swingarm bearing upgrade

[Magman]

I need to replace my swingarm shaft and bushings. Actually the shaft and bushing on the right side are failed because they are opposite of the greese sert. Brilliant! I can get a replacement shaft and expensive replacement bushings that will require match reaming if I want to go that route. The reaming is an addtional expense because I dont have a reamer that would ream the 2 bushings in line. This is an expensive repair and a poor design to start with from the factory that will have another short life after repair. Since there is only one grease sert (on my 2 bikes) on the left side, the right bushing will soon starve of grease and turn to crap same as the original failure. I starting looking around and there are kits for modern bikes that have changed design to use low profile roller bearings that may retrofit into the Duc's. These can be purchased for around $50-$60 U.S.A. Has anyone upgraded a Ducati Single swingarm? If so, would you please share what you tried and what level of success you experienced? I am considering a redesign for my bike that would allow replacement back to the factory setup if possible. Anyone interested to kick this around a bit and see what we come up with?

Magman

[LaceyDucati]

Magman

I have replaced the bushes with ball races on both my road and race bikes and several customers race bikes both narrow and widecase. It's a tricky job to machine the bearing housings in line with each other and the spacer/s between the bearings need to be correct to avoid loading the bearings. beyond that it's a spindle and nut for a narrowcase and on a widecase a couple of adapters in the frame.

I've never had a failure in over 20 years of doing this, just no play and an easy replacement should it be necessary. Although I have tried taper rollers and angular thrust bearings most have just been 6202 2RS bearings the same as used in the wheel.

Anyone familiar with small block Guzzi's which are 350 to 750cc will know that is what is used for their swinging arm bearings. They are considerably heavier than a Ducati Single and tend to do higher mileages, without too much of an issue.

It probably won't be a cheap conversion if you are paying someone to do it, but if you have access to machinery and time, it's for peanuts! As this conversion has been used over many years racing on the Isle of man on the mountain circuit, I know it works on all levels!

I do have some sketches which I am prepared to share when I have time. Nothing special, but they would give you the idea.

Best Wishes Nigel

[Magman]

[quote="LaceyDucati"]

..the spacer/s between the bearings need to be correct to avoid loading the bearings.

I have a lathe, precision measuring tools and misc hand tools for metal work.

..I do have some sketches which I am prepared to share when I have time.

Please do, thank you. That would be great. I am curious how you retain the ball bearings. It sounds like the bearings load against the spacer so the spacer needs to be square and the correct fit to the bearing races and all clamped up with the bolt to the correct preload. I could turn a piece of the original shaft to the length needed and use that for a spacer if I understand the application. I am not familiar with the swingarm in the other bike to visualize the bearings but I will look around for those bearings. I am going to sketch up a few ideas and bounce them back also.

best regards
Magman

[Jon Pegler]

For most road going Ducati singles, I usually use the original set up, but fit a grease nipple at each end.
The right hand grease nipple needs to be mounted so that the rear chain doesn't wipe it out.

For a conversion I did fit a widecase 450 with a pair of metalastic bushes, along the lines adopted in a Featherbed framed Norton.
I used two metalastic bushes in the swinging arm, with a tubular spacer between them.
At either end and mounted in the frame were two stainless steel plugs, bored to take a 12mm rod threaded at each end, which passed through the whole lot and bolted up with a nut at each end.
It worked very well, with no sign of sideways movement.

I think I had to thread the two plugs internally, as when it was all bolted up it was difficult to take apart.
When the plugs were threaded internally, I removed them with a slide hammer and the swinging arm dropped out fairly easily.
I also remember having to machine the metalastic bushes to get them square and skim them slightly to be a press fit into the swinging arm.

I'm not sure that it was really any better than a standard arrangement, but it was an interesting idea and it worked.
Also, entirely maintenance free.

Jon

[Jordan]

The rubber bushes are an interesting idea. I have them as standard fitment on my BSA B44VS as well.
Once I tried putting some Silentbloc bushes on an AJS. The available length was limited, so the bushes as fitted were too short. It resulted in the most horrible handling bike.
If you want Featherbed-like handling, make sure the rubber bushes are nice and long.

[amartina75]

I wouldn't say the original design is a poor design. If you want to see a poorly designed swingarm look at old Jap bikes. The Ducati is rigid and actually works when set up right and maintained. Of course a second grease fitting would seem to fix your main complaint, all the Duc swingarms I have are already like that. The Ducati is a 50's race design and supposed to be lightweight and good handling, and it is.

