Knocking at low revs

[T0MMY]

I've noticed a bit of knocking that I can hear as well as feel that only comes on when applying power at low revs, as in so low the engine is almost labouring. At higher engine speeds it's fine.

I figured 3 possibilities, balance shaft wear, big end bearings or piston slap, but I've never experienced any of them so I've no idea which, if any, it would be.

What do my symptoms suggest?

[fallenmikethebike]

When was the power valve last decoked?
Mike

[knackeredMk1]

CRM engines are quite noisy. They were never very quiet when new and now some are 23 years old.

Mk2s in particular are prone to a noise that sounds like 'pinking' at low throttle openings but that is just the way they are. I have had various barrels and heads on my bike and they all produce different noises. As have the various other bikes I have seen/listen too. I would say if you haven't made any changes to the bike and the noise is not getting worse then leave alone as it is probably 'normal'.

I believe that a lot of the clanks and pings at lower revs are due to the power valve rattling.

[T0MMY]

No idea when the powervalve was decoked; I've only just bought the bike and am steadily working through fixing it's various problems.

It's not like a pinking type sound or a light rattle...quite a heavy knocking but as I say, only when labouring the engine so not usually a problem. It may just be that it does chug a bit when you labour it like that.

I will have a look at the powervalve though; checking the operation was next on my list of jobs with it anyway although the bike makes good power throughout the rev range so I assume it's working to some extent at least.

[fallenmikethebike]

As KNMK1 says, my AR used to sound like diesel bus sometimes, but it was just the P/clanking away.
Mike

[njhardy]

Might be a good idea to take off the LHS stator cover off (when the bike is warm) and feel for any play in the main bearings by trying to wobble the flywheel side-to-side- if you can feel any more than a tiny bit of play, your mains could be on the way out- hence the knocking noise...

[T0MMY]

I'll have a look at that...thanks for the replies chaps.

The bottom yoke on my trackbike just snapped though so sadly that is taking up my tinkering time...

[fallenmikethebike]

I'll have a look at that...thanks for the replies chaps.

The bottom yoke on my trackbike just snapped though so sadly that is taking up my tinkering time...

Holy carp.
Mike

[T0MMY]

Yeah, that's what I thought! Just waiting on a replacement now that's taking a suspiciously long time...glad I paid by Paypal as I suspect I've been scammed...