Block it and see what happens, will increase spring rate slightly.
yes I know but I was affraid that this will increase the air pressure inside and lead to sealing failures. Actually I think the fork spring rate is too soft for my taste, is it common for twinshock trial riders to put some spacers under springs?
I want to ask a question about the number 5 part on the exploded view above. is it normal to have a very tiny hole on it which enables the fork breathe in-out during travel? I hve never seen thhis before, many mx bikes have bleed valves or screws but this is completely open to the atmosphere. And yes there is oil leaking a bit under full compression landings.
this is a casting defect, porosity or oxide film. it can lead to a recall but in some cases this can be a singular fault. For example when permanent mold casting, first couple of pieces following the start of production, comes with defects due to thermal cycle. it is in fact possible to detect them with x ray and most of the quality casting shops make %100 x-ray inspection. if the broken part is inspected by an expert, the problem can be understood.
Hope you could ride your bike as soon as possible.
unfortunately there is not enough space for 2 7mm height seals. so I fabricated custom spacers. for the moment they are working as they should I guess.
I've sent you a PM. I don't know what is wrong with your forks but from your last post it sounds like they could be bent, the shiny chrome stanchion part is what I'm referring to.
I have measured the straightness , there is no problem. the diameter of inner down tubes are around 1mm larger than the stanchions, so there is fair amount of play without the spacers I fabricated. difference in dameter makes the stanchions touch the outer tubes on 2 points instead of a large surface, under braking especially. My theory this 2 point contact is not enough for the oil film to hold on and as a result the chrome coated tube scrubs the aluminum housing creating a big friction, if I could explain. when the fork is taken away and pushed down on a straight line wit 0 bending moment it works just fine , but under braking force which creates a bending moment it just locks itself. What ever it is with the custom spacers and narrover seals it is working now ( like each of the forks on other bikes have).
The spacer is keeping the stanchions on the same axis and preventing the play on the down tubes.May be the forks was used without oil inside for a long time and this ruined the setup. hope my solution lasts long enough to have some fun for this winter.
I've attached the page from the MH 349 parts manual showing the fork internals, looks to me like only 1 seal per leg and no spacers. It's the same in the 349/4 and 350 manuals I have also. No extra threaded hole in the head for a decompressor on any of these models.
Thanks for your help. I dont have the original parts manual for MH 349. it would be great if you can share that one with me. At the moment I could make the fork function by manufacturing custom spacers under the seals. Without these spacers the fork tubes rub againgst the fork outer aluminum lower tubes under compression and this makes great friction. May be this problem is becouse I am using aftermarket seals. these seals can not hold the stanchions co axial with lower tubes, so with hard plastic spacers stanhions is held in place and on the same axis with the loer moving part.
a few things still needs to be sorted . even with new seals, fork is leaking little bit, clutch oil is leaking , need a front fender , but it starts very easy at firtst kick.
This was the first time I have ridden a trials bike, it feels very light and fun. the engine is strong and seems un stoppable. I need some time to get rid of clutching addiction.
As for your fork seals, if you can, just buy seals of a width that takes up the space between the seat and the circlip. That spacer in the parts diagram is not a guide for the fork tube, it is just a spacer. Two narrow seals per side or one wide double-lipped seal per side will do the job of sealing the forks. The fork tubes are held centrally in the seals by the precision-machined bores of the sliders.
If you are really determined to make plastic spacers for the fork seals, just make them the right width so that the circlip just touches the top of the seal.
Bear in mind that a couple of my old Spanish trials bikes have no circlips on top of the fork seals and I have sealed up the vents in the fork caps and I run enough oil to firm up the last bit of fork travel using internal air pressure, and those fork seals have never moved out of position. From memory I think the seals are double-lipped and 10.5mm wide.
I could not find a suitable seal which the space could take two of them. I will try to use one seal with single lip and see the result. This is what I can find at the moment and I want to ride the bike on September. I ve got soooo litle time toooo many projects
I will definately make them in size with the seal which has 47x35x6mm dimensions.
By the way I can't say the bores of the sliders are precision machined unfortunately. The fork tubes are 35mm but the bores are 36. and at the current stage the forks was moving realy stiff after a few cm. And the only thing I could find is the missing spacers. Actually I will check again for a bent tube before installation, I could make it straight if there is any bent part.
If you use the type of decompressor that resets itself, you set it to the open position using a knob on the end of it, move the piston to the right spot, kickstart the bike and it then closes itself.
There is also a type of decompressor that has a handlebar lever so you can open it while easing over TDC, kicking it, and for braking effect while riding.
Are you sure your head doesn't already have a hole for a decompressor? It was fairly common back then to have a decompressor hole.
Cota 349s do take a lot of effort to kickstart. I have a 348 which is only 310cc and kickstarting it is usually the most tiring part of riding a trial and 349s are even harder to kick over. It would be good to just leave it running all day but it is fairly hot here and they overheat if you leave them idling for too long.
