fresh top end KZ200 still smoky

just did rings, valve seals, valves lapped gaskets all done.

I thought for sure rings would do it. still blue cloud everywhere it goes. IT started on the first kick and runs DAMNED good though...

maybe the cylinder is totally warped at the bottom of the stroke? I Checked it but maybe not thoroughly enough? cant figure it out. REALLY dont wanna take it apart AGAIN lol or put TOO much more money in it...

Anyone with a kz style engine ever had this? what would you do?

pretty bummed out.

-Buy used cylinder hope its better?
-send this one somewhere for boring, get new piston?
-leave it lol

***sigh***

Did you hone the cylinder before installing the new rings? Maybe the oil control ring spring expander is overlapping? You wouldn't be the first to befall that misstep.

Here is a link to someone that just figured out that problem with the "oil control ring spring expander overlapping"

vintagebikeforum.freeforums.net/thread/2...ing-80-kz1000?page=3

When it was apart how badly oil sooted were the exhaust port/s on the affected cylinder/s? How many miles have you put on it since the rebuild? Before taking it apart again ride it for at least 20 odd miles giving it the beans on occasion to ensure you have burnt out any residue from the port and pipe. If after then you still get the same amount of smoke its time to take it apart again. If it is less then go for another ride.
It takes a surprising amount of time for just hot exhaust gas to burn out the mess left behind from leaky valve seals.

thanks for teh replies.

how i got here. barn find. only has 5000 miles. I was told it had two previous attempts to revive it. running briefly in early 90's and early 2000's

step 1: smoked, ran poorly, idle all over the place.... tore apart to see why. head gasket was SHOT...in multiple pieces. . replaced, put back together thinking for sure that was culprit. DETAIL cleaned the head. put back together, still smoked, but the small leak out the head/cylinder union gone. I have not since done compression test because theres nothing left in the top end to do ha!

step 2. 2nd rebuild. rings, valve stem seals. cleaned/lapped valves... honed cylinder. runs amazingly, but still smokes. This is RIGHT after first start. Ill hope it goes away.... but being its the same exact level of blue smokiness, it makes me think i missed something.... but what...?

some notes: valves and head were filthy with soot.. seems as though maybe it was ran hard that way for awhile... it was obivous someone had jacked with everything else... carb/points.. etc...

maybe valve guide seal not tight and popped out? or, cylinder out of spec or not round and I just did a p*ss poor job of checking that lol

pretty sure I got the rings right..took quite a bit of time to be careful there...its been years since ive done a piston.. maybe I got the wrong set of rings? I had to grind them down a bit to get the gap right. Maybe I got the .02 over ones on accident?

its odd. not many other things it can be that I haven't already done.... how does oil return to the bottom in this head?through the chain opening? i can't tell lol


I don't want to pull it apart again but...may have to... ITs only been run through 3 cycles, maybee 20 minutes... SO well run it for awhile longer. see if it breaks in some more... but, its a fair amount of smoke, doesnt seem right.

If its been burning oil before the carbon build up in the port will be soaked in oil. I've even seen it where the lowest point of the exhaust has a pool of oily sludge sitting in it. Remember there (should only) be hot fumes coming out the exhaust valve and no flame. So effectively you are trying to boil the residue off not burn it off. With it just ticking over theres not much volume of hot gas coming out, thats why you have to give it the beans to get it hot enough to clear it.
I would take it out for decent length ride and evaluate from there.

OK took it on a couple rides. 20 miles the other day... Power is there, so i assume compression is ok havent checked though.... it runs pretty well. but the oil burning blue cloud is obvious and not diminishing whatsoever...again, the rings are new and cylinder was honed.. i did valve guide seals too, there was no change. that wasnt it...

what would you do, how would you proceed? re-re do the rings? I suppose i could have jacked up the oil ring?

I'm not an expert but.... besides that, what else could it be on this little motor? lol thinking out loud again:

leak through intake side somehow? crack maybe? a stretch i guess.
cylinder out of round? I did not mic it but i moved the piston through up and down... and checked clearance... no issues.
is the oil not returning and sticking up top?
prob just fubared the rings....but my ego isnt allowing me to accept it LMAO

did a comp test and leakdown. passed both, but that latter was up and down, plus I had borrowed the tool, have a crap compressor, and have little skill at it lol

so we just tore it down. I did NOT overlap expander. But it did feel like oil rings were NOT giving much outward pressure. added photo that shows this. maybe?.
looking at my part number notes, I may have bought .02" over rings.. LOL! I have this feeling i also used the old expander...we got interrupted by a couple days....

only has 5300miles on it but its 42 yrs old! ha!

game plan. have the cylinder checked for taper and round, then go from there.

new gaskets,rings.. overbore piston if needed.

any other thoughts? Im well past budget to get it running lol

check your breather

DoctoRot wrote: check your breather

Rather than try to source an oem air filter... also remove the mice nest from it, we yanked the airbox and just put on a separate crankcase filter. no issue here.


thanks though!

Your oil ring looks like it's not protruding out past flush with the piston. Something wrong there. Regarding the rebuild, did you hone the cylinder? I doubt there is out of round or taper issues with a bore with low miles like you site.

Ring end gaps perhaps? Are they staggered?