trapezeartist

What's the theory behind the rear suspension on a trials bike? There has been a trend towards leaning the suspension units forward on twin-shock bikes. This implies a falling rate as the angle between the unit and the swinging arm reduces as bump deflection increases. On the other hand, dual-rate springs imply a rising rate. I find it hard to work out what's going on with monoshocks as the linkage mechanism is partially hidden. It would need careful measurement and drawing to sort that out. But perhaps someone already knows.

BVM seems to be the trader closest to home, so that has to be a possibility. I just had a look at TMXNews: a few interesting adverts but it's often hard to tell where they are. With only a mobile number they might be just around the corner, or in Scotland.

Thanks for all the suggestions, guys.

Where are the places to look with a view to buying a secondhand trials bike, either private or from a dealer? I've found eBay, Gumtree and the advert section of this site of course. I've also found a few other websites that just re-hash adverts from other sources (pretty pointless). Are there any others I should be looking at? What about dealers? I've found a few in the north of England but they're too far away, and anyway I'd rather buy a bike that hasn't spent too much time bouncing off rocks. I heard of BVM but they don't seem to have much on their website apart from new and nearly-new. I also found RCM in Cornwall but they are also a long way away, in the other direction, though it would be a more attractive journey. Any others?

sirdabalot: a man of exquisite taste. (I trust you're a fan of Adge Cutler too.)

Try http://www.gasgasmotos.es/en/manuals.html The manuals I've looked at there have the service intervals near the front and the torque settings near the back.

Far more important than the colour-scheme, I like it for it's design: I like the frame construction, I like the forged swinging arm, I like the offset rear spring/damper (creates a lot of offset loading, but everything is so stiff I'd be confident that it is "good enough" (oni nou )). The real proof would be in the performance though.

That age-old design conundrum: is "good enough" good enough? As a returner to trials I have no direct experience of the GasGas kickstart: someone complained about it not being good enough. I looked at it purely like I would look at any new design and commented on what I see as the potential cons. If the known problems with it don't correspond to my hypothetical criticism of the design, I'm happy to accept it as "good enough".

If you're adequately hydrated, consider the headaches may be due to tension in the back of the neck (you spend a lot of time with your torso leaning forward and you head up). I used to suffer similar. Solution: take a paracetamol before the headache starts.

I quite like it, insofar as it matters at all. Quite an interesting bit of two-colour trickery at the steering head.

I'm not convinced the design is OK. The fine serrations need to be held to very close tolerances, and even then, a steel shaft in an aluminium body! If it has to be steel and aluminium, I would prefer to see a slot and pinch-bolt.

What's the difference between a TXT and a TXT Pro?

When I came to photo 3 I expected to find a micro-model resting on the seat. Now that would be cool

There was one of those (or something very like it) at the last trial I observed on. I was intrigued, but by the time I had packed up my section and got back to the car park it seemed that the bike had gone home. Despite looking like a Honda 50 engine, it seemed to have enough poke for the modest climbs on my section, and it sounded nice in a 4-strokey sort of way.

Although I've done some pretty awful things to iron liners in the past, using emery cloth, I wouldn't do it to nikasil. And I'm not sure green scotchbrite is much better. There is a white scotchbrite which is described as "non-abrasive" but I think that must mean "less abrasive". I've never used it, but I might be tempted to try it on the marks left from a piston seizure.

Very interesting. Thanks.

I'm not sure what a ball hone is. Is it one of those things that looks like a bottle brush with a little knobble of abrasive on the end of each "bristle"? If so I wouldn't use it on a 2 stroke cylinder as the balls will go into the ports and possibly round off the edges.

TYs seem to be the frames people modify the most. I'm still trying to come to grips with all this. Looking at your photo it looks like you have also cut off the rear frame loop and the bit under the engine. Is that right? I worry a bit about removing the rear loop in case it allows the rear suspension pickups to clap hands a bit. (Any comments, anyone?) What was involved under the engine? New, thicker, bashplate? Any other extra brackets?

Obviously the piston has nipped-up at some time. It's worth cleaning up the scoring on the piston with fine emery and see what it's like then. As for the bore, you can still see the honing marks at the bottom below the ports so I would guess the bore is generally good, especially as you can't detect a ridge above the top ring. I would clean up the bore with a soft, fine abrasive and see how it looks then. Not sure exactly what to use as I've never done it on a nikasil bore.

Probably doing about 15,000 rpm, though we didn't have rev counters in those days. I worked out the mean piston speed once and it was crazy high. Added to tiny narrow bridges in the exhaust port which wore quickly, and that was the reason for the frequent rebores.

It was an Upton Manx (using Komet internals) that came unstitched due to the big-end failure. I did subsequently use both Parilla and TKM. They were all ridiculously fragile motors. Thankfully the world has moved on.

If it's any consolation, when I was karting in about 1980, piston rings lasted 1.5 hours, it needed a rebore and piston at 3 hours and a big-end at 6 hours. There were some alloy-caged big-ends that were only good for 1.5 hours but I didn't know that. You can guess how I found out.

Quote from the Amazon page: "Smallest meter available (19 inches x 1 inches x 59 inches)" That might prove quite tricky to fit on a bike!

Great value and quality (I would imagine). Shame about the colour.

Could it be that the engine appears to idle at 1800 rpm because the engine produces a spark every 360deg even though it only needs one every 720deg? I know old Hondas like my CD200 work that way. Perhaps the modern Honda in a Montesa does too.