TY250A Flywheel question...

[johnnyjazz]

Hello friends,

Having read on here about the modifications people do to the weight of the flywheel to affect performance, could someone comment if my flywheel has been adjusted or if this is standard? it appears to have some holes drilled in it and doesn't look exactly like the pic in the parts manual.  i know the previous owner was serious enough to swap the front 14 tooth sprocket to a 12 so I'm curious as to whether the flywheel was modified also or is standard.

And would someone be kind enough to briefly recap the difference between a heavier or lighter flywheel and the effect it has on the bikes performance?  (I'm still a little unsure)

with many thanks in advance and very best wishes from NYC, Johnny

Edited June 13, 2020 by johnnyjazz

[feetupfun]

The holes drilled in it are to balance it and were put there by the manufacturer.

The steel ring/band on the outside of the "cup" of the flywheel does look to have been machined slightly narrower but it is hard to tell for sure with your photo.

Trials two strokes generally have more flywheel effect built into the crankshaft than trail bikes and MX bikes. In the case of the TY250 motor the additional flywheel mass compared to the trailbike motor that the TY motor is based on is in the form of that steel ring fitted to the flywheel cup. The next and subsequent models of the TY250 twinshock have a bigger steel band there than the A model.

Trials two strokes benefit from the additional flywheel effect because it smooths out the response of the motor at low RPM to changes in throttle input. This smoothness is important when riding trials sections to help with controlling the bike. The ideal amount of flywheel effect depends on the skill level and personal taste and riding style of the rider. The B and later model TY250 motors have a very strong flywheel effect which helped them perform well in the 1970s but since then the performance of tyres and the way we ride trials has changed so much that reducing the flywheel effect on those models is nowadays a popular modification.

Back when the A model TY250 came out it was perceived as having a motor that was a bit too responsive which is why the steel band on the flywheel was made bigger. Nowadays the A model flywheel effect is seen as close to the ideal.

When riding a TY250 on trails and roads, the additional flywheel effect of the TY compared with a similar motor in a trailbike with less flywheel effect is of no practical benefit.

[johnnyjazz]

Thanks David, really appreciate your succinct and as always incredibly knowledgeable advice!   not that i have any intention of messing with it, but glad to know it's as it should be.  Methinks i just got a wee bit confused looking at the parts pic where i couldn't see those holes that were drilled, and it seemed that the nuts holding the steel band on look recessed in the parts pic whereas on my mike they seem to protrude from the band hence making me wonder if something had been removed.  i was researching the threads on here about TY flywheels and they spoke about removing a steel band so good to know what that actually means now! 

on an aside, i see a lot of people talking about the modification of electronic ignitions... am I correct in thinking that the general consensus is that the TY250A isn't a bike that benefits greatly from this and the original ignition system is perfect (esp. if road legal with lights etc)?  Not that i am seeking to perform this upgrade as my bike runs great, more just curious as to whether it is beneficial from a performance perspective.  I'm also presuming the more upgrades one makes like that it lessens the value of the bike from an 'original' standpoint? 

many thanks always...i continue to learn so much! very best from NYC and hope all is well down there in the Antipodes  

Edited June 14, 2020 by johnnyjazz

[feetupfun]

Those drawings in parts books often contain things that are misleading. I've seen a drawing in a parts book for the internals of the forks of one bike (maybe a TY) and they have drawn the springs unrealistically which can cause confusion.

Yes there is a performance advantage if you fit an ignition that changes the timing to suit the engine RPM compared with the standard TY ignition that has fixed spark timing. A fixed spark timing is only perfect at one particular RPM and choosing what timing you run it at is a compromise for the rest of the RPM range. In the case of your bike the advantages would include less tendency to kick back when starting and more power in the mid to high RPM range. My seat-of-the-pants estimate for the trials bikes I've fitted them to would be about an extra 10-20 % power available in the mid to high RPM ranges.

There are probably modern aftermarket ignition systems that also have stator coils for lighting.

