Questions about Broken down 3ASV and S3BL

3ASV
I took KS7631 @ 692 yesterday,
however, its front door could not open,
(Its middle door ran properly, so everyone got on 7631 from the middle door]
so I would like to ask

1. What factors caused the door out of order?
2. How can the problems be fixed?

S3BL
From http://www.hkitalk.net/HKiTalk2/viewthread.php?tid=322473&extra=page%3D1&page=2

原帖由 葵盛東居民AMN36 於 2008-8-29 09:57 發表
FA9288早上有出的, 不過因黑煙太大問題要整車, 可能整整下就換車了

3. What factors caused the strong smoke?
4. How can the problem be fixed?

ps 5. I have heard the terms "掃尾牙" and "斷尾軸", can anyone what they are refered to

Thanks for your kind attention and reply

[ 本帖最後由 12A 於 2008-8-29 21:39 編輯 ]

原帖由 12A 於 2008-8-29 13:03 發表
ps 5. I have heard the terms "掃尾牙" and "斷尾軸", can anyone what they are refered to

''斷尾軸'' is the 尾軸 had broken.

P.S.:The topic is''Broken'',no ''d''.