Bevel Camshfts

[Ed VR]

Instead of finding out the hard way...
Can I remove the cam shafts from my 860GT engine without removing the rocker arms?

I have a chipped bevel gear that should be replaced and from what I can tell from the service manual, I need to pull the cam in order to get the bevel gear off. With the cost of a new set of bevels, I am hoping that I do not have to buy the tool to remove the rocker arm shafts.

By the way, I am a new member who has admired Ducatis for some time. This 860GT is my first Ducati. I am working on putting it back to it's original look and making it reliable for some longer distance rides. If anyone has any good original 860 parts (seat, bodywork with original paint , or a bevel gear set) laying around, let me know. They would go to a good home.

Hope to meet you all this summer,
-Ed

[Rocket Rick]

Hi Ed,
Yep, rockers gotta go, but...
If it's only one tooth missing 1/4 or less, leave it. More than that, or damage to both gears means replacement. Replacement gears are a matched set. Don't buy unmatched gears unless there's no other way.
Unmatched gears must be shimmed by checking the mesh with prussian blue, like you would for rebuilding a differential.
It is most important to find the broken bits. If they weren't in the bevel gear housing, the heads must be pulled. For the front, pull the carb, exhaust, tach cable & spark plug, set the crank to TDC, and loosen the head nuts 1/4 turn at a time in diagonal pattern 'til they're loose, then back 'em off. The head has to be lifted slightly to totally remove the nuts. If the head is stuck tap it with a rubber mallet. Don't break any fins.
The back head requires the engine to be partially removed. Remove the same parts as the front head, plus chain, nuetral switch, alternator & ignition wires, and anything else that's needed. Place a jack under the front of the motor, and pull the front and top rear motor mounting bolts.
lowering the jack will let the engine pivot out of the frame on the lower rear bolt. Stop when there's enough clearance to remove the head.
With the head on the workbench, romwve the bevel shaft bearing retainer by undoing the two screws either side of the shaft gear. Remove the bevel shaft, it's a sliding fit in the housing and will come away with the bearing & bearing holder. No bits yet? Look in the lower shaft holder. If they made it past the lower shaft bearings, they probably damaged them. They'll have to be pulled for inspection/replacement.
Now back to pulling the cam shaft. Remove the rocker covers, bend back the tab washer, and place a steel bar between the rockers and the top of the cam box. This will stop the cam from rotating when loosening the nut. Then loosen the nut. REMEMBER IT IS A LEFT HAND THREAD. Now remove the cam end cap, pull the rocker pins, and rockers. pull the cam gear, remove the woodruff key, and remove any shims. Now push the cam out.
The new gears will have to be shimmed. To do this you need a selection of shims. There may, or may not be enough shims or the correct shims left from the previous gear set. Placing the old shims back in their respective places will not do. You also need a dummy tube that will hold the shaft central while checking the shimming.
Put the cam back in, and install and tighten down the end cover. You then place the bevel shaft in its bearing and stack shims on it until there's no end float when the snap ring is installed. place the cam gear on the cam and do up the nut. The nut has to be tight enough to hold the gear fully home, but doesn't need to be fully torqued as for final assembly. Line up and install the shaft gear, tighten down the bearing retainer, install the dummy tube, and check the mesh. It should be pretty loose. You will notice a flat spot ground across both gears, a few teeth to one side of the timing marks. You want to get the middle of the ground spot even across both gears, and the gears shimmed for zero backlash and no binding through a whole rotation of the cam gear. This is unlikely, as most gear sets have a high spot, so settle for no binding at the highspot. Check the ground spot by dragging the blade of a jewelers screwdriver across it. When the gears are set, tighten eveything down and recheck. Then re-assemble the rest.
Some more points: replace any bearings uncovered, They're cheap at a bearing supply store.
Never remove steel bearings from alloy housings cold. Always heat the alloy to 250-350 F and the bearings will fall out. Heat the alloy for installation as well.
Do a valve job & check the guides while you're at it
Check the piston to wall clearance
Check the seal of the head to cylinder by looking for evidence of blow by on the sealing surfaces. If present, lap the head to the cylinder with valve grinding paste.
The same O'rings and valve seals are used on current 2 valve Dukes
Good luck, any further questions just ask.
Cheers, Rocket

[Ed VR]

Thank you very much for your info. Both of my bevel gears on the front cylinder are chipped. They move valves but the sound is horrible. .

Am I correct in thinking that there are adjustment shims above and below the bearing for the bevel shaft so that you can adjust the height without having end float.

Thanks
-Ed

[Rocket Rick]

So somebody put the tach drive on and didn't make sure the coupling was properly installed, eh?
I realised after I submitted that I was unclear on that part. What you do with the bevel shaft gear after you've shimmed the bearing for zero endfloat is move the shims one at a time from the snap ring side of the bearing to the gear side. You also have to stack shims behind the cam gear at the same time. You mix and match shims on both gears, assemble and disassemble until you get the correct mesh. It takes any where from 20 minutes to four hours. Instead of making a tube to hold the shaft central, you can place the head on the motor and use the oldham coupling to align the shaft. Partially lift the head to change shims. Don't try short cuts like aligning the shaft by eye, or not doing up the screws and nut more than finger tight. You'll also find a micrometer necessary to measure shim thickness to help you decide which shim to use.
Good Luck, Rocket

[Ed VR]

It wasn't me that let the tach drive get loose. I just got it that way.
Thank you very much for your help. If all goes well you'll see me this summer on a Ducati.

-Ed

[BevelHead]