Topic: Rattling 400/4

[blackiex]

Dear SOHC4 members,

I am a bit dissapointed. Few moths ago I posted a question on the greenspun SOHC forum about my rattling CB 400 Four. Somebody told me that I should tighten the camchain, that would help. I did it, it is tight as it shold be but my bike is still rattlig at all revs, doesn't matter whether the clutch is on or not, or the engine is warm or cold: it is just doing it. I don't have any idea about that, I've already checked the valves, too. Of course they seem to be fine.
What do you think the problem could be?

Thanks in advance!

David - Hungary

[Harry]

And the carbs are balanced? Unbalanced carbs give rise to a fair bit of rattle. Take a long screwdriver and put the handle to your ear, use the other end to touch various parts of the engine to see if you can localise the noise.

[Tim.]

Primary chain rattle, piston slap, loosey goosey (technical term) transmission, could be any number of things.  How's your compression (my current woe)?  How's the tappet clearance?

[Uncle Ernie]

Hey David,
Hard to diagnose through e-mail... is the rattle coming from the engine or you're not sure where? Does it increase (get louder or speed up) when the revs go up? Is it a buzz or does it sound like a can of nuts and bolt getting shaken, kind of "thumpy" (sorry about all these technical terms), low register or high pitched? How many miles are on the engine? Has it ever been run with the oil really low? Could it be a loose nut behind the handlebars?
I have a 400 and it always has a little cam chain noise- this is my 3rd and I suspect they all do. I had a buzz that went away when I tightened up my speedo. If your drive chain is real loose that would sound more like a slapping noise.
More info/creative writing   ?
Uncle Ernie

[blackiex]

Hi again,

Thanks for all the useful advices, I will check them as soon as possible.
A bit more info:
The noise sounds like is somebody would hit a piece of aluminium inside the engine. Its frequency is similar to the camshaft's (it is getting faster when revving up and vice versa, like the camshaft does)  but I have checked the camshaft a few months ago and nothing seemed to be wrong, it was not loose or anything like that. The tacho drive thing must be OK, I tried with and without it, too.
I think the chamcain tensioner is OK, because if the chain had got in contact with it (and that would rattle) I couldn't have done any tensioning on it... Or I'm just not experienced in four stroke engines enough (yet)... 
The little "blacktop-grater" has about 40 000 miles in the clock.

Thank you!

David

[bryanj]

Sorry to throw another problem on you but Honda have discontinued that tensioner part. Last i heard cmsl in Holland had a couple  at a high price but nobody else not even david silver.

[blackiex]

Dear supersport_CB400F,

I'm sorry, but I can't see that picture. I have tried to take a look but the system always said that I have to log in to open or download images - of course I was logged in, just like now.
Anyway, which bolt shall I unlock? The lower that pushes itself to the plunger's side or the upper one, that stands right above the plunger? And what is that changing the headlight bulb naked thing? I don't get it..
By the way, I saw a lot of pictures about the camchain and the methods of tensioning but I don't understand how the arm could be pressed against the camchain. This means that my tensioner blade is worn and too short to keep the chain away from the lower arm?

Thanks!

David
 

[Harry]

have a look at the photo, can you see this photo? can anybody see the photo?

Me! Me! I can! 

[Uncle Ernie]

So Super- is there any preventative measure I can take to keep this from getting bad?

[blackiex]

Hello again,

Well, I have tightened the camchain - the way you told us -  until the factory whining came back but it is still rattling. This means that the primary chain is loose, isn't it? On idle rpm the noise is a bit louder, it gives out a TACK TACK TACK noise....

[Harry]

TACK TACK TACK ??! Sound like the same noise I had until I followed Bryan Jone's suggestion and tightened my headers. I had one loose header bolt, tightened it and the "ticking" stopped!

[blackiex]

Allrighty, I'll try to check my header bolts. Anyway, is the primary chain a vulnerable part after 40 000 miles? What happens if the chain is the problem and I ride it in this condition?

[blackiex]

Hello again!

Well, I couldn't record the noise of the engine, because I can't get a device for it. It sounds like if you were pulling a chain on tarmac; a high pitched noise, volume and frequency are in synchron with the engine's rev. It doesn't matter whether the engine is cold or hot, the volume of the noise is the same. I just don't dare to rev the bike above 5000 (in 6th gear it is about 90 kph), because the noise gets tremendously loud there. Above 4000 it is vibrating as vell. I wouldn't worry if I had more money to get it to a mechanic, but I have to repair it myself and I am a bit scared about opening up the engine without a "suspect". I hope it is an easily reachable part, like the alternator or something like that. Any further idea?

Thanks in advance!

David

[Tim2005]

Hi. I can't see any mention anywhere that you've checked the tappets.. could it be that one is loose? If you've ruled that out, I'd think primary chain is very unlikely to be worn out at 40k, but camchains are usually tired by 30k. If it was mine I'd pull the rocker cover off and check that the camchain is tensioned (there shouldn't be any slack at the points where it leaves the sprocket, nor should it be possible to hold the chain at the very top and lift it off the sprocket by more than a mm or so). Also, have a look at the cam lobes & followers while you're in there, check for major wear, light pitting won't cause a rattle.

[tony darburn]

Luvly photo