I have had my YS 110s for 2 years or so during which time it usually ran very well apart from the usual novice 'fuel line/ pressure valve/ and regulator issues' which I've now got my head around and so they happen much less frequently. A few weeks ago I noticed a rather harsher sounding engine note which lasted for a few minutes and then seemed to sort itself out but unfortunately it eventually stopping running properly. To cut a long story short, it now seems to have very low compression and will not pressurize the fuel tank despite the valve functioning correctly and therefore will only run for a few seconds at most (fuel shortage at a guess). I decided to strip down the engine to check for any obvious problems with valves, piston ring and bore, and bearings. On removing the air box , crankshaft back plate and carburetor assembly together with the complete head and valve assemblies I can now remove the piston and can clearly see that both the piston and bore are heavily scored. The conrod bearings are smooth with no visible signs of damage, the small amount of oil that was collected around the crankshaft area was clean with no visble metal swarf, and the bearings feel pretty good with no notching or tightness. At a guess, a glow plug element parted company about the time of the initial engine problem as I remember having to change the plug during that session. I'd appreciate a little help with the following........

Am I correct in assuming that the heavy scoring to piston, ring, and bore will account for the lack of compression and therefore tank pressure?

That means a new head, piston and ring?. plus ancillory seals and gaskets?

I am at the stage where I have two pieces of engine, the head with valve assemblies still attached, and the 'bottom half' with crankshaft, prop driver assembly, front and rear bearings and the crank shaft ring still in place. To remove crankshaft completely from case is it just a case of a smartish tap with a hammer shaft to release the shaft backwards or is there some other internal fixing that's stopping the crankshaft from being withdrawn?

Ive read the tech.flyswg.org article which gives a good description of the re-assembly process, but not a detailed description of the actual complete strip down.

Thanks for your patience..........any other advice would be appreciated as well.

Bob Vaughan, Mansfield, UK.