Tweaking the Jumbo

Following the first couple of trials, the Wye Valley classic trial and the 1st Sammy Miller round, the Vic Ashford Trial , it was time to look at what was working and what isn’t working with the Jumbo and make some alterations if needed.

Following the Wye Valley trial, there were a couple of problems with the bike;
– it was clear that the kickstart shaft was knackered and I must have put the bottom kickstart knuckle back on the shaft about 10 times; so much so, I gave up turning the bike off and left it runnng for most of the three laps.

With Gavin rebuilding the 320TLNW I had sold him a couple of weeks before, he noticed that his kickstart spline was also screwed, so suggested a modification. The problem is that the kickstart shaft is hollow, with the gear selector shaft running inside. Therefore, you cannot overtighten the kickstart bottom knuckle as it pinches the selector shaft and it tends to slip on worn shafts.

Therefore the solution was to put a line of weld on the outer half of the splines on the shaft, so that they lined up with the gap in the bottom knuckle, giving it something to tighten against. Drilling or trying to attach the knuckle to the shaft in someway is a little tricky. The only downside is that having a 2-3mm line of weld on the shaft makes it a little awkward to remove to the clutch cover…

Other encountered problems on the Vic Ashford trial
– decompressor cable broke, so luckily the modified kickstart shaft held up for 28 of the 30 sections.
– chain tensioner spring also broke
– leaking fuel cap
– lack of low down power, especially in first gear.

My soldering skills (or lack of them) was to blame for the cable and the tensioner was a little tired, so simply replaced the spring. Need to make another fuel cap seal, so will carve another one out of an old inner tube.

The power issue was a little puzzling, as the Jumbo has a fearsome reputation, so some further investigation required. One thing to try first, was to repack the exhaust mid box, as when it was looked at originally I took out the packing. In hindsight, this has changed the back pressue characteristics and probably contributed to the missing spurt of power in bottom. More on this after the next trial to see if it has improved the situation.

Vic Ashford Trial: 11 March 2007

1st round of the 2007 Sammy Miller Classic Bike Series. Excellent weather, great trials country and the 5 East South Wales bikes all finished, just.

Only a 2.5 hour drive down from Hereford to Rippon Tor rifle range, to the start of the Vic Ashford Trophy Trial. After the previous Sunday’s torrential weather, the forecast turned out to be correct, with 15 C and nice sunshine. Gavin on the 1980 280TL came too, with the first big outing for the Jumbo.
Team Hungerstone SWM
Burger van at the start took care of breakfast, signed on and then just watched and listened to the pre-65 eligibility banter. Whatever the rules and concerns over trick bikes, they are quality pieces of engineering and it could be argued needed for the difficulty of the ACU Classic Trials. Whatever the bike, its the quality of the rider that counts; I could ride the trickest bike in the world and still come last.

Managed to snatch and earlier start than anticipated so that I could start off with Gavin and the Tredegar Twinshock contigent.
The East South Wales twinshocks at the start
The first two sections were just past the start on the moor and were fairly straightforward, though the second sub had a pool which turned out to be deeper than it looked. I dropped a stupid couple here. Nice steady start for everyone else and plenty of people and bikes around.
Third section saw me try to do it in 4th gear rather than 1st (whoops), so first 5 of the day. The bike then wouldn’t start, so swapped the plug and it fired up. However, my previous soldering fix on the decompressor cable also failed, so it was muscles required all the way round to kick the bike over. Luckily, Gavin’s kickstart shaft modification seemed to have done the trick and it held up for the whole trial.
Alan on the TL250 at Section1
Off to the next group at Ruby Rock’s, nice sections across the rocks and through the streams. A 2 and 2 on the first double sub, whilst Gavin looked like getting a double clean until taking a wide line on the last step and having to pull it over. Kevin also made a good attempt, but went off line in the stream in the second sub and took a flyer off the top of a large rock. Entertaining stuff. Everyone cleaned the next sub, whilst the next had a tight turn and a difficult exit, which Gavin got through for a one. The top sub was again back in the stream; Gavin cleaned and I took a three after getting the line wrong in the stream.
Kevin on the TLR250 at Ruby Rocks
Thr next group had a tricky group over rocks, whilst the final sub before the road saw me missing markers and taking a 5. Also noticed then that chain tensioner spring had dissappeared so got to work with a couple of cable ties blagged from Mark.

Somehow, the chain didn’t fly off on the piece of road work that took us round to the next group (I will get the programme and make a note of the section group names…) Couple of tight sections over rocks, which saw me go 5,0,3, 0 which an interesting step on the bottom section which I just got completely wrong. The third section was probably the trickest of the day, with a tight turn followed by an awkward traverse across some tree routes.

Another group in and around a muddy stream then some road work, past the Hound Tor car park (with a break for drinks, as word got back of queues down at the next group). Sections 23-26 were long, with some tricky turns and then into the a muddy wood, which was probably the hardest group of the day, especially the first with a boggy slot to negiotiate. I’d clean the third sub, but hit the gear selector on a rock, which bump it out of gear and didn’t notice until it was too late.

Final group of the day and the second sub was the trickiest with a deep mud hole, which could be taken on the right, wall of death style. Gavin had a go, but concious of the barbed wire fence slipped off. Got through for a dab by using Jumbo power directly at the muddy groove. Last section was also pretty muddy, but got through for a single dab again.

Both SWMs survived the long run back to the finish intact and completed the trial. Though my riding was pretty diabolical at times, all in all a brilliant event which makes the Sammy Miller series the right level for any riders with a road-registered bike. Ok, there are some very,very good riders, but for the enthusiastic lesser mortal like me, its really what twinshock trials are all about