Bevel Gears Binding

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DewCatTea-Bob
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Re: Bevel Gears Binding

Postby DewCatTea-Bob » Sat Jul 24, 2010 1:05 am

By: 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 . "

____ Previously it had not occurred to me that you would've indicated your binding-issue was seemingly due to just the LOWER bevel-pair, while the cyl.head was still left installed & to be suspected.
Now that you've seemingly found that the tower-shaft/cyl.head is the likely location of your binding-issue, it's still a seemingly strange occurrence to have encountered !
How exactly did you run-into this binding-issue? _ What were you doing when you discovered it for the first time?
__ I would've suspected that the cyl.head has been installed out-of-time with the crankshaft (by an amount that allows the piston to make contact with one of the valves), if you hadn't been able to turn the crankshaft more than just two turns. _ But in this case of yours, I'd first suspect that the bearing for the upper tower-shaft has gone-bad, (assuming that all the teeth on the upper bevel-pair are still good!).
__ Rather than tackle your issue with the overwhelming shot-gun approach as has already been suggested by 'bevel-bob' - (although definitely not to imply that any of his suggestions should not be tried-out anyway, regardless of first solving your issue !),
if your upper bevel-bearing checks-out to be perfectly good, then remove one rocker-arm at a time and check to see if your binding-issue goes away, after each change you make. - (You should be able to do so with the cyl.head off the engine.) _ And if your binding-issue still remains after both rockers have been removed, I'd then only suspect that the right-side cam-bearing has gone bad & allows a lock-up situation to occur.


" I just noticed some small metal chips laying in the bottom of the case from the horizontal bevel gear. "

____ You mean the driven bevel-gear down within the motor-case?
How is it that you NOW seem to be sure that chips have been broken from that particular bevel-gear?
At this point, it would seem more likely that the upper bevel-pair would have some chipped-teeth (to find the pieces of, and also possibly get jammed between teeth).
__ It seems that you need to closely inspect all the teeth of both bevel-pairs, to make sure that they are all as perfect as those of an original set, and that no tiny pieces (of anything) are getting between any of those bevel-teeth.

____ Please keep us updated !


Hopeful-Cheers,
-Bob
PLEASE NOTE... If this-post is not-yet signed-off with '-Bob', then I'm still in the process of completing it,, and if not also included with 'DCT' near bottom as well, then I may edit this post's wording at a later time. - Dct.Bob

Bevel bob
Posts: 1043
Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: Bevel Gears Binding

Postby Bevel bob » Sat Jul 24, 2010 2:21 am

I agree that its quite likely that the valves are misstimed, perhaps due to missing gear teeth.Gears do come up on E -Bay. You need to check all the cam drive components after studying a manual, replace old circlips, to do this job you need to really understand how it all works,or find someone who does. Your troubles could have resulted from wrong timing causing the piston to hit valves and so breaking drive teeth---or--- bad gear meshing breaking teeth allowing timing to slip with same result.Gear without shims is a pointer to wrong assembly by DPO. Trust nothing,check everything.

matzb
Posts: 11
Joined: Tue Jul 20, 2010 4:40 pm

Re: Bevel Gears Binding

Postby matzb » Sat Jul 24, 2010 8:08 pm

Should the gap between the cam tower flange and the case be this wide? The picture is taken with the gasket out.
Oddly enoughI get no binding of the gears as it is set up in the picture, there is however about .005 of up and down play in the horizontal bevel gear.

The horizontal gear has no missing teeth, only some small chips on the narrow end of the gear teeth.

The piston has never hit the valve, this motor is just being assembled and has never been run.
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Bevel bob
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Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: Bevel Gears Binding

Postby Bevel bob » Sat Jul 24, 2010 9:11 pm

That is odd, I would have expected no gap if you are missing the big shim or a very small gap, Take off the crank bevel and the whole assembly( Bush,bearings and horizontal gear) will likely squeeze or be tapped down. its the crank bevel thats holding it all up and thats a bad mistake ,IE no shim behind it and its too far in. It must have a shim behind it and if the gears dont mesh then some dope has also transfered the horizontal bevel shims to below the bearings. The proceedure to get this right is the one that will make you cry.I have made the same mistake, I now know better.To get the mesh right when the gears are down in the right position first you need to sort out the housing so it holds both the bearings down in the bush and at the same time holds the bush down to the crankcase thats trickey balancing the (missing) shim thickness against the gasket thickness. Once this assembly is fixed and cant move then you can play with the shim pack (above and below the bearings!! To do this means taking off the housing and the circlip and shims tapping the bush up (use a drift under the horiz bevel to get it started then lever up) this will leave the bevel gear sitting loose on the crank,recover the shim(S) that are sitting on the gear (use a magnet.All these shims constitute the shimpack, You now have to Guess which to move above or below to change the mesh.Repeat the process about six times (at least!) and you may get the gears to meet before you suffer a breakdown .You can't do the job without a good selection of shims a notebook and a micrometer . I nearly forgot to mention that BEFORE you remove the circlip you need to check that its not possible to fit another shim under the clip ,IE the shim pack only just fits , for this you must use a selection of shimms and the mike . If the bearings are shagged it will all be a waste of time . Now you know why it costs a lot to get the motor built by an expert, and Ducati lost money making them. And you still need to start with finding the big shim 29.2x35x0.2or0.5 !! The memory of it all still haunts me. OH and be wary as while the housing is off nothing is held down and misstakes are easy, finally check it all after tightening down the housing and be prepared to do it again if if changes. Last thought, if the housing is that high its likely that theres no clearance between the shaft joint and when you tighten down the head it will distort the head or damage something.And it WILL JAM UP!!.
Last edited by Bevel bob on Mon Jul 26, 2010 3:06 am, edited 5 times in total.

Bevel bob
Posts: 1043
Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: Bevel Gears Binding

Postby Bevel bob » Sun Jul 25, 2010 8:07 am

My 250 bevels were in a terrible state and it still ran , all the bearings were scrap and the "professionals" that built the motor just shimmed it tight to hold it all together,what with a wobbly crank and lots of crank float its a wonder it would still do 80mph, Now it will do the ton I'm sure.Get the basics right first ,components held firmly in the right position before setting the bevels. If you can't get the missing 29.2x35 shim you may still be able to hold everything down by doing away with the thick gasket and using a thin paper one plus goo, the important thing is to have a few shims behind the crank bevel so its not lifting things too high.What do you think Dew-Cat??


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