So how do I figure if it's rings or valves? Any point my unbolting anything else or should I just put back together and hand to a pro?
Also, seen these on eBay: https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/131985019262 I assume it wouldn't be as simple as unbolting old, whacking these on with a couple of new gaskets, sticking the belts back on and off I go... Would it?????
Those plugs look like they centre electrodes are quite worn mate when was the last time you changed em? As you're getting the valves done soon anyway I'd suggest you just order some ThreeBond and get the valve cover off, clean it and the sealing ring, and then put it back on as per the manual. The manual shows you where, exactly, you need to put the ThreeBond when reinstalling. Both of those compression values are a bit low TBH, the V cylinder being lower could be due to a bunch of things, including the valve clearances tightening up and/or as mentioned earlier the valve stem oil seals or the piston rings. Leak down test will tell you quite a few things but again just take the valve cover off and check/reseal it for now as you have a valve job coming up.
seeing as its the vertical cylinder a wee squirt or two of oil down the bore will eliminate the rings if its still low.
Plugs are just over 1 year/3k mls old. I'm not needing to ride bike again this year, I have other bikes and no TDs booked, so unless it will tell me something I won't take heads off. No need to reseal I think. If it was June it would be a different matter!
Sorry, crossed wires. Yes agree it needs sorting. What I'm saying is, as I won't be riding the bike again no need to reseal. As it'll only need to come apart again anyway to get the valves done. I'm just trying to diagnose.
Pistons are pretty big on these bikes mate so 2 or 3 teaspoons full should do the job, the oil acts as a temporary seal around the edge of the piston. Stick the oil in then do a compression test and write down the result.
Oh. Google says piston at fault. That'll be the expensive option then. Thanks guys, I think it's time she went to a pro.
That all sounds about right. As usual it could be a few things or something else, could be a scored bore, damaged or worn piston ring, some tw*t not spacing the ring gaps out, probably one of those. Nothing serious anyway. Sounds like the valves aren't being held open which is good or if they are, not by very much.