Swing Arm Issue

[Dean]

Has anyone run into a swing arm failure such as shown in the photos below? The swing arm was removed from my vintage road race Vision.

Background...
Rebuild engine to 644cc for 2018 VRRA season
One race event in Calabogie but had carb jetting issues (stock carb)
Next event at Mosport, used FAST air fuel meter for Friday practice session, one lap, then into paddock to adjust high speed fuel and air jets. Repeated 3 times.
Air Fuel was improving but the bike felt loose and became very crazy to ride.
Came into paddock and the swing arm was obviously damaged.
Replaced swing arm Friday night and back to the track for Saturday.
One practice session then raced for approx. 15 minutes.
Same swing arm damage again.



 

[George R. Young]

Might the universal joint be getting a mite warm?

[Dean]

Thanks for the response...I didn't notice any issues with the U-joint

[fret not]

That looks like it took a 'whompin' or two.

[Rikugun]

That looks like it took a 'whompin' or two.

And how. Have they incorporated jumps into vintage racing!? 

When I got into Visions and first noticed the swingarm design I thought it a bit sketchy. Having said that, I can't remember hearing of any failures.

It looks like the welds pulled away where the bushing is affixed. It doesn't appear the stock bushing weld goes all the way around. Also, is that just a really clean break or did the swingarm tubing seam come apart as well? Maybe have the next swingarm TIG welded to strengthen that area?

[jefferson]

I am betting the tubing spit apart from braking because the bung that the axle threads into pulled out first and the swingarm was trying to move rearward as the bung was no longer attached. I can't for the life of me figure what is going on to break the bung out on 2 different swingarms.

[fret not]

Did ya have any 'high-sides' lately?   

[Ken Williams]

I knew someone back in the day who had a Vision swing arm crack while endurance racing at Road America.  I didn’t see that one to compare the damage to yours. 

[Dean]

The bike did spit me off last year when the connecting rod seized. The bike doesn't appear bent but I was thinking along the same lines.

[fret not]

There is a lot of inertia when a Vision gets moving, and it manifests when the vision comes into contact with another object, like the track.  Graceful in midair, but those brutal sudden stops . . . . . .!

Keep the rubber side down as much as possible.