Choosing a new front tire.

[Tillerman6]

2 hours ago, feetupfun said:

Your triple clamps are TY Yamaha. Your fork sliders are MX or YZ Yamaha and your brake backing plate is MX or YZ Yamaha. The lines on the fork tubes are there as a reference for where to clamp them on the bike that they originally came from. If they are longer tubes than TY250A then they are not TY250B, because all the TY250 twinshocks have the same length fork tubes. I would expect that the fork tubes are also off a MX or YZ Yamaha.

To maintain the standard TY steering geometry you should set the tubes so that the axle is in the same position as it would be with TY forks. If the travel of your forks is longer than TY forks you may need to fit travel limiting spacers to the damper rods, to avoid the mudguard or tyre hitting the lower triple clamp.

Feetupfun!  Great info and good news.  I was afraid the triple clamps were not TY in which case it would throw off the rake and trail. The lower fork legs have a TYB sticker on them. I guess they still could be from an MX or YZ Yamaha as the TYB rep said that TYB sells to OEM source makers.

I was able to steer and manouver fairly well with the old  high fender setup and with the fork tubes sticking up out of the top triple clamp about an inch and a half before I took the bike apart for the engine overhaul.  The new fender is a TY replica from DC plastics and it looks pretty authentic, so I'm hoping I can get it to work with the new brackets I made.

Lots of things to do before I can mount the new fender it though, as I need some dry weather so I can paint the frame and swing arm.  Should happen next week I hope. I ordered the new front tire, some fork oil, and some new fork seals in the last couple of days. I guess I will wait for the seals and get the forks back together before I try and mount the new fender. It might be easier to have the bike on it's wheels and just leave the fork springs out until I can see how far the wheel moves up with no springs installed.?

The rear shocks are Falcon brand and 13 5/16" center to center or 338mm. Is that longer than stock? How much ground clearance do I need for novice trials?

 

Had to drill out one of the bottom allen screws to get one of the fork legs off. The threads were stuck to the innards of the fork metering rod and would just spin and not let the allen head screw back out. Somebody had put some yellow goop on the threads of the allen screw and it grabbed the metering rod threads permantly!.

I ordered some 15 weight oil. don't know if that was a good choice or not, but gotta start somewhere.

There is a small captive steel  "washer" at the bottom??? end of the main springs( same OD as the spring OD) -looks like a small top hat with a hole in the middle.  Is that supposed to be at the bottom of the spring or the top end?

 

Thanks for all your help!

[2stroke4stroke]

I would imagine the longer springs, if suited to MX or YZ, will be far too stiff for trials use, ditto the damping control set up.  15w is far too heavy an oil anyway.

You don't say what your bike actually is, what is it? There was an implication of it being a trailified TY but then you mention an expansion chamber which points to something else. I can't, in that case, help but feel that it would be better and cheaper in the long run to take cleanorbust's advice about getting a trials bike - you haven't even started on rear suspension or footrest position queries yet, let alone the unsuitability of an expansion chamber equipped motor.

[feetupfun]

5 hours ago, Tillerman6 said:

Feetupfun!  Great info and good news.  I was afraid the triple clamps were not TY in which case it would throw off the rake and trail. The lower fork legs have a TYB sticker on them. I guess they still could be from an MX or YZ Yamaha as the TYB rep said that TYB sells to OEM source makers.

I was able to steer and manouver fairly well with the old  high fender setup and with the fork tubes sticking up out of the top triple clamp about an inch and a half before I took the bike apart for the engine overhaul.  The new fender is a TY replica from DC plastics and it looks pretty authentic, so I'm hoping I can get it to work with the new brackets I made.

Lots of things to do before I can mount the new fender it though, as I need some dry weather so I can paint the frame and swing arm.  Should happen next week I hope. I ordered the new front tire, some fork oil, and some new fork seals in the last couple of days. I guess I will wait for the seals and get the forks back together before I try and mount the new fender. It might be easier to have the bike on it's wheels and just leave the fork springs out until I can see how far the wheel moves up with no springs installed.?

