250sx clutch problem

[wildacres00]

I'll check it out tonight. I won't be able to take the bike apart until later this week. Thanks

[Howdy]

Test the clutches to find which one is bad.
How to test:
If the clutch don't engage until higher RPMs and then is fine it's you centrifical clutch.
From a dead stop: put the machine in 3rd or 4th gear and hit the gas. If the motor revs up but the machine don't take off much then it's you manual clutch.

If it's the manual slipping:
It is possibly the pressure plate for the clutch disk isn't seated correctly on the groves. The Fix: Pull the clutch, remove and turn the back plate 1/4 turn and see if the clutch pack closes tight and the plates won't turn. You should be able to squeeze the clutch pack together ( front and back pressure plates ) with one hand tight enough that the disk won't turn. If any disk does turn you probably have other issues to deal with.
Howdy

[wildacres00]

I was able to measure the spare metal and fiber plate along with the used clutch plates.

------------- NEW ------------- OLD

Metal plate:--- .056"----------- .054"
Fiber plate: --- .120"----------- .106"
Spring:-------- ?---------------- 34 mm

I cross-referenced these numbers versus the service manual and found them to be acceptable. I will have to take the motor apart to check what the new springs will measure.

Howdy;
Which disc are you speaking of, The metal plates? Also it is slipping from a dead stop and also when I'm moving down the road and punch the gas it is slipping, so I'm not sure which it is.
I thought the centrifugal clutch engages and disengages the engine to the transmission each time a gear is shifted and then the manual clutch takes over to connect the engine to the transmission during the revving of the engine?

[dougspcs]

No now I'm getting a different spin on your issue I'm agreeing with Howdy.

The centrifugal clutch is the one you feel 'hit' when you drop from neutral into gear..if it doesn't 'hit' until you rev up the engine then you're not chasing a manual clutch issue but the centrifugal..

Take a good look at that primary clutch..

[wildacres00]

Not really sure what to look at on the primary. I can take some measurements but everything looked good when I changed out the one way clutch and shoes.

[dougspcs]

I know you said you scuffed the centrifugal drum up a bit to remove the glazing..

I always just look for a replacement primary when I have problems so I don't know this but is there a service limit listed in the manual for the drum?

If so it may be out of spec and needing replacement.

[wildacres00]

There are some specs on the drum and the shoes. I'll give them a check when I break it down.

[Howdy]

The back ( manual as I call it ) clutch has 3 main parts. The ones I am talking about is #2 and #6 in the picture. The grooves on #2 is where the 5 steel plates fit on. I have seen the grooves on #2 and #6 didn't match up unless I turned #6 1/4 of a turn. Then they matched properly.


How many steel and fiber plates did you install? You have to have 5 of each.


Did you do the clutch test yet?
Howdy

[wildacres00]

I have not taken the bike apart yet. I installed 5 fiber plates and 4 steel plates. The pic shows that you need 5 fiber plates and 4 steel plates also or am I missing something? When I break it apart I will definitely look to see if both pressure plates are meshing properly. Thanks

[Howdy]

I have not taken the bike apart yet. I installed 5 fiber plates and 4 steel plates. The pic shows that you need 5 fiber plates and 4 steel plates also or am I missing something? When I break it apart I will definitely look to see if both pressure plates are meshing properly. Thanks

yep 5 and 4 is correct. I was busy when I posted that and posted it wrong.
Howdy

[barnett468]

I have not taken the bike apart yet. I installed 5 fiber plates and 4 steel plates. The pic shows that you need 5 fiber plates and 4 steel plates also or am I missing something? When I break it apart I will definitely look to see if both pressure plates are meshing properly. Thanks

There are some specs on the drum and the shoes. I'll give them a check when I break it down.

Hello


Here’s what your new clutch thickness is doing.

------------- NEW ------------- OLD

Metal plate:--- .056"----------- .054"
Fiber plate: --- .120"----------- .106"
Spring:-------- ?---------------- 34 mm

New 5 x .056 = .280 + 4 x .120 = .480 = .760

Old 5 x .054 = .270 + 4 x .106 = .424 = .694


.760 (new clutch assy thickness) - .694 (used clutch assy thickness) = .066 which is the amount of additional preload the new clutch plates are putting on either set of clutch springs over the previous worn clutch plates. The total preload on new springs vs the previous springs is currently unknown and may be too low.

.694 (worn clutch assy) + .014 (estimated clutch wear) = .708 (estimated thickness of new OEM clutch assy) subtracted from .760 (new ebay clutch assy thickness) = .052 amount of additional preload on clutch springs over estimated OEM original clutch assy thickness.


1. Since you claim your inner clutch hub is smooth it is unlikely to be worn out of spec and therefore is likely not the problem, but as suggested it’s a great idea to check it.

2. If in fact your centrifugal clutch shoes are OEM as you think they might be they are definitely not the problem. Do you still have the package they came in?

3. Since the total of the thickness of your new clutches is .052 greater than the estimated thickness of an oem set of clutches, the thickness of your new clutches is not the problem.

4. Since the thickness of your new clutches is .052 thicker then the estimated thickness of OEM clutches the new clutches increase the preload on the previous springs by .052 over what stock would be. This amount is more than enough to compensate for any loss of preload to the original spring by years of compression and heat cycles etc. so the original springs are not likely the cause of your problem. I know you are using your new springs now so this is why I wanted you to measure their length and pressure compared to the previous ones the best you could.

