richty250e Posted May 25, 2009 Report Share Posted May 25, 2009 Dear All, I know this has been discussed before but hoping for a few tips. I'm currently 'remanufacturing' a TY250E for mildly competitive fun use and have just spent a day stripping the forks. It all came apart reasonably well (half an hour with an air powered impact gun eventually removed the damper tube bolts). A bit of careful cutting of slots with a Dremmel got the oil drain screws out and deft use of a centre punch got the old oil seals out. So now I have a collection of parts which seem relatively unworn, but one damper tube was rusty so must have been sitting in water for a while. The stanchions are pitted and will be sent off for straightening /rechroming /grinding etc. The sliders look in good condition as far as the bearing surfaces go and will just get a bit of a cleanup and polish on the outside. I notice that a lot of people fit the forks from a TY mono to improve things on the front end. I really want to keep the original front forks but try to make them work a bit better while they are apart. What do people consider to be the biggest problem with the original set up? The springing looks to be standard with progressively wound coils and spacers under the top nuts. From a quick look at the standard valving arrangments it appears that the original forks have a damper tube attached to the bottom of the slider with a valveless piston located inside the stanchion to create an upper and lower chamber. The damper tube has holes which allow oil to flow between these two chambers as the forks compress/extend. The rebound damping action looks to be controlled by the size of two small holes in the top of the damper tube, whilst compression damping is controlled by the two holes in the damper tube and a spring loaded check valve in the end of the stanchion (located under a circlip) which allows the oil to bypass the damper tube. The check valve has a castellated section, the size of the castellations controlling the oil flow. There will of course be a certain amount of oil bypassing the piston due to bearing tolerances, wear etc. So the main areas in which 'adjustments' can be simply made would be changing the oil weight and / or changing the size of the two small holes in the top of the damper tube (for rebound damping) and increasing the compression damping by machining the top of the castellated section of the check valve (thereby making the 'gaps in the castle' smaller). As far as changing the spring rate goes, I weigh about 13 stone (180 lbs) so maybe shortening the spring and lengthening the spacer might be an option. I suspect that just clearing out all the muck, a thorough clean, and fitting a set of new seals and fresh oil to the correct level will give it a fighting chance. I did notice that on top of the damper tube was a small projection of 14mm diameter with two flats machined at 12mm AF. Could be possible to adapt a 12mm hex socket to fit the flats and thereby avoid having to use the air gun to loosen and tighten the damper tube bolts. If anyone has any experiences of getting these forks to work properly I would appreciate any suggestions. Cheers Rich Quote Link to comment Share on other sites More sharing options...
feetupfun Posted May 26, 2009 Report Share Posted May 26, 2009 If you shorten the spring, there will not be enough travel left in it. There is barely enough intercoil space already for the fork travel. I find that both the rebound and compression damping is too light even with 20wt fork oil. I weigh about the same as you. When you push the front down and up by hand, the forks sound like there is not enough oil in them (ie they snore) even if you fill them up to 125mm below the top when bottomed with the springs out, which is a fair bit more oil than the specs list. Heavier springs are available, but while they resist bottoming better, they exacerbate the lack of rebound damping amongst rocks. They are good except for the effect when riding rocks. I want to try cartridge emulators, but will wait till I need to change the fork seals next, as the forks are tolerable the way they are. YSS make the right size emulators for the TY250 forks (emulators intended for YZ250/360 from the 1970s) Quote Link to comment Share on other sites More sharing options...
tony27 Posted May 26, 2009 Report Share Posted May 26, 2009 Have looked at fitting the YSS PD valves as suggested but have run out of time for 3 day event this weekend, bike not finished yet so need to travel to my interisland transport tommorrow. Basically a spacer/mounting washer would need to be made from details that are on their website which will fit on top damper rod & below spring. Preload spacer would need to be shortened by amount of washer & valve Hope to try this before end of year myself Quote Link to comment Share on other sites More sharing options...
richty250e Posted May 26, 2009 Author Report Share Posted May 26, 2009 Feetupfun: Thanks for the pointer towards the YPP valves. Looking at the website the valves appear to be an adjustable check valve that controls the oil flow through the damper tube (with the holes drilled larger) on compression hits. I guess the idea is to give you more freedom to increase the oil viscosity to improve the rebound damping without making the fork too stiff under compression. An interesting idea, food for thought. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted May 27, 2009 Report Share Posted May 27, 2009 (edited) Yes thats it. The "check valve" for compression damping is a round thin steel shim designed to provide rate-sensitive compression damping by flexing out of the way of the oil. Edited May 27, 2009 by feetupfun Quote Link to comment Share on other sites More sharing options...
