Saturday 10 September 2022

The SR500 sidecar - finally gets ready for daily use

Just because the sidecar now "runs", the old girl was pretty far from being actually usable in its intended role. 

The department of exceptionally good looks - totally working in our favour.

Especially for breaking in the new engine a working tachometer would definitely come in handy, so that was one of the first things to be tackled to align the racket the engine makes with some real life rpms.

The next highly important thing is to do some destructive quality control in the form of breaking the rear innertube (which was new). 

With the tube swapped (twice), because the first new innertube suffered from a magically appearing snake-bite, when getting mounted, it was time to turn to another issue. The locks in the fuel cap and the ignition barrel weren't even remotely compatible.

Take the actual locking tabs out.

 And almost magically it's a universal fit lock.

I'll admit I was more than just "a bit anxious", so when the engine had outlasted the last one's 67km a photo had to be taken. 

And then there was the other issue of dialing in the carb - as some may recall, I drilled the airbox-cover to allow proper airflow and let's say, I might have overdone it a bit. What followed were COUNTLESS rideouts with a big car battery in the sidecar, a wideband AFR-sensor in the header and the display on the handlebars. 

And they would reveal a few things, first of all that no matter what I did, my inlet rubber and the TM36 wouldn't get along very well. Right after the installation of the carb, everything was fine and the bike was running plenty rich.

But after a few seconds of running, it would go stupidly lean. Now I always install carbs into slightly greased rubbers. (Vaseline is rather handy to have around the shop.) Apparently it takes about 10 to 15 seconds with an ill-fitting carb to suck away the vaseline and make the carb leak and draw in air.

In parallel to this, the accelerator pump acted, to put it mildly, rather random, so a plug for the actuator was quickly turned on the lathe.

I wasn't aware at the time that the whole situation was inlet-rubber related and thus continued to tape up all the extra holes and the result was... exactly the same. (Aside from mains and needle being slightly better fits now.)

So out came an old friend. A trusty (and super simple) Mikuni VM32 out of my XT500. 

Ever since I owned this carb, the mainjet "quick-access" cap was stuck and as I rejetted that carb A LOT OF TIMES, I decided to chance my luck, heat up the float chamber and then give it my best effort with a 14mm nut.

Ultimately my efforts were rewarded, the mainjet looks big enough to be considered reasonable accomodation for some not so small animals, but to be fair, the wideband doesn't lie.

Tell people you've "done science" without telling them... seriously though, I noted down the changes including the corresponding lambda-values and I am sure to follow up on this to see for example how much a dirty airfilter affects AFR etc.

At this point things were looking pretty good, but there was still a notable rattle. To cut a long story short, it turned out that I was missing a damper disk between the camchain tensioner's plunger and its spring. As I didn't have one handy (obviously, or I would have installed it in the first place), I had to make one myself. 

This worked like a treat, even though admittedly it needed a revision as the damper shown above was a bit too thick on its base and thus limited the max. stroke of the camchain adjuster and the 6mm center hole was dragging on the plunger's rod.

At this point, I was pretty convinced that all was well... until it wasn't. There's a distinct reason, why cheap aftermarket ignition barrels are cheap. Mine decided to shed its M4x12 bolts that hold the actual barrel to the baseplate. This in itself wouldn't have been too bad, but it also meant that it would eventually lose contact and thus cut out. Now imagine this happening in Friday late afternoon city traffic. A set of allen head bolts and generous amounts of loctite made sure that the next time I would wonder how to get the barrel apart. 

If an eye injury hadn't stopped me in my tracks, I am sure there would be a few more tales on adjusting the needle and then subsequently going over the main jet once more and hopefully a tale or two of some nice rideouts with the old girl. But, this will have to wait another week or two.