The rear shocks are Falcon brand and 13 5/16" center to center or 338mm. Is that longer than stock? How much ground clearance do I need for novice trials?

 

Had to drill out one of the bottom allen screws to get one of the fork legs off. The threads were stuck to the innards of the fork metering rod and would just spin and not let the allen head screw back out. Somebody had put some yellow goop on the threads of the allen screw and it grabbed the metering rod threads permantly!.

I ordered some 15 weight oil. don't know if that was a good choice or not, but gotta start somewhere.

There is a small captive steel  "washer" at the bottom??? end of the main springs( same OD as the spring OD) -looks like a small top hat with a hole in the middle.  Is that supposed to be at the bottom of the spring or the top end?

 

Thanks for all your help!

The writing on your MX YZ forks is not TYB, it's KYB, which is the company that made forks for Yamaha at the time. KYB is the trademark for Kayaba.

Yes you will need to have the fork tubes sticking out the top for it to steer properly.

Yes it is best to leave the springs out when testing fork travel.

Those Falcon shocks are a good length if you are not lowering the footpegs. Original shock length was 325mm. The ground clearance with those Falcon shocks will be fine. Set the sag with you aboard to 40-50mm. If you want more ground clearance you can fit longer shocks but with longer shocks, standard position footpegs will be too high for the bike to handle well with you standing up.

15WT oil in MX YZ forks may be too heavy damping for a trials bike but try it first. It is easy to replace.

The MX YZ springs will probably be too stiff for trials riding but try it first and you can fit TY springs later if you need to.

The top hat washers should sit on the top ends of the fork springs. Yamaha use that sort of washer so that the cylindrical preload spacer that usually fits above it can be made very thin-walled yet not slip past the end of the spring.

 

[feetupfun]

3 hours ago, 2stroke4stroke said:

I would imagine the longer springs, if suited to MX or YZ, will be far too stiff for trials use, ditto the damping control set up.  15w is far too heavy an oil anyway.

You don't say what your bike actually is, what is it? There was an implication of it being a trailified TY but then you mention an expansion chamber which points to something else. I can't, in that case, help but feel that it would be better and cheaper in the long run to take cleanorbust's advice about getting a trials bike - you haven't even started on rear suspension or footrest position queries yet, let alone the unsuitability of an expansion chamber equipped motor.

From what I've read, he's got a TY250 twinshock that has the trail riding kit that was available from Yamaha (and popular in  the USA) when they were new. It sounds like someone has fitted a YZ 250/360 or MX 250/360 front end from the mid 1970s to the TY.

[Tillerman6]

15 hours ago, feetupfun said:

From what I've read, he's got a TY250 twinshock that has the trail riding kit that was available from Yamaha (and popular in  the USA) when they were new. It sounds like someone has fitted a YZ 250/360 or MX 250/360 front end from the mid 1970s to the TY.

Yes, tried to cancel the order for the 15 wt and swap it for some 5wt oil.  Hope that sounds better?

As far as the source of the forks- Close as I can figure out it looks very similar to the 1974 Yamaha YZ 250 setup.Not 100% identical, but close enough.  The axle is positioned on the centerline of the fork legs and anything newer than about 75 has the axle in front of the centerline.

As soon as the seals and the new 10mm Allen bolt comes in I can at least put the forks back together (less springs and oil) and check for clearances around the new TY style front fender.

From looking at the parts breakdown of the TY it looks like they use two sets of springs instead of just one big long one in each fork leg.  Don't know if it would be possible to change out the MX springs for some TY springs? I hope so because the wheel hub I have now is also from a YZ and it does not fit a TY fork leg like it is with it's tennon and notch situation on the brake backing plate I have now.

Buy a trials bike? Sure send me some $$$. As long as it is taking for the engine overhaul, paint, new seat, fenders, fork modifications, it would be nice to have another bike to ride !!!

