ty 250 improvements

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ty 250 improvements

Postby yamaha man » Mon Aug 27, 2012 11:18 pm

Hi I have just purchased a 1984 ty250 trials bike as a project then to enter in clubman.

I am looking to do some improvements and was wondering about what sort of improvements are doable to improve the bike.

I have heard about moving foot pegs, increasing rear shock length, some throttle mods to change it to a 1/4 throttle along with flywheel mods and big boring with a dt piston.

Are these mods good or bad and what are the measurements if they work well.

Also any other modifications you can think of would be appreciated.

thanks :D
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Re: ty 250 improvements

Postby FM350 » Tue Aug 28, 2012 7:51 am

Lowering the rests is a good idea, as is a 28mm OKO or Keihin carb. Best piston to use is Wiseco intended for the Yamaha Tri-Z 3 wheeler. Stock exhaust is very poor, but its not that difficult to modify to work much better, and use a modified MX back box.
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Re: ty 250 improvements

Postby yamaha man » Tue Aug 28, 2012 7:41 pm

Cool thanks for those ideas.

Is there any other mods anyone can think of. Especially in the handling department I need all the help I can get.

How would I set the forks and rear shock up as i am unsure i am 6'1 and 65kg

Thanks
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Re: ty 250 improvements

Postby yamaha man » Tue Aug 28, 2012 8:21 pm

Does the tri z piston fit straight in or do parts need to be modified. And does it give any performance boosts.

Also what jetting should be run in those carbies.

Thanks
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Re: ty 250 improvements

Postby FM350 » Tue Aug 28, 2012 9:11 pm

You will need to modify the Tri-Z piston slightly to fit. Steering angle steeper by 2.5 degrees will improve handling, and rebuilding the rear shock will make for much better suspension performance.
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Re: ty 250 improvements

Postby David Lahey » Tue Aug 28, 2012 9:13 pm

FM350 wrote:You will need to modify the Tri-Z piston slightly to fit. Steering angle steeper by 2.5 degrees will improve handling, and rebuilding the rear shock will make for much better suspension performance.

What if the steering geometry has been altered already by a previous owner?

I suggest that yamaha man posts some relevant photos in case the bike has already had (very common) mods done to it
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Re: ty 250 improvements

Postby yamaha man » Tue Aug 28, 2012 9:42 pm

What sort of modifications need to be done to the piston?

Will this give more power?

The bike is completely stock at the moment.

How difficult is changing the steering angle?

Has anyone heard about shaving weight off the flywheel
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Re: ty 250 improvements

Postby David Lahey » Tue Aug 28, 2012 9:48 pm

yamaha man wrote:What sort of modifications need to be done to the piston? I haven't done it myself, but friends have told me the skirt interferes with something has to be trimmed shorter to miss

Will this give more power? if it is a bigger diameter and is done right, probably yes

The bike is completely stock at the moment.

How difficult is changing the steering angle? by lengthening the shock, or modifying the linkage where the bottom of the shock mounts to it, or doing a frame chop

Has anyone heard about shaving weight off the flywheel - yes it commonly done to that motor so it picks up revs quicker. The steel band on the outside of the flywheel cup is machined smaller or removed, depending on how radical a change you want to make
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Re: ty 250 improvements

Postby yamaha man » Tue Aug 28, 2012 9:52 pm

How do u modify the length of the rear shock and whats the measurements?

Is the flywheel mods worth doing and if so how much should be taken off.
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Re: ty 250 improvements

Postby David Lahey » Tue Aug 28, 2012 10:01 pm

yamaha man wrote:How do u modify the length of the rear shock and whats the measurements? There is a diagram somewhere on the web that shows the suggested mod to the lower shock mount on the linkage. If you want a longer shock, you could find one the right length from for a different bike, or get the shock modified by a shock specialist. To work out how much longer, you could make an adjustable dummy piece to replace the shock and try different lengths until you achieve the length that will alter the steering angle to what you want. The most common mod in the 80s was to modify the bottom shock mount to lift the bike, as previously mentioned. Nowadays with a plethora of shocks available, and lots of people who are capable of modifying shocks, there are more options available.

Is the flywheel mods worth doing and if so how much should be taken off.This is entirely personal taste, and will depend on what other mods you make, so there is no single correct answer. If it was me I would not touch the flywheel till you are finished fiddling with the rest of the motor
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Re: ty 250 improvements

Postby yamaha man » Tue Aug 28, 2012 10:03 pm

Thanks for that.

Can you think of any other mods that could be done?

What could be done to shed some weight from the bike?
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Re: ty 250 improvements

Postby FM350 » Wed Aug 29, 2012 12:41 am

The purpose of steepening the steering angle, is to reduce the distance from the front wheel spindle to the crankshaft centre line, thereby altering the front/rear weight distribution putting more weight on the front. Fitting longer rear shocks wont help with this, and in some cases longer shocks will mean less wheel grip, as this alters the rear suspension squat geometry.

