High Mileage Woes - power loss and starting to burn oil

Well, I feared this day might come. My wife has been riding the Seca 550 a lot, and it now has over 115,000 km (about 71,500 miles); and these are all city miles (stop/go). While the bike overall has been maintained the best I can, it is now starting to both leak some oil (looks like base, head, and VC gasket all seep somewhat) and burn some too (some bluish smoke from exhaust on acceleration, and smell). It lost about 1/2 to 1 litre or so of oil over the summer riding (4,500 km). It also does not seem to have the normal power and has some hesitation and generally gutless performance in the mid range. The performance problem does improve somewhat with the enrichment circuit on halfway, and once its warmed up the symptoms improve (but performance is still lacking), but besides running too lean, the idle is rough and the acceleration is not crisp. Pilot screw and sync adjustment attempts have proven futile.

First things first - I need to do a compression check and see what is going on. Last top end rebuild was over a decade ago at 54,000 km, with only a few shims needing swapping. New valve guides and seat polishing done at that time. Original sleeves, rings and pistons.

Just looking for opinions on what I might expect to be facing with that many miles, and what my best options are. I do have a spare engine from a parts bike that has about 14,000 km (less than 10,000 miles), but it sat outdoors for years with all sorts of filth and rust, and has an unknown history. One spark plug broke off at the base trying to remove it, and I had to pull the head and drill it out almost fully then chip out the remnant. (Pics below). This may be a good donor head, or even a good donor engine , I'm just not sure how good the sleeves, pistons, valves and rings might be on either engine without doing a full teardown on both. Any advice appreciated.

 

well, you did a grand job of getting that broken plug out,
i would have thought the valves and guides will be ok at , what , 36,000 miles.
yeh, time for a compression test, before anything.
while you're at it , do a compression test on the spare engine, if it turns

 

Thanks - getting that plug out was nasty; basically drilling to within a few micrometers of the threads, then using a sharp edged needle file to create linear grooves, then a jeweler's screwdriver and small hammer to try to break the thin cylinder of remnant spark plug away from the threaded edges by cracking it loose, splitting it along the 2 grooves, then grabbing and twisting the broken edges inwards with small needle nose pliers. It all worked well enough to preserve the threads such that I can spin in a new spark plug by hand, i.e. minimum thread damage.

Yes, the spare engine turns but that is the one with the heads now removed . IIRC, it turned fine 11 years ago when I picked up this parts bike, before I removed the heads. If it wasn't for that damn broken plug I would not have removed those heads in the first place. I needed to get at it from both the top and bottom

I bought an all-inclusive gasket kit when I did the first refresh on the original engine at, yes about 36,000 miles, and since I was in there polishing valve seats and re-shimming I used the new valve seals that came with that kit. Now, I'm not sure about which engine to refresh; and although the parts bike engine has a lot fewer miles (according to the odo), it looks nasty from the outside and may have been abused, I just don't know. Lots of carbon in the exhaust ports. Pics of it:

 

Supposing I did want to refresh this parts bike engine, what is the best, most cost effective way to clean up the exterior?

 

Great job on the spark plug removal. That had to be a little nerve racking. I don't see any pics of the current engine, I would guess the pics above at the donor motor? Would like to see what the piston tops of the oil burning motor looks like? Any visible issues with valves or the pistons of the engine in trouble?

 

Couple of things to look at.
If you have the current bike in pieces check the bores with a bore gauge.
If in spec, according to the service manual, a crosshatch hone and new rings are the way to go.

Same applies to the other engine.

Cleaning up the other engine externally is, always to the end users liking.

If it looks awful but runs great
Or
It has to look sparkling and also runs great.

I spent a lot of time polishing and sand blasting and lacquering and... Eventually I gave up and went for just running great. I appreciate a shiny engine but I don't have the stamina it seems.

 

Yeah, it was a bit nerve racking, since I didn't want to wreck the threads on what I thought might be a needed donor part. And yeah, these pics are of the donor "parts" bike engine with about 10,000 miles (?). I have not yet pulled apart anything on the running bike, not even the valve cover, and won't until I do a compression check to see how far off everything is. Just waiting on that tool right now. Back when I did the first refresh, everything looked great and when I finally got it back together, running and in sync, it ran great. Now, not so much - plug chops and needing choke until very warm indicate a lean condition overall, but it does not have the power or smooth acceleration mid-range, and does burn a little oil, and has high city mileage, and has some minor leaks, so........

 

Well, its the wife's ride now (mostly), so unfortunately it needs to be the 2nd option, that's just the way she rolls. Besides, the rest of the bike is pretty sparkling for its age and gets her compliments, so if I'm going down the repair engine or swap engine hole, I'm going down deep anyway. But so far even Simple Green isn't cutting it, and it would probably be preferable to swap that "parts" engine into the bike, just given its lower mileage, assuming a full teardown reveals no further issues. Good recommendation on the bore gauge measuring, don't have one but I'll see what I can source.