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TY 175 suspension mod q's

kevin j

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Same TY as I had the petcock question. Hasn't been ridden a lot in a few years, but getting it out and going again.

I am 6 ft 0 inches, 200 lbs, ride pretty moderate easy stuff. Ride a 200 GG in modern, so I am used to minimal power, but motor is fairly fresh and surprisingly strong. Occasionally ride it, trying to improve it a bit but on a fairly low budget. Has the SM peg kit slightly down and back.

-Front forks: I have a set of 250 yokes and forks to RB and install. Have had 10 yrs so not sure of shape. Beyond normal rebuild, what are the mods good for me. Preload spacer, oil viscosity and amount, tubes above top of yoke, possible replacement springs, any orifice modifications.

-Rear shocks are spring retainers only, no damping left. I would relocate the upper mount. What dimensions work well for the move of the mounting point? What shock length eye to eye, and recommended brands.  (USA stock, or  someone who ships here.) Spring rates?

-Carb is the original (TK?), not bad, but is worn, and not as crisp as I'd like. Anyone used the OKO flat slides? sizes, models, jetting, etc.   Or, should I go VM26 Mik?

-Clutch is not precise, lot of hysteresis from disengage to engage to disengage. Cable is fairly new, well lubed. I will check cable, adjust the tapered shaft thing on the left, and check basket and plates. Any other tricks? Granted, in the day, clutch in and out at the gates only, but I like to use it a lot.


No rush but thanks for help.

Kevin J,   Minnesota USA

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I'm about 210 pounds and found that standard TY250 forks had a pretty much perfect action on a TY175 after slightly reducing the spring preload (5mm to 10mm less) and using 5wt fork oil set at 125mm from the top. I find the standard damper rod oil hole setup works very well for me. If you don't mind the expense you can buy aluminium damper rods and a lightweight front axle which will reduce unsprung mass. I run Gold Valves in one set of TY250 twinshock forks and after proper setup the action feels a bit better in rocky streams and no better riding anything else. While it was a fun experiment, I'm not planning to do it on any of my other bikes with TY250 forks.

If you want more fork travel for some reason you can leave out the anti-topping springs, but you may get some topping out on steep ascents. I leave the anti-topping springs in all of mine because I find that the standard fork travel keeps the steering geometry just how I like it. Same thoughts apply to the length of the damper rods.

TY250 forks are shorter than TY175 forks so if you want to preserve the standard height at the front, they need to be flush in the top clamp to be the same as TY175 forks with 20mm protruding. If you fiddle with the height of the rear end you will probably need to experiment where you have the tubes in the clamps to get the steering sweet.

Where you move the top shock mounts to depends on the steering head angle you want. 340mm is good with standard mounts if you want a modest rear end lift, and if you relocate the top mounts to the frame upright you can please yourself how much rear end lift you get by choosing where (fore and aft) you put the mount relative to the frame upright.

360mm shocks raise the rear end quite a lot using standard mounts. Some people like that effect. Using 360mm shocks combined with standard lower mount and top mount relocated to the frame upright will give too much rear end lift. You can move the rear frame upright forward to correct for this, but because 340mm and 360mm shocks both have 4" shaft travel, there is nothing to gain except mass by using 360mm shocks if you are going to move the top mount.

A rear end mod that is popular for TY175s is to lengthen the swingarm behind the bottom shock mount by lengthening the axle plates. This increases rear wheel suspension travel and lengthens the wheel base. Swingarm length is usually increased by 30mm ~ 45mm. If you do this mod, 50 pound springs. There are no decent trials twin shocks made in the USA. There are a few good brands to choose from, all made in the UK. I use Falcon Trials Classics which I think are imported into the USA by B&J Racing, Tennessee,

A bigger carby is no better for power unless you are also hotting up or enlarging the motor. Standard is a 22mm Yamaha-Mikuni. A pre-jetted OKO would be a good thing if you want a modern design carby. Google mid-atlantic vintage trials for info on pre jetted OKO carbies for twinshock era trials bikes.

Need more info about what the problem is with the clutch. It could be notched basket fingers, cratered cam surface, shiny plates, bent plates, wrong oil, water in oil, old friction plates, cheap friction plates, uneven spring length, wear in the basket bushing, axial movement of the gearbox shaft. They have a pretty good clutch action compared to other bikes of the era when it is working properly.


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Thks, great info.

-250 forks, I will RB them stock and install as starting points. Good to know not need to start chasing parts or machining or welding, which was what I needed before tearing the bike apart.

-125 mm oil level, is that 125 mm down from top, with legs compressed and all springs and dampers out of the fork tubes?


-Rear, 50 lb springs. Meaning 50 lbf per inch of compression?  What overall free length, or what brand preferred?

-I didn't mean US made shocks, not much made here, but available in US. Bob G used to have Falcon and one other brand, but his webpages are all messed up now. No parts or prices or availability shown. Will have to call him. 

-Clutch, I haven't torn into yet. Would check all the normal mechanical, just wasn't sure of what the final goal was. If they were always lousy or not. Given Yamaha, I'd expect pretty good, which this is not, so hopefully the mechanicals will be answers.

-Carb: I'll get it going again as is and refresh my memory form last year. The MidAtl site was where I first heard about the OKO. I think I was searching for 175 replacement carbs some years ago for another 175. I did find that a Mik carb from a (DT100 ?) was the same body but jetted a lot different, and ended up switching jets and parts over to that one.

I also have a TY350, my first 'real' trials bike, with a rattly TK that I think I will try OKO. Trying to find a mono 250 head ( I have a cylinder) and build that bike to a 250 instead of 350, but that's another story.  


Thks again. Kcj

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Yes springs are pounds force per inch of overall length change. If you use standard shock mount and swingarm length (approx 4 inch axle travel), use 40 pound springs. If increased wheel travel (5 to 6 inch axle travel) suspension design use 50 pound springs.

Oil level is with springs out and fully bottomed. The last bit of travel when bottoming is very slow due to the hydraulic anti bottoming, so keep pushing until you feel metal-to-metal

I did already suggest shockie length of either 340mm or 360mm, depending on what steering head angle and shock mounting arrangement you want to use. If it was me and using TY250 forks, I would use 340mm shocks, retain the standard shock mounts and extend the swingarm behind the lower shock mount.

If you want more ground clearance at the expense of steering quality, use TY175 forks fitted flush with the top clamp and fit 360mm shocks.

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Overall length I meant the springs only. I.e. How much preload once installed on the shock body. Or is there only one choice?

Looks easy to modify swing arm, a bit tougher to move top mount, so I will start at swing arm end. I can weld thicker metal, but don't have TIG for top area thin tube and maybe chrome moly or higher carbon. 


I'll start on the forks next week hopefully. Just finished off a big 100cc chainsaw build and have another waiting.


thks again. Kcj


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Shockie spring preload is adjustable over a wide range and you set it to give about 50% sag with full rider weight on footpegs. If you have the correct rate shockie springs, after setting the preload, there will be a few mm of sag with no rider aboard.

TY175 axle plates are mild steel

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There are 2 or 3 different swingarm extension plates available,

1 type involves cutting the swingarm plate off at approximately 45 degrees the same amount both sides & welding the new parts on. The ones shedworks sell should lengthen the swingarm 40mm or so.

The other type I've seen on eBay involve cutting the end of the axle slot off & sliding the new part in for welding which should be easier to get the axle slots perfectly inline. These ones may give slightly more length

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