Piston slap?

[moff747]

Hi, I have an 02 ec300. I have recently noticed a rattle on the down rev, when I rev the bike I hear a rattle (chatter)as the revs drop. more so when its warm. It dosent make this noise under load. Is this piston slap? I have also been told that you can get a rough idea of the top end condition by looking at the piston through the exhuast port. Is it time for a topend inspection? any help thanks.

[PEB]

You can see alot of the piston through the exhaust port. The power valve can rattle as well as the chain slider.

Paul B

[stay_upright]

I think a piston rattle would be more tinny and a powervalve louder and more 'mechanical'. I had what I thought was a PV rattle on my KTM200 and it was like that for years (never actually worked out if that was the noise but I thought so) and never did any damage.

Looking at the piston through the exhaust port if you see brown/black deposits underneath the piston rings then you are getting blowby of the rings. The effect of this is to lower power and torque so if you have this and want more power/torque then replace the rings. My experience with pistons and bores is that they wear very very little and so doubt your rattle is piston slap and it's unlikely you would need a new piston as well if it's been replaced in the last 1-2 years after that I don't know... If it were me I'd only replace rings/piston if you fancy more power...

A compression meter is a good way to check the condition of your piston/rings as well and particularly useful for benchmarking the performance a new set of rings gives so you know when it's down on performance - they are cheap and easy to use.

[stay_upright]

One more point my KTM200 used a set of rings every year and I would notice the performance difference as well however I asked my dealer how often he replaced rings on GG300's and he said never! I replaced them anyway and compression (performance) was the same as the old rings...

[Loosenut]

I really notice the power difference on my 300's after a top-end or ring replacement. It's not a huge difference, but noticable to me.

[moff747]

Thanks everyone, I will have a look through the exhaust port. The bike hasnt lost power and seems to have good compresion. I remember reading somthing about worn exhaust o'rings allowing the exhaust to rattle on the spiggot, anyone experianced this? also does anyone know the correct o'ring size? I will change them while im there. Thanks

[stay_upright]

Yes the Exhaust o rings wear rapidly and/or break often (as in my case) Sounds like many people use RTV. I measured my o rings yesterday at 30mm x 3.1mm.