Author Topic: odd knocking sound? (Read 6024 times)

wyntrblue · « **on:** July 20, 2005, 03:21:57 PM »

hi peoples,

i just got a bandit 400 (variable valve) for my first "big little bike" to replace my 125 death trap. only thing is that at low revs there is a knocking sound that comes from the top of the engine. i have had the rocker cover off for a look and cant find anything wrong with the inner workings (bearing in mind i have about as much mechanical aptitude as a fish) so i put the cover back on.

tryed to start it and found i had connected the wrong hose to the tank (doh) but thats now sorted and the bike started (woo) only the knocking noise is still there and now its only firing on 3 cylinders...grrrr

anyone got any ideas on what could be wrong with it?

gsxr400 racer · « **Reply #1 on:** July 20, 2005, 03:36:56 PM »

change the plugs first and see if it fires on all 4 and still has the knocking noise then reply back

Maniac · « **Reply #2 on:** July 20, 2005, 03:51:18 PM »

How 'low rev' are we talking?

If it was rods or bearings you'd get a louder/faster knock as the RPMs went up, so I think we can say that your probally fine there. However if it's only at low revs I immediatly start thinking oil pressure. At idle the engine should be around 1400-1700 RPM.

Like Jay said, try some new plugs. Do you know what cylinder isn't firing? Is the spark plug damp or dry after running? Try swapping it's plug out with one that is, did the problem move?

If new plugs don't do it and the plug is damp (IE: Has fuel in the cylinder) then we move on to checking the coils and compression. But for now, let's just worry about the plugs and if it's getting fuel or not.

Something else the knock could be, and I think Jay is thinking this too, is a misfire or preignition at low RPMs. Not normal, but there are a ton of things that can cause it, from inproper timing to plain old bad gas or, yes, bad plugs.

It's hard to diagnose 'knocks' and other noises without actually hearing them. We'll try and point you in the right way, though!

wyntrblue · « **Reply #3 on:** July 20, 2005, 03:55:23 PM »

the knocking sound was there before i had a look inside, and is still there now, knocking happens between 1000rpm to about 6k-7k rpm then vanishes, so my first thought was that the tappets on the low speed setting needed adjustment, so i checked all the gaps while i had the cover off and couldnt see anything wrong with it.....

i will swap the plugs tomorow when i next head over to my mates garage where its stored atm :)

thanks for all ya help

Maniac · « **Reply #4 on:** July 20, 2005, 04:01:47 PM »

Is it a loud metal-to-metal or is more like a soft ticking?

wyntrblue · « **Reply #5 on:** July 20, 2005, 04:27:11 PM »

more like a soft ticking i think, tho not being that knowlagable about such things i could be wrong.... when i had the rockercover off i couldnt see any sign of ground metal or metal chips so im pretty sure its more a soft ticking type knock, but it is louder than i would expect it to be.

my friend who has been helping me says

"both a soft metal on metal ticking"

hope that helps

Maniac · « **Reply #6 on:** July 20, 2005, 04:30:54 PM »

Well, if it's a softer ticking then I don't think we need to worry about a rod shooting out of the block anytime soon. More than likely it's related to your valve lash, but it could also be preignition/misfiring.

Let us know how the plug checking goes.

Red01 · « **Reply #7 on:** July 20, 2005, 07:06:02 PM »

Don't the V models make different noises above and below the point where the VVT takes over? Could this be related to that?

Maniac · « **Reply #8 on:** July 20, 2005, 07:09:19 PM »

It -could- be, but it's hard to say since I've never heard one. It's a mechanical advance, right? Could just be the mechanical advance making noises.

todius · « **Reply #9 on:** July 20, 2005, 11:43:36 PM »

This may seem silly, but it may be spark plug wires. Before I replaced my plug wires, mine would make a knocking/ticking noise at low rpms, but as I revved it up, it went away... turns out it was running on 3 cyl's at low rpm and when I revved it, the spark got stronger and was able to fire on the 4th cylinder. Might try feeling around the exhaust pipes while the engine is idleing... if one of the pipes feels cool around it while the others are hot.. you've got some sort of ignition prob. (Disclaimer: Don't physically touch the pipes while the bike is running, they are HOT!)

wyntrblue · « **Reply #10 on:** July 21, 2005, 11:40:59 AM »

ok heres the update, got it firing on all 4 again... turned out i had got the order wrong when reconnecting the ht leads (doh)

Maniac · « **Reply #11 on:** July 21, 2005, 01:38:28 PM »

That'd do it!

Did the knocking stop too? If so then it was just misfiring.

wyntrblue · « **Reply #12 on:** July 21, 2005, 01:41:48 PM »

no the noise is still there and i think it may even be slightly louder, tho now i am in no hurry toi fix it as i wont be able to ride it for a few months now anyway, due to not having the cash to pay for my full test.

i lost my job today :(

Maniac · « **Reply #13 on:** July 21, 2005, 01:44:53 PM »

Man, that sucks. Good luck finding another one, hopefully a better one! One that will allow you to afford to ride

cdyer77 · « **Reply #14 on:** July 21, 2005, 03:30:36 PM »

I get that noise too! But it ended up just being me banging my head against the wall!