[Tillerman6]

Feetupfun-  Just looking at your advice about the flywheel weight band- do you know if it is removable and replaceable?  I want to try trail riding with the TY 250 A and I'm looking for a little more performance.  The heavier flywheel seems to make the motor very slow to rev up and if you are trail riding  (not trials riding) and come around a corner and laying across the trail is a log- it takes too long to rev the motor up for lifting the front wheel.  I'm fairly certain that my flywheel is stock and un- modified- it has about 6 bolts around the circumference that seem to be holding on a metal band- I am assuming that this is the extra weight that can be removed?  What if you simply remove the band entirely for riding single track in the woods?

 

[feetupfun]

1 hour ago, Tillerman6 said:

Feetupfun-  Just looking at your advice about the flywheel weight band- do you know if it is removable and replaceable?  I want to try trail riding with the TY 250 A and I'm looking for a little more performance.  The heavier flywheel seems to make the motor very slow to rev up and if you are trail riding  (not trials riding) and come around a corner and laying across the trail is a log- it takes too long to rev the motor up for lifting the front wheel.  I'm fairly certain that my flywheel is stock and un- modified- it has about 6 bolts around the circumference that seem to be holding on a metal band- I am assuming that this is the extra weight that can be removed?  What if you simply remove the band entirely for riding single track in the woods?

 

That steel band is a tight fit on there. Yes it can be taken off and put back on but one would need to take great care in the process to avoid damaging the magnets or the flywheel cup. Using a purpose-designed flywheel holder and pushing/pulling tool would remove most of the risk. I was so cautious when I removed one of them I cut it through with a hacksaw to release it and minimise the risk of damaging the flywheel. I lend that flywheel to people who are thinking about taking their weight band off so they can try their bike that way first. None of them have removed their own band after trying that flywheel out first, but some have lightened their BCDE models weight band. Note that the A model already has a light weight band, much lighter than the BCDE models.

In my experience, trail riding an A model is brilliant fun and you can ride the things very fast in single track conditions even with the standard 16 HP engine with standard flywheel, due to their broad power, light weight and excellent handling.

95% of riding over expected logs and unexpected logs is rider weight transfer. The trick with going fast with one of these bikes is to stay on the pegs and stay in one gear and use the broad power. Low gearing gets 3rd 4th and 5th gears close together and these are the gears you use trail riding. Road gearing makes for big gaps between those gears.

[Tillerman6]

6 hours ago, feetupfun said:

That steel band is a tight fit on there. Yes it can be taken off and put back on but one would need to take great care in the process to avoid damaging the magnets or the flywheel cup. Using a purpose-designed flywheel holder and pushing/pulling tool would remove most of the risk. I was so cautious when I removed one of them I cut it through with a hacksaw to release it and minimise the risk of damaging the flywheel. I lend that flywheel to people who are thinking about taking their weight band off so they can try their bike that way first. None of them have removed their own band after trying that flywheel out first, but some have lightened their BCDE models weight band. Note that the A model already has a light weight band, much lighter than the BCDE models.

In my experience, trail riding an A model is brilliant fun and you can ride the things very fast in single track conditions even with the standard 16 HP engine with standard flywheel, due to their broad power, light weight and excellent handling.

95% of riding over expected logs and unexpected logs is rider weight transfer. The trick with going fast with one of these bikes is to stay on the pegs and stay in one gear and use the broad power. Low gearing gets 3rd 4th and 5th gears close together and these are the gears you use trail riding. Road gearing makes for big gaps between those gears.

Feetup fun- That's good to know information!  I was all ready to remove that band and give it a whirl, but sounds like it's not that good of an idea after all.  You probably saved me a lot of heartache!  But question- I had been running a 12-53 and first gear speed is "too low" to be of much use for trail riding- it takes valuable time to shift thru first, second and you are not moving fast enough to give the wheels any "gyro effect" so there is not much stability until you are moving at about a fast walk at least.  So first gear is almost useless.  So I put on a 13 tooth front sprocket and that is more "user friendly" my shifting is a bit less often and I'm not needing to change gears as much while reaching a stable speed.  Seems like about 10- 15mph is a good starting point.  My new boots are stiff enough that you need a definite effort to shift, and that gets old pretty fast on the trail.  I'm almost 72 now and that has a lot to do with all this, but do you think a 14-53 is better all around or a 13-53 for single track?  Some of the trails here are rocky and fairly steep. I also am looking into Boyesen reeds or anything else that would help me jump a log When- not IF that becomes necessary.  What is your opinion on Barkbusters and what tools you carry if you are 20 miles from the truck?