ausy300pro Posted June 4, 2009 Report Share Posted June 4, 2009 I know slightly off topic but are there any inprovements to be made to the TY175 forks ? are the emulators mentioned suitable for the 175 ? Thanks for any help Quote Link to comment Share on other sites More sharing options...
richty250e Posted June 22, 2009 Author Report Share Posted June 22, 2009 (edited) update on fork mods I have just got my stanchions back from the chroming shop and built everything back up again. Did a couple of mods to see what I can do with whats already there before going down the cartridge emulator route. To stiffen up the rebound damping I filled one of the 2 mm holes at the upper end of the damper tube with solder (and filed it flat/smoothed with 1200 wet and dry). I also filed the small cylindrical projection on top of the damper tube into a 12 mm hexagon, this allowed me to hold it with a 12 mm six sided socket and a long extension when tightening the damper tube bolt. I have rebuilt the sliders with Allballs racing three lip seals and new dust seals. I have blended 10w fork oil with hypoid gear oil to arrive at an approximate SAE 30 viscosity. After assembly I filled the fork to 15mm above the damper tube at full extension (spring not fitted). The fork was primed and left to settle to remove air bubbles and the level rechecked. The oil level at full compression is 130mm below the top of the stanchion. I wanted to retain as much air space above the oil as possible to give a little spring assistance. The coil springs were refitted and 25mm nylon spacers were fitted above the springs to add some preload. Testing the forks on the bench the rebound damping on longer strokes is much more controlled, with short stroke being less affected. the compression damping seems still quite light so hopefully the forks will still respond quickly on the roots and small rocks but be less bouncy on the bigger stuff. The triple lip seals seem to work very well as there is very little 'stiction' even on a newly rechromed/reground stanchion. heres some photos I took along the way. http://i575.photobucket.com/albums/ss194/r...rfulllength.jpg http://i575.photobucket.com/albums/ss194/r...E/damperhex.jpg http://i575.photobucket.com/albums/ss194/r...mper2mmhole.jpg http://i575.photobucket.com/albums/ss194/r...ampersolder.jpg Edited June 22, 2009 by richTY250E Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 23, 2009 Report Share Posted June 23, 2009 If you using both a 25mm nylon spacer and the standard yamaha spacer and are using standard yamaha springs, you will definitely be suffering coil-bind before the hydraulic anti-bottoming starts working. This means the forks will bottom with a bang and will have reduced stroke compared with standard forks. The oil level sounds fine. Quote Link to comment Share on other sites More sharing options...
richty250e Posted June 23, 2009 Author Report Share Posted June 23, 2009 Hi Feetupfun, Yes, I know the spacers are a bit long, it's all a bit experimental at the moment. I am building the back end up with 13.5" Betor gas shocks and 40 lb springs but haven't had a chance to check the front/rear sag yet as I'm still waiting for the swing arm bush tube to arrive. Once I get to a rolling chassis stage I can set up the sag and hopefully shorten the front spacers a little, at least being nylon it is easy to cut them down if coilbinding is a problem. Do you have any advice regarding the amount of sag to aim for and the positioning of the stanchions in the yokes? I am running 5 inch rise bars, standard footrests and I'm 6' tall so a fair bit of weight goes over the front end. I was going to run them about 5 mm above the yoke and take it from there. Would be good to know what works well on yours. Cheers Rich Quote Link to comment Share on other sites More sharing options...
alan_nc Posted June 23, 2009 Report Share Posted June 23, 2009 (edited) As to tube position in clamp: Don't you really want the bike to sit level (front to back)? If you end up using slightly longer rear shocks and drop the clamp down on the fork tube wouldn't you end up with the front end much lower than the rear? I ended up going with a 6" rise bars as I found at the end of a Trial my arms were really tired from having so much weight on them. I also have the clamp even with the top of the fork tube. Rear shocks are 14" eye to eye, with standard foot peg position. With my size and weight (160#, 5'10"), I don't seem to have the problem with the forks bottoming out (no spacers -other than stock) and dampening seems fine. Guess you just have to play with it and find what works for you. Alan Edited June 23, 2009 by Alan_nc Quote Link to comment Share on other sites More sharing options...
