Scooterotica

Possible schoolboy error!

Is there a way of telling which is the correct way to fit the piston on my LI 125 Series 2? There is no arrow marked on it. I *think* I've put it back on the same way it was before, but I'm finding it difficult to start, although it does eventually run for a short while.

Would it start at all if the piston's the wrong way round?

Ring pegs to inlet side

also windows downwards towards the exhaust port

Thanks guys! Before I strip down the top end to check, would it even run if the piston was in the wrong way round?

it could- but not very well at all.

Looks like you are going to have to do a partial strip down- go as far as sliding the barrel off the piston but don't remove it entirely (i.e. leave the ring area in the pot). You can then tell if its in upside down


Chris

Easiest way to check is remove your exhaust and look in the port, If you can see your ring pegs it's the wrong way round.

Thanks again fellas. I just quickly connected up a compression tester, and I'm only getting around 70psi, so something's definitely amiss.

I'm hoping it's the piston, and not something like a blown seal ...

Right, exhaust is off, and no sign of the ring pegs. So that means it must be something else that's giving me low compression and almost impossible starting.

You can just about make out on this pic that there is a lot of oily deposit around the rings. The piston was clean when I fitted it, and has been run for a couple of minutes at most. Does this look normal, or are the rings not doing their job (which would also explain the low compression number I guess)?

Have you measured piston to bore clearance and pushed the rings in to bore and measured the ring gap.ive just fitted a gp 150 top end bored to 63mm . The scoot was a sod to start before and turned out to be worn bore and rings. Lots of blow by marks under rings.

bazza3004 wrote:Have you measured piston to bore clearance and pushed the rings in to bore and measured the ring gap.ive just fitted a gp 150 top end bored to 63mm . The scoot was a sod to start before and turned out to be worn bore and rings. Lots of blow by marks under rings.

What he said ^^^^^

Difficult starting + low compression pressure can quite often be the result of a worn cylinder/ring/piston combination......usually a simple re-bore and new piston resolves it,