Pistons

[humbucker88]

Is there anyway to tell which piston belongs to which cylinder or are the all identical? I ask as i'm considering buying some used pistons/barrels as my old piston rings aren't bedding into my new barrels. Problem being, most sellers appear to have mixed up the pistons so there's no way of knowing which one belongs to which cylinder, any chance the pistons are labelled 1,2,3,4 or is that wishful thinking?

[richfzs]

If your old rings are not bedding into new barrels, why would another pair of second hand ones be any better? Surely new rings are the answer?

[humbucker88]

The idea would be to buy different barrels together with their respective pistons that are already bedded in (ca. £40) rather than 4 sets of new pistons (ca. £200).

[midden]

Are the barrels brand new or just new to the bike?

[darrsi]

I must say, you're the first person i've ever known on this site to mention changing pistons/piston rings?
It was a very common thing in the old days, but i barely even top my oil up ever between recommended changes with no oil loss whatsoever, and i've had my bike 5 years!
2 strokes were part and parcel, but what made you change them?

[Gnasher]

Surely new rings are the answer?

This is the way to go.

That said you mention "new barrels" do you mean rebored, brand new or just secondhand new to this bike?

You shouldn't mix pistons, rings and barrels they wear in together to form matched pairings if you do you will suffer all manner of issues, you can fit new rings to old pistons/barrels providing both are undamaged and within spec.  Like Darrsi mentions this is in my experience very unusual I've only ever had to change pistons/rings/barrels after serious failure what happen to your engine?   

[humbucker88]

Old barrels had a small crack in cylinder 3. The current barrels are brand new as a garage was closing down and getting rid of stock. The current pistons/piston rings are original. I'm essentially trying to find a way to solve the problem of blow back without spending £200 on new piston rings.

I can't comment as to why one of the cylinders had a crack in as I bought the bike like that but the cooling system works as it should so I'm not too worry about it reoccurring.

[Gnasher]

I'm essentially trying to find a way to solve the problem of blow back without spending £200 on new piston rings.

There's isn't matey, new barrel block with old in spec non damaged pistons and NEW rings is very possible but not absolutely certain, only sure way is new pistons and rings.  What you are doing is very likely to wreck the new barrels and even with new rings fitted now you will loose compression, pressurise the crankcase and possible burn oil.

I'm assuming you do mean low compression/pressurised crankcase when you say blow back?   

[humbucker88]

Ye, compressions not TOO low but the pressure is pushing oil up the crankcase breather into the airbox. Maybe I'll just swap out the engine then, would be cheaper in the long run probably.

[Gnasher]

Change the rings it's work but cheaper then a good replacement engine and you should get away with it providing you've not damaged the new bores, you could have them honed as a precaution. 

[Ianboydsnr]

Ye, compressions not TOO low but the pressure is pushing oil up the crankcase breather into the airbox. Maybe I'll just swap out the engine then, would be cheaper in the long run probably.

You sure you have the breather pipes in the correct place and or not trapped?


I had a mate who has a diversion 900 and he trapped a pipe iit pushed out the rocker gasket, it seems odd that the compression is ok, but it's pushing oil out!