Is the swing arm drillable?

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750 Commando......new swing arm spindle and bushes. Though on assembly the spindle appeared to be snug in the frame with the rear wheel in place I could spot some movement. Would it be reasonable to drill and tap for 1/4 x 28 through the cradle cross tube and spindle? That should hold everything snug. I know there is a kit with clamps available but why won't my idea work and it won't be so visible? Unless the spindle is some hardened material.
 
As Baldy said, plus the tube is too thin for tapping, hence the need for Keigler clamps.
 
I did it a few times, but it is not easy.
( drill and tap the spindle, not the cradle tube..)
The spindle is hardened, but can still be drilled.
I found that not all spindles have the same hardness.
If you are 'lucky' yours is on the soft side.
Tapping is the hard part: It is very easy to break a tap when tapping in a tube.
Best grind flat spots first.
IMO, it is a neater and more elegant solution than the crude and heavy Kegler clamps.
Never liked them..
 
I discovered the "problem" after everything was installed. I could use 5/16, the drill and tap would be stronger for the process. I could also use a pair of U-drive rivets but they would make removal a real bear.
 
There are 2 decent fixes that I'm aware of for the sloppy swingarm tube. The kegler clamps are one, and I've seen guys drill the tube and weld a pair of threaded nuts over the holes to the outside of the tube so they can apply pressure to the spindle inside the tube with a pair of bolts.

I wouldn't do what you propose. How do you bolt the threaded spindle to the tube? Does your bolt rest on a pillow block that is scribed to the swingarm tube? or just hit the high spots on the tube?..

I made my kegler clamps, like nipper suggested. I think the parts cost $34. at mcmaster-carr. It fixed a lifelong problem my bike had. It's the best money I ever spent on that bike, meaning it changed it from shitty, weird, snake handling to solid, predictable, and confidence inspiring.
 
Drill, tap, now use those tapped holes to locate thick nuts that you weld to the tube. Your tapped hole is strong enough to clamp each nut to the tube for welding. Now you have the tapped threads of the tube and the threads of the new nut for spindle clamping force
 
I drilled two holes in the tube and welded nuts over the hole, as described above. still ok after many years of service. I had not heard of Heinz Kegler at that time, but I think I did that mod before he was even born.
 
I drilled two holes in the tube and welded nuts over the hole, as described above. still ok after many years of service. I had not heard of Heinz Kegler at that time, but I think I did that mod before he was even born.

Yeah, apparently you don't know how old Heinz was.
 
The 'welded nut' solution is poor engineering.
What it basically does is pushing the cradle tube and spindle apart, deforming the cradle tube.
A bolt is intended to clamp parts together through stretch, not compression.
If too long, it can come loose, so you need another lock nut.
Ugly..
Kegler clamps work on the same principle, but are much stronger.
( still don't like them..)
 
Buy a new spindle - it will have two flats milled on it. Measure the distance to these flats from the the center lock bolt hole then locate the same on the cradle tube . Drill and tap for cap screws - place two nuts on the cap screws, run screws into cross tube a little and then run nuts down finger tight and TACK ONLY ! Remove screws and weld all around. When cooled chase all with tap.
Is the swing arm drillable?
 
The 'welded nut' solution is poor engineering.
What it basically does is pushing the cradle tube and spindle apart, deforming the cradle tube.
A bolt is intended to clamp parts together through stretch, not compression.
If too long, it can come loose, so you need another lock nut.
Ugly..
Kegler clamps work on the same principle, but are much stronger.
( still don't like them..)

The welded nut application focuses the pressure on the large surface area of the threads of the bolt and the nut as it drives the spindle into the concavity of the tube... Where as your solution places a huge amount of force on the intersection of the flat head of a bolt and the convex tube which the bolt is fastened against. How is that better? Do you have a pillow block of some kind scribed in place to support the convex tube on one side and the flat head of the bolt on the other???
 
The only loads that the nuts/ threads take up is a minimal amount of play due to wear . A new spindle and bushes will assure the minimum amount of play .
 
I drilled two holes in the tube and welded nuts over the hole, as described above. still ok after many years of service. I had not heard of Heinz Kegler at that time, but I think I did that mod before he was even born.

Me too. I've used that solution on several cradles, and it does remove the slop. Maybe not perfect in theory, but it does work. It was a pretty common solution among Commando racers back in the '70s and '80s.

Ken
 
..Do you have a pillow block of some kind scribed in place to support the convex tube on one side and the flat head of the bolt on the other???

I make a flat spot, just like the factory did on the top bolt.
3 bolts in different planes instead of a single bolt.
Technically this is the best solution.
If you can't do it, Kegler is second best.
Welding nuts comes third..
 
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I drilled two holes in the tube and welded nuts over the hole

+1 no contest
Welded nuts. 1/4-28
Bolts push forward in same direction as thrust from rear wheel. What is under compression stays under compression.
Pennies to do and repetition not required if you choose to put a new pin.
Kleiger clamps OK if they were free...and still have to drill cradle tube...and drill/tap the clamps

The threaded swing arm pin method has the 1/4 bolt asking to pull the full thrust of the drive train into the rear of the tube which is against the drive thrust...
Requires another big drill/tap job if you decide to refresh.
 
the different plane of the third bolt is key to locking the spindle. I have that same third bolt along with the kegler clamps... I think that third bolt in the perpendicular plane from the other 2 is the best design.... obviously you do too.

A pair of flat spots weakens the tube. I think the welded nuts with the third bolt is better IMO...
 
+1 no contest
Welded nuts. 1/4-28
Bolts push forward in same direction as thrust from rear wheel. What is under compression stays under compression.
Pennies to do and repetition not required if you choose to put a new pin.
Kleiger clamps OK if they were free...and still have to drill cradle tube...and drill/tap the clamps

The threaded swing arm pin method has the 1/4 bolt asking to pull the full thrust of the drive train into the rear of the tube which is against the drive thrust...
Requires another big drill/tap job if you decide to refresh.
May be true if you wait till your cradle tube is completely wallowed out.
Knowing a weak point, I prefer to do something about it before it shows.
Your point about replacement spindle sticks.

Edit:
not too long ago, you made a case about swingarms thrusting backwards under rider +passenger weight with enough force to collapse the isos..
 
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Personally I don't like the look of the clamps or the nuts welded on the back
I converted mine to MK3 cotter pins years ago
I made a spigoted bolt fitted with an oil line to replace the 1/4" locating bolt
And I have a remote master cylinder resvoir under the seat to keep it topped up with oil
 
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