Today I tore the engine down. I found some concerns! For background information I rode this bike quite a few km last year, its first time on the road in likely a decade or two.
I re gasketed the top end last year but that was about it for engine work. The carbs had some slight corrosion issues, lapped the valves, one of which really only barely cleaned up. #3 intake valve was likely open for a long time while the engine sat, the seat was badly pitted.
Initial compression test was 1:190, 2:170, 3:150, 4:160
It improved after gaskets and lapping but #3 was still weak.
All along, when cold, the bike was a bear to get started. Fine when hot.
With lots of spare time this year, here we are.
The engine was full of crusty black stuff - almost feels like dirt grains. Turns out it's petrified black RTV. Don't use black rtv for your bike cases, please?
Engine had two oil changes and two oil filters last year - pan full of sludge.
Crank bearings don't look awful, but some scuffing at the shell edges.
I know it's hard to tell what you're looking at in this photo, but that's where the transmission drive chain has apparently been slapping the case?!?
Is that normal? I can't help but suspect it is NOT.
Crank journals look like they enjoyed the oil contamination.
three pistons look like this - some slight scuffing, looks normal to me.
#3 looks like this: 
and #3 bore
Measured all bores and pistons with vernier calipers and telescoping T-gauge. Not a bore dial gauge, but reasonable measurement accuracy in any case.
All the pistons measured out, from thrust faces - 58.37 to 58.42 mm. Service limit in the book is 58.35mm. standard size 58.5.
I measured the bores top of the ring sweep and bottom.
The bore tops (most worn) measured out at:
1: 58.52
2: 58.5
3: 58.58
4: 58.49
serviceable limit 58.6mm
So I'm sort of getting the feeling I could do with a fresh set of standard size pistons and rings, although #3 might need a hone and an oversize?
I was not pleased to find all the dirt inside the motor. As I said, it's had a couple oil changes and the pan has been off and cleaned before as well.
What do the more experienced members think?
This isn't my first kick at the can, I've built a couple car and bike engines before, but every case is a little different and I would really appreciate some help!
Here's the imgur gallery of the tear down today.
http://imgur.com/a/IegfXBj
