still trying

Hi, I know this is a bit late but here's what I did to my KT; Designed a completely new frame which required; a new air box a new exhaust, and silencer system and a new tank There's heaps of discution in weld or braze, and a picture or two in projects this way I haven't chopped my original frame, but seriously upped the work required.

Hi guys, thought I'd add to the confusion. Here in NZ we went through a whole lot of drama when they phased out leaded petrol in the '90s. The petrol companies started using tolulene and other not so nice stuff to get the octane rating right. This resulted in a lot of fuel systems (generally older ones) having major issues, dissolving seals, hoses, fires etc. Now we are going through the same with ethanol. The guts of it is that we, like you now have to use the appropriate materials to suit the new fuel, (and tune our engines). Octane Vs compression ratio is all important. More power can be got out of a piston engine using ethanol, but the consumption goes up. If this was not the case then Top fuel dragsters, motorcross and cart racing people wouldn't tune there machines to run on the stuff. So we need to change how we deal with our fuel; Use airtight containers Use fresh fuel (buy it on the way and mix it at the event maybe) At the "end of the day maintenance" might include running the carb dry, and draining the tank if not using for a period. I don't do this and use a 98 octane 10% ethanol fuel in my car and bikes (KT 250, '96 gas gas JT35 contact) and have no problems. My bikes tend to sit for many weeks at a time. I do buy fresh on the way to rides however. I feel for anyone with a fiberglass tank. Made to cope with lead and not ethanol. I cant say I was convinced that a fiberglass tank and riding around rocks seems like a good combination. A bit of history; In the early 1900's the motor industry was looking for a way to get rid of preignition (detonation). GM had a chemist looking at it and he found two solutions, ethanol and a lead compound. GM owned a paint company that made the lead compound to put in paint, so they sold this as the solution to the world. And made a packet. Also poisoned quite a few people.

Hi smokey, I've just hunted out your bike, very cool!! It looks like it will be a lot of fun to ride, love the tank, Did you make it yourself?, And what is it made out of? Your bike gave me a thought, Perhaps we should all start riding pit bike trials.(groan not another class to cater for) I've just been to a brilliant trial, where the organisers set out two trials basically. A normal one with 10 typical graded sections and 5 separate sections with only red and white markers in and out a small dry ditch and in, out and around trees in gentle sloping terrain for beginners and kids to ride. This allows the beginners space to ride without having to worry about dodging the rest of us. The kids sections I could ride in third and without walking. Bang on for those just starting, easy to read and not frightening. Anyway I'll stop dribbling now, Cool bike

Oops had a stuffup with my computer and thought I'd lost the draft and re did it, choose the one you like best, sorry

Hi Smokey, Like you I'm an engineer and decided to have a go at building a bike. As I didn't have access to large amounts of cash or high tech materials and machining systems needed to compete with modern machinery, opted to build a "special" that fits into the Twin shock catagory. as there is less need for these. As I see it Twin shock class bikes should; Have an air cooled motor Have drum breaks Have the rear shocks mounted directly to the frame and swing arm with little or no progression. The limits I set were that the; motor, forks, and breaks had to come from the 70's bike, (in my case a KT250). Also the twin rear shocks had to be directly mounted to the frame and swing arm with no built in progression. That is, that the distance from the swing arm pivot to the center line of the shock doesn't change much, (about 3-4 mm in my case). This keeps the leverage on the shock constant, therefor no progression. I have stuck to period available materials, and not use plastic petrol tank or carbon fiber for airbox, guards etc. For those that buy an existing bike, the amount of knowledge and development available is huge, (including lightweight frames !!). How many people have changed the front forks or carbs to more modern units on their bikes? You will have some advantage with hind sight but the development is all you. You will also get to choose how compromises are sorted (ground clearance Vs C of G, and seat height for example) I am going to have a big task sorting out the rear spring rates and dampening, which will last a couple of seasons probably. Also there is the risk taken with the steering geometry, which could make or break the whole project, (nervous about steep drops in my case. If the C of G is low enough I'll get away with it, maybe). I hope that the locals are fairly open minded and reasonable for you. Good luck and enjoy the build. Cheers Roger

