Bevel Gears Binding

[matzb]

When I rotate the crank 5 or 6 full revolutions the bevel gears in the case will bind. I don't have any shims on the crankshaft bevel gear. With the crankshaft bevel gear off, there is some vertical play in the bevel gear that rotates horizontally in the bushing that is  attached to the cam drive shaft. Is this normal? When the crankshaft bevel gear is on, is has no play?

[DewCatTea-Bob]

Welcome as one of our newest members, 'matzb' !


" When I rotate the crank 5 or 6 full revolutions the bevel gears in the case will bind. "

____ Could you please detail exactly what you mean by "bind" ?
__ How about rechecking that with the crankshaft's key -(which locks it's bevel-gear) removed? _ You should find that the bevel-pair meshes with constant/even pressure regardless of the crankshaft's position - (try it every 45-degrees of a rotation of the crankshaft).
Note that rather than spinning the crank itself to test the meshing of the bevel-pair, you'll instead have to twist/turn the bevel-shaft, for this bevel-gear meshing-test.


" With the crankshaft bevel gear off, there is some vertical play in the bevel gear that rotates horizontally in the bushing that is  attached to the cam drive shaft. Is this normal? "

____ I don't think that it really ought to be but, it indeed seems to be.
I would think that it ought to be between .001 & .010", of such slop.


Dukaddy-DUKEs,
-Bob

[matzb]

When I say binding, I mean if I turn it anymore, somethings going to break in the lower bevel gear set.
I removed the crankshaft bevel gear and replaced it just make sure everhting was cool and the woodruf key was in place.
After turning the engine over 9 complete revolutions, the same problem occured (binding to the point of breaking.

The mesh test that you mentioned, I assume you mean removing the head and cam tower and turning the lower bevel gear by hand?

[Bevel bob]

Dont run the motor!!, The reason there is no shims behind the crank bevel is likely because the horizontal bevel gear is not in its rightfull (low) position and some dork brained dope has removed the shims to compensate , the horizontal gear must not have any side to side play.Either the bevel bearings are shagged or just as likely the shim under the tunnel housing is missing or not thick enough to hold the bushing (and bearings and horizontal bevel) down in its position.If you use too thick a shim you will not get the housing to seal on the gasket, Also too thick a gasket will allow the gear to rise out of position!!, trickey stuff. These large diameter shims are not readily availiable , useing a mike and feeler gauges I worked out that needed a 7 thou packing between the shim and housing which i made myself.The gears now meet and shims are needed behind the bevel.The bottom bevel bearings need a small preload to work properly but this is difficult to do so nil claerance is usual.To see what I'm waffling on about ,with the head removed tap the gears down then use a drift to tap under the horizontal bevel, you will be amazed to see the assembly go up and down, this is no good, and is the cause of many troubles.You also need the crank end float to be nill for it to work, Welcome to our world!!.----0-Opps, forgot to mention, the above process is only half the story, the bevel gear also has to be shimmed within the assembly to have nil clearance under the circlip and after that shims transferred above or below to get the mesh right!! This process will make you cry. Also check that the drive side gears dont have a tight spot (mine did as the crank was out of line, or the gearbox shaft could be bent) , happy daze??.

[Bevel bob]

Me again!!, some bevel experts don't see a problem in the bush assembly rising and falling, I'm not happy with this,they remove shims from the crank bevel and allow it to support the assembly, this sort of works if the mesh is also adjusted but if the main crank shim wears against the crank radius the crank and bevels develop play which allows the bush to rise and fall and wear and then revolve in its alloy housing !! . Ducati did not always do the shimming jobs right in the first place either (I hear).Some well known and respected experts also build engines without gaskets to avoid problems! I would not reccomend you to try this at home. Ignorance is bliss ,i wish i haven't learnt all this.

[matzb]

You were right, their is no shim in the tunnel housing. As you also stated, these shims are hard to find. How did you make yours?

[Bevel bob]

I made a cardboard packer to sit under the shim, I suppose you could make a shim from alloy sheet using tin snips and file it to shape, it does not fit between moving parts, or try one of the ducati restorers . you will still have to get the thickness right. try fitting the housing with no gasket to check the gap,you may be able to make do with a paper gasket.home made plus sealer.(dont tighten the allen screws as you could distort the housing)

[DewCatTea-Bob]

By: matzb...
" After turning the engine over 9 complete revolutions, the same problem occured (binding to the point of breaking. "

____You must mean with the crankshaft's w.key still in place?
In any case, this is very strange ! ... There shouldn't be any issue that can go from free-turning to lock-up anywhere up to 5 to 9 turns of the crankshaft, (except perhaps a bearing which has a broken cage) !
By what means are you turning-over the crankshaft? _ The kick-starter?

" The mesh test that you mentioned, I assume you mean removing the head and cam tower and turning the lower bevel gear by hand? "

____ Well of course, (except the tower will stay as attached along with the cyl.head), as I don't know how you could've narrowed-down your peculiar issue to the lower bevel-pair, whilst the cyl.head is still left installed !?! ...
Could you please explain your reasoning as to how you came to suspect that your "binding" issue is any at all due to the lower bevel-pair?
__ You need to do the suggested mesh-test (with the w.key removed), in order to eliminate any suspicion (which YOU seem to have), that your lower bevel-pair is at any fault at all for your unheard-of lock-up issue.
____ This strange-issue of your's is one for the books, so please keep us informed as to what you finally find to have been the actual cause of your bind-up situation.


Hopeful-Cheers,
-Bob

[matzb]

With the head and cam tower removed, I can turn the crankshaft with a socket continously and the gears seem to mesh fine. When I put the head and cam tower back on and tork the head bolts , I get the binding that I was talking about previously ( after 8 or 9 full revolutions of the crankshaft . I just noticed some small metal chips laying in the bottom of the case from the horizontal bevel gear.

[Bevel bob]

Remove the head and the crank bevel gear. check that the remaining bottom bevel has no side to side play and no vertical play and spins freely, you will need to use a drift to tap it up.Remove the primary gear to eliminate the drive side. Check all the bevel teeth.Does the crank wobble? Mine did!!Does the crank spin freely?Once you have checked the bottom bevels remove the rockers to check the top endbevels.Bevel gears can have a tiny hard to feel clearance all round to be safe.Lever the gears with a screwdriver to see if they move up and down.Fit some shims where there are none,The head gears are best checked with the head off but the shaft must be held central in the tube. Use a suitable half inch drive socket to centralise it.We are all agog to know whats up!!