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Lengthening TY175 swingarm


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#1 feetupfun

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Posted 29 January 2011 - 08:29 AM

One of my TY175s has been a test horse for modifications since I got it in 1976. The latest change I have made is to lengthen the swingarm by 45mm. The frame on this bike has already been changed in a way that has produced a steeper steering head angle but retained the standard wheelbase. It also has TY250B forks and a 205cc motor. The wheelbase before the swingarm extension was 48.5 inches, which is quite short for a trials bike. I felt it might be nicer to ride with a longer wheelbase and with the weight bias further forwards, so I decided to lengthen the swingarm to achieve this. I had heard that others had extended TY175 swingarms by between 25mm and 50mm.
There are many ways to lengthen a TY175 swingarm but I decided to make new, longer axle mounting plates from 6mm x 50mm mild steel strip and weld them to the stubs of the existing axle plates. This avoided having to make new shockie mounts. Its probably not obvious in the photos, but the centre line of the new axle slot is lined up with the centre line of the swingarm side arms, which is also the case with the original axle slots. The length of the new axle slots and the location of the cam stops relative to the slot ends is also the same as for the standard setup. I made a cardboard template of the new axle plates, sized to have the axle slot 45mm further back than standard, and marked the cut line on the existing plates. I made the new axle plates from the template, carefully making them exactly the same shape and size and slot position. I ground a vee on one side of the new axle plates, cut the first axle plate off and made a matching vee on it. I then tacked the first new plate in position. I then ground a vee weld prep on the other side of that joint and welded it. I then welded the other side of the plate.
I used a flat surface and a dummy axle to make sure that the second plate was going to be positioned exactly right and welded it on.
I then welded on the cam stops, made from the shank of an 8mm steel bolt.
The brake plate link is now too short so I am planning to make a longer one. The brake rod may be long enough as is, as I have rotated the brake arm on the spline. The chain needed a few extra links. The rear frame loop needed to be bent up a bit to provide tyre clearance at the rear end of the guard.
I've ridden it since the mod and there is more weight on the front end as expected and the stability when turning uphill is much better. I can tell that the front wheel needs a wider arc in tight turns but it is still taking a smaller arc that my non-TY175 1970s twinshock trials bikes. The longer swingarm has also increased the travel of the rear wheel slightly, which has softened the rear suspension action nicely.

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Edited by feetupfun, 29 January 2011 - 08:56 AM.

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#2 gazzaecowarrior

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Posted 29 January 2011 - 05:59 PM

Nice job mate. Really like your work. Let me know how it rides.

#3 rock hopper

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Posted 29 January 2011 - 06:02 PM

I was wondering about mod you did to frame steering, how much did you change it and did you copy it from another frame or do yourself

#4 tlrmark

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Posted 30 January 2011 - 12:13 AM

v ery much enjoyed your post of the swingarm modification, excellent design and execution. a picture of the complete bike with the modifications would be great. cheers mark

#5 tony27

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Posted 30 January 2011 - 01:52 AM

Thanks for posting that up David, I was sure there would be a lot of interest in what you had done :thumbup:

#6 feetupfun

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Posted 30 January 2011 - 08:37 AM

I was wondering about mod you did to frame steering, how much did you change it and did you copy it from another frame or do yourself

The steering frame mod detail:
I wanted a steeper steering angle and for the bars to be further forwards but to avoid shortening the wheelbase. I added 25mm length to the top frame tube. To accomodate this, I bent the front downtubes at a point just above the front motor mounts (approximately the same distance from the ground as the front axle). This steepened the steering angle and moved the steering head forwards by approximately 25mm and slightly upwards, but did not move the front axle forwards or aft. Because of the change to the top frame tube, I had to make new front fuel tank mountings and relocate the HT coil.
With 340mm shockies in the standard position and TY250 forks fitted with the tops of the tubes flush with the top triple clamp, the steering angle was indentical to a standard TY250 fitted with 340mm shockies.
Of course since then the steering has become slightly steeper because I have extended the swingarm which has caused the back end of the bike to be slightly higher.
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#7 feetupfun

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Posted 30 January 2011 - 08:38 AM

v ery much enjoyed your post of the swingarm modification, excellent design and execution. a picture of the complete bike with the modifications would be great. cheers mark

Photos coming up soon - yet to make a nice-looking brake stay
There is nothing good or bad, but thinking makes it so

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#8 feetupfun

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Posted 31 January 2011 - 01:40 AM

I still haven't made a new brake link but the rain stopped for a while so I took some photos. The yellow TY175 has the modified frame and swingarm. The orange TY175 has a standard frame and is there as a visual reference.

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#9 ducman

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Posted 31 January 2011 - 11:33 AM

I still haven't made a new brake link but the rain stopped for a while so I took some photos. The yellow TY175 has the modified frame and swingarm. The orange TY175 has a standard frame and is there as a visual reference.


