4 Stroke Conversion?

[Guest]

Good evening gents

I am just resolving a few minor issue's with my TY250 twin shock that I have been restoring over the past few months and I am in the lucky postion to have a spare bike albiet in bits sitting in the garage.

I have been thinking about what to do with this bike as it needs a complete restoration and instead of restoring or breaking it I would like to do something differant and build something that is suitable for a bit of road work and green laning, so I am considering going along the lines of putting a four stroke engine into a ty250 Frame, Possibly a 400 cc single pherhaps a XT400 engine.

I do seem to recall reading about a French chap who has done something simular but I cannot find the link for his website.

As this is just the planning stage do any of you chaps have any suggestions such as other Modifications that should or could be carried out, My first one is improving the brakes as the standard ones struggle stopping a standard bike the forks are shot on my bike so I might upgrade these as well.

Any suggestions welcome, and I know it would be easier just to buy a differant bike such as a XT400 but its nice to be a bit differant.

Many Thanks

Mark

[feetupfun]

There is no XT400. The bloke in France modified an XT500 to look like a trials bike. An XT500 motor will not come anywhere near fitting in the space of the TY250 motor. Run a tape measure over a few 4 stroke motors (mainly the height of the motor but also the length) and compare them to the TY250 motor you will see what I'm on about.

A TTR125 motor would come close to fitting (with reduced ground clearance) but I suspect you are after something bigger.

Edited September 13, 2009 by feetupfun

[Guest]

thanks for the reply, I have thought about using a small 4 stroke but I am thinking that if I am going to the agro of converting the frame etc I might as well put in something big ish and I would still like plenty of Torque so it really needs to be a thumper.

A few years back I owned a XT400 and I seemed to remeber that the engine was physically smaller than the 500 version so that was my first idea but I would like to avoid doing any major frame mods such as moving the back bone of the frame as I would like to keep the orginal lines of the bike so to speak.

As you correctly say I need to get the tape measure out and work out what will fit but as mentioned I did not know if anyone else had gone down this route to save me some leg work.

Many Thanks

mark

[timbo]

Try one of these; http://www.loeil2fred.com/photo/12658-Moto...e-fleurs-bleues

[feetupfun]

I see the bike you are talking about now. We didn't get that model here but it looks just like the XT350 we did get till about 1984. Yes the XT400 motor is way too tall to fit in the TY250 frame.

[andy m]

Try one of these; http://www.loeil2fred.com/photo/12658-Moto...e-fleurs-bleues

Looks like they got bored with the XT500, that's an XS 650 engine

Jon V8 on here is grafting a Serow engine in to a Ty 175 frame, they are 225cc.

Edited September 14, 2009 by bo drinker

[woody]

Yamaha were working on a 500cc 4 stroke for Mick in late 70s. There's a picture of it in his book with the motor installed. It's big and the frame had a lot of work done to get it in. The pressed tube that extends into the toolbox is missing, the engine is tilted forward and the head sits right up in the angle of the top tube/downtube by the headstock.

[timbo]

This is the site for more info; http://www.frederic-fleury.com/xty/

[jon v8]

If its any help I'll stick a tape across my XT motor and one of my 250 frames.I've never bothered before as the 175 frame was totally stripped before I started.(It was a complete but totally worn out box of bits - the engine was absolutely totalled,so it was an ideal donor frame.) I only bought it originally to stop it from being scrapped,then the XT225 came along as a bad debt so it had to be done.Is the XT400 engine the same as the 4 valve XT350 ? If it is I dont think it would make a very good trials motor,I had one for several years as a green laner.I geared it right down,stripped everything off it for weight etc,but it was really not happy plodding - much better revving above 2-2500 rpm.

I hoped the XT225/TY175 would be ready for the Dartmoor 2 day,but its still far from done.Excellent weekend of fun,met Mick Andrews - he kindly signed the tank on my 250. He made a really good impression at the trial,everyone commented on what a decent bloke he is.

Woody,which book is it you are talking about ? Are there any copies around on Amazon etc ?

[woody]

Woody,which book is it you are talking about ? Are there any copies around on Amazon etc ?

It's called the Mick Andrews Book of Trials and was published in 1976 when Mick was with Yamaha. No idea if it is still available but copies come on ebay every now and again. It appears that Yamaha never finished the 4 stroke project.

[Guest]

Thanks for the advice guys.

I am thinking that the XT400 engine could be too tall, the problem is that they are not that common so getting the measurments is not easy, But I do think they are the same engine as the Xt350 however Jon V8 you do make a good point about the engine in as much that it is not that happy at the lower end of the rev range but if you could measure the engine I can then have a look if it will fit.

Funnily enough I have been considering the Serow engine after Feet up suggested a smaller cc engine, Having riden a friends serow last year I was quite impressed with the power from a small 4 stroke, Problem is that the engines are not that common so if I was to go down this route maybe it would be prudent to buy an old Serow and break it.

Jon have you had to do many frame mods to get the serow to fit?

And thanks Bo that was the website that I have been trying to find! I am thinking that is a very long term project! but would be nice to do if I had enough time on my hands.

I have got a bit of spare time at the moment as I am recovering from a back op and I am working from home so I can pop out in the garage for the odd hour here and there, I totally stripped the frame yesterday but I do want to get my first TY finished before getting stuck into a new project otherwise it will never get done.

Going to have a look for the book as well , Please keep any ideas coming in! as its great to discuss various options before getting started.

[cvgmmartin]

You should consider putting a 500 triumph engine in it, the twin is a much shorter engine than a single so is easier to fit in a two stroke frame. I put one in a Bultaco sherpa and the only frame change was to cut out the bottom tubes and make a alloy sump plate which then bolted onto the front down tube and onto the frame tubes just below the swinging arm pivot. An oil tank was made to fit under the seat where the air filter normally goes. The engine is also easy to tune or detune depending on use. The only problem with this special was that it didn't steer very well, it looked good but it was lousy to ride, not until a made a special frame and was able to play with weight distribution and steering head angles and trail was I able to get it to ride and steer like a trials bike should. I remember seeing in the Motorcycle news many years ago (more than 30 years) a special with a 500 triumph engine in a Yamaha enduro chassis, the perfect green laner.