 

[motovita]

23 minutes ago, Tillerman6 said:

Feetup fun- That's good to know information!  I was all ready to remove that band and give it a whirl, but sounds like it's not that good of an idea after all.  You probably saved me a lot of heartache!  But question- I had been running a 12-53 and first gear speed is "too low" to be of much use for trail riding- it takes valuable time to shift thru first, second and you are not moving fast enough to give the wheels any "gyro effect" so there is not much stability until you are moving at about a fast walk at least.  So first gear is almost useless.  So I put on a 13 tooth front sprocket and that is more "user friendly" my shifting is a bit less often and I'm not needing to change gears as much while reaching a stable speed.  Seems like about 10- 15mph is a good starting point.  My new boots are stiff enough that you need a definite effort to shift, and that gets old pretty fast on the trail.  I'm almost 72 now and that has a lot to do with all this, but do you think a 14-53 is better all around or a 13-53 for single track?  Some of the trails here are rocky and fairly steep. I also am looking into Boyesen reeds or anything else that would help me jump a log When- not IF that becomes necessary.  What is your opinion on Barkbusters and what tools you carry if you are 20 miles from the truck?

 

 Jumping logs is a technique issue rather than a power issue. I suggest you ride some Trials events and work on learning good technique.

 Handguards are invaluable if you need to plow through brush.

[Tillerman6]

14 minutes ago, Tillerman6 said:

Feetup fun- That's good to know information!  I was all ready to remove that band and give it a whirl, but sounds like it's not that good of an idea after all.  You probably saved me a lot of heartache!  But question- I had been running a 12-53 and first gear speed is "too low" to be of much use for trail riding- it takes valuable time to shift thru first, second and you are not moving fast enough to give the wheels any "gyro effect" so there is not much stability until you are moving at about a fast walk at least.  So first gear is almost useless.  So I put on a 13 tooth front sprocket and that is more "user friendly" my shifting is a bit less often and I'm not needing to change gears as much while reaching a stable speed.  Seems like about 10- 15mph is a good starting point.  My new boots are stiff enough that you need a definite effort to shift, and that gets old pretty fast on the trail.  I'm almost 72 now and that has a lot to do with all this, but do you think a 14-53 is better all around or a 13-53 for single track?  Some of the trails here are rocky and fairly steep. I also am looking into Boyesen reeds or anything else that would help me jump a log When- not IF that becomes necessary.  What is your opinion on Barkbusters and what tools you carry if you are 20 miles from the truck?

 

Here are a few observations I have made with my 12-53 ratio riding on the TY 250 A- 

#1 the "Granny low" first gear is a mixed blessing for trail riding- Can't say I don't use it at all, as I do get into tight "dead stop" situations where the front wheel is against a rock and there is no way to get a run at the obstacle and use momentum.  However, it's a pain to have to shift twice or three times to get moving again and really enjoy the riding.  I'm not sure why, but standing on the pegs and tying to shift is not my favorite thing to do. There is always that jerking and trying to balance while absorbing the speed changes and rocky terrain that makes balancing such a tricky manouver. 

I probably made this a little harder myself with my "oversize" foot pegs.  They are about 5" wide and 3.5" front to back.  Your foot cannot really rock on the left side because the pegs are so big.  - back to the drawing board on that one- I have some "drop mount" plates that came with the bike, but they put your feet so far back that you have to stretch and bend forwards while standing to reach the handl bars- even with the 2" risers I have on there now it's tiring to ride standing up for very long. 

 

[Tillerman6]

7 minutes ago, motovita said:

 Jumping logs is a technique issue rather than a power issue. I suggest you ride some Trials events and work on learning good technique.

