How do I know when to change piston?

[lirkipirki]

Hello!

I'm very novice tinkering with 2-stroke engines and I recently bought a 2008 GasGas 300EC to ride.

However the bike has no hour meter and the previous owner has no idea how long he has been riding on this piston.

The bike runs perfectly (in my layman eyes) but I'm thinking it might be smart to change the piston and rings BEFORE parts start flying around breaking the whole engine?

What would you do in my situation?

Since I'm very novice tinkering with 2-stroke engines I don't know if my piston is good or bad upon visual inspection..

If I just continue riding what is the worst that can happen?

[Elvis74]

I'm measuring the piston and cylinder from time to time, est every 30 hours...


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[motopsycho87]

The better jetted and more 2 stroke you use, the longer it will last. It was not uncommon for 2 stroke pistons to last 10,000 miles or more. Now somehow with forged pistons and ultra low friction nikasil bores we think we should change them every few hours...

What changed?

The oil ratio. In which once jetted properly, your bike will smoke no more than a bike running 60:1.

[memphis2857]

The new oils don't require 32:1 like back in the day. I have been running Motul 800 at 50:1 for many years now and I never even consider a rebuild until 150 hours. My suggestion to you is pull the pipe off and have a look at the cylinder and piston. Look for signs of blow by under the rings and look for wear lines on the piston and cylinder. If everything looks kosher slap it back together and ride it. Or you could throw a piston and rings in it for $150 and forget about it.


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[motopsycho87]

I dunno, castor oil still outperforms many fully synth oils and they used that at up to 16:1 GAINING power the more oil that was used. Only problem was the gumming and glazing...

[(F5)]

Best bet is choose a time when you have a couple of weeks without rides on & pull the top end down. During this you can properly clean out the powervalve as justification for doing this. Measure end ring gap & look at general condition.

If ring worn you might as well get a Woosner kit which appears at least over here as best value & good kit. (If required) Bits arrive, put it back together & ride & ride & ride. My 200 had a Wiseco in it & I bought a new one, first owner said he'd replaced the rings but didn't really need it. They were like new end gap but I'd already bought the piston, it was mint & wasted some money.

My 07 300 had a Vertex & it was worn. Oil & airfilter maintenance + any water drowning might affect wear.

[Leo]

Or a compression test. If the reading is more than 120psi, it's probably ok

[lonetree]

my cheats way is to pull the exhaust off every now and again, and have a look at the piston through there. if its looking all polished, with no machining marks, i rebuild, usually round 80 hrs on my 250 and 100hrs or so on the 300....