Mystery noise! (AKA the tale of the Kawasaki Balius and the newbie concerned owner)

[Cynos]

Well, I can't really disclaim responsibility by calling myself a riding newbie these days, but I'm still a huge mechanical newbie, so please forgive me any omissions.

I ride a 1991 Kawasaki Balius (AKA ZR-250) which has been doing a fair few k's.

Recently, it began making a rattling noise.

This noise:

* As far as I can tell, appears to be coming from the top end of the engine
* Occurs between 2.5K - 4K revs when accelerating or deaccelerating
* Only occurs after long periods of riding - heat related?
* Sounds to me like a rattling cam chain, but to other people it sounds like the "big end bearings" or "valves" so I really have no idea

May or may not be related to the fact that petrol was getting into the oil ways - after having my bike sitting in a garage for 3 - 4 weeks, I emptied the oil, and most of it was petrol. (Turns out that the off position on my fuel tap is not the one labelled 'off'. Who knew) Is petrol supposed to be able to do that?

So, this is probably vague and I should probably just have asked for recommendations for a mechanic, but I'm hoping the appearance of the noise at a certain rev range, while accelerating/deaccelerating, when the engine is hot, rings a bell for someone.

Otherwise, suggestions of good diagnostic mechanics in ChCh welcomed.

[Max Preload]

For a start... big end bearings are in the bottom end, not the top end so if the noise is definitely coming from the top that's not it.

If your oil is full of petrol it will have quite an effect on it's lubrication properties. Petrol is a mild lubricant, but nothing compared to oil.

The fact petrol is getting into the oil suggests a faulty float needle valve in the carburettor. If the fuel tap was not actually off, that's the most likely explanation. The carb needs disassembly to rectify this (replace the valve & reset the float height). That should be the priority.

There's a guy in TradeMe who I've seen selling them. I'll see if I can dig his name up ad post if for you.

[Cynos]

Thanks Max. I'll have a look at the carbs, put fresh oil + filter in, and see if I can replicate it, and then go from there.

[Devil]

It's most likely the cam chain tensioner getting stuck. They're known for that. You can pull the tensioner out and clean it up yourself. Two screws. Get pics of either side of the engine and i'll point it out. Easy job.
Eventually if the tensioner is too far gone (or the camchain or both) you'll need to get them replaced. Approx $300 for cam chain, tensioner and labour.

Been there, done that.

The Balius doesn't have an off on the fuel tap, there's On, Reserve and Prime.
Prime just lets fuel flow straight through (ie, not requiring a vacuum to pull it through). Leave it on 'On' when you're not using it.

[Cynos]

Cheers Devil, will do. _b

[Max Preload]

This is the guy I was thinking of on TardMe.

[Cynos]

Cheers Max. I'll give him a try. I'm going to start disassembling the engine tomorrow night, so will see what I find.

[Cynos]

Well, resurrect this thread. It's a big-end bearing. Seems to be a common problem with the ZXR engine from asking around. Got quoted $1000 to fix it, but I suspect the pricing of parts plays into that. Considering I bought it for $3K, not sure if it's worth it...