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Thread: center part of clutch casing exploding off

  1. #16
    apriliaforum expert jess67's Avatar
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    Did you find any witness marks on the pressure plate and the cover thats dislodging?
    After market slippers and non oem clutch packs can require the clutch plates installed differently than oem. Maybe check insallation guides of STM slipper.

  2. #17
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    @kzmille: You mean that oil might get into the breather exit, because I don't have the diaphragm anymore? That's actually a really good theory I haven't thought about. In post #8, Bill R. Mentioned that he centered out an existing diaphragm. This would make sense since it would prevent oil to get near the breathing tube connector.

  3. #18
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    @jess67: I did not find any marks no. I don't have the installations guide for the stm, but the dealer said he checked the manual and told me it was installed correctly. Even plugging the breather tubes is part of the installation I think. Can anyone with an stm clutch confirm?

  4. #19
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    Is there anything that can cause a sudden big expansion/pressure buildup/explosion in the crankcase in these engines? Just so I check these off before I go for another ride with the carbon cover on. I'm just worried it would happen again and the pressure has nowhere to go now.

  5. #20
    apriliaforum expert kzmille's Avatar
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    Quote Originally Posted by Jestersimpps View Post
    @kzmille: You mean that oil might get into the breather exit, because I don't have the diaphragm anymore? That's actually a really good theory I haven't thought about. In post #8, Bill R. Mentioned that he centered out an existing diaphragm. This would make sense since it would prevent oil to get near the breathing tube connector.
    I was just responding to your previous post that I'm still not sure I understand. If you don't have a full diaphragm in there than that is definitely not the problem. With no diaphragm the tube for the vacuum line on the clutch cover should be capped.

    The only thing I can imagine causing a build up of crankcase pressure, sudden or otherwise, is a restricted crankcase breather.
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  6. #21
    apriliaforum Member Bill R's Avatar
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    Quote Originally Posted by Jestersimpps View Post
    @kzmille: You mean that oil might get into the breather exit, because I don't have the diaphragm anymore? That's actually a really good theory I haven't thought about. In post #8, Bill R. Mentioned that he centered out an existing diaphragm. This would make sense since it would prevent oil to get near the breathing tube connector.
    The oil will find its way past the centered diaphragm but with the closed off vent tube, I used a cap bolt inverted back into the cut hose held by a hose clip. It doesn't matter.
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  7. #22
    apriliaforum expert jess67's Avatar
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    Quote Originally Posted by kzmille View Post
    In fact a member here had a strange clutch slipping problem. I helped him track it down and the problem was that he had added a catch bottle to the crankcase breather which was too restrictive. Think about it; the oem slipper works by a vacuum on the outer side of the diaphragm. Any build up of crankcase pressure applies a force to the inner side of the diaphragm which has the same result as a vacuum on the outer side. Result, slipping clutch. He opened up the breather in the bottle and that ended the problem.
    Have you heard of any other issues like this one and the OP's, kz?
    Would some of the older engines with worn compression rings, build enough crankcase pressure where the 3/8 breather becomes restrictive?

  8. #23
    apriliaforum expert kzmille's Avatar
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    I remember one report of the cover popping off. Probably the one in the link in the 1st post.

    I'm not really inclined to think it is a breather problem. In the first post the two instances occurred at idle. If it were from excessive blowby you would expect this to happen up in the rev range with the throttle open, not at idle.
    This is America. Use your turn signals or WE WILL KILL YOU - remember Sandra Bland

  9. #24
    apriliaforum expert theknurl's Avatar
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    Thumbs up ?

    The crankcase breather is a 7.8mm hole.......kind of hard to make it more restrictive
    I ran my breather up toward the tail and filled it with a pot scrubber....
    At the low spot I put a "T" , the line from there "T" s into the vent line from the oil tank to the transmission
    No oil in my air box
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  10. #25
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    Today I had some time to take the stator housing off with a friend of mine. This is what we discovered.
    It seems that one of the copper wires was fully exposed because the encapsulation had been burned off. The part of the wire that was exposed came in very close contract with the stator housing. Could it be that a spark between the housing and the stator ignited oil mist which caused an explosion? Anyway, this stator will be replaced. I'll report back of this solved the problem.Click image for larger version. 

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  11. #26
    apriliaforum expert kzmille's Avatar
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    We've seen lots of stators like that but very few covers popping.
    This is America. Use your turn signals or WE WILL KILL YOU - remember Sandra Bland

  12. #27
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    So I replaced the stator and put back a lead acid battery. The problem seems solved. I did a 500km trip this tuesday and it didn't happen again. Seems like it was a stator issue after all.

  13. #28
    apriliaforum expert kzmille's Avatar
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    So you think the stator was somehow igniting the oil mist?
    This is America. Use your turn signals or WE WILL KILL YOU - remember Sandra Bland

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