 

15 hours ago, feetupfun said:

From what I've read, he's got a TY250 twinshock that has the trail riding kit that was available from Yamaha (and popular in  the USA) when they were new. It sounds like someone has fitted a YZ 250/360 or MX 250/360 front end from the mid 1970s to the TY.

 

[feetupfun]

3 hours ago, Tillerman6 said:

Yes, tried to cancel the order for the 15 wt and swap it for some 5wt oil.  Hope that sounds better?

As far as the source of the forks- Close as I can figure out it looks very similar to the 1974 Yamaha YZ 250 setup.Not 100% identical, but close enough.  The axle is positioned on the centerline of the fork legs and anything newer than about 75 has the axle in front of the centerline.

As soon as the seals and the new 10mm Allen bolt comes in I can at least put the forks back together (less springs and oil) and check for clearances around the new TY style front fender.

From looking at the parts breakdown of the TY it looks like they use two sets of springs instead of just one big long one in each fork leg.  Don't know if it would be possible to change out the MX springs for some TY springs? I hope so because the wheel hub I have now is also from a YZ and it does not fit a TY fork leg like it is with it's tennon and notch situation on the brake backing plate I have now.

Buy a trials bike? Sure send me some $$$. As long as it is taking for the engine overhaul, paint, new seat, fenders, fork modifications, it would be nice to have another bike to ride !!!

 

 

I didn't say to buy a trials bike. That was someone else.

The TY250 parts book does show two springs but they really only came with one main fork spring. I'll have a look at the parts book tonight and that will remind me of what you are looking at. Many people have said the same thing as you previously about the parts book.

Yes TY250 fork springs for 34mm Kayaba forks will fit in 34mm Kayaba MX YZ forks. You would need to make custom length preload spacers.

Trivia fact No 1 -  you can fit Race Tech Gold Valves designed for MX YZ DT 34mm forks in 34mm TY250 forks.

You say your forks are similar but not identical to 1975 YZ250. What do you see that is different?

Trivia fact No 2 - if you have a look at photos of some of the early prototype bikes that Mick Andrews rode while developing the TY250 you will see what looks like your front hub and fork sliders in use - straight out of the Yamaha parts bin.

[feetupfun]

Here is the forks page from the TY250A parts book. The graphic artist who drew the anti-topping spring has drawn it to be about 100mm long when in reality the anti-topping spring is only about 25mm long. I'm talking about the spring that is shown fitted below the piston of the damper rod (item number eight)

Edited May 21, 2019 by feetupfun

[Tillerman6]

17 hours ago, feetupfun said:

I didn't say to buy a trials bike. That was someone else.

The TY250 parts book does show two springs but they really only came with one main fork spring. I'll have a look at the parts book tonight and that will remind me of what you are looking at. Many people have said the same thing as you previously about the parts book.

Yes TY250 fork springs for 34mm Kayaba forks will fit in 34mm Kayaba MX YZ forks. You would need to make custom length preload spacers.

Trivia fact No 1 -  you can fit Race Tech Gold Valves designed for MX YZ DT 34mm forks in 34mm TY250 forks.

You say your forks are similar but not identical to 1975 YZ250. What do you see that is different?

Trivia fact No 2 - if you have a look at photos of some of the early prototype bikes that Mick Andrews rode while developing the TY250 you will see what looks like your front hub and fork sliders in use - straight out of the Yamaha parts bin.

17 hours ago, feetupfun said:

I didn't say to buy a trials bike. That was someone else.

The TY250 parts book does show two springs but they really only came with one main fork spring. I'll have a look at the parts book tonight and that will remind me of what you are looking at. Many people have said the same thing as you previously about the parts book.

Yes TY250 fork springs for 34mm Kayaba forks will fit in 34mm Kayaba MX YZ forks. You would need to make custom length preload spacers.

Trivia fact No 1 -  you can fit Race Tech Gold Valves designed for MX YZ DT 34mm forks in 34mm TY250 forks.