5. Since your clutch does at least work it is unlikely that the discs are hanging up on your clutch hubs.


SUMMARY

Based on the info you have provided it looks to me on the surface that your slipping problem is most likely caused by one or more of the following problems which in addition to measuring the diameter of the inside of the centrifugal clutch hub and looking for an obvious problem I personally would address in the following order. Others would do it differently.


1. 2 metal and 2 fiber discs together. Suggest visual inspection without disassembling clutch assy.

2. New clutch disc springs are weaker and/or shorter than OEM. Suggest reinstalling previous springs or buying OEM if available or increasing spring preload on new springs by approximately .020 using “AN” [thin wall] washers.

3. Centrifugal clutch shoes not expanding completely for some reason. Suggest checking pivots and reinstalling previous springs if you replaced them.

Did you replace the springs on the centrifugal clutch also? If so I suggest using previous springs since in this case a weaker spring is better. Reducing the spring pressure [tension] on a centrifugal clutch allows the clutch shoes to do the following.

a. Begin engagement at a lower RPM.

b. Have full engagement [so to speak] at a lower RPM ie, engage firmly enough to a point where they will not slip under high loads.

c. Reduce the RPM range [the engagement curve] over which initial to “full” engagement occurs.


4. Inadequate friction material on fiber clutch discs [as suggested by Dougspcs] ie “they suck”. Suggest replacing with OEM.

[barnett468]

The centrifugal shoes were replaced. I bought them from a different seller on e-bay. The packaging looked OEM to me but I did not verify the company name prior to installation.

Hello


If you no longer have your original package for your centrifugal clutch shoes you can easily determine whether by comparing them to the following photos.

OEM shoe friction material is dark brown and smooth and hard. It is hard to dig a fingernail into.

Aftermarket shoe friction material is orange [the wife says shrimp, peach or salmon. I told her I wasn’t gonna use any of those words to describe it here, lol] and possibly has a rougher surface possibly caused by being surfaced with a more abrasive material and/or from being made from a material that is more susceptible to “tearing” when being sanded/surfaced etc. Many if not all of the clutches I have seen that have friction material that looks like this are fairly easy to dig a fingernail into, whatever that really determines as far as it’s friction capabilities are concerned.

There are some specs on the drum and the shoes. I'll give them a check when I break it down.

Centrifugal clutch shoe friction material thickness spec is .120”, service limit .112”.

Drum id spec is 5.50”, service limit 5.520”.

Spring spec is 34.98 mm-34 mm min, 1.377”-1.340” min. At 34 mm your previous springs are ok. Since this is a reduction of length of .037” and your new clutches are .052 thicker as an assembly then the estimated thickness of an OEM assembly your previous springs would still be preloaded by .015 more than they would be with an OEM clutch assy. Your spring preload with the previous springs is not the cause of your slipping problem.


OEM MANUAL CENTRIFUGAL CLUTCH SPECS PG 8-1

http://www.kb0nly.info/ATC/index.php?dir=ATC250SX%2F


OEM CENTRIFUGAL CLUTCH PHOTO

http://www.cmsnl.com/atc200es-big-re...h_22461ke4771/


AFTERMARKET CENTRIFUGAL CLUTCH PHOTO

http://www.lakeregionrepair.com/esho...UTCH_SHOES.htm

[barnett468]

I thought the centrifugal clutch engages and disengages the engine to the transmission each time a gear is shifted and then the manual clutch takes over to connect the engine to the transmission during the revving of the engine?

Hello


CENTRIFUGAL CLUTCH - No, the centrifugal clutch shoes are engaged and disengaged by engine RPM only.

ONE WAY BEARING/CLUTCH – This is fully engaged upon deceleration in gear only and is not designed to “slip”. It acts independently of the centrifugal clutch and releases at either low or 0 vehicle speed [I don’t remember which].

MANUAL CLUTCH – When used in conjunction with a centrifugal clutch [in an automatic system] this clutch is operated by the shifter and is designed to engage and disengage with minimal to no slip. Because it is designed to operate with minimal slip compared to the centrifugal clutch it is subjected to less wear when the vehicle is ridden in an RPM range that allows the centrifugal clutch to “slip” frequently otherwise if the vehicle is ridden at an RPM where the centrifugal clutch is mostly continually fully engaged and the engine is shifted frequently it is subjected to more wear when compared to the centrifugal clutch. .

[wildacres00]

I'll have to check if I have the package the shoes came in. Ill also check the thickness of the shoes in reference to the service manual.

The pivot point on the centrifugal clutch shoes is something I'll look at. They pivot in a set groove on the hub and don't think they can be installed improperly but who knows. Right now I'm doubting everything I did. I did not replace the centrifugal clutch springs.

Do you think I should install that spare friction and metal plate that came in the kit if nothing else is the obvious cause? Would the added plates do anything adverse to the bike?

Thanks for the help.

[wildacres00]

Does anybody have the measurements of a New OEM manual clutch pack? I wonder what the difference is between my cheap replacement and an OEM kit. The clutch does engage just not well. Maybe it's acting like a half worn clutch and needs a tighter adjustment. When adjusting the clutch how much tension should be felt before backing the screw off 1/4 turn?