My trials bike is a 1999 Bultaco 250 2-stroke Graham Jarvis replica. They scrapped the '98 bike and designed this bike from scratch and it is literally just an engine and wheels, the whole thing only weighs 69kg. They did such a good job that neither themselves nor any of the competition could improve on it for 6 years, until Montesa brought out a four-stroke fuel injected bike. 1999 was the only year it was produced under the Bultaco badge, later becomming Sherco.
This bike never ceases to surprise me. The weighting, gearing and power delivery are so perfect , the limiting factor is definitely my skill. Liquid cooled 250cc 2-stroke with high-inertia flywheels for low-rev torque, 18" rear, 21" front, no indicators, no mirrors, no seat!
"Trials bikes are basically choppers" -Renshaw
With the engine done it was time to fluff up the gearbox aka transmission aka seized ball of rust.
Good start, the corrosion turned out to be superficial and the seized turned out to be a screw someone had dropped in it.
Tony Bairstow, above, and a bunch of old bearings, below.
Below are some of the parts that needed to be replaced. Avoiding mumblings about OEM parts, virgin steel and Polish crap I ordered the cheapest repro parts on the net, from Flatland 45 parts depot (USA).
BIG MISTAKE! They were rubbish, all dimensions out by at least a few thousandths.
This repro gear came parkerised. I'm only a beginner at this stuff but am pretty sure that if a part spends itself in a box full of oil then it doesn't need to be parkerised. I'm also pretty sure that parkerising increases all dimensions slightly and it doesn't fit. At all.
Hours were spent filing and emery paper-ing to turn the black bits shiny. Also smoothed off all my fingerprints and was left with approximately 2.5 fingernails. Then I noticed that the dogs weren't even undercut so ended up putting the old one back in.
After much massaging and sanding of washers we got it all together and... the damn sprocket didn't fit. Thin taper on the repro shaft resulted in the sprocket hard up against the case. Beer time.
Tony Bairstow, God of 45s, has been my saviour spending his time to show me the way with all matters engine and gearbox.
The engine actually started with Tony, Renshaw got it off him about 20 years ago in London and then it passed to me last year. Tony had moved to the country, luckily only 10 mins from where I live.
None of us knew what state the engine was in but the first session was to strip it all down and check.
Every part was in perfect condition. It was as though someone had rebuilt it then stored it. All tight and oiled.
Put it back together but still need to sort out electrics. Kinda want to hurt the heads with an angle grinder or a drill or something.
35mm trees from Mullins Chain Drive. Barry, my local engineer, taught me to use his lathe and we shortened and narrowed the stem, made a top-hat shaped sleeve and got it all to work with the old ball bearings. I remember builders on biker build off boasting that they taught themselves everything but having someone show you is way easier.