Looks good and a lot of ground clearnce.Does the yellow have the 250 Forkes and yoke's?

Chrs:Mike

#10 feetupfun

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Posted 31 January 2011 - 11:44 AM

Looks good and a lot of ground clearnce.Does the yellow have the 250 Forkes and yoke's?

Chrs:Mike

Yes TY250B forks and yokes - running with 10mm less fork spring preload than standard for those forks.
Regards
David
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#11 tlrmark

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Posted 04 February 2011 - 01:46 AM

Yes TY250B forks and yokes - running with 10mm less fork spring preload than standard for those forks.
Regards
David



#12 sir dabs alot

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Posted 11 February 2011 - 09:26 PM

Does the fender on the modified bike hit the frame or pipe?
Hopeless Betaphile
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#13 feetupfun

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Posted 11 February 2011 - 11:44 PM

Does the fender on the modified bike hit the frame or pipe?

No it doesn't. That is because the positional relationship between the front frame tubes and front wheel has not been changed, and the exhaust port is now very slightly (approx 1mm) further away from the front wheel than standard.
Clearance for the front wheel and guard can be an issue if the steering head angle on a bike is changed by making the cut where the steering head attaches to the frame, but I didn't do it that way.
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#14 ty_steve

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Posted 26 April 2011 - 01:50 AM

The steering frame mod detail:
I wanted a steeper steering angle and for the bars to be further forwards but to avoid shortening the wheelbase. I added 25mm length to the top frame tube. To accomodate this, I bent the front downtubes at a point just above the front motor mounts (approximately the same distance from the ground as the front axle). This steepened the steering angle and moved the steering head forwards by approximately 25mm and slightly upwards, but did not move the front axle forwards or aft. Because of the change to the top frame tube, I had to make new front fuel tank mountings and relocate the HT coil.
With 340mm shockies in the standard position and TY250 forks fitted with the tops of the tubes flush with the top triple clamp, the steering angle was indentical to a standard TY250 fitted with 340mm shockies.
Of course since then the steering has become slightly steeper because I have extended the swingarm which has caused the back end of the bike to be slightly higher.


Hi feetupfun

Great information you are providing for everyone here! I have a 1976 TY175 and would like to undertake similar suspension modifications. I have a couple of questions - with the frame/head angle modification and the extended swing arm extension do you find the steering to be more along the lines of a modern bike, or would you suggest an even steeper head angle? Are you happy with the outcome? I'm assuming that you have ridden newer bikes... I've only ridden one newer (2001 Sherco) and really liked the geometry and how well my weight was balanced over the front end. It would be ideal to get a somewhat similar set up on my TY if possible?
Also, on the bike pictured at left with stock geometry I see you have swapped out the autolube setup and replaced the case cover. I have tried to do the same but the cover I purchased didn't quite line up - very annoying. Would you have any advise on how to get the correct case cover? What year/model I should be looking for? All the bolt holes lines up but one, and there didn't seem to be adequate space around the kick start area for a proper fit. Other than that the cover looked the same....

Thanks for your time and keep those TY175 posts coming! I'd like to see how you finished off the brake link as well if you have the time to post some more pics.
Steve

Edited by TY_Steve, 26 April 2011 - 02:04 AM.


#15 feetupfun

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Posted 26 April 2011 - 03:13 AM

Hi Steve
The steering on that TY175 with the frame mods is as good as I have ever felt on a twinshock, so I have no desire to change the steering angle. I suspect that the fore-aft weight balance of the bike+rider also has a lot to do with the steering as well as the steering geometry.
Yes I do ride (other people's) moderns now and then and find that there are so many differences to a twinshock in how they are to ride, that I have trouble riding anywhere near the same standard as I can on a twinshock, so can't really comment on differences in the steering.
I think that the TY175 with the frame mods has better ergonomics than the standard TY175 because the handlebars are now higher and further forwards, which gives more room to move around on the bike, and the stance is slightly more upright. I am only average size but feel a bit cramped on the standard frame bike. A smaller rider may not find those changes to be a benefit.
The TY175 with the YZ125 clutch cover has a motor which has the bottom end from a 3H8 prefix motor (DT175E I think). The motor came with that YZ125 clutch cover. I haven't tried to fit the YZ125 cover to a TY175 motor. I'm only thinking it is a cover from a YZ125 because it looks the same to me as covers on late 1970s YZ125 (DEF) and IT175 (DEF), which lines up age-wise with the DT175E. Maybe the earlier YZ125 motors (ABCX models) had slightly different clutch covers that will fit the TY175. An easy way to check these things is to look up the part numbers for the clutch cover gaskets for the different models.
I will take a photo of the longer TY175 brake link and to avoid external photo hosting, will probably post it on the Aussie trials website.
There is nothing good or bad, but thinking makes it so

William Shakespeare




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