Friday 21 January 2022

The SR500 sidecar - absolutely not modifying a Velorex 562 frame (part 11)

 ... I mean it would be the sensible thing to do to pretty much do nothing at all. Would. Have. Been. On the other hand stock mounts are 29mm tubing and relatively thin-walled too. (We're talking about 2.5mm wall thickness before it got attacked by rust. There's quite a few tales of snapped lower front mounts on Velorex'es actually.)And on the other hand, there was this absolutely gorgeous 30x5mm thick wall seamless tubing sitting on my bench. 

... the sort of rust one finds on a tube that was sealed off properly. Doesn't take much imagination to work out what one of the more exposed tubes might look like on the inside.

Modify the new thick wall tube for clamping ...

 and then weld it in.

And the same on the rear. (If you tell me, starting with an IZH Sputnik sidecar frame would have saved me from a fair bit of work... yes, it's essentially what I copied and yes, it would have been cheaper as well.)

Bit of bracing in the corners and as mounting points for the upper struts.

And with those welded on it was well about time to decide on the geometry of the sidecar, draw it up on the floor and then make the swan necks. Lead was decided to be 265mm and the track width 1080mm.

Strictly speaking, at this point it's a sidecar.

Obviously the rear strut is "a tad" long. Now the simple way would be to just throw it on the bandsaw and weld it back somewhere in the middle. (See the soon to be replaced front strut.) Now there's two problems with that: First you shouldn't load a weld with bending forces or if that's not an option, at least put a reinforcing tube on the inside. In the case of these struts said tube would get into serious conflict with threaded adjuster. There is a right way though. In original form, there's a pin which slides into the tube, so if one has to shorten one of these, start at the base and free the pinned end.

Also due to the beefyness of the pin, cranking the welder up to 11 is an option.

And there you go...

... or do you? I had to make one more set of top hats, so the flange bolts would only be loaded under tension and not on bending. (Same idea as above.)

At this point I realised that my sidecar sits about 40-45mm too high and the sidecar swingarm needs to be modified. With the stock Velorex shock being questionable and unreliable at the best of times, the next step will be to make a new sidecar swingarm, which will then incorporate a regular length SR500 rear shock. This will give me more suspension travel and due to the different shock angle also a stiffer suspension. Oh and those extra 40mm should also allow me to fit the 18inch sidecar wheel within the stock mudguard without trimming off the lip like on the last one.

Sunday 9 January 2022

The SR500 sidecar - finishing the sidecar mounts (part 10)

First things first, last time when I returned the next day after the little Zinc-plating session, I was shocked to find some very rusty parts in my shop.

A quick rubbing with some scotchbrite solved the situation and another go in the bath (much longer this time) made sure it hasn't happened again since then. 

After this shock I started with the first and most simple mount on the bike as far as the clamps are concerned, the rear upper mount. Unlike on my last SR-sidecar I wanted to retain the inner rear mudguard as it keeps a lot more dirt away from the engine than one would think.

And with that out of the way, it was time to turn towards the front lower sidecar mounts. Marked the parts on the lathe and then drilled and milled them. As I had decided to go with 12mm thickness one of the struts was used as my thickness gauge. 

The downside of my beefier front mounts is the fact that I have jack up the engine to get the inner mounts between frame and engine. Once in, everything clears nicely, even though I had to shorten the left-side stud a bit as it was touching the engine, once tightened.

Now the bit between those two clamps was meant to be a very simple case of some 30mm stainless bar that I had over from some other work. Turns out my 10.5mm drill decided to call it a day on the second hole and wallowed said hole out to 11.xx mm. No chance of drilling a half usable M12-thread in there. Lobed the other end of (and got a few new drills the next day) and made two spacers with M12 threads in the middle and grabbed some 20mm stainless bar from the shelf.

With a little recess machined into the back they were a breeze to TIG onto the 20mm bar.

There you go, looks overly complicated, but works just fine - front top mount is more of the same.

Ball-head was straight forward and that knife-head really works nicely, if you put on some fresh inserts...

And then it's spot all 4 mounting points on my SR500.

At this point it could be all so simple: shorten the struts, alter the lower front sidecar mount so it can connect to ball joint and weld on a block for the rear swivel mount. Easy three or four hours of work (it's the small stuff that takes time), put the wheel on the axle and be the coolest kid in the neighborhood.

I swear I had the best intentions to leave the sidecar-chassis alone. Really.