You say your forks are similar but not identical to 1975 YZ250. What do you see that is different?

Trivia fact No 2 - if you have a look at photos of some of the early prototype bikes that Mick Andrews rode while developing the TY250 you will see what looks like your front hub and fork sliders in use - straight out of the Yamaha parts bin.

The only difference I can see is that at the bottom of the right hand slider, there are two studs sticking out of the bottom of the fork leg to hold the axle clamp.  If you look at the parts manual online: https://www.yamahapartshouse.com/oemparts/a/yam/5004177af8700209bc784bdc/front-fork

There are no visible studs showing on either fork leg. \ Could be another "artist" problem as you mentioned before about the springs.

There are also possibly some differences in the internal parts between the diagram and what is on my work bench but I would have to line everything up and take another look.

However, I am more than willing to try the TY springs if I can find some later on.

 Spacers are no problem. I have a good ol South Bend 10K metal lathe.

What would the Race Tech Gold Valves do for this situation?

You are indeed the Yamaha Guru! 

Don't know if the YZ setup is any heavier?  I think the front rim is wider than the one on the TY.

Had another look at the Falcon rear shocks today.  I do indeed have the 50 pound springs on there. And the shock body should be on top to get the shock action working both ways 100% if that is the desired result.??   I might adjust the spring clip all the way down (up) and see if I can get the 50% sag  situation to happen.

I can get a used TY front wheel and hub for about $100.00 US, but the condition could be a problem. Worth it?

 

Also I can get some Very used looking TY forks (pitted and worn chrome on the tubes) Seals shot for 170 Us, but there again, condition looks like a problem.

 

 

 

 

[feetupfun]

https://www.yamahapartshouse.com/oemparts/a/yam/500418cdf8700209bc785182/front-fork-250b-c-400b-c

DT250B DT250C has the two stud clamp

[feetupfun]

2 hours ago, Tillerman6 said:

The only difference I can see is that at the bottom of the right hand slider, there are two studs sticking out of the bottom of the fork leg to hold the axle clamp.  If you look at the parts manual online: https://www.yamahapartshouse.com/oemparts/a/yam/5004177af8700209bc784bdc/front-fork

There are no visible studs showing on either fork leg. \ Could be another "artist" problem as you mentioned before about the springs.

There are also possibly some differences in the internal parts between the diagram and what is on my work bench but I would have to line everything up and take another look.

However, I am more than willing to try the TY springs if I can find some later on.

 Spacers are no problem. I have a good ol South Bend 10K metal lathe.

What would the Race Tech Gold Valves do for this situation?

You are indeed the Yamaha Guru! 

Don't know if the YZ setup is any heavier?  I think the front rim is wider than the one on the TY.

Had another look at the Falcon rear shocks today.  I do indeed have the 50 pound springs on there. And the shock body should be on top to get the shock action working both ways 100% if that is the desired result.??   I might adjust the spring clip all the way down (up) and see if I can get the 50% sag  situation to happen.

I can get a used TY front wheel and hub for about $100.00 US, but the condition could be a problem. Worth it?

 

Also I can get some Very used looking TY forks (pitted and worn chrome on the tubes) Seals shot for 170 Us, but there again, condition looks like a problem.

 

 

 

 

Your fork sliders look like DT250/360/400 B/C. I've posted a link to parts diagram in a separate posting.

Race Tech gold valves are fun to set up if you like suspension tuning and if you get it right they work pretty well.

The brake drum might be heavier (haven't seen a photo of your front wheel yet). The rim and spokes from MX YZ DT IT might be a little bit heavier. That brake backing plate in the photo will be pretty much the same weight.

Most Falcon shocks require the body at the top to work properly. Some Falcons work either way.

Should be easy to get that sag with you aboard if you weigh more than 60 kg (but then I haven't seen a photo of your shocks yet). On my bikes with 50 lb springs and 340mm Falcons the clip is nowhere near either end of the range. Something like third groove from the top from memory.

