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Hi there. Im new to these forum things. So apologies for the trypos. I’ve a CBR6 and a KX500 , and my wife has a 1977 400/4. She’s had it 4yrs & circa 3k miles. It came to us alledgedly after a rebuild, but has always had a knocking noise that is greater when cold, goes when warm or with the revs abov 2.5k. Can’t pin point the sound – best I can get is to behind the block right side which tended me towards he clutch bearing but the sound dosnt go when the clutch is pulled. I have asked other owners who said theirs did similar but they ignored it! Problem is this noise appears to be getting louder. I can only guess its either piston slap or the clutch spider bearing. Any other 400/4’s out there that do it? – or anyone know the fault. All advise (except bin it) most welcome!
Difficult to say without actually hearing it, but your suspisions regarding the clutch seem fair enough. Could be tricky to investigate. Have you tried a dedicated 400/4 forum or ownners club? They might be able to offer more specific advice
https://cres1.lancs.ac.uk/~esarie/honda/techbrd.htm
I have not tried it, so don’t know if it will be any good. Hope that you get sorted. Let us know how you get on
Anyway, welcome to the site and take a look around
https://bikemeet.net/forums/topic/great-posts-pics-across-the-site-part-2/A lot of the older jap 4’s used to suffer from noise like this. (i.e. GS, Z, CB etc)
your clutch suggestion is certainly a good one but also i would try getting the carbs balance properly (professionally or by someone who really knows what they are doing) as this used to cause a lot of uneven lumpiness that become noise from various places due to general imbalance.
Hope that helps.
Hi Col and welcome. I have heard a clutch bearing that was faulty still make the noise when the clutch was pulled in so don’t dismiss that immediately.
Other likelies on the 400/4 are cam chain tensioner or blocked oil galleries (or should I say the results of having blocked oil galleries!). I think the camchains on these have a tensioner that needs a bit of manual assistance to do the tensioning, even if they are automatic (which I’m not sure they were back in 77…).
Can you locate the sound better if you use a wooden handled file or screwdriver with the wood bit touching your ear? An old trick but it has helped me a few times to isolate engine noises.
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