 Handguards are invaluable if you need to plow through brush.

motovita- I try to stay on the trails pretty much, so not a lot of brush busting on my rides, and the full wrap around brushbusters seem like overkill - more weight and expense.  Unfortunately in my area there are very few trials events within driving range.  I can't find a seat option (Trials type seat pan and cushion that is designed for trials for this bike. )  Also my suspension system is pretty stiff for clearing logs- seems like it's bottoming too easy without moving much and the rear shocks are also not moving much- makes for a fairly rough ride. - can't find any help for either one of these problems!

[b40rt]

Sounds like you need a trail bike, horses for courses etc.

I dug mine out recently, so much more space, better gearing, brakes and suspension, bigger tank, comfortable seat.

Edited May 18, 2021 by b40rt

[motovita]

18 minutes ago, Tillerman6 said:

motovita- I try to stay on the trails pretty much, so not a lot of brush busting on my rides, and the full wrap around brushbusters seem like overkill - more weight and expense.  Unfortunately in my area there are very few trials events within driving range.  I can't find a seat option (Trials type seat pan and cushion that is designed for trials for this bike. )  Also my suspension system is pretty stiff for clearing logs- seems like it's bottoming too easy without moving much and the rear shocks are also not moving much- makes for a fairly rough ride. - can't find any help for either one of these problems!

 It sounds like yourTY has been converted for trail use, Yamaha offered a large optional seat, I don't recall ever seeing one, how about a photo of your bike? A used Trials seat should be fairly easy to find.

 The help for your suspension is easy to find in the last 40 years of motorcycle developement, as in a newer bike.

 There is a Trial next month in Newman Lake, WA, about 46 miles from you.

[Tillerman6]

On 5/18/2021 at 8:38 AM, motovita said:

 It sounds like yourTY has been converted for trail use, Yamaha offered a large optional seat, I don't recall ever seeing one, how about a photo of your bike? A used Trials seat should be fairly easy to find.

 The help for your suspension is easy to find in the last 40 years of motorcycle developement, as in a newer bike.

 There is a Trial next month in Newman Lake, WA, about 46 miles from you.

 

Edited May 30, 2021 by Tillerman6
updating bike pics with new rear tire.

[motovita]

13 minutes ago, Tillerman6 said:

 

 That is definitely an enduro seat, brake pedal too, looks odd with the Trials peg position (your pegs look good though). That low profile rear tire won't do you any favors when jumping logs. 

 Bar risers with the forks slid up like that seems counterproductive.

[Tillerman6]

42 minutes ago, motovita said:

 That is definitely an enduro seat, brake pedal too, looks odd with the Trials peg position (your pegs look good though). That low profile rear tire won't do you any favors when jumping logs. 

 Bar risers with the forks slid up like that seems counterproductive.

Well, I agree 100%.  But what you are seeing is not original equipment.  The forks are off of some other model of bike, so is the front hub and brake plate- notice that there is no tie rod to the brake plate and the fender mounting is all my own doing.  Those fork tubes are about 2 inches longer than stock if my guessing is correct- could be off of an IT 250 or equivalent.  I slid them up in the clamps to get something like a normal steering geometry.  IF I put them all the way down in the clamps the bike would not want to turn very well- that's my guess.  Anyway it is what it is for now.  

I know of another ty in my neighborhood that may come up for sale- i't has a trials seat pan and stock front end.  the compression is no good.  It- barely fires at all then dies, But it's almost 100% complete.  I don't know what it is worth- the fork seals look ok- not leaking and the rear shocks are stock.  I might offer the guy 300 for it if I can find him again.  Chance meeting the first time.

On my bike the rear shocks are Falcon.  I have them set to the softest position but they are still very stiff for my mostly sitting down riding in the woods style.  Can't find any softer springs for these and the front forks need to be put back to original configuration but I don't have a diagram or parts list for them - I think they are IYT or something like that???  If anybody knows - please speak up!

The- photo is not the greatest but the peg position is normal for trail riding- I think.  I got two triangular plates with the bike and they allow the pegs to be moved down and back about 2 inches- I m assuming that that is the trials bike position.  

Yes the rear tire is or looks too small.  I have a rear trials tire that I bought for the trials work I thought I was going to try, but haven't put it on the bike yet- maybe today!  It's a bit taller.  

By the way- do you own or ride a TY?

Edited May 18, 2021 by Tillerman6
updating info