There is no real world benefit in using a TY front hub unless what you have is a lot heavier (I haven't seen yours yet). The backing plate needs to match the fork leg or there is more work to do.

As for buying TY forks, why not just try what you've got first. You can always change things later if you want. If the chrome is worn through on a fork tube, the sliders will probably be worn out too. Seeing you have a lathe it wouldn't be hard to sleeve the top ends of the sliders back to the right shape/size.

[Tillerman6]

42 minutes ago, feetupfun said:

Your fork sliders look like DT250/360/400 B/C. I've posted a link to parts diagram in a separate posting.

Race Tech gold valves are fun to set up if you like suspension tuning and if you get it right they work pretty well.

The brake drum might be heavier (haven't seen a photo of your front wheel yet). The rim and spokes from MX YZ DT IT might be a little bit heavier. That brake backing plate in the photo will be pretty much the same weight.

Most Falcon shocks require the body at the top to work properly. Some Falcons work either way.

Should be easy to get that sag with you aboard if you weigh more than 60 kg (but then I haven't seen a photo of your shocks yet). On my bikes with 50 lb springs and 340mm Falcons the clip is nowhere near either end of the range. Something like third groove from the top from memory.

There is no real world benefit in using a TY front hub unless what you have is a lot heavier (I haven't seen yours yet). The backing plate needs to match the fork leg or there is more work to do.

As for buying TY forks, why not just try what you've got first. You can always change things later if you want. If the chrome is worn through on a fork tube, the sliders will probably be worn out too. Seeing you have a lathe it wouldn't be hard to sleeve the top ends of the sliders back to the right shape/size.

Feetupfun, Glad to get your help! I think the DT250 B/C is exactly what I have. You would not think that KYB would make so many different forks for bikes that are more or less the same thing.

Tell me about the Race Tech Valves.

I'll send you a pic of my brake drum, but I'm guessing it is also DT250 B/C since the forks are.

No problem with having enough weight I'm 180 lbs.

Shocks will go on with body on top. (no mystery now)

Will stick with the DT forks for now unless there is a windfall of TY parts coming my way.

They sell sleeves for the fork sliders ready made. They would need a special jig made to hold them concentric if you were going to make your own on the lathe because they are so thin walled.

You could not put them in a 3 jaw or 4 jaw chuck because they would distort from the squeeze of the chuck.

When I get the new Dunlop D 803 GP installed I will weigh the front wheel without the brake backing plate and let you know what it weighs.  I'm sure the rim is wider than a TY rim, but it might not weigh that much more. 

Made my own handle bar risers to get my standing riding position to be more upright. Tomorrw is my 70'th birthday, so I can't be riding all hunched over for too long

Thanks for all your help! Wish you were in North Idaho- you could see my pile of parts! Or we could go fishing!

 

 

 

[feetupfun]

2 hours ago, Tillerman6 said:

Feetupfun, Glad to get your help! I think the DT250 B/C is exactly what I have. You would not think that KYB would make so many different forks for bikes that are more or less the same thing.

Tell me about the Race Tech Valves.

I'll send you a pic of my brake drum, but I'm guessing it is also DT250 B/C since the forks are.

No problem with having enough weight I'm 180 lbs.

Shocks will go on with body on top. (no mystery now)

Will stick with the DT forks for now unless there is a windfall of TY parts coming my way.

They sell sleeves for the fork sliders ready made. They would need a special jig made to hold them concentric if you were going to make your own on the lathe because they are so thin walled.

You could not put them in a 3 jaw or 4 jaw chuck because they would distort from the squeeze of the chuck.

When I get the new Dunlop D 803 GP installed I will weigh the front wheel without the brake backing plate and let you know what it weighs.  I'm sure the rim is wider than a TY rim, but it might not weigh that much more. 

Made my own handle bar risers to get my standing riding position to be more upright. Tomorrw is my 70'th birthday, so I can't be riding all hunched over for too long

Thanks for all your help! Wish you were in North Idaho- you could see my pile of parts! Or we could go fishing!

