OzVMX Forum
Clubroom => Tech Talk => Topic started by: DR on May 06, 2009, 08:02:23 pm
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The bump stop rubbers on my old remote res Kayaba's on the 400C and 125C have all but vanished. How costly is it to have new bump rubbers fitted as I don't see any way of disassembly and shock surgery is not something I'm familiar with. Thanks
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i have a 78 Rm shock and there is one crimp line. you have to cut below that line to get the shaft out, but you can get the seal head/wiper etc out once the body cap is removed. Do yours have a press in body cap? The lower eyes on my RM shocks are permanantly attached to the shafts and dont uncrew. I would have to have a closer look at mine to see if there is at all any possibility to machine off the lower eyelets and then put a thread on the shaft and put a new bump stop on and then screw on a new readily available end eye, but i have doubts this is possible to do with out loosing some shaft travel...... hmm yes just grabed a RM shock shaft you would loose about 10mm stroke and overall length. You could make up for the overall length by fitting a longer lower eye no problems but you would loose a little travel. You could make up for this buy using a shorter bump stop than the original to give you more exposed shaft before contact with the bump stop is made. Most OEM RM twin shock bump stops i have seen are 37-39mm long, so you could fit one thats shorter than that.
Other option is to get something like some Polyurethane adheasive sealant like Sicaflex and mould one onto the shaft with out pulling the shocks apart. you could slowly build it up and then finish it off by brushing over it with paint thinners for a smooth appearance. Sicaflex is strong stuff and i think it would work fairly well. You could even tape a little bit of thin clear plasctic around the shaft first (like plastic off a blister pack ) and then put the sicaflex onto that. Then the bump stop can float around on the shaft like original ;)
Maybe also consider RAD shocks to just pull the shocks right apart and do it for you for a couple hundred dollars. I think they still charge about $200-$350 for a complete overhaul?
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Doc,
The only way I know to replace the bump stops is to put the shocks in your car, take 'em to rad's, return in a few days with some money and exchange it for shocks and hey presto, new stops plus fresh oil and nitrogen........your shocks will love you forever.......not that they don't now ;)
Don't be tempted to buy some then cut them in half and slide around the shaft, they may disappear very quickly.
Not much help really am I, one day I hope you will return the favor ;)
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Doc you can get them from Shock Treatment in the Sydney area. They have Kyb and Showa in different sizes for about $30 a pair. You'll have to clamp the shock shaft with soft jaws in a vice and heat the shaft where the end screws on with a heat gun to soften the loctite then it should undo so you can fit the new bump rubber.
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Yes Johnny but only if the lower eyes uncrew. Many KYB's have the lower eyes permanantly fixed to the shafts and they are not threaded on ;)
this is the closest KYB bump stops i can find for the twin shocks
http://www.teknikracing.com/s.nl;jsessionid=0a010c441f435fd06e3b760d4d4a8187e663e6dece21.e3eTa3aSaxmTe34Pa38Ta38Pb350?it=A&id=2039
i just saw the price :o they seem to have gone up since i last ordered. Shock treament http://www.shocktreatment.com.au/ sell the exact same bump stops in Race tech brand and they might be cheaper.
i have plans to get the original red ones re-made
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Ok i've never tried to pull those kyb's apart, i was referring to most other shocks. If that's the case it aint easy Doc..
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Sorry Doc the only way I've been able to replace the bump stops was to convert the shocks to rebuildable.
KYB's have the eye welded on. I do have one set with screw on eyes but this was done to experiment with different lengths and as Lieth said you loose travel.
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I reckon the best way to replace the bump rubbers on those kyb's is to throw them in the bin and bolt a set of ohlins on. :) :)
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good point but maybe he wants to keep them for originality and the bike is not a racer.
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hmmm..thanks guys...this is kinda what I was fearing. I don't really want to have the shocks rebuilt but if it requires disassembly for just the rubbers then I'd be a bit silly not to have them re oiled and gassed at the same time. $ I don't have right now. Okay here's a theory that's been rattling around in the void where my brain should normally reside, 'if' I were to find some nice urethane (however it's spelt) bump stops what's the chance of slicing it to slip over the shaft and then affixing the whole deal under the stop to the shaft with a little adhesive? I figure the spring on the outside and adhesive on the inside may well work?? Any thought's as to why it wouldn't. Obviously the bump rubber has deteriorated over time from age and not from compression as I rarely bottom the suspension with my flyshite weight ::)
:D Johnny, you're talking Utopia! Ohlins would be nice but not in this lifetime for the piddly amount of riding I have left in me :D Leith I want to keep them because for me it's the most practicle thing to do..if something ain't broke don't mess with it ;) wouldn't say they are broke but my back maybe if I don't see fixing it somehow ::)
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Maybe make a bump stop, or find something suitable, and cut it in a spiral so it wraps around the shaft.