Other than the obvious modifications to the stock chassis on the TY, you need to look very carefully at the intake and exhaust systems, and ideally fit modern 38mm forks which will work better than OE 36mm ones, and mean you will no longer suffer from the stock tiller type top yoke. Its also possible to fit the rear shock and linkage system from a newer different make bike, which will mean improved rear suspension, which wont cost that much to do if you can find good used parts.
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Re: ty 250 improvements

Postby Jon V8 » Wed Aug 29, 2012 5:18 am

I can see the point of changing footrest position and fitting a different carb,(Its probably well worn) etc to a Yam mono,but back when they were new the whole spectrum of riders had a great deal of success,(And fun) on these bikes in standard or slightly modified state.Unless you are at a high level of competition the bike will be more capable than you.You just need to remember its not a 2012 Gas Gas.... (Or buy a 2012 Gasser if thats what you want the Yam to be)
One thing that hasnt been mentioned is changing the front brake cable for a full length outer type - everyone did this back in the day.I also wouldnt recommend removing flywheel weight unless you are a very good rider,stalling in a section gives a 5,slipping the clutch if you have to is no crime for a quick get go, and loses no marks.
I'd get it up together and ride it - they are very tough bikes and hard to wear out.The one I had in 1988 was an 85 TYR,well worn when I bought it and I treated it very badly, but it never let me down and was easier to ride and gave me more success than the Fantic 241 it replaced and the Honda RTL that followed it.Enjoy !
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Re: ty 250 improvements

Postby Guy53 » Wed Aug 29, 2012 7:47 am

Jon, at the time was the footrest mod ( lowered ) done to your bike?
I spoke to Mick Andrews this weeckend and the first thing he told me was " the pegs are too high " , but appart from that he told me to check the exhaust and clean the carb, for the rest I have to agree with you. When I talk about the piston he simply said the a piston with the 2 ports hole is less efficient than a piston with a cressent shape skirt ( as discussed in another thread ) but would wear out quickly.
Guy
PS Jon , have you finish that TS TY and if yes what are your comments.
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Re: ty 250 improvements

Postby FM350 » Wed Aug 29, 2012 8:29 am

Things have moved on a great deal since the 80's, and the main reason for altering an old style bike to have more weight on the front is to provide more front end grip (and much improved steering), and this is now feasible due to modern rear tyres which grip far better than those available back in the 80's.

The difference between old style bikes manufactured when low grip tyres were all that were available, and current machinery is shown here:
http://www.wmta.us/bikes.html

All current bikes have weight bias toward the front end, whereas old type machines were 45/55 rear bias. Try riding a modern bike then get on something like an old TY twinshock, and you will immediately notice how much better the modern bike steers and handles.

Unless you are someone who wants to use low grip rear tyres, altering the chopper steering angle of any older bike is the going to make a great deal of difference, and will mean bikes are far more competitive and more fun to ride.
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Re: ty 250 improvements

Postby Guy53 » Wed Aug 29, 2012 10:27 am

Good lord.
I do not want to start a war but for the second time this friday I attended a class on how to ride a TS and the first point was the riding position to make sure NOT to load the fornt wheel. I certanely won't go to a trial with section made by you FM.
Guy
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Re: ty 250 improvements

Postby David Lahey » Wed Aug 29, 2012 11:21 am

I just did some calcs using that table that FM350 provided a link for. I'm guessing that FM350 is looking at the unladen weight balance in that table for his theory about front end loading but bikes are not able to ride themselves so I worked out the load on the front wheel with a 180 pound rider aboard for the 2003 GasGas, TY250 mono and TY250 twinshock, using moments about the rear axle for bike weight and rider weight, assuming all the riders weight is applied to the footpegs (just like we are taught to ride).
Gas Gas 0.513x150+180x17/53=134 pounds
TY250 mono 0.468x184+180x14.25/52.25=135 pounds
TY250 TS 0.45x201+180x15.5/52.5=143 pounds
So the oldest design has the most weight on the front end, and the TY250 mono has slightly more than the 2003 Gas Gas
Maybe a different explanation might be required for why modern bikes are easier to ride (rather than front wheel loading).
I think the main contributing factors are improved mass centralisation and reduced weight.
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Re: ty 250 improvements

Postby FM350 » Wed Aug 29, 2012 6:07 pm

David Lahey wrote:I just did some calcs using that table that FM350 provided a link for. I'm guessing that FM350 is looking at the unladen weight balance in that table for his theory about front end loading but bikes are not able to ride themselves so I worked out the load on the front wheel with a 180 pound rider aboard for the 2003 GasGas, TY250 mono and TY250 twinshock, using moments about the rear axle for bike weight and rider weight, assuming all the riders weight is applied to the footpegs (just like we are taught to ride).
Gas Gas 0.513x150+180x17/53=134 pounds
TY250 mono 0.468x184+180x14.25/52.25=135 pounds
TY250 TS 0.45x201+180x15.5/52.5=143 pounds
So the oldest design has the most weight on the front end, and the TY250 mono has slightly more than the 2003 Gas Gas
Maybe a different explanation might be required for why modern bikes are easier to ride (rather than front wheel loading).
I think the main contributing factors are improved mass centralisation and reduced weight.



I guess you have never tried altering the steering angle on an older bike? The vast improvements to be found here come from increasing front wheel grip, by moving the front wheel spindle closer to the crank centre line. As motorcycle tyres have improved over the years, steering angles have gradually become steeper, mainly in order to increase front end traction and improve steering. Some very interesting information on steering geometry can be found in Tony Foales excellent book covering motorcycle chassis design.
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Re: ty 250 improvements

Postby FM350 » Wed Aug 29, 2012 6:14 pm

Guy53 wrote:Good lord.
I do not want to start a war but for the second time this friday I attended a class on how to ride a TS and the first point was the riding position to make sure NOT to load the fornt wheel. I certanely won't go to a trial with section made by you FM.
Guy



Try riding a tight and very slippery turn with all your weight over the back end of the bike (as you have been taught) and then give it a go with weight over the front to provide more traction.
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Re: ty 250 improvements

Postby David Lahey » Wed Aug 29, 2012 7:19 pm

FM350, have you ever ridden a trials bike in a trials section?
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