Oil in #4

Greetings All, 

Thanks to the wisdom of this forum, I have solved my carb issues and now have slightly too much money in a perfectly functioning set of BS34s on my 82 LTD1000.  Thanks for that!

Now that I have resolved that issue, it has left me with another puzzler.  I have oil in cylinder #4, after 50-100 miles the plug gives up.

I had the head off to replace valve seals and pulled the jug to check for worn/cracked rings across the board.  I didn't see anything that appeared to be out of order, so I reassembled it and low and behold, still issues in #4.  When I purchased the bike from the 2nd owner, the carbs were junk and it was un-rideable.  It showed 4997 on the odometer, so I wasn't thinking I'd have to be in the engine (wrong).

I ran compression and leak-down and it wasn't bad, the intake and exhaust were silent but you could feel it puffing through the crankcase vent, so to me that says rings.  Compared to the other cylinders, it was lower (photos).

I'm not seeing another option except a 2nd consecutive teardown (has less than 200 miles on the rebuild).  I'm thinking of rings just for that cylinder and see if she likes it.

So the question to this group would be, anything in particular I should look for during disassembly inspection of #4 to determine the root cause of the oil?

Any info is always appreciated.

Thanks

You've ruled out the obvious stem seals so at best it probably needs a hone and new rings and at worst a rebore if the piston to bore clearances are beyond the service limit.
That is of course unless the cause is an uncommon fault such as a cracked liner, piston or  fracture in the cylinder head through from a cam bucket bore to the combustion chamber.etc.

Just make sure on re-assembly that the ring end gaps are rotated 120 degrees apart. If the gaps are in line you will get blow-by

Before you start tearing the engine make sure that is oil !. Check if it puffs blue smoke form exhaust when riding best is to have someone riding behind you .if it smells oil and there is blue smoke it is buring oil .  Or black smoke (gasoline)
Have you notised any smells when riding and coming to a stop  i mean if it smells gasoline or oil ? try to smell the exhaust when on idle .
You might be lucky and this is fuel floding because of running to rich on cyl 4 .worth a check before tearing engine

Your correct,  before I got the carbs sorted out, I had black smoke and the plug smelled of fuel. 

Since I got the carbs sorted out, it's now blue and the plug has no smell of fuel, just oily. 

Update:I disassembled the top end and was hoping to find am obvious issue like a compressed oil ring or broken wiper ring..... no such luck. 

I see the "N" stamped on the wiper ring,  but not on the compression ring (thought there was supposed to be stamped on both rings).

I don't see anything visibly wrong,  but thought I would throw in some pics and ask if anyone has any ideas.

I'm planning on checking the bore and doing a light hone and a new set of rings on number 4.

If these pics are as it came apart it looks like the "end gaps" are in line (they should be 120 degrees apart across the three rings. If the end gaps are in line you will get "blow-by" heave you measured the end gaps before you spend out on new rings ?

 

This pic was after inspection.

The install was really close to 120 degrees.  The rings had already "walked" to around 100 degrees at disassembly, but were not lined up like in the pic.

Appreciate the feedback! 

Unless you did a typing mistake the ring marked N is the compression ring and it is the top ring.My tired eyes is not 100% sure but it looks like the scraper ring is the one that has no mark it has a ridge .The rings look worn did you replace them ? The ring end  gapping is not very important unless you done a rebuild .the ring end gapping instructions is so that the engine has best possible compression on startup on a new engine,¨.The rings rotate on the piston as the engine runs.

Here's a pic at disassembly
 

The pick is not good enough for me to see clearly if the top ring has a scraper ridge .if it has that is placed wrong.The ring marked N is comp ring and sits on top and the ring with a ridge that has no mark in eariler pickture is the second ring and the ridge is faced down.

The 120 degree positioning of the piston rings is to get the best compression value on the first engine start to get the highest ring pressure to the cyl. surface during the break in time and to get the full ring to cyl. surface fitment/sealing ability.