Hi Smokey, I'm in a similar position as you, an engineer wanting to build a special.But without spending a huge amount and not quite having the resources couldn't compete with the ultra modern bikes. I have chosen to build to an older technology class. Hence I have aimed at "Twin Shock" As such I avoided any progression in the mounting of the rear shocks, They are mounted directly from the frame to the swing arm. I used knowledge that has been around before me to design it. Light as possible (using period available materials, NO carbon fiber etc) Skinny as possible As much ground clearance with as low as possible C of G As low a seat height as possible This was a bucket list kind of project for me and as such I have chosen that if there is too much upset when I ride they are quite welcome to not count my score. With building from scratch (80% kept old engine, forks and wheels) you end up with a huge setup / development risk that the factory built bikes don't have. They have had years and hundreds of people developing the setup knowledge (Even building lightweight frames!). Personally I think that if you stick to the guts of the "Twin shock" meaning, (period engine,forks,breaks,& twin non linkage rear shocks) then people would be pretty unfair if they disallow your creation from competing. After all the Big para dine shifts; mono shock linkage systems, disc breaks, water cooling are what made all previous machines obsolete. But as I Don't live in your end of the world, how the locals react, I have no say, I hope you enjoy the build as much as I have. Cheers and good luck .

................. hers some spare ones that I didn't use!

My old JT95 (327cc) used to do this big time. I made a 3 mm head gasket out of ali (bit of a bugger machining the O ring grooves) and this drop in compression worked brilliantly. IT also smoothed it out when accelerating off the bottom. Try two base gaskets, or make a 2mm copper one. Then you wont have to keep on cleaning the head and piston. I also run 98+ octaine which helps.

Hi Gordo, yeah lots of thought..All those years of wondering why builders didn't do it this way or that, and an oppertunity to put my money where my mouth is. The pressure mounts as you get one bit right, to not stuff up the next bit. Makes you think lots and ponder the options before building. You certainly learn heaps.There are some very clued up guys here at trials central that have been great fun talking to about different aspects. I don't have as much spare time as when I started but I'm still making progress (just), and yes I will post results good and bad. I spend a bit of time balancing on it as it has a nice stable feel and is easy to balance on. Can't wait to see how it works dynamically. I suspect it will be finished for new years events, only because of time constraints. Cheers

Hi Dave, Looks fantastic! At this rate you'll make the next twin shock trial, well done.

Thanks Biff

I found it easiest to learn front wheel hopping first after learning balancing while stopped I started in the garage with the bike stopped and one foot down and both breaks on.( Gear leaver side foot on the ground) I did this to get the rhythem of the forks. I pushed down on the forks and pulled back (weight forward on the forks and as soon as compressed pull back at the speed the forks want to go, but continuing until the wheel is off the ground about 200 - 300 mm, then back down and up repeatedly until it becomes a smooth motion). Next try to repeat this while balancing. Concentrate on maintaining the motion and speed as above. If you have to foot on the right then the front wheel needed to land further right, and same if left. So when the forks are compressed if you pull up and to the side the bike "hops that way" aim to land the wheel under your balance point. You will find you use your legs and arms (basically whole body) to do this efficiently. Just balancing and hopping the front wheel is excellent exercise for trials. Try no motor and hopping continuosly for 10 min no stops. Good luck

It sounds like its a timing / weight issue. Timing of applying power (clutch) while weight is in the wrong place Ride it again thinking about what you are doing with the clutch, have you got any power going to the back wheel as you land? Try pausing once the rear wheel has landed before lifting the front (land - recover - take off). This will give you time to get your weight in the right place to lift the front. It also means that you are planning a brief stop (mentally) which should make you less rushed and give time to get timing right. You should have the clutch fully pulled and using the breaks as you land/pause to prevent the front sliding away (no drive, no push) Once you get it with a pause shorten the pause until it becomes one motion.. Good luck, hope this helps

Basic physical properties for a trials bike; Good ground clearance Low seat height low c of g (look for all the heavy stuff mounted as low as possible) Thin as possible (lets you move the bike around without you being forced off balance, it also lets it fit between tight gaps) low foot pegs (helps with balance) low seat height (same reason as thin frame) Steering lock as much as possible, 60+ deg from straight common Light as possible (modern bikes are in the 60 - 70 kg range, old mono bikes around the 80 - 90 kg's, twin shock bikes high 80's - 100 kg's) How much modifying are you prepared to get into? Go for a skinny frame Modify the steering lock to get it tight go for a light 200 - 250 cc motor big sprocket on the rear to go slow shock travel, forks around the 200 - 250 mm and soft Rear shocks around the 200 mark, (note these can be used to raise the ground clearance and steepen the steering angle of frame, which can be useful) This is what I look for anyway. hope this helps