There is a blank space for the decompressor but it isn't drilled and tapped. As soon as I know older ones have the place for it. This is MH 349. The only type of decompressor I could find are the ones for hacksaws I think they can be used instead . I had a KTM 400 SC and it realy starts much easier. I will try to do my best on ignition and carburetor and wait and see how it performs on kick start. Or I will carry a rope to tie it to my friends bike for a running start
Keep it idling is out of practice its already 35+ degrees here. My biggest fear was the starting of this bike since my right ancle has problems, Ktm is a left kicker.
Well I measured the seal places. The seals you have mentioned are 35x47x7 mm, and there is only 8.8 mm under the circlip for seals. So it is impossible to fit two7mm height seals in place, besides there are 2 different part numbers so I dont think they are the same parts. I am confused :(.
By the way I sent inmotion an email describing my problem, waiting for the reply.
thanks for your feedback. I've been thinking about it but machining will be necessary, this involves the removal of the cylinder head. I have never used a decompressor before and I dont know how to use it. So I could not be sure about the benefit. I know that it will relase the compression, but is it only for taking the piston to tdc? or can I kick start while pulling the decompressor?
The air filter sorted out. The points gap is set and it starts at the moment. But i should say it is really difficult to start with tons of compression. Is there an easier way? I have already trashed 2 shoes :-)
The front suspension was not working properly, so i took it apart.as soon as i see from the diagram there are 2 parts under the circlip. One is the seal the other is the bushing i guess. Well the bushing is missing:-( on both legs. There are 2 part codes there. C000.993547 which i think the seal and 0CM1.35037 (seen on the diagram below) which i think the bushing.i have purchased the seal 6x35x47 mm dimensions, but i couldn't find any information about the bushings. I am about ti machine them out of some kind engineering polimer. But a proper picture would be helpful really. so I can machine out a similar one
Hi dr. I think I've traced why my forks didn't work properly when the wheel was in. They work perfectly without a wheel regardless of the rotation of the stansions. As you said neither the hub or brake plate belong to my bike and when I sent some pictures to InMotion trials they said the brake plate was off a Fantic and had no idea what the hub was from. I had to prise the fork legs apart to get the wheel in.
I had a friend machine the brake plate either side and take a little off the spacer so it was 1mm narrower than the forks and this seems to have worked.
I looked at a diagram of the 349 forks and the part you say is actually a second fork seal. When I rebuilt mine my local trials place who just happens to have an extensive knowledge of Montesa and Bultaco twin shock looked it up on his microfiche. I've attached the 349 manual I saw it on and hope it helps.
Thanks for your information. well ı havent seen the part in person, ı havent seen any pictures but it is a little odd to me to use a second seal at that place. one reason is there shoul be some pressure build up inside the seal to seal properly. if there is a second seal under the actual seal , it would prevent pressure buid up and the actual seal becomes useless.
cota 349 is using 35 mm fork tubes, but the inside diameter of the fork legs is around 36 mm. so imo there should be some kind of friction bearing material under the seal. my bikes forks had to be used without those parts for long time and I can see the signs of wear on the lower part of the fork tubes. Besides every other fork that I have taken apart up to now had some kind of friction bearings in that place. so I have drawn a piece to be manufactured out of engineering polimers that you can find below. if anybody needs to make one of these, this drawing belogs to a piece to be used with 6mm height seal. the seal dimentioned should be 47*35*6 mm.
I will some oil chanels and install them in shortest time. I can share the result.
But I still wonder what the actual part is under the seal. Even if it is second seal, a picture would help me a lot. I live in turkey and I think this is the only example around.
the hub is definately not from a cota 349. to be sure about the straightness of fork tubes , remove the wheel and put the axle on, be sure that it can be installed easyly. Remove the axle turn one of the fork tube from the triple clamp 180 degrees and apply the same procedure . The axle shouldbe easyly anstalled on each attempt.
I have a similar problem by the way. the forks arent moving freely. it requires a lot of pressure to compress the fork. I tried to refurb the forks but I found that the parts under the seals are both missing. The part number I can on the spare parts is C000.993547 ( if this is the right part??) . make sure they are in place
Anyone have any picture of this part? any dimensiones related? I will probably have to make one since I could not find it any where.
Sounds odd. Maybe the oil is leaking down out of the inner tube when the shock is not moving. Does the free play go away after a few rapid strokes? (mounted on the bike so you can work it quickly)
Yes exactly, the oil is leaking to the outer tube. I thought this was normal. I think i have a problem. This is the first time i have attempt to rebuild a shock. When i pressurise the inner tune with my breath, i can hear air leaking from the bottom. So i guess there should be a 2 way valve on the bottom of the inner tube. There was a nut that i didn't unscrew i guess thats what i should deal with.
I don't remember the amount now but I usually put in just enough so that they don't snore. You can test for this before screwing the top on.
