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Advice/thoughts on top end and clutch. 74 TY250A


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Hello esteemed, revered and acclaimed masters of mechanical know how!

i have found tillerman6's posts/replies enlightened learning and would like to thank you all for your input.  Thank you sincerely as no here (in NYC) even seems to know what a trials bike is!

so question 1, as a noob who is trying to get more confident, i was feeling inspired to try and do a top end tear down and learn more about the piston/chamber etc and at least assess current conditions and hopefully allow me to feed the addiction of buying new parts if needed and replacing (or stashing for later)...

having already asked on here about the oil seals, and been encouraged to go down the route of  'if it ain't broke don't fix it'...i am wondering should i apply the same philosophy to the top end as i did a compression test today and got exactly 7.0kg/cm2 as per the manual. (fyi, it had been idling for about 10 mins so was warm and i kicked it 5 times without adding any oil to the chamber)

deep down i feel to leave it alone even though i want to  learn more.....

question 2, when taking the clutch cover off, i noticed the friction plates looked like they were rusty.. is this normal? 

the clutch feels and works fine and the bike was stored inside for the last 30 years with only little farm use from new...could it be feasible...gasp...that its actually still ok or is it likely i should replace the springs at least?

i want to measure the thickness of the clutch plates/springs as per the manual but am curious if getting the clutch apart is something that a noob could tackle and does it need the clutch holding tool just to check the plates?

again,  thanks all so much for your help.  And tillerman6, god bless ya man...riding out into the sunset on ol' mellow yellow 70 years young....i hope it goes well getting your new piston sorted.

best wishes from a sweltering NY :)


few pics for you.









Edited by johnnyjazz
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No special tools needed to remove the plates, only if you're removing the hub & basket

Probably nothing wrong with the friction plates, have the feeling the only steel in the clutch is the drive plates & that the friction plates are plastic but I could be wrong. If you do strip the clutch either deglaze the steel plates with wet & dry sandpaper or get them blasted

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  I am just guessing, but by looking at the pictures it looks like that brown on the clutch plates may not be rust at all but just some sort of brown coating that looks like rust. ??   It seems hard to understand how rust could develop inside a sealed clutch compartment that is filled with 1000 cc's of gear oil?  Unless it is only on part of the periphery? 

Unless you have lost most of your gear lube before you took the clutch cover off?  And if that was the case then all the gear teeth should have also been rusty too, and they are not, So it the clutch was working properly you might be better off just checking out the parts manual diagrams and know that when the time comes, you will know what you are looking at in terms of parts placement and how a motorcycle clutch is constructed.

P.S. Thanks for the encouragement on my bike.  It is a labor of love for me.  I wish I had another one to ride while I'm waiting for my cylinder to get overhauled.!   It is a slow process and I would have waited until the snow was flying to tear into it if I could have, but it was making so much noise that I was afraid to run it any more without seeing what was causing all that racket.  As it turned out it was mostly (I think) just a clogged up silencer that was the culprit, and not so much the piston slap, 

So when you put that new gasket on the clutch cover and fill it back up with 75 Weight gear oil (I use Belray)  and lube and clean your clutch cable and lever and adjust the linkage,  Then go have a look at the condition of the silencer and see if it needs cleaning too.  Mine was so bad that it almost would not start, and when it did, it would blow blue smoke out of every joint in the exhaust system for a second or two until the carbon in the restriction portion of the spark arrestor finally opened up enough to let the gasses out the rear end! 

That "modification" to the cylinder wall is still a mystery, but no longer a factor with the "new" cylinder now on it's way to Millenium.   Thank God for Ebay!

And P.S.  I only changed the main seal on the left side of the engine under the magneto.  And that was enough of a challenge to get the points to work again that if you really want a challenge, look no further than that.  (or the spark arrester)  

P>P>S  There is a trick to pulling those seals, so you don't have to split the cases to get the seals out.  Just drill a 1/8" or smaller hole in the hard part of the seal ring and insert a wood screw with the tip ground off slightly blunt on the end so that you don't scratch your bearing inside. I did it that way and used two holes at 3 and 9 oclock so that I could get some equal pull on both sides of the seal. Mine was really stuck in there!  Be very carefull with your drill and use a drill stop on the bit to only allow a 1/16" deep hole!  The bearings are right behind the oil seal so use extreme caution and be sure to clean out any chips that may fall behind the old seal.

