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Tuesday, November 01, 2005

The SuperCity restoration project

Joe picked up a slightly tired Cagiva Super City 125 for seven hundred quid. It ran OK but lacked power and was generally tired. It looked like it had been kept out in the rain a little too often and desperately needed some TLC

Initially we were simply going to fix what was needed and pretty much leave the bike untouched, but Joe was concerned about a couple of small patches of rust on the frame and wanted to make the bike feel a lot more like new. He also wanted to customise it to his colours as Joe always does. So the decision was made to tear the bike right down, and put it all back together again. Unfortunately I neglected to take photos of it the day it was bought so there are no reference images I’m afraid.

First up, we removed the engine. The bike had seen over 8000 miles, and we had a few issues.It had been restricted all its life and was pretty badly coked up.


we felt we might as well give the top end of the engine an overhaul. We also needed to find out why it lacked so much power (this is the same engine as the might Cagiva mito, after all). We gave it a good clean on the outside before opening it up to prevent any dirt getting into the crank casing. Next up, we removed the head and barrel and inspected it. It wasn’t so bad, although it looked as though there may have been a slight coolant leak and the two halves didn’t mate perfectly.




These engines are unusual in that instead of having a large fibrous gasket that that forms a seal along the entire face, they have instead two rubber rings that seal out the coolant, and the seal is metal against metal. It therefore has to be mirror-flat and perfectly torqued in order to maintain a decent seal.



We grabbed some valve paste and an old mirror and set about gently grinding down both faces, first with the coarse, then with the fine-grain paste, cleaning everything up in between. The result was a gorgeously flush surface that was sure to provide decent compression.





Next, I noticed a nasty ridge in the exhaust port that was sure to make the gas flow turbulent, so I smoothed with out with a small grinding head.


Finally, for Joe’s vanity, I polished up the head and barrel and sprayed them with heatproof paint.



Before taking the engine out, we found that the lack of power was due to the C.T.S. (Cagiva Torque System) not functioning. These problems are electrical 90% of the time, if not more so with an Italian bike, but to be sure the valve was dismantled, polished, greased (for what it’s worth), re-sprayed and remounted. The motion was far smoother and lighter as the entire casing of the valve was previously filled with manky used 2-stroke oil that was less than fun to take apart. It should also be noted for future reference, that the valve casing was stuck fast together and was a sod to get apart. A careful move with a sharp blade brought the two halves apart just enough to be pulled apart.



With all parts cleaned, polished, “flowed” and painted, it was time to put the top end back together. New gaskets were slapped in all round, and sealing paste was used in the valve casing. A new piston and ring set was inserted and the whole lot torqued up and put back together.

Finally, there had been an issue with the starter motor not working properly (as in hardly ever turning) so I took it out, polished the commutator, checked the brushes and connections, gave it a cleanup and put it back in. Worryingly, the inertia one-way system that would connect the starter motor to the flywheel had locked into place, so the starter motor must have been spinning when the engine was running which is less than ideal for both power and longevity of the motor. This was disassembled, cleaned up and was put back in smoother than a baby’s butt.



Since the engine was otherwise OK, this was sufficient at this stage.

Onto the frame. The bodywork, electrics, suspension... everything... was removed from the bike and given a once-over. The frame was sent off to be professionally



sand-blasted which took an inordinate amount of time since it was done through a ate of a mate of a mate, etc and was returned to us with a decent powder basecoat on it. All we had to do was spray it.

Three cans on this delicious blue and a couple of cans of stinky lacquer got the frame looking pretty good. I’m not sure what Joe’s final plan is with the colour scheme, but I trust he has it sorted in his mind. A few evenings’ worth of painting and the frame was looking sweet. Onto the tricky part.



Back at the ‘workshop’ we set the frame on a makeshift bench and started rebuilding the bike. The workshop manual we found on the internet was as useful as a chocolate teapot, but at least the useless, poorly translated, confusing drivel it contained was available in three languages. Nevertheless, with patience, time and a hammer we managed to get pretty much everything back in there.



It was found that a dodgy connection in the solenoid was what caused the malfunctioning starter motor, and again I believe it was another electrical issue on the CTS servo that was preventing that from working.



I had polished every connector and switch within the relevant circuits in order to get things going. A multimeter is invaluable for this.

So with the bare frame fitted with all the essentials, it was time for the big test. First turn of the key and all appeared to be working. The CTS servo buzzed into life and reset itself. Miraclously, every single electrical component worked perfectly. We filled the bike with all relevant fluids and manually turned the engine over a little to get things in place (a word of advice: when remounting a barrel, line it with 2T oil so there is never a direct metal-on metal moment when you first start it).





We wheeled the supercity outside, and on the first blip of the starter motor, she purred into life, well, not exactly purred, but as smoothly as a single cylinder two-stroke can!




Of course, it needed running in, but right away a lot of extra power could be felt from the engine. The only worry now is whether the big-end bearing will hold out since these engines are renowned for coming to a crunchy, metal-grinding end prematurely.



Here's a quick video of one of the early runs of the bike after it has been run in a little. Notice how sharply it starts and idles. Naturally I was testing the steering and suspension, hence the somewhat erratic riding style. Please excuse my random dancing whilst putting my gloves on...