Weird knocking noise on my bike under load

**cheese** · 27th September 2010, 18:25

I was at the WMCC ride the other weekend, and my bike started making weird noises under load and it was like a weird knocking noise. The power didn't feel too out of the ordinary, so I thought it was probably a snapped power valve cable, but both look fine, I've just checked it but not pulled it out (I'll do that next).

Its just had a new piston fitted and it's done about 4 hours on it so far. Its been running really well.

what else should I check? The brake pads are all well worn and due to be replaced, but I doubt that would make the noise??? Also the noise didn't seem to be at the same speed as the Revs (thats why I thought it was the power cable). Oh the bike is a 04 CR250.

**Rupe** · 27th September 2010, 18:32

Originally Posted by cheese

I was at the WMCC ride the other weekend, and my bike started making weird noises under load and it was like a weird knocking noise. The power didn't feel too out of the ordinary, so I thought it was probably a snapped power valve cable, but both look fine, I've just checked it but not pulled it out (I'll do that next).

Its just had a new piston fitted and it's done about 4 hours on it so far. Its been running really well.

what else should I check? The brake pads are all well worn and due to be replaced, but I doubt that would make the noise??? Also the noise didn't seem to be at the same speed as the Revs (thats why I thought it was the power cable). Oh the bike is a 04 CR250.

burn it, then get something more practicle

**LittleJohn** · 27th September 2010, 18:53

Does it make the noise when you sit there and rev it our of gear or only when you are moving??

**vr4king** · 27th September 2010, 19:32

Power band getting loose maybe?

**barty5** · 27th September 2010, 19:37

Originally Posted by vr4king

Power band getting loose maybe?

You mean rubber band ????

**sugilite:Me** · 27th September 2010, 19:53

Crap/contaminated fuel causing detonation?

**B0000M** · 27th September 2010, 19:57

id first blame non 98 or higher fuel, - detonation

another thing to check would be the upper chain roller (on the sub frame) it makes some nasty noises when the bearings are flogged out, but only when the rear suspension compresses.

**barty5** · 27th September 2010, 20:09

Originally Posted by B0000M

id first blame non 98 or higher fuel, - detonation

another thing to check would be the upper chain roller (on the sub frame) it makes some nasty noises when the bearings are flogged out, but only when the rear suspension compresses.

Oh shit are we back on stale fuel again

**CHOPPA** · 27th September 2010, 21:06

chain.............

**cheese** · 27th September 2010, 21:15

Ok, given its a new piston and the compression is up it probably is detonation. I'll treat it to some 98 or higher.

**Ktmboy** · 27th September 2010, 21:30

Originally Posted by CHOPPA

chain.............

Chain....?? Start with the basics.

**B0000M** · 28th September 2010, 07:34

being a cr250, with possible low grade fuel, and a new top end (more compression), and under load, and cr250s being notorious for detonation on poor fuel, and only under hard load, and only after cheese filled up half way thru the day, all things point towards detonation