Engine Rattle at hi revs

[Squid]

Hi Guys,

Well I have finally got my 95 (GJ77A) 250 bandit on the road and she is a really nice ride. I upgraded from a ZZR 250 and the bandit is a much nicer ride for sure.

Well to my question. I was giving the bandit a bit of throttle and when the revs went past 10k I heard a rattle in the top of the engine. well I think it was coming from the top end.  the engine is quiet at idle and under 10k and heaps of power.

When I had the tappit cover off I check the valves and they were all in spec.  so i am thinking that the oil addjusted tappits are adjusting to much and are hitting the pistons (valve bouncing), or maybe not adjusting enough.  Not sure so any ideas would be helpful

Cheers
Squid

[wfrpalm]

I don't know anything about the 250 but if the octane is too low for the compression ratio or the ignition timeing is advaced too much the motor will rattle at high revs. Good luck.

[pmackie]

It depends on what type of rattle you're hearing.

As suggested, you might be hearing a "detonation" rattle. This would normally occur under high load conditions, ie: when accelarating hard, or climbing a hill. If this is the case, then firstly try higher octane fuel. Detonation can put a hole in a piston pretty quickly.

Another possible option to check is the Cam Chain - if it is badly worn, it could be making noise. Check your chain tensioner and/or inspect the cam chain for wear.

Let us know what you find.

[Squid]

Thanks guys for the comments.  the fuel I am using is a higher octain, I think it has 95 oct level.  I am sure that the cam chain is ok as not noise at idle or med revs. I did inspect the chain when I had the tappit cover off and it looked good and the eng was clean.

I think I will look at the timing, isn't that controlled by the CDI unit? Not too sure how to adjust the timing but I will find out.  Thanks again for the ideas, and keep them coming.  Well let you know how I do.

Cheers

[Rejektid]

If the 250 like the 400, timing is adjusted by setting the crank to a specific spot. Then pull the cam chain tensioner. Then remove the cams and set the cams to a specific spot and making sure the proper marks on the cam gears are the proper number of links apart on the cam chain. Refer to your service manual for proper instruction to set timing though.