Gear Box Selector Tolerance ??

[Lynxx]

Hi all, I have a 1985 MTX200 and the 2nd gear is shot, anyway i have a spare transmition and i was wondering how much slop is natural in the 2nd gear and the shift fork that slots into it.

The shift fork i have is worn down on one side but the gear is in perfect condition. MAX 1mm slop in the selector/gear. If anyone could tell me the tolerance for this ?

Thanks Tom
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[bikenut]

:karma: hi dude,

mtx200 you lucky dude.......

is there not a manual on this site even for a 125mtx?

if the selector fork is worn down on one side there must be a reason?

a worn selector fork will result in poor gear changing with the gear not moving the required amount resulting in gear only half selected, wearing drive "dogs" and jumping out of gear( which could be very disasterous.)

new selector fork and gear and find out why the uneven wear ( over selection perhaps )

feedback please with some pics?

[Pete.]

Bikenut's right the slop will be in the selector fork. The fork wears a lot faster because of the small contact area compared to the whole circumference of the slot in the gear, plus the gears are usually harder.

Could be any number of reasons why the gear is worn one side But most likely is plain old wear and tear. Dave Silvers might do you a new shift fork, if not you could effect a repair by welding up and filing/grinding back to shape.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Lynxx]

Well the 2nd gear is a common problem in the mtx, and the forks are near impossible to get, I've tried Dave Silvers and probably over 40 different breakers to no avail. I have 3 spare forks, but they are all worn down on the one side (mtx fault).

I have not stripped down the 200cc yet, i just know what the problem is (that 2nd gear, or the fork) So i have a replacement 2nd gear, and the gear next to it. The only bad part is the shift fork, i cannot find one of these for my life. SO will it work with the pad on the shift fork worn down ?

SPECS so far, good gears have about .5mm slop, the bad fork has 1mm slop.

Will it work ? or will i have another crap transmition and a waste of time.

Thanks Tom

ohh and ill upload photos in a few.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Lynxx]

https://desmond.imageshack.us/Himg10/scaled.php?server=10&filename=img0035ov.jpg&res=medium

https://desmond.imageshack.us/Himg17/scaled.php?server=17&filename=img0038sf.jpg&res=medium

https://desmond.imageshack.us/Himg209/scaled.php?server=209&filename=img0036tw.jpg&res=medium

https://desmond.imageshack.us/Himg651/scaled.php?server=651&filename=img0037ww.jpg&res=medium
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Lynxx]

if i was to weld the fork, which i could do for free or for a very small sum of money. Would i need to case harden it ?
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Pete.]

That is no easy question to answer without some metallurgical knowledge and knowing what they are made of. Bit beyond my scope of knowledge but as I see it there are several options:

Find out what material they are lkely to be made from would be my first choice. I would think, some high-nickel steel alloy is likely, but that is only a guess.

You might weld them up with normal welding filler, mill and grind back to shape and use them as-is. Or do the same as above and case-harden. The more heat you use the higher the risk of distorting the hole that the fork rod fits with a sliding fit.

You could weld them with a hardfacing rod or some other high-nickel rod and grind back to shape.

You might try asking on a welding forum such as mig-welding.co.uk as to the best chance of successful welding without wrecking the fork itself. What do you have to lose, they are knackered anyway?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Lynxx]

True, they are aluminum. If i was going to weld them i would use my ex employers MIG alloy welder and file the weld back to profile.

I could probably weld it for free or for a few quid, so i will give it a go in a few days. Only problem is, if i weld it and its too soft.. i get metal shavings spread all over the inside of my engine. Luckily its not a 4 stroke, and the transmition is separate. I've already fried the rocker arms, cam and cam cover on my XL350 with metal shavings blocking the oil pump filter to the cam !!

What i dont understand is how will .5mm make it not go into gear ? if you look at the shift drum, when it shifts gear it moves at least 6mm to go into gear. so hows .5mm causing such a big deal ?
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Pete.]

Don't assume that because there is 6mm of dog to engage it will use all of that 6mm. Very often I have seen dogs that only just caught on the edge (like Binge's CRF). Look at the wear on the dogs to judge how much engagement you've been getting. also allow for a bit of flex and endfloat in the assembly under load.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Lynxx]

yeah, that's a point. Every MTX gear box i have dismantled had the ears on 2nd gear worn down and polished, Luckily the transmition i have is in perfect condition other than the selector fork.