[SP3]

I wouldn't say the original design is a poor design. If you want to see a poorly designed swingarm look at old Jap bikes. The Ducati is rigid and actually works when set up right and maintained. Of course a second grease fitting would seem to fix your main complaint, all the Duc swingarms I have are already like that. The Ducati is a 50's race design and supposed to be lightweight and good handling, and it is.

bingo.

[LaceyDucati]

Firstly, as for the original set up:

Yes if you reposition the grease nipple it will prevent the nipple getting wiped out by the chain. Also if you grease it regularly the bushes should give reasonable service.

In principle the original set up should be adequate for most needs. In practice it is my experience that the two housings that hold the bushes on a narrowcase are far from in line, round or parallel. So much so, some times I am left wondering whether the holes were in fact machined after welding. Therefore pressing bushes into such holes is going to limit the accuracy of the final finished hole. My experience is that the replacement bushes were around 0.3mm (12 thou) undersize and even after reaming or line boring evidence of the original hole could sometimes be seen! I have replaced many bushes and the best thing was to stop when you could turn the spindle, but it was still rubbing. Letting it just bed in the last bit, any slacker and play would soon become apparent. My opinion is that, it just fits where it touches! I've witnessed many a racer trying to get through scrutineering by jamming in side shims attempting and limit movement

On the subject of sideplay, there is no side thrust face in the original design. once the grease is washed out, the side of the swinging arm and the frame are just left to grate together. Nice design feature

It's a cheap period design that is mostly adequate. If it suits leave it, otherwise.........

See below a sketch I did around 20 years ago. The shim between the bearings proved unnecessary and I have subsequently used one bearing each side without issue. The sketch shows outriggers which is how I intended this design to be used. Without the outriggers it would probably be best supported using 4 bearings (2 each side) one either end of the boss, with spacers between them. The centre spacer could be one piece, with relieved faces to ensure the outer race of the bearing did not rub. The centre frame spacer in the sketch is only in 3 parts as with the outriggers in place a one piece spacer could not be removed. Not that you should need to remove it, unless the side faces were to get damaged. Centre spacer was alloy and the others were steel.

Both UK racers Doug Snow and Nigel Palmers Narrowcase race bikes were modified this way.

With time and a bit of ingenuity it can all be done on a lathe. My original set up was all machined on an old lathe in a workshop in my parents back garden. Even the swingarm was clamped to the toolpost to be bored! It all worked perfectly and the set up still exists and the bike is still being used in anger for hillclimbing and sprinting.

Image (2) (1000x727).jpg

Regards Nigel

[Jordan]

Thanks Nigel - interesting mod.

May I ask, how did you get both sides of the swingarm to be in line and in the correct position for machining?

Jordan

[Magman]

I wouldn't say the original design is a poor design. If you want to see a poorly designed swingarm look at old Jap bikes. The Ducati is rigid and actually works when set up right and maintained. Of course a second grease fitting would seem to fix your main complaint, all the Duc swingarms I have are already like that. The Ducati is a 50's race design and supposed to be lightweight and good handling, and it is.

FWIW- Any Motorcycle or Motor vehicle for that matter with a critical rear wheel drive line and suspension system that will commonly fail in 6,000 miles from the factory is a very poor design. These were sold world wide as public transports not just limited production race machines during the 50"s. Please dont get me wrong, I am not here to throw mud but I am still a realist. I love my old Duc's with many innovations in design engineeing but NOT the swingarm bushings. The design with only one greese fitting on one end having to flow grease through the bushing grease channels on both bushings on both ends will flow the grease out the bushing on the near side as the path of least resistence. The amount of weight and volume of grease it would take to flow grease through the far bushing grease journal would be to high a resistence and the grease would mostly flow grease straight out the end of the swingarm in the near side bushing and not lube the far bushing adequately. We will always have an early failure of low mileage and need to replace the bushings. Also, in order for the new bushing(s) to flow grease the new bushing needs to be drilled after installation at the grease fitting. The new bushings need to be in-line honed for proper fit and are highly specialized making them unnecessarily expensive and requiring special tools and expertise. The design should have been such that critical items requiring regular maintenance should be owner friendly with common tools and designed to use inexpensive replacement parts or designed to be very robust with very few lifetime fauilures. This design was out there and failures were common yet the design was not changed for mass production sales. Seriously, not adding an inexpensive yet required grease fitting to a critical drive line component with a know failure history was a poor engineering design decision.

I am soon off on vacation and will need to get back to this when I return with some sketches. thank you for sharing Nigel. I sincerely appreciate your sharing a solution and compassion for excellence.
best regards