That might just help it stay in place.
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I think you've got the answer doc if you can find the right glue to stick them together..
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Araldite Johnny ;) gotta love the stuff ;D
I like the spiral idea too Brent but it sounds a little hard to do without losing fingers :o ::) the TM bits will leave tomorrow by the way, I been a bit slack ;)
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if i were to slide something over or cut a slit in a bump stop and then glue it back together, i would always be riding along worried about it comming off. I think my idea of using urethane sealant out a tube is pretty good and alot more re-assuring. You can get it from places like supercheap auto. Sicalfex is the brand name stuff but you can buy it in a cheap black and gold type brand called 'moto' something? you then just need a dispenser to squirt it out. I use that stuff on side car grab rails and when its stuck to the grab rail its on there it makes a nice rubbery grip for the swingers and will stay on there for ever and will never come off. Another possible soloution is to use a normal rubber or foam bump stop and sand it down a bit all over, then cut a slot in it, fit it around the shaft, then glue it togther with urethane aheasive i mentioned before and then cover the whole bump stop in the stuff and build it up a few mm thick to make up for the amount you sanded off. That way it will have a good covering and hopefully the slot in the bump stop wont pull apart, but if you use the urethane adheasive i think it should be Ok.
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Leith the bump stop rubber can't really fall out when it's much larger than the gaps between the springs, there is nowhere it can go except up the shaft so I think I'll go with this plan. I don't mind using a nice thick larger dia rubber instead of the piddly little stock item. I was thinking of maybe as Brent says and make the cut a little spiralled which will aslo reduce the chance of it slipping straight off. Will have a play over the weekend.
Wasp, the bump rubbers you have, is $12 for the pair or individually? cheers
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Doc,
If you slice it on one side and and wrap around shaft then glue it together as soon as shock bottoms on bumper it will split open again as the stop gets compressed.
No short cuts allowed ;)
Also, if stops are old enough to have perished, what condition is the oil/gas in the shocks....well past thier use by date I'd imagine.
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Evo the shocks are my original '78 RM400 and '78 RM125 units. They are definately old but still very nice and for my type of riding they work perfectly fine, there are no other problems except the rubbers so the cost outweights the benefits when I ride the bike for maybe an hour once a year. In a perfect world I'd like to have them all rebuilt but in practicle terms the TM125 is my main ride bike so that's where I'd spend the money. With a little collection happening I've already had to replace 40 or so shocks in the past few years. Add that to all the multitude of new tyres, new cables, chains, sprockets, etc and you'll begin to see why I need to spread my minimal funding thinly. 'IF' I had just 1 or 2 bikes then yes, they would be the super bling machines but I would be bored out of my head with nothing to do except look at them :( I have a plan and if it works it'll be great and if it doesn't work, well I haven't lost anything. I understand perfectly well where you are coming from though and yes, I'd thought of the splitting also but they are kinda contained ;)
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I rebuild my RM kybs myself .a bit fiddley but not brain surgery, you need to have access to a tig to put the top back on.Cut the top off preferably in lathe .undo inside . remove shaft , replace seals, clean etc and reassemble , tig top back on fill with oil and done.
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yeah, that would be nice John and I wouldn't mind a new challenge but for mine they don't need the rebuilding and if I touched them then would most surely need replacing not rebuilding :D it's just the dang bump stop perished is all ::) be an easier pill to swallow if the gas and dampning were totally shot but it's not ::) I'm off to have a look at a few urethane items tonight that may or may not work ;) you coming over for CD6?
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True no point in pulling them apart if ok.I have used nolothane from car suspension joints in one of my cooper shock sets . I did what you said and cut them and re glued (good old supa glue), as they were hard to start with they havent split (yet)and even if they did they wouldnt fly apart I Lathed them to fit just inside the springs.its good stuff that red nolathane .Yea I am coming to CD6 Doc (doing the second honeymoon thing, only way I could swing it ;D)will be flying in Thursday out Tuesday spending Friday and Saturday near the track.Will see you then.
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sounds good bloke will seeya there for sure ;) also the bump stops I'm looking at are slightly bigger OD than the springs ID so I hoping to do the same kind of deal with having them an interference fit to stop the split. I was just looking at the stock rubbers and jeez they're piddly little soft things, no wonder they're rooted ::)
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my 465 yz has a sikaflex bump stop , i used a toilet roll core and some tape for a mould , bike ridden rarely but , and it is only a temporary thing