richty250e Posted June 23, 2009 Author Report Share Posted June 23, 2009 Hi Alan, I was told that the 13.5" was the standard length shock for my '78 TY so hopefully the bike should sit level. I was a bit wary of the chain rubbing the top of the swing arm or the rear flywheel/sprocket cover mounting boss with the longer shocks. The shocks fitted when I bought it are a couple of inches longer than stock and made the bike look unbalanced. I have spent years riding xc mountain bikes so the low bars are ok for me, and it makes it easier to keep the front end down. regards Rich Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 24, 2009 Report Share Posted June 24, 2009 Hi Feetupfun,Yes, I know the spacers are a bit long, it's all a bit experimental at the moment. I am building the back end up with 13.5" Betor gas shocks and 40 lb springs but haven't had a chance to check the front/rear sag yet as I'm still waiting for the swing arm bush tube to arrive. Once I get to a rolling chassis stage I can set up the sag and hopefully shorten the front spacers a little, at least being nylon it is easy to cut them down if coilbinding is a problem. Do you have any advice regarding the amount of sag to aim for and the positioning of the stanchions in the yokes? I am running 5 inch rise bars, standard footrests and I'm 6' tall so a fair bit of weight goes over the front end. I was going to run them about 5 mm above the yoke and take it from there. Would be good to know what works well on yours. Cheers Rich Sag 40%-50% with you on board and balanced fore/aft ie all weight on footpegs Set the fork tube ends level with the top of the top clamp and use 340mm shocks (also with 40% to 50% sag). TY250 steering is perfect when set up like this. You will lose precious ground clearance if you slide the tubes up in the clamps. 40lb springs will be too light if you weigh more than about 65kg Quote Link to comment Share on other sites More sharing options...
richty250e Posted June 25, 2009 Author Report Share Posted June 25, 2009 Well I've taken your advice Mr Feetup and cut down the spacers to 5 mm and moved the stanchions to flush with the top yolk. The shocks I have are the correct length so just a matter of spring rate. I weigh about 80kg and bought the 40lb spring version after talking to John Cane at TY, and also looked at other sites selling the Betor shock where they were recommending the 50lb spring for 90kg and over riders. I guess setting the rear sag to match the front will be the test, if the circlip ends up in the top groove it will be spring changing time. I've always been a follower of the Lotus suspension philosophy - soft springs/stiff dampers - rather than the other way round. cheers Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 26, 2009 Report Share Posted June 26, 2009 Well I've taken your advice Mr Feetup and cut down the spacers to 5 mm and moved the stanchions to flush with the top yolk. The shocks I have are the correct length so just a matter of spring rate. I weigh about 80kg and bought the 40lb spring version after talking to John Cane at TY, and also looked at other sites selling the Betor shock where they were recommending the 50lb spring for 90kg and over riders. I guess setting the rear sag to match the front will be the test, if the circlip ends up in the top groove it will be spring changing time. I've always been a follower of the Lotus suspension philosophy - soft springs/stiff dampers - rather than the other way round. cheers Yes you will find out eventually what springs are best for you and your bike. Betor shocks do have a noticable compression damping effect compared with other trials shockies so that might tend to compensate for the soft springs. I found that I needed to use max preload circlip groove setting on Falcons with 40lb springs to achieve 50% sag and they topped out with no rider. I prefer to have ~5mm sag with no rider aboard hence the 50lb springs recommendation. If you weighed 65kg I would have recommended the 40lb springs. I use 340mm Betors on my 348 Cota and with the increased leverage ratio on that bike compared with the TY250, the action of the Betors fitted with 60lb Falcon springs works out nicely. Quote Link to comment Share on other sites More sharing options...
richty250e Posted July 25, 2009 Author Report Share Posted July 25, 2009 update: rolling chassis completed. Well I finally received the last batch of swing arm parts and completed the bike to a rolling chassis. When initially trying the bike for suspension sag the suspension had almost no sag so I removed the additional 5mm spacers from the forks and set the rear shock circlip into the next to bottom groove. This has given me about 25mm sag front and rear with me standing on the pegs and no engine fitted. The rear suspension seems firm so I don't think the 50lb springs will be needed. The fork rebound damping also definitely feels firmer with the mod. Here's a pic of the bike, engine is away for new conrod and rebore. Quote Link to comment Share on other sites More sharing options...
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