 

 

I'm pretty sure that fork slider sleeves for those forks would need the sliders machined out to allow them to be fitted because those forks don't have removable bushes. The fork tubes run directly on the bore of the sliders.

Your brake backing plate is not DT. If it was DT it would have a speedo drive built in. The backing plate looks like MX B or C or YZ 125 B or C or X to me. It could also be an MX YZ 250/360/400 backing plate. If you measured the OD of the brake shoes it would tell you if it is MX YZ125 or MX YZ 250/360 backing plate. Same for the hub which I still haven't seen. If it is a 125 backing plate the brakes would marry with a TY front hub.

Race Tech Gold Valves are sometimes called cartridge emulators and are designed to be fitted to old bike forks and attempt to mimic the way that the damping works in modern forks. Google search on Race Tech and there will be lots of info on their website.

I'm always happy to help and have a fabulous birthday tomorrow. It's a great time to be alive

[Tillerman6]

20 hours ago, feetupfun said:

I'm pretty sure that fork slider sleeves for those forks would need the sliders machined out to allow them to be fitted because those forks don't have removable bushes. The fork tubes run directly on the bore of the sliders.

Your brake backing plate is not DT. If it was DT it would have a speedo drive built in. The backing plate looks like MX B or C or YZ 125 B or C or X to me. It could also be an MX YZ 250/360/400 backing plate. If you measured the OD of the brake shoes it would tell you if it is MX YZ125 or MX YZ 250/360 backing plate. Same for the hub which I still haven't seen. If it is a 125 backing plate the brakes would marry with a TY front hub.

Race Tech Gold Valves are sometimes called cartridge emulators and are designed to be fitted to old bike forks and attempt to mimic the way that the damping works in modern forks. Google search on Race Tech and there will be lots of info on their website.

I'm always happy to help and have a fabulous birthday tomorrow. It's a great time to be alive

Well the UPS truck brought the new front tire today and I put it on the rim today.  (pics below)

The rim itself is a 21 x 1.6 after all.  Apparently they measure between the rim edges on the inside and not the outside.

The brake drum diameter is 130mm if that helps any.

The shoes are marked "322-00".

I was surprised at the weight of the new trials Dunlop D803GP at around 7 pounds whereas the knobby I took off was only about 6 pounds!

Anyway, the width of the rim is probably the same as a TY rim at 1.6", so the weight of the wheel should fall in close to the TY wheel overall.

The brake backing plate is magnesium, so that will not be a factor.

I think the OD of the shoes will be very close to the 130mm ID of the brake hub if that helps any..

[feetupfun]

Thanks for the wheel photos. It's a nice-looking wheel.

TY front brakes are 110mm as are MX YZ125 B, C, X so your wheel with its 130mm brake drum is from something else. I see your front hub has speedo drive lugs on the opposite side to the backing plate so your backing plate that has no speedo drive may well be the one that originally went with that wheel. My memory is telling me that DT250/400 speedo drive is on the backing plate but I might be wrong. If I'm right then your wheel is probably IT175/250/400/465/490.

If you have a close look at the wheel rim you might see a manufacturing date code.

I also have a mystery front wheel. It came on a TY175 I bought and I've never worked out what it is from, but it is some sort of off-road Yamaha with 110mm brake drum and alloy rim and heavy spokes. The hub has equal size spoke flanges and looks like TY175/250 except it is painted black and it looks to be the original paint. The date mark on my rim is something like 1981. I'm thinking mine might be from an IT125G but I'm open to suggestions. My wheel works perfectly matched up to a TY175/250 backing plate although it is a bit heavier than a TY wheel due to the heavy spokes and stronger rim.

It will be good to hear how you get on with the forks and tyre/mudguard clearance.

Edited May 23, 2019 by feetupfun

[feetupfun]

I'm thinking your front wheel might be from one of these

https://thumpertalk.com/forums/topic/899705-my-76-yamaha-it400c/