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TY Mono Frame crack and footpeg mods

kevin j

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     I've had this TY350 mono (I am in US) for 15+ years. I rode it quite long as the kids got the modern stuff, but it has been parked about 5 years. I want to get it going for a 'reunion trials' this weekend. Beyond the usual carb, fuel, fluids, etc,, what started out as 'I should check and redo the dog bone bearings' became 'this is really thick dirty greasy and needs cleaning' became 'I found a frame break under the gunk' became 'I may as well lower the foot peg mounts while I have the engine out.'

     I would do the Chris Johnson frame mods to bring the front wheel back, but don't have the money or time to buy a shorter shock that is a part of those changes. So, just lower the pegs at least.




     It is the crosstube under the left side rear of engine, outboard of the motor mount and inboard of the frame gusset for swing arm mount and pegs. It has been brazed, so has broken before, The rubber pad is under the engine over the skid plate, and I watch all motor mount bolts for tension.

     I assume others have seen breaks here, and it appears to have been broken quite a while. I ride low skill level and low obstacles.

     I would like to grind out the bronze, pull it back closer to alignment, and weld.



-Is the frame mild steel or 4140 or other alloy?


-No access to TIG. Can I MIG weld it? Access will be difficult, but possible. (Engine is out.)

Edit: I could bronze braze it. 


-Can I MIG cold rolled or stainless tubing to the frame material to reinforce?


-Any ideas about reinforcing? The outboard end of cross tube is tapered and welded closed, so I can't put a sleeve inside to back up the weld, although I think could grind open the end and plug weld it back closed when done.




     While apart, I may as well lower the pegs as planned for 'someday'. The TY feels SO tall as stock. My thought is to weld two thin plates per side, with tube spacers in between at bolt points, and use some sort of bolt on removable plate with peg clevis welded to that. That is extra weight compared to welding clevis mounts directly to the frame, but then I can move pegs around, or use different clevis/bracket dimensions if needed.



-Frame material and weld questions as above


-I will go as low as possible, staying maybe 1/2 inch (1 cm) above bottom of skid plate or cross tube, whatever is the lowest point. I will go where it mounts well, and was not intending to move front or rear, but I would if readers think I should.


-I want to use modern wider pegs.


-I have a 2003? Beta in the garage I could rob for pegs and mount brackets. Beta has a U shaped bracket one plate outboard and one inboard of the frame, and looks pretty sturdy. Has anyone used the Beta assemblies?


-Are the Beta clevis dimensions 'modern' such that I can use any pegs? Beta pegs aren't real wide front to rear, but much better than the TY nails. I'd like to go wider later.


-I'd like to make the changes without cutting loose and lowering the TY plates, or cutting the TY studs off the frame, until I know the new mounts work. (i.e. I want to ride it next weekend and may have to keep TY pegs in place if I don't use the Beta parts.)


-Does the brake pedal pivot point need to be relocated down, or just turn the lever on the splines to move the tip down? It seems like it would feel strange with tip being well below the pivot point (the sine/cosine stuff), but I really don't want to get into relocating if I don't have to. However, if I need to do something to the new brackets to plan ahead to relocate later, or ideally to change to hydraulic rear brake and wheel (mainly so I can use tubeless wheel with obtainable spokes, that I have sitting in the garage), I would make the brackets planning ahead.




-I have the needle bearing and seal interchange data for the dogbones, and am getting data for swing arm pivot area parts.


-Has anyone modified the swing arm pivot bolt and sleeves to add grease fittings? Not so much for lubrication, but for purging out dirt and moisture more frequently than the complete teardown every 10 years…..


-Anyone have sources for the sleeves/pins and bolts? Mine are ok. I am just changing bearings and seals, but eventually they will get pitted. Maybe not in my riding lifetime, so maybe it is a moot point.


Thanks, Kevin J     Minnesota USA


Edited by kevin j
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For the lower footrest positions use 16swg mild steel sheet with stiffening provided by bolt hole sleeves as per your post. You need 2 sheets per side about 12mm apart.

Mig weld the crack. Before MIG welding polish / sandblast the area to bright metal then warm it with a propane torch until it starts to turn straw colour, then weld it immediately. If the tube is badly corroded near the crack cut out to good metal. Get some pipe with a slightly thicker wall and turn it so it has spigots on each end that slip inside the existing tube.

Do not use stainless steel.

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No idea what type of steel the Frame is made from ,

but if you look round the frame at all the other welded joints you can usually tell if it was manufactured with - MIG , TIG , ARC or Bronze Weld

{you may have to clean off some paint to do this}

if you have any doubts get an experienced Welder to look at the welds

if it was made with MIG welds then repairs with MIG should be fine

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  • 3 weeks later...


save but still editing


I meant to follow up on this as to what I did but pretty wild the last two weeks.

I intend to post some pictures later when I have more time. I did get it ready for that weekend to ride, but ........

Cracks:  The frame welding appears to have been Mig welding just by the quality of the welds everywhere. So that's what I did. The lower rear crossmember had quite a bit of rust and corrosion inside and had some expansion like it had water in there that had frozen at some point. I think there are holes in the frame tubing that allow water to get down there.  Once I was done I drilled a couple drain holes at the very bottom.

I took a piece of about 1 inch OD tubing, slit it lengthwise to give me about a 7 inch long half circle piece of tubing  that fit well around the outside of the existing frame tube. I clamped everything up around the outside of the damaged tube and then welded. Seemed to work well, fairly easy to do, but did add several ounces of weight. Long-term reliability/cracking will remain to be seen 


Pegs:  Since I was into it I added the plates and lowered the pegs. I used about 11 gauge material, which was way too thick and too much weight. I should've used 14 or 16 but I didn't have any.  Since I didn't know what direction I was moving the pegs, I made a small triangle shaped plate that the actual peg clevis welded onto and then used three flat head screws to bolt that to the new plates that I added. The bottom screw is at the bottom edge of the peg, and by putting thin cone shape shims under the screw head in the plate I can adjust the peg contact to screw head to make the peg fllat to the world. That turned out to be an accident al benefit. it wasn't part of the plan.


I lowered the pegs about an inch and a quarter or more. It makes a huge differencein feel.  I did not move the pivot point for the brake lever but had to reshape the brake lever to bring the tip down considerably  and for the lever to clear the new bracketry that I added. I don't like to feel the way is now but I didn't have time to re-locate the pivot. If I end up going to hydraulic disc in the back then I would do some changes at that point  


Overall the peg location makes a huge difference in how the bike feels, stability, and not falling into turns so much. It feels much more modern. Wider pegs much nicer. I would highly recommend the peg relocation. 


 Unfortunately after being parked for three years, in the rush to get the frame repairs done, I forgot to rebuild the front brake caliper, and the pistons were sticking. I only rode about four sections and then had to put it on the trailer and switch to a different bike, we can do that in my class. 

 brakes are fixed now and I look forward to riding it in a couple weeks 


 thanks to all who gave input, and I will try and post pictures later 

Edited by kevin j
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