ATC90 Clutch Problems

[kb0nly]

Ok i am at my wits end with this thing...

So back story, ATC90 that was having a heck of a time with a slipping clutch, first gear worked but it would slowly launch and sometimes you had to push it a bit to get it going. Tore it apart today took the clutch apart, washed it out, put in new clutch discs, the metal discs actually looked fine but i gave them a cleanup as i have done many times before with 120 grit sandpaper, checked they were flat, no warpage, the old clutch discs were just shot, the interior of the clutch was full of clutch material, measuring them they are below spec and you can barely see the grooves between the squares on the clutch plates, it had a hard life before i owned it apparently!

So anyway, got the clutch back together, tested it in hand, spins freely with just a bit of resistance in the clockwise direction, counterclockwise it locks up with about 1/4 turn or so, just like the picture shows on Dr ATV.

http://dratv.com/clutchtesting.html

Everything seems fine and is what i am used to when i have done these before. Put it back together, adjusted the clutch, shifter goes down and clicks into first and returns nicely, shift linkage all seems good, shift drum stopper is good, everything i can think of is fine.

But... It don't work! With it running if you put it in first gear she just jumps and stalls, it will free wheel when you test it in your hand but back in the motor its like the centrifugal clutch isn't working and for the life of me i can't figure it out. I never had one do this before. I've had it back apart and put it back together a total of seven times now, same result every time. So i am stumped, i never had one that passed the test spinning it by hand but then behaves like this installed. Anyone got any idea whats going on here??

[kb0nly]

Still trying to figure this out if anyone has some ideas??

[shortline10]

I’ve had this problem when trying to use aftermarket fiber plates , they were made to thick , OEM , Vesrah or Barnett are the only plates I will use .
It should free spin with very little resistance one direction .
Also make sure you have the little pin springs installed correctly .

[kb0nly]

They are Vesrah, that's what I use also, free spins one direction little resistance, taken apart and verified the springs a half a dozen times. I have to get some new case screws at this point, had it apart so many times over three afternoons the heads are about shot. Clutch still not working right.

[DAM shop]

Is this something that was like that when you bought it? Or did you just start to experience It? The reason I ask if it was an issue you inherited maybe it’s a wrong part installed.

[shortline10]

Parts 4 , 16 , 22 and 17 are the centrifugal part of the clutch . I have seen these worn and broken and cause clutch issues as well .
https://www.partzilla.com/catalog/ho...atc90-a/clutch

Did you check eBay ? A used clutch assembly might be your best bet , if it slipped as badly as you say it’s probably ready for the whole assembly .

[kb0nly]

This is the 90 I have had for years now, I had a rebuild thread on this one when I got it. Always worked fine but we have not rode it a lot until the last year or so, that's when I noticed the clutches were a bit soft, but I never replaced them when I cleaned up the motor because they were working. I do have a complete second clutch, it's a spare I have had on hand, I was going to swap it but I didn't know if it was much better so I decided new clutch discs instead.

I took the spare apart compared it step by step piece by piece with the one in it, and they are put together identical.

I did discover one thing... I took it apart again and when I put it back together I put the clutch nut on at the lower end of the torque spec, I forget what that was today was busy, but the manual had a range and I tightened it to the bottom end of that range, and now the rebuilt clutch is not locking up and jumping when put into gear. It does however slip the smallest bit on takeoff from first.

That's odd.... Looking at the spare clutch why would the clutch nut torque affect lockup of the centrifugal clutch?

I might have to put the spare clutch on when I get time and some new case bolts and try that for comparison. It is currently working though, it can idle in neutral or while in gear again and not lockup.

Maybe I should give the clutch nut just a bit more torque and see if that affects takeoff in first. Just odd!

Comparing the spare and rebuilt clutches though, even down to measuring parts with a micrometer, I'm not seeing much difference in wear of the centrifugal clutch parts though.

[GTO]

I had a similar problem with an old ATC70 engine that I rebuilt the top end, clutch was working prior to the rebuild but I installed new plates anyway, but afterwards if I engaged 1st gear it would move forward or stall.
I know I had adjusted the centrifugal clutch correctly(done it plenty of times), it drove me crazy I reset the adjustment, changed the clutch plates back to the old ones, clutch mechanism seemed to be working, checked the idling countless times.
I asked on a few forums including this one but no answers, I almost gave up on it.
The other day I was wondering what if I try turn the adjuster further in, I had turned it in as the manual says until resistance is felt like I do on all of my ATCs.
So I turned it until resistance was felt but it could actually go further in until it was really tight so I turned it until it couldn't turn it anymore. The gear lever was solid and it wouldn't move so I backed it out slightly about an 1/8th of a turn like the manual says.
My problem was solved no stalling or moving forward!
Thats all it was!

[kb0nly]

I will have to check that also! I ordered some new case bolts, hex head instead of phillips head, and once those arrive i will go back in there one last time to check the torque on the clutch nut, probably put it to the middle of the range, the manual says 29-36ft lbs. If i put it up at 36 then the grab and stall happens, if its at 29 it don't but it has the smallest amount of slippage in first gear from a dead start. So im going to set it to 32-33ft lbs and then put it back together again and i will check the clutch adjustment again and go from there. At that point if it works good enough that it doesn't stall and only a minor slip i will probably just leave it until its had some hours on it and the new clutches are broken in.