Knocking noise on non load and acceleration

[jonnyboyg]

Hi all,

I'm a new member but have owned my G2 CSR 250 for about 5 years. It has developed a knocking noise, that seems to come from the engine area. Starts and runs well but I just can't bring myself to ride it as the noise gets louder at 40 -45 mph. Its has baffled everyone I have asked who knows anything about bikes.

I have checked the following bits:
all lubricant levels, crankshaft, conrods, pistons, push rods, alternator stator, clutch (replacing bearings and damper rubbers) both duplex chain and main chains. The old guide book I have suggests a duplex chain tension of 3/8". Is that correct? All look and feel great with no unwanted rattles, leaks or movement. It happens while running it on the centre stand, as well as on the road so I presume I can rule out rear chain slap on load to rear wheel.

Has anyone got any ideas? I'm gutted as she used to run so well and a really underated bike. Have also asked the usual experts AMC spares etc, but they normally deal in heavyweights.

Regards

John

[SPRIDDLER]

Hi all,

It has developed a knocking noise, that seems to come from the engine area.

Welcome, John.
Is it a heavy, thumping knock or a tapping knock? Is it at engine speed - i.e. once per revolution or at a greater frequency?
You need to more accurately locate the source of the noise; at least whether it emanates from the head, barrel or crankcase. Put one end of a 'listening stick' (piece of wood, e.g. broomstick, screwdriver, about a foot long against your ear and then against different parts of th'engine to locate the source of the noise.

I have checked the following bits:...... crankshaft, conrods, pistons,

Pardon me for being pedantic, but you've thrown me a bit there as there should be only one piston and conrod.
How did you check the conrod, piston and the crankshaft? Not by stripping th'engine I assume or you'd have a better idea of the potential source of the noise.
Standing by..........

[Janet]

I know this will sound silly but have you checked the engine mountings?

[dave16mct]

Years ago a friends lightweight was making a noise like this. It turned out to be the timed breather. I think it was in the chaincase on the mainshaft. I think it had to be lined up with a radial hole to breath at the correct time. Amplified by being in the chaincase it made an awful noise! Worth a look? Dave

[jonnyboyg]

Firstly - many thanks for all your help and suggestions, and hi Spriddler. You are of course correct that there is only one conrod and piston, sorry my brain non engaging! I have tried to listen with a block of wood but to honest, as everything is amplified, I still couldn't locate the precise area for the noise. It does seems to be per revolution rather than random which is why I thought I'd rule out the piston and conrod by removing the rocker cover, head and barrel first.

Hi Janet - yes, I have checked all the engine mountings and all are nice and tight. Which it was that though! Would have been nice and simple....

Hi Dave16mct - I think I have read something about this... but the old pink manual I have is a little bit 'old English' and a little vague on sorting it if it is. Do you know any more about this timed breather or could recommend a different manual that might help me?

Thanks again

John

[dave16mct]

Never had a lightweight, but I'm looking at the 57-64 Workshop manual which covers all models. Its inbetween the drive side main bearings in the crankcase On page 43 it says theres a breather stator 042220 and its held in place by a bolt. I seem to remember it was this bolt that wasn't located in the stator properly and the stator was rotating causing the noise. All distant memory I'm afraid, it was years ago! Perhaps Cibriani can throw some light on the subject. Dave

[cbranni]

Hi John, there were problems with the breather on early models, the hollow bolt fixing the breather stator would wear causing noise, (the book advises copper plating the end to improve the fit) but your CSR would have the modified fixing which is the stator is now fixed by a bolt from outside the drive side crankcase, to get at this bolt you would need to remove chaincase, clutch, primary drive and the inner chain case, if I remember rightly the bolt is at 4 o' clock.

The engine breather exits the engine just above the gearbox drive sprocket, when the engine is running you should be able to feel a timed blast of pressure every rev.

Saying all that not sure if this helps unless you find the bolt loose or broken, if you have physically checked the engine and cannot find the any issues then maybe its worth an hours work to check this bolt. I have never heard the noise a loose stator makes so I can't advise you of the sound.

Below is photo showing the bolt and the breather hole is bottom right.



Colin

[jonnyboyg]

Thanks Dave16mct and cbranni,

I will spend some time this weekend dismantling again. Fingers crossed.

Regards

John

[Janet]

Hi Janet - yes, I have checked all the engine mountings and all are nice and tight. Which it was that though! Would have been nice and simple....

Silly me! I see from your profile that you also have Beezas so, of course, looking for bits falling off would have been the first thing you did.



Janet, married to a BSA fanatic so speaks from experience.

[cbranni]

I did have a nasty noise on my B40 after a lot work I traced to a worn key on the main timing gear, but it wasn't a knock more of a sharp ting!!! but that was half engine speed, there is a post on here somewhere.
Colin