Good luck!






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Those clutch plates are meant to be rust-coloured.

If you want to do some useful maintenance on your bike, the things to fix on an old TY250 that has not seen much use are usually the steering head bearings (rust), the steel inner bush in the swingarm pivot (rust) and the magneto side crank seal (gone hard)

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hi feetupfun/anyone else, i  took your suggestion and today inspected the swing arm for wear.  the bolt and steel inner bush just slid right out (thankfully) but i noticed a few things on the way and am just curious.  i know there's no such thing as a silly question and we are all ignorant about something, so if you might indulge me....

i noticed there were no shim/spacers in the thrust covers...does that matter?

also noticed i seem to have two extra lipped washers that don't seem to be listed in my parts manual (top far right in pic).  they go at either end of the swing arm bolt on the outside of the frame.  is this normal or has someone done something- should that bolt be up against the frame? 

and lastly, i noticed my inner steel bush has holes in it.  i can see how this would help distribute the grease, but in my parts manual the bush looks solid as it does on tytrials website of their swing arm replacement kit. wondering did someone do this themselves or was this standard?

maybe its all exactly as it should be or maybe not...but i'm certainly no expert!

learning so much on here from you all.

as always pics attached and many many thanks!!!

swing arm.jpg


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Those extra washers on the outside of the frame plates are unusual. Possible reasons are:

Your swingarm pivot axle may be a bit too long. The trail riding kit for TY250s may have included a longer bolt to suit the trail riding footpeg mounts being attached at the swingarm pivot, and your bike may have one of those axles.

Previous owner thought it would be a good idea to spread the forces. Is there damage at the holes in the frame plates?


Shims are used if the width of the swingarm is less than the distance between the frame plates. Some bikes match without shims and some bikes need shims.

Holes in the inner tube:

Yes, original inner bushes have holes and if you loosen the swingarm bolt before using the grease nipple then you may get some grease to flow into the space between the inner bush and the axle. However, because you can slide the axle out to grease it or to apply anti-seize, the holes are not necessary.

They also serve to lighten the inner bush. If you are serious about lightening your bike, you can buy ready-made aluminium inner bush and aluminium axle.

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thanks feetup fun!  you the best.

yes, now that you point it out..of course! thanks for helping me figure it . the bike came with the long seat and long brake pedal, so it figures it could have had the trail kit pegs fitted. someone must've taken them off and kept the longer spindle.  i see i can pick up those foot peg lowering brackets still...though im assuming down and forward isnt the best for trials, would it be more down and back? - though seeing as the ol beaut is street legal and 90% riding i do is on road maybe it might make it better sense? -  though probably make much more sense to get a decent road/trail bike! haha 

great to know inner bush isnt wierd and no shims isnt a problem if i dont need them.  thanks always man.  really!

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The modern aftermarket TY250 footpeg kits have the footpad slightly lower than standard and back a little bit which makes it more comfortable to ride sitting down compared with the standard location and better for trials too. The TY Trail kit footpeg location is terrible for trials being too far forwards, but is probably the most comfortable for riding while sitting down.

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   A little more researching and looking at clutch replacement kits and I discovered that the brown tips of the plates you showed in your picture are actually made from friction material which is naturally brown already.  So that is not rust you are seeing in the photo, just normal friction plates!  Makes sense to me.  Every other plate is steel, and every other plate is friction material,

So I would leave it alone until you know you have a problem.  But since you drained the oil you might want to try some Belray 75 weight gear oil.  That stuff is great and the clutch pulls in like butter.

Does not seem to need as much clutch lever force as before to get it to release either, so I think I will stay with it.

If you are still thinking about replacing the main seal under the magneto (mine was leaking 2 stroke mix)  I put in a photo of the seal that was removed with sheet metal screws and some very carefull shallow drilling of the metal ring which is built into the seal itself. 5b989858e3f96_LeftMainSeal.JPG.87f18274f403c5299652d5ab7d2dd29b.JPG5b98985c9b031_LeftSealremoved.JPG.651e713fd495cb7ce68bbd534ff9d99c.JPG

Edited by Tillerman6
Add photo and comments to my last post
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