or other problems. Checking play can only be done successfully if all nuts are fully torqued up, bearing housings secured, shim stacks snug under the circlips, crank shimmed correctly and head torqued down (if you are doing the top bevels). If any of these are not done then you won't get a true clearance. The head being torqued down for the top bevels if often overlooked, but the head will deform slightly when torqued down. This is the same reason the valve clearances alter about a thou when the head is torqued, none of this happens with a bevel twin as the head is fixed below the rocker box.

Just a few more thoughts....

Nigel

[Paddy]

Obviously when matching bevel gears we are talking about minute tolerances hence the need for Blue but i just took this picture for your interest of a Spanish gear on the left and an Italian on the right. Different face width and quite a different form if you look closely, also a much cruder piece of engineering TBH.
I would recomend that people regard Spanish and Italian engines as two completely different models/types. Do not mix and match.
Everything from crank cases to crankshafts, bevel gears to kick start mechanisms are different. Both have their merits but very little is interchangeable.

[Paddy]

Another reason why its best not to mix and match

[Paddy]

And another



Although i have put a dob of white paint on the alignment dot on one you can see from the position of the d drive flats one of these is nearly 120 degrees out.

[Rocla]

Hi again...

I'VE JUST RUN 10 KM with my new mesched bike and the noise is absolutely different. I will describe it, and I would like to get your opinion. The accelerations are very good, the engine is more comfortable in high speed than before, and the idle is OK, the engine doesn't look like forcing

More interesting : when the engine is running, you can ear 4 types of noises :
- the exhaust
- the inlet rocker (but very low)
- the exhaust rocker (very low too)
- and a new noise that replaces the clinking sound before : the sound of the bevel gears. I will describe this noise because I am sure it reveals many thinks. It is a very soft and continuous noise, a kind of gentle hiss, not loud at all, that looks like the hiss of the Harley Davidson Electra Glide engines.

So, I am both happy and anxious. Happy because the sound level of my engine has drastically decreased! But anxious because, given your remarks, and given it was a new job for me, I have some difficulties to analyse this sound: is it normal, a good clue, or on the contrary, a bad sign?