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Discussion Starter #1 (Edited)
As per the title I'm finally getting around to rebuilding my 900ss from top to bottom.

I had hopped that with only 6,500 miles on the engine since the MCC Illinois built it into a 944 that all I would need to do would be check the valves. Turns out they're fine, but the crankshaft roller bearings are sloppy. The crank is a lightened Falicon and the bearings were replaced at the time of the build. It has been run only on Royal Purple oil since new, What could take out the bearings so quickly on a street ridden bike?

I almost have the cases split, but I've come across some other oddities.

The rotor was missing the key stock and was held on by a single nut with no lock washer as is mentioned in the manual. It was loaded with green Loctite and I had to use a small puller to get it off.

When I removed the flywheel I didn't note the spline location. The manual mentions a dot that lines up with the keyway, but I see only a very faint dot on the flywheel hub and I don't know if it was lined up with the keyway. Is there an easy way to check this with another reference point?

Another anomaly is that the crank/flywheel has only 6 splines. Seems all the 900 crank images I can find on the internet have move small splines. Mine looks like a 906 spline. The PO said there had been a change, but not what it was. Any insight would be helpful.
 

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Yes the early 900 cranks were 6 spline. You will also find you have a shorter crak with early alternator cover. look at pictures of alternator covers and you should see yours is flat where later ones have an additional bump. Early covers are obsolete and scarce so take care of that one. Early cranks did not have a belville washer and just one nut on the crank. There is often no room with the short cover.

I cannot second guess the builder or the motor to know if there was a reason they did not use a keyway on the rotor other to say it does not sound right. So I would look for a reason that they may have done so other than mechanics error, in the end there may be good reason or it was a mistake. Motors that are very built some times have odd things done to them so anything is possible. It makes no sense that you would leave one out to me.

What do you mean by bearings are sloppy? Bearings should be preloaded so are you talking end float (should be no -end float as they are preloaded) or up and down play? Mains that have been setting in old old nasty can soften and flake so you could be flaking a ball or inner race.

Do you have a picture of the flywheel? On an early 6 spline flywheel it should bolt to a steel hub that then mounts the crankshaft. There should be a locating pin on the flywheel to hub and yes the hub should have a dot that lines up with the keyway groove.
 

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Discussion Starter #3
Hi there. I need to go look at that case cover. It has a broken tower where the stator mounts and I bought a spare that I thought was identical. I'll be checking that, thank you!!!

The only defect I see on the slot in the crankshaft for the rotor is that it seems to be worn and rounded a little on the edge that is to the rear of the bike when you are looking at the left side of the engine. Like it must have hammered the key tried to climb it at some point, odd.

I split the cases yesterday and found was that while still assembled the crank had zero axial play. However, it had enough radial play to make a “clunk” sound when moved up and down, at least .010" and likely closer to .020". My first Internet search (before I split the cases) came up with a theory that the synthetic oil had caused the ball bearings to slide in the groove instead of turn and flat spotted them, but that seemed like an old wives tale. The story went that some poor SOB lost his Ducati warrantee for using synthetic oil, but there are way more posts on the Internet about Ducati’s coming off the showroom floor with incorrectly shimmed bearings.

After splitting the case and removing one bearing the balls seem perfectly round and there is no visible scoring in the inner race (I haven’t cut it opened yet). No large bits of metal in the oil either. They seem to have eaten themselves up at a very slow rate. Oddly enough the removed bearing has about the same axial and radial play, but the crank had no end play, WTF? It should have had a bunch of end play as well based on the wear, no? I’m thinking maybe they put too many shims in there. There is one shim that measures .020mm on the RH side and two that combine for .063mm on the LH side, but with the bearings worn out there is no way to know what it was originally, but there is evidence that the bearing had turned a few revolutions inside the steel housing that is pressed into the cases at the factory. The bearings are a snug fit, they can be tapped out easily with a little heat and a hammer, they are not a high pressure press fit, so what would cause them to turn in the casing? I’m thinking excess lateral pressure would do it.

So next I start looking for replacement bearings. Seems Ducati specified one RPH bearing and one NSK (same manufacture) These are angular contact bearings and come in a variety of load angles. Supposedly 18 degrees for Ducati, but the one bearing in this engine that I’ve removed is a KOYO bearing and all indications are that it has a 40 degree load angle.

I pulled out the bills from 1996 and they show a Ducati part number as well as an industry part number and they cross over to RPH and NSK respectively.

In short it looks like the shop supplied cheaper non-spec bearings and/or may have installed them incorrectly. Unfortunately I don’t know which it is, so I can’t risk installing SKF or KOYO bearings. Hell, at this point I’m not even sure I want to trust an RPH bearing if it doesn’t come in a Ducati wrapper LOL! I guess I’ll see what the dealer quotes me for OEM and go from there. No other issues I can see so far. I guess the bushings on either side cover held the crank in place enough to keep it from tearing up. I’d rather not pull the rod caps, but likely should while I’m in there.