5WT is better than 10WT for them
Well i searched for seals today and get the same answer in the industrial equipment shops"this is a very specific seal you can't find it". And yes, they are specific. 11x24.5 mm like a disc. But they don't appear to be completely gone. I have manufactured the valve springs and tested. There are 2 adjustments for rebound. 1st the valve opening amount 2nd preload. But what ever i tried the shock is either have a free play about 15 mm or it is going hydro lock just before bottoming. May be i have to put a bump stop about 20 mm to prevent a hydro lock. But the shocks are working with less free play when they are upside down??? There is no pressure valve so the level of oil inside the inner tube is under the piston level, if i add more to keep the piston in oil when fully extended, then it hydro locks before bottoming. Any suggestions?
Read this one, but this is a different design, the valving and retainers are different. Mine has a screw on retainer with the seal. My problem is yhe seal
Hi, I am currently working on it. Betor twin tube oil shocks actually. If I can achive some good results I will share. Did you come by a good solution?
There is a bloke in the USA who makes new shaft seals for 1970s Betor shocks. I've bought and used some in the Betor shocks that came on Alpinas and OSSA explorer. I saw them listed on eBay by this person about a year ago. I looked for ages and have not seen them available from anywhere else. These might not be the right size for your Betors though because some 1970s trials Betors have a thinner shaft than the one I rebuilt
You can always turn up a new seal retainer for your shocks and use whatever hydraulic seal is available locally to suit your shaft size
Hi
I will probably machine the existing retainers to suit a proper hydraulic seal. Any ideas for the oil (10wt?) and level?
Where are you?.....post gets to most places....I've even sent a letter to the North Pole
Well, i am in turkey, and it seems like i am the only one in here with a twin shock trials bike which was accidentally brought here by a Spanish family with a caravan and left over here 8 years ago. This means i have to refurb or fabricate everything by myself. Luckily i am mechanicaly mean and have good experience :-)
I have realised there is no damping left in my shocks. So i made my mind to take them apart and inspect. first of all I am happy its a a rebuildable design. İt has a threaded cap that lets you to reach internals.I opened the cap and saw the spring on the bottom of the piston rod is broken. I can make a new spring thats not big deal. The shocks are twin tube design the o rings and seals are far gone. I can replace the o rings but the shaft seals seems to be very narrow design . I can not find any information on rebuilding this kind of shocks. they are not gas shocks . Any information will be very helpful. Major problem is the seal dimensions and availability, amount and type of oil. I have to rebuild these shocks there is no alternative product here and no chance to be imported. I will rebuild these or stick with chinese stuff
Could be a non-standard coil, that metal plug cap is definitely not original.
Gearchange mechanism can be fragile - I'd raise the gear lever to avoid hitting rocks.
Posssibly Marzocchi rear suspension? Bits for rebuild should be obtainable even though they stopped making motorcycle stuff a couple of years ago.
It won't run at its best with the altered air filtration arrangement, this might be part of your problem.
I have inspected the shocks again, they are betor shocks. The cap is not plugged it is treaded which is good. The seals are far gone and internals seems to be ok except a spring. But i can make new springs, no problem. Will try to find oil seals.
Air filtration is terrible, there is only 25 mm air passage behind the cone filter. This can lead to wrong operation of air correctors. There is big repair on fuel valve on the gas tank. The threaded inserts in the plastic tank came out.The air filter box had a big hole. I am repairing them at the moment but i can't share more pics i think there is a limit which i wasn't aware and i have used it all by mistake.
The engine seems to be picking up fine but then it loses power when i am expecting it to kick in. After air filter system is ok i will try to deal with the timing.
I hope the needle jet is in good shape, that will be difficult for me to source one.
Stripping the forks should be fairly straightforward. You'll have to unscrew the allen bolt in the bottom end of each slider, holding the internals to stop them spinning as you turn the bolt. Be sure to fully unweight the front end when you unscrew the fork caps (bike on a box or stand with wheel off the ground) as they have very fine threads which can get damaged if there is much pressure on them from the fork springs just before they come to the end of the thread.
Thanks, where can i find info on refurbing rear shocks. Searching the web for hours but didn't cone by a shock with similar internals. I think this is a twin tube design but base valf system seems to be located on the damping rod :-( i am confused....
Hi Here are few more pics. I couldn't stop myself from taking it apart.
It has a broken air box, but luckily ex owner put a kone filter in there bit with a narrow connection about 30 mm
Exhaust is leaking heavily from the silencer inlet
Take one of the shocks apart. See it can be rebuilt. The valf spring inside is broken. Not sure if the seals are ok. I really need some information on rebuilding these shocks.
The fork isn't feeling ok. I couldn't find a clue it is bent, but it doesn't operate smoothly, any info on rebuilding these?
Someone has been played.with electrical system. The book i jave.states that cota is 6v system but this one seems to be 12. There is a rectifier and some.relays for headlight and horn. I want to get rid of them anyway but affraid to ruin something before undetstanding what is what
Front brake pivot tread is completely gone, i should retap it with m12 i guess
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montesa cota mh 349 help needed
in Montesa
Posted
yes I know but I was affraid that this will increase the air pressure inside and lead to sealing failures. Actually I think the fork spring rate is too soft for my taste, is it common for twinshock trial riders to put some spacers under springs?