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Ty250 Flywheel Weight Removal


mollygreen
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I have recently removed the flywheel weight from my TY250 Twinshock and went out on it this morning to try it out.

What a difference!

Much more responsive. It pulls right off the bottom of zero revs and I can now ride a section that requires 2nd gear somewhere in the section and ride the whole section in second, without having to think about changing up.

This is where it is most noticeable as it will now pull second instead of dying if I'm not revving it enough, as before.

Also I've had to turn the tickover screw out 1/2 a turn now the engines not dragging the extra weight around.

The weight (and bolts) weighed 750 grams. The flywheel now weighs 1650 grams with it removed.

Phase two could be a few lightening holes carefully placed to reduce the weight further, to say 1500 grams.

If you have it in mind to remove your flywheel weight, I'd say give it a try. I don't think you'll regret it!

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  • 4 weeks later...

I removed the weight from my 250 after work this evening,I only had a quick ride around the yard for 5mins - lots quicker on pickup and also dies back down again nicely rather than rolling on.This will make life easier in the sections as the brakes arent the best,(what make linings do the best job ? ) it also had me thinking that some clever type could come up with a much slimmer flywheel cover to help slimming the motor down.If you look at the existing one its far bigger than it needs to be. There is also about 8-10mm on the end of the crank serving no useful purpose.I've seen the Majesty ones which are smart enough but I've heard they are too strong and break the crankcase rather than fail themselves,they also dont seem any more tucked in than the original.

Maybe I'm being fussy !

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They reckon the stronger outer cases cause you to damage the crankcase if it gets a clout as they are that strong. Magical Mick mentioned it testing a Maj in Classic dirt bike mag. PS dont get drilling lightening holes in the flywheel you are bound to f**k the balance of the motor. I will be removing the weight off my Majesty soon :)

Rode Pitleys a while back and it was just right.

Edited by bo drinker
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Call me old fashioned Gents, but, the must have been a good reason for Mr Maj. to torture the standard Yam crank with hideous fly wheel weights. The Beamish had the same I think? My Maj. for example has a huge non standard fly wheel. I expect the response is not up to Fantic spec at the bottom end but if you get into limited traction situations you can back off and the fly wheel will carry you through. .....I think! Also, please dont drill holes in any proper Majestys, just go on a diet.

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I find it very hard to imagine anyone wanting extra flywheel mass on top of what Yamaha fitted to the TY250B,C,D or E motors. The first model TY250 had a slightly lighter flywheel than the later models and some people might find that model needed a bit more.

Micky are you talking about 250cc Majesty motors or 320cc Majesty motors?

I've tried a range of flywheel weights on my 250cc TY250 motors and have found that with the band removed, it feels great to start with - nice and peppy for jumping obstacles with no runup, but suffers in the traction stakes in slippery going and tends to stall easily amongst dry rocks. With the standard size band fitted, the motor is on the slow side for most riding but very good in slippery stuff. After 3 tries machining a bit off at a time, I've ended up using the band but with about 1/3 of the width of the band machined off (on stock standard D and B model motors both in very good condition).

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I remove all the weight and reposition the footrest lower and about 1 inch further back to increase traction.

Modern tyres make all the difference and the reason weight was added in the past to use momentum on slippy parts.

No need for it today. Take it of and ride it like a modern engine.

Obviously personal choice but easy to try.

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As I said I only had a quick 5 mins around the yard last night,but it felt alot better.Back in 1985 when I started on a 250 Beamish I removed the weight on that and found it alot easier to ride.Its the way that the engine slows quicker that I'm after - not so much the pickup.My footrests are the SM lowered/rearward type and I really like the way it grips and steers.If I could get the brakes to work better then there wouldnt be much else to do.(Just find a decent rider for it)

Micky,mine is not a Majesty,just a standard Ty,But lose weight - are you serious ? It has cost thousands and many years to look this good !