More to come...
 

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If the crank keyway groove is egged out that could explin sone but even when we use green loctite as a last resort we still use a keyway with it .... any help is better than none unless they were afraid it would break the rotor. vs just letting it spin on the shaft if it came loose.

I would use oem main bearings from Ducati for the rebuild as any time I have found them from a bearing house the price was no better and the piece of mind having the correct bearing is well worth the difference. I am going to building one of the same as I have one apart right now. The cases should be back in my hands tomorrow. , If I get the time I will check on the main bearings and see what I have.

With new mains you will preload them about .006-.008" I final set them by feel but new bearings will be .001-.002 tighter than used so keep that in mind. Checking/freshening the rod bearings is something that you should do the cost is not so great and the downside of missing something too great.

New mains should be around $200ish a set, better than the 695 main I just changed that was $200 for one side. They call that progress.

I call total BS on the synthetic oil myth. Wrong preload can cause failures as well as flaking due to old dirty oil being left in a motor (acid stew) but then there is always the defective part to worry about.

Did you have a center case gasket made of paper or sealant? no one uses paper and if you change then you need to check/re-shim the gearbox.
 

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Discussion Starter #5
You were right about the LH cover, I bought the wrong one LOL. Anyone need the newer style? It's in good shape, just a little paint missing near the sprocket area. It does need a bearing as well.

My engine did have a case gasket in it and the kit I ordered from Bevel Heaven comes with one. I may use it, not sure yet. A couple more questions:

- If not using the gasket how thick do you assume the case sealant to be when assembled?
- Does Ducati have a radial tolerance for the crankshaft, or just an axial?

I ask the last question as I wonder if simply adding a little more shim would have removed the play from my crank? The LH bearing does have a very slight roughness to it when spun flat, but the RH bearing seems very smooth.
 

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NO measurement on liquid gaskets but it will be thinner than a paper gasket for sure. All shafts get measured after the gearbox is aligned to make sure it shifts properly. Shims are then aded/removed to get the proper clearances. this means after you set the gearbox up you assemble the cases and bolt them down, measure clearances and then pull it apart to shim for size. put it together again and bolt it together for final inspection and then check for operation. If the gearbox is not shimmed correctly you may not have all gears working as the shafts may not align with the drum.

keep in mind an aftermarket paper gasket (Athena in your case) may not be the same thickness as a oem gasket either.

Axial is all that is measured, if you suspect a bent crank measure it now that it is out of the cases. Keep in mind preload will give you radial movement, too much will give more but the side covers help support the crank for this reason as well as the fact once the motor is hot the growth lessens the preload. I have been led to believe this is why you need the preload because if you have too little when the motor expands you will have the crank floating in the cases causing the bearings to take a beating and fail.

This is a case of....
Too much preload costs hp but also will break things.
Too little frees up HP but will break things

A hot motor lessens preload through expansion of the cases.
 

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Discussion Starter #7
Keep in mind preload will give you radial movement, too much will give more
Thank you so much for the insight, but I'm still not understanding something.

If I'm reading this (above) right you're saying that by adding shims to the crank and consequentially preloading the bearings that the radial movement will increase? Would the opposite not be true? For example, as soon as I broke all the case bolts loose both the radial and axial movement of the crank increased and that was just a half turn or less on each bolt, barely enough to get an oil drip to form below the engine cases.

I would have though adding more shims would tighten the crankshaft up in both directions. I'm not saying you're wrong, just that I don't understand it (maybe a typo?)

Thanks again for walking me through this.

PS. Bearings were $250 :(
 

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Axial should increase as you remove preload, you are no longer setting the bearings into the race just like steering head bearings. Tight no play -loose has play.

Radial as you load the shafts on the crankshaft you are pinching the crank in the middle but it is supported only at the pin on one side. The more you pinch the more it bends the crank around the pivot that its the crank pin. Too much preload can cause the ends of the shafts to orbit a small amount, keep in mind as the motor heats up and expands the preload lessens and the orbiting is reduced. Too little preload will allow the bearings to give the crank movement too as the bearings are not holding the crank centered anymore.

Simply check the crank for straightness if you are going to re-use it and then preload it for new bearings and you should be done. If you fear the crank has been damaged this would be a good time to get the crank checked for cracks and the keyway groove fixed.

OR use this opportunity to swap out the crank for a later style that will then use the much more available cover (that you already have). Yes you will need to re-balance for the rods/pistons you are using but it may be a better long term solution unless you need to keep the motor correct for the year (such as in a superlight).
 

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Discussion Starter #9
Thanks for the explanation. I will be using the same crank if it's straight. if the day ever comes that I need to replace it I'll get the newer one.

