Hardcore clutch splipage on XR250 with 287cc big bore

[tysonzane]

Hey, im overall pretty new to motorbikes but have done a full season of trail rides with my XR250 so when it came time for a rebuild of some valve train etc, i decide to put a big bore in with a Wiesco piston and just freshen up everything else. The big bore kit was great and it felt like a new bike. Since then i have had clutch problems usually 20 k into a typical trail ride i get some really bad slipage and it doesnt become fun or easy to ride anymore.

I have taken the clutch appart and lighly emeriod up all the disc's and plates and this made a slight improvement for a while but it came back. The plates now have hot sports on them and appear to have warped. The discs are just on the service limit and apear to not be getting enough oil.

I have aquired a good second hand pressure plate and clutch holder basket along with some very good metal plates. I will buy six new fibre clutch plates. The existing springs are 3 or 4 mm over the service minimum so are okay.
Questions: Can you get heavy duty springs and from where?
I hear you can drill extra holes in the clutch holder to let more oil in and around the plates to help "cool" the clutch - is this so? and where do you drill these holes? There are four sets of holes (two each) around the clutch holder - do I double up on these?
Thanks for your help on this.
regards
TysonZane

[spiller]

As for the springs, you may be able to use ones from a larger XR. The guy I trail ride with rides a worked ex-shane king KTM 125sx, using 250sx springs.

[Brian d marge]

The trouble is with stronger springs is that they are a quick and easy fix Using uniformed pressure ...the torque carried is proportional to the number of contacting surfaces the upshot of all this is ....for the same lever feeling you get better results by trying to get an extra plate in there ,,

The time ole dodge of roughing up the plate works for 2 or three clutch actions then you now have even smoother clutch plates and havent actually fixed the problem

Drilling the inner basket allows more oil into the plates ,,,the oil is there to remove HEAT ,,thats all the oil does( so if there is no signs of excessive heat...) and may cause plate sticking in which to plates stick together and act as one ,,,effectively reducing the torque carring capacity to half ....( I my MX bike I use ATF ,,,its good for ONE or TWO races ONLY ,,but makes a difference )

So if you are just trolling around trails ..then the heavier clutch may be the answer ,,but IF you are using the clutch like a mad man on acid ,,in a 4 hour Iron man ...then you want to see if you can reduce the lever pressure by adding extra plates ...( I have same problem on my MX bike,,,feel the clutch on an older CR and on the new crf ,,,the crf is a one finger job ,,,,,,...

Good luck

Stephen

[Motu]

Replace all components with new - that's your starting point.Seeing as you have modified your motor the clutch may not be able to take it,there is not a hell of a lot of reserve built into these things....just enough.If a completly new standard clutch can't take then you'll have to try an aftermarket one.But stop stabbing in the dark with secondhand parts,do it right the first time.

[tysonzane]

Thanks for the reply guys. I was hoping to hear from somebody who has an XR250 how has bored thiers out to around the 280 mark, because it is apparently a common problem when doing the upgrade because of the healthy increase in torque .

Cheers :thumbsup:

[Brian d marge]

And they will tell you what we have already told you ....( or should do ) ...As Motu say ..make sure the clutch is in good working order ..( measure and check ) , if not chuck a new set of plates and springs in..... DONT worry you will need to use them anyway ,,,which ever way you go

Second . Decide how you are going to use the clutch ... ( me i need it one or two finger operation as I use it A LOT )

If You decide that the Heavier clutch springs are the way then go with that ,,but you will get increased lever pressure which will tire your hand in tricky terrain ...

Third investigate installing another plate , ( this is the most difficult, and a good engineer with the clutch basket in front of em ,,there are heaps of after market stuff for those ,,,especially in America ...( read big bucks ) )

You can get a bolt on automatic clutch for CR 250 , and I would be at all surprised if they shared a common basket ...

But your clutch slippage shows how close to the edge of the design the clutch is ....


Stephen

[marty]

it's the oldest adage - don't freshen the top without freshening the bottom - works for heads, clutches etc etc. find an xr500 clutch, or better still, just find an xr500! (i don't even know if the 500 clutch will fit...just winding ya up!)

[rudolph]

Try pulling the clutch apart and washing the fritcion plates in petrol, get someone to beed blast the steel plates and check with the book how meny in the stak.

None of this heavy spring crap

[NordieBoy]

My XR250 got the plates beadblasted, new fibre plates and heavy duty springs.
Clutch feels very heavy when trying it stationary but when on the move I don't really notice it.
But I wouldn't say no to being able to stick an XR500 basket in there.
What do they have? 11 plates? Mine has...... 4

[Brian d marge]

My XR250 got the plates beadblasted, new fibre plates and heavy duty springs.
Clutch feels very heavy when trying it stationary but when on the move I don't really notice it.
But I wouldn't say no to being able to stick an XR500 basket in there.
What do they have? 11 plates? Mine has...... 4

there you go 4 plates ... 1/2 the size of a 500 with 1/4 of the torque capacity ...most likely slipping evn when new ....

As for shot blasting the plate ...friction is independent of area all it does is make a lot of hills and valleys which sort of inter lock ( this is the simplified version as there is 6 min before I finish work ,,,,)

The tops of the moutains break of easier causing debris , and ia little increase in heat ...and when all the tops of the mountains have gone you are back to square one ....

That 500 basket sounds like a good plan ...you could even run ,,,softer springs ,,as in other peoples Old ones !!!!

after forty min of fanning a laverda clutch ,,you would be beggin for a soft and gentle wee spring!!!!

Stephen

must check the cr when i get home to see what it has !!!!