Project Yamaha CS3C Part 7 - Going Cranky!

Scoop and his mates carry out various surgeries to the CS3C’s heart. Nurse, scalpel!

- Steve Cooper

This instalment’s missive is all about the engine and the faults, the issues and the subsequent rebuild.

Those readers who haven’t yet lost the will to live may recall the chaos that was the top-end of the original motor and the spare pair of cylinders. There was a hope that they’d only need a light hone, remember? And then we found out that the wretched things were considerably worn. So worn in fact, that they needed to go out to maximum oversize at 1.00mm.

Well, I’d like to report back to say that everything went according to plan but, of course, anything involving a ‘Scoop Scoot’ generally throws its owner a curve ball.

And some things don’t change: the barrels presented Rob Pemberton of SPA Motorcycles a challenge. They appear to have come from a similarly ill-treated CS3 that, amazingly, has seen even more abuse than mine. Apparently, the suspicion is that the crank that partnered my now re-bored barrels must have been spectacularly worn with con-rods that were almost flapping from side to side. Huge wear to the thrust washers and/or big-ends must have seen pistons floating out sideways. This presented its own unique challenge and meant Rob had to re-bore five-thou off centre. According to the Guru of the Gauges: “Yes, I’ve seen similar before but it’s all in a day’s work for us.” Quite why he tolerates me and my bikes I’ve yet to fully grasp!