Hello Dockhead
I'm a bit late to the party but I recently did almost exactly what you are proposing on my JH2E, so maybe my experience will be of some help. I'm also assuming that your evaluation of the cause is correct. Running well but smoking at 830 hours makes it very likely that it has glazed bores - mine had the same symptoms when I got it at 1120 hours. After putting up with it for a couple of years I finally fixed it two years ago. My
Yanmar doesn't smoke (now!). Yanmars don't need to smoke but glazed bores do seem to be more common in Yanmars - I have no idea why. Maybe it's my imagination.
As for doing it in place, that is absolutely possible if you have enough room to remove the oil pan - don't forget that you need to pull the pan down to clear the oil pickup, so you need the
depth of the pan in clearance under the engine to drop the pan into, so that it can be slid out. ('hope that makes sense). Once the pan is out of the way the big end caps (rod caps) can be unbolted and the piston/rod assembly removed through the top. Also I would imagine that
cleaning the
gasket surface on the bottom of the block for the new pan
gasket would be quite difficult. I didn't have enough room so I used a board and some straps to move the engine into the
cabin.
My bores were perfectly round and without any wear or taper but were glazed so they were honed and new rings installed. The pistons were perfect so I cleaned them and had the crowns ceramic coated and the skirts anti-friction coated - not really necessary but I used to coat the pistons in
race engines, so why not? It reduces heat transfer and also makes it harder for carbon to adhere to the crowns... at least in theory. There was a little play in the valve guides, so they were replaced along with the
seals - the new ones also have a little play (less but not that much less) so I'm not sure if it was really necessary. The
exhaust valves were replaced and the seats lightly cut as there was some pitting. The inlets were fine and were just lightly lapped. The valve springs were tested and reused. I replaced the big end bearing shells, just because it was already apart, but in that there was so little wear anywhere I looked, I didn't disturb the crank or cam.
I terms of cost, it came to just under $2k US for the
parts including the gaskets, coatings, new engine mounts (which were surprisingly expensive) and all new hoses. I did all the of the labor. BTW, the injectors were tested and were fine.
One other thing; it took much longer than expected for the rings to
bed in and the smoking to stop, especially when cold. Maybe it was because I used a slightly coarser hone that I would have liked to. I didn't have the correct size and the one I wanted was back ordered. I used
cheap oil for a couple of hours to flush out any debris / particles (about 6, 20 minute heat cycles with varying throttle and partial load) and then changed to regular Rotella, Whatever you do, do not use synthetic until it is fully broken in (if at all).
It now doesn't smoke or use any oil. Really! At least not enough to register any change on the dip stick between oil changes.
Personally, in your case, I would pull the cylinder
head to see exactly what you are dealing with and proceed from there.
Other thoughts:
If the bores are glazed but are round, don't have significant wear (no step), then a flex hone / ball hone / whatever you want to call it hone, is absolutely the CORRECT type of hone. Other types of hone are used in other circumstances but can remove too much material in this scenario. You are already at the correct size and want to remove as little material as possible. This is what I think; This is what
Yanmar thinks; Many, many others think so as well. I only differ from Yanmar in that I use honing oil.
After honing, clean the bores by wiping with paper towels and wd40 until they come back completely clean. Then use paper towels and engine oil until the towels come back completely clean. A lot of paper towels. Then do it again... you missed a bit.
I don't believe that running low on oil will do anything to help.
Glazed cylinders are very hard and I don't think using Synthetic oil such as T6 will help and may make things worse. It's not really the synthetic part, but that synthetics have a high TBN because of the extended change intervals. This is a cause of cylinder polishing in lightly used engines. I've had this argument many times so I won't rehash it. See these links. Anyone who disagrees - that's fine... it's your engine.
Oil for yacht engines – Cox Engineering
Bore glazing and polishing in diesel engines – Cox Engineering
There are special high detergent, very low TBN oils that, in conjunction with high load running, purport to cure glazed cylinders. I have no experience with them and am somewhat dubious. I guess it doesn't cost too much to try but I would worry about sufficient lubrication for the rest of the engine, especially with a turbo.
Replacing liners may or may not be straightforward on your engine, your manual will tell you. A good automotive machine shop could probably do it on the JH2E but it can be bored much more easily and one oversize pistons are available. In that your engine starts easily, I doubt that there is enough wear to justify either. It's definitely not junk.
Anyway, I hope that this diatribe is of some help.