SOHC.co.uk Forums > CB350/400
400 four knocking noise.
stevie:
Hello all, can someone please give me some advice about a problem with my 400 four that I am restoring? On tick over there is a knocking noise coming from the bottom end (quite bad). This goes off when the revs are raised. It is the same when hot or cold. I have split the engine and all of the shells look ok and there seems to be no play on the conrods. The crank journal shells also have very little rub marks. Any ideas? Some one suggested that it may just be the carbs that needed balancing. Also can someone tell me how if or how you check the primary chain needs replacing?
Thanks
Steve
hairygit:
It certainly sounds like carbs needing balancing. It is not to difficult to do yourself if you have or can beg/borrow a set of vacuum gauges, but before attempting to balance carbs you must ensure that the engine is in a good state of tune generally (points gap/ignition timing, valve clearances, engine oil condition/level and air filter. If you don't feel confident enough to give it a go yourself, try to find an independant motorcycle shop to give you a fixed price for doing it, it shouldn't be too extortionate ;D
Tomb:
If it knocks at tickover and goes off if revs are lifted, try pulling in the clutch lever, the noise should reduce the same-ish. Its clutch rattle and pretty normal on Hondas of this era. It is made much worse when carbs are out of balance so do as HG says. ;)
K2-K6:
Are you sure it's running on all 4 at tickover? start it without choke if poss and run for about 30sec, switch off and check if all the exhaust header pipes are getting hot.
If one is cold it cold be a slow speed carb jet blocked and preventing one cylinder from firing properly at low revs which starts as you lift onto more main running jets, can give a quite low thuding that sounds as if it's bottom end.
Sounds as if the bearing shells are all intact, are the gudgeon pins also ok (it's unlikely these are worn but just possible)
As the other posts say, just a general checkover of ignition etc may turn up something.
stevie:
Hello everyone thanks for the replies. Checked it is running on all 4 and it was. Also tried the clutch and the knocking continued. Am going to start the rebuild in the next couple of days. I am replacing all parts that are worn as I go. I will check and set up carbs and see what happens.
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