My other complete but non runner 250 I'm thinking about making into a Majesty,by altering the existing frame myself.But I've never ridden one and I'd really like to try one before I go to all that work.

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Some people make it sound like they are using weights that bolt on to the outer face of the flywheel and others like they are referring to a ring shrunk on to the periphery of the flywheel. Did Yamaha use both methods?

I want to add some more flywheel mass to my KT250 as it can have the "tends to stall easily amongst dry rocks" type of episode if I don't pay attention and hit something that momentarily slows the bike when running dead slow. I'm not a "clutcher", when I started riding people typically just let the clutch out and left it alone after that.

The KT flywheel is 142mm/5.6" OD. What size ring is shrunk onto the TY flywheel? If I'm going to add metal, the ring will give the most effect for a given mass compared to the end plate.

cheers,

Michael

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Guest majestyman340
Some people make it sound like they are using weights that bolt on to the outer face of the flywheel and others like they are referring to a ring shrunk on to the periphery of the flywheel. Did Yamaha use both methods?

I want to add some more flywheel mass to my KT250 as it can have the "tends to stall easily amongst dry rocks" type of episode if I don't pay attention and hit something that momentarily slows the bike when running dead slow. I'm not a "clutcher", when I started riding people typically just let the clutch out and left it alone after that.

The KT flywheel is 142mm/5.6" OD. What size ring is shrunk onto the TY flywheel? If I'm going to add metal, the ring will give the most effect for a given mass compared to the end plate.

cheers,

Michael

Not seen inside a KT igntion case since the 1970s, but seem to remember the flywheel is already pretty close to the insides of the case, so may need a new case to allow fitting a heavier weight?

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Some people make it sound like they are using weights that bolt on to the outer face of the flywheel and others like they are referring to a ring shrunk on to the periphery of the flywheel. Did Yamaha use both methods?

The monoshocks used a pressed on ring/band/pipe around outsidecircumference of flywheel. I machined off about 50% of it.

Apparently the twin shocks used a bolt on or additional disc on the end face of the flywheel.

k

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The Ty 250 twinshock uses a bolted ring around the O/D of the flywheel,whereas my old 250 Beamish had a plate bolted to the outer face of the flywheel.Think I may have a go at making a slimline cover for my Ty when I get the rest of it 100%.

BTW does anyone know the correct torque setting for the clutch hub nut on a Ty250 - I have mine apart to dress the clutch basket tangs and I'd like to torque it properly.

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Yes, the KT cover is pretty closely wrapped around the flywheel, and an end weight would need a case spacer (I think I saw those for some of the modern bikes with that kind of accessory weight) or I'll have to make both an adaptor plate and a different cover if I use a ring on the periphery of the flywheel. Either way would be a fun project.

I'll definitely use steel for the weight. The price of brass is pretty staggering by comparison, and it is only a little bit heavier/volume. A 6.25" x 5.6" x 1" wide ring in steel is 3.24 lbf and brass would be 3.51 lbf. That is moderately significant, but the the price difference is majorly significant.

cheers,

Michael

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Yes, the KT cover is pretty closely wrapped around the flywheel, and an end weight would need a case spacer (I think I saw those for some of the modern bikes with that kind of accessory weight) or I'll have to make both an adaptor plate and a different cover if I use a ring on the periphery of the flywheel. Either way would be a fun project.

I'll definitely use steel for the weight. The price of brass is pretty staggering by comparison, and it is only a little bit heavier/volume. A 6.25" x 5.6" x 1" wide ring in steel is 3.24 lbf and brass would be 3.51 lbf. That is moderately significant, but the the price difference is majorly significant.

cheers,

Michael

Not that i'm any kinda expert but are you sure using stell is a good idea? Wouldnt the magnets have a magnetising effect? Would it then affect the ignition? Wasnt this why the manufacturers used non magnetic materials? I mean using Brass was hardly a cost saving measure after all.

Just a thought :)

Edited by Old trials fanatic
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