I think the one in my bike at the moment is good, but not as good as the one i have on the table. I built the transmition in the bike at the moment out of a box of gears, so i used the best parts available.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Lynxx]

OK so here are the list of problems i was having...

2nd gear (the moving one) the fingers on it were rounded off..

2nd gear (the stationary one) the slots in it were rounded.

2nd gear shift fork.. worn down like all the others.


So i replaced all the gears in the transmition, and re-used the selector fork. It will last a while i guess, not the ideal fix, but when a gear box comes up ill get a new fork.

Will upload some photos of the broken parts as soon as the camera battery is finished charging.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Pete.]

If the dogs and slots were rounded that suggests minimal engagement. What I would do is take one of the other worn out shift forks and build it up with TIG and re-shape it, then fit that the next time I have cause to take the engine down.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Lynxx]

i apologize for the brightness of the photos, but you can make out the effected areas.

https://desmond.imageshack.us/Himg717/scaled.php?server=717&filename=img0044qi.jpg&res=medium

https://desmond.imageshack.us/Himg706/scaled.php?server=706&filename=img0045bq.jpg&res=medium
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Lynxx]

https://desmond.imageshack.us/Himg689/scaled.php?server=689&filename=p0043060212.jpg&res=medium
1st picture you will notice the dog is completely gone and is rough

https://desmond.imageshack.us/Himg856/scaled.php?server=856&filename=p0044060212.jpg&res=medium
2nd picture you will notice the fingers are worn down where they slot into the other gear (below)

https://desmond.imageshack.us/Himg838/scaled.php?server=838&filename=p0045060212.jpg&res=medium
3rd picture you will notice where the gear (above) slots in, it is rounded right off, making it hop in and out of gear when under strain.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[steven_191]

looks like that smaller gear will need replacing if im seeing it right. I assume that step on the edge of the teeth isnt supposed to be there. It looks fairly worn but even still, i dont see that once its in gear, that would be the cause of it dropping out.
Im no expert on gearboxes but really i dont see why that would cause much issue at all.

I would build the gearbox up in one side of the engine casing so that you can turn the shafts and move the selector drum and see if there are signs of the gears not engaging. I would start by looking at wheather or not the drum/selector is pushing the gear in enough to properly engage?
if the worn edges are the reason for the difficult gear selection maybe they can be rounded off to ease the gears slotting together?

If you have spare gearboxes try to find the best parts out of the lot as a cheap alternative to buying replacements, especially if they are rare.

[Lynxx]

yeah the parts are rare, i tested it all and it seemed to shift good.. the bikes 2nd gear worked today for a little while then started its crap again. I'm going to see if i can weld the shift fork or just buy another one.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Pete.]

Yep poor engagement on the dogs. They aren't terrible to be honest but clearly enough to let it jump out.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Lynxx]

Its just a terrible design on the bike overall, i don't know what the japs were thinking when they designed it.

- The water pump is incredibly poorly designed
- To remove the cylinder you have to take the head off (any other 2 stroke has 4 bolts accessible without removing the head)
- 2nd gear is designed to go (3rd gearbox I have replaced)
- and that stupid head cover that cracks a lot ?? whats that for, why not just go like a RM or CR and let the antifreeze flow through the head and cylinder..

And parts are as rare as chicken teeth...

this is not the 1st part i have welded, on my last engine i welded the cases where the transmition exploded and tore up a 200cc case.

My plan is to weld the fork, cool it in used motor oil to harden it.. file it down to profile then heat up (not red, but hot) and dip in the oil again... hopefully the oil will give it a case hardening effect.

ohh is it wise to make the tab longer on the fork ? i think if i make it bigger (longer) it wont wear out as fast ?
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[Pete.]

I agree they would be steel or some alloy of it. A quick touch on the grinder would tell. I wouldn't weld it more than the original size.

If you have more than one spare, why not experiment with some hardfacing rod. That would last a very long time.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Lynxx]

yeah i was wrong they are steel, i thought by the coloring and texture they were aluminum.

Owell steel makes it even easier. And by the coloring of it, it also looks like the part that needs welding was never hardened (its a lighter color) the other part that takes a lot of strain looks hardened (its a darker color).
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

[gwernybwch]

[Lynxx]