Spoke to the PO. He says the rotor spun at one point and rather than risk using the key and risking a failure he went with the Loctite. It worked once, so I plan to do it again.

Parts are on the way!
 

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I remember the same thing happening on a 888 race bike and we used the keyway but green loctited it in place and had no problems doing so. If there is no key on there I would think the only risk is that the crank nut may be more prone to loosening so yes on the loctite and you might look at other ways to fix it so that it cannot turn. There should be nothing trying to turn in other than inertia but if the starter clutch is bad at some point the shocks may break it free.

Why not have it repaired while it is out of the cases?
I see no reason you could not cut a second keyway groove other than changing balance some which might be minimal. You might check with some automotive machine shops and see what they can do for you. fixed should be better than hope.
 

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Discussion Starter #11
I forgot to mention that upon further inspection it seems to have spun pretty good and is not as smooth as I would like. The crank is a Falicon unit and replacement would be pricy. I would think a second groove might weaken the end a bit too, no? I'm sure they could build it up and turn it down to like new, but at what cost?

I may live to regret it, but if it held with Loctite for 6,500 miles and needed a puller to come off I'll take the risk to do it a second time, but I continue to appreciate your advice and acknowledge it is the better of two choices.

Now may be a good time to confess that the cam pulley drive shaft is repaired with titanium weld paste. Some crackerjack wrench wedged the key in caddywhompus back in 1992 while trying to tighten aluminum pulleys he'd on it earlier. Not only did he trash the shaft and a pulley, he butchered a second pulley by putting a pipe wrench on it. That was at a Ducati dealership. The repair has held for 24,000 miles.

Has anyone seen aluminum gears for sale for this model? I have two that are close to new that I wouldn't mind using if I could complete the set.
 

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Discussion Starter #12
Look at pictures of alternator covers and you should see yours is flat where later ones have an additional bump. Early covers are obsolete and scarce so take care of that one.
You weren't kidding about the scarcity of these things. Since you posted this I have been looking for a spare religiously as mine has two cracks that have been repaired with JB Weld and up till last month the only one I found for sale was in Australia and the guy was asking somewhere around $390USD plus almost $180 for shipping! The ad was up less than a day before the part was sold. At that point I realized these things were perhaps made of unobtanium, so I grabbed up a 1993 crankshaft to go with the 1993 cover I had mistakenly purchased a few years back just in case the JB Weld didn’t hold.

I’d setup my eBay to notify me anytime a Ducati alternator cover was posted and would contact all the sellers that had parts for 91 & 92 models frequently asking if they had covers. I can’t count how many said yes and then sent photos of the 93 and up covers claiming they were removed from 1992 bikes. I don’t know if they were refit, or if engines had been swapped, but no one seemed to have a 91/92 cover and most sellers didn’t even know there was a difference between an 92 and a 93 cover.

Then last month I received and email from a past eBay source saying that he was parting out two 1992 900’s. I contacted him about the covers and he said one bike didn’t have an engine and the other didn’t have a cover, but he had a friend that “might” have one. A few emails and phone calls followed by photos and a deal was made.

I drove up to the States to pick it up last week half expecting that it would have a crack, or some other defect when I opened the box, but this is what was inside.





I don’t know how many miles were on this bike, but it couldn’t have been very many. One could easily remove the gasket sealant, wipe the oil off and call this thing NOS with some shelf wear, it’s that clean.

So all this said, can anyone tell me what this cover is worth? I’m not looking to sell, just wondering if they are as rare as my experience would indicate and if they truly are worth as much as the one in Australia appeared to have sold for.
 

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That is exactly like mine, I'd better take good care of it then if they are that rare.
 

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I had a 92 for years and had something fail in that side. Cant remember what but it cracked the cover.
I had it repaired and it held but I had also bought a spare one.
I just went to look in the garage but don't know where it is at the moment. but almost remember it being the larger one and not working on the 92.
This was back in the early 2000 too which it was hard to find then.

Not sure what its worth btw but I would imagine if they are that hard to come by its whatever someone will pay.
 

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I would guess they are worth at least what the one went for in Australia, simply because there are no more. There will be some picked up cheaper from people who do not know of the rarity. This is an oem part on Superlights so at least those will be looking to fix rater than part the bikes out. This leaves a relatively small pool of bikes that had that cover and then you need to wait for someone to part one out.

I have one good cover and one repaired cover (not for sale) if it is going on a track bike you simply need to protect it and know you may need to repair instead of replace it later on. Most damage to them comes from either a bad main bearing or more often a bad (loose) chain. I see plenty of them crashed and seldom damaged from a hit.

Buying a later motor and plugging it in is not a bad idea as those covers are much more available for now but that pool of engines is still only 1993-1997 so they too will dry up and cost more. Look at Bevel parts and you get the idea of where the 1990's bikes are heading, as the bikes values rise good parts will be in greater demand and there are examples of this already.
 
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