Ultra 250X engine rebuild

[lau-de]

Hi gents,
I am in process of rebuilding an Ultra 250x engine and have some points that are much clear to me
1. I'm going to replace the pistons; should I take these of 250x (PN 13001-3738) or better 260x (PN 13001-3740)? are they interchangeable? 260x seems to have a higher compression ratio...
2. Will the original ring set (PN 13008-1196) fit a re-sleeved cylinder block?

[dcuhpw]

Yes to the 260x pistons. Or go with a forged set. Are you installong some darton sleeves or just boring your cylinders? If you bore remember that they will need to be replated.

[lau-de]

Are you installong some darton sleeves or just boring your cylinders?

I'm installing iron sleeves and Woessner has a suitable ring set which would fit cast iron liner as well as nikasil or chrome cylinder for 30 EUR
if you are really sure 260x pistions would work in a 250x engine I'll take them; the original pistons seem to be the cheapest option, I'm going to keep the ski fully stock...

[dcuhpw]

I'm installing iron sleeves and Woessner has a suitable ring set which would fit cast iron liner as well as nikasil or chrome cylinder for 30 EUR
if you are really sure 260x pistions would work in a 250x engine I'll take them; the original pistons seem to be the cheapest option, I'm going to keep the ski fully stock...

260 pistons were a revised casting from the 250x. Yes they will work and add a small bit of compression. Why are you sleeving your engine though?

[lau-de]

Why are you sleeving your engine though?

I have bought it with a stuck engine; as far as I could check the cylinder walls with a borescope by purchase they had some scratched in the upper part
as we disassembled the engine we found a spark plug shell in 3. cylinder with a broken extractor so it seems the previous owner tried to extract a broken plug and did not succeed; then the engine was presumably run on 3 cylinders => gas gone into oil (the drained oil is pretty thin) causing excessive cylinder/pistons wear
then ski was stored for years without spark plugs so the pistons got seized by corrosion
the supercharger is a scrap, rotors corroded, PTFE coating peeled off completely; but mint overall condition, only 78 hours