1978 kz750 smoke

Dry test 50 psi wet test over 200 psi. All other pots around 150 psi, engine tested cold.



New pistons, rings and rebore time at 45 000 miles? maybe not.

gpz750 had only done about 800 miles in previous 10 years, I've done about 500 miles now in a month after recommissioning it and it runs great, I will retest compression soon. I think the rings were gummed and I'm hoping the solvent soak and thrashing will improve or clear the problem.

You've had my advice, what I try firstly in the same situation...

Thank you for the help I should be getting the rings on Wednesday. Just pulled the motor and will start disassembly. I'll kepp you guys up to date with what I find inside

ok good luck , you seem to know exactly what you are doing here.

Usually stuffed bores/rings would yield blue smoke, perhaps with some exhaust smoke coming out of the oil filler cap caused by blowback gases. On aircooled motors white smoke is usually condensation....

The other point being if the bore is damaged beyond honing, unless you can find another servicable block - or press a new liner in, you'll be needing oversize piston(s) and rings anyway.

Update... I pulled the motor. Tore into it and found that my oil ring broke in three pieces. One is in the crank case hopefully I can find it without splitting cases. Pistons look good cylinder walls look good. Thank you all for your help.

Thanks for the update.
Steve

oil ring broke in three pieces. One is in the crank case hopefully I can find it without splitting cases. Pistons look good cylinder walls look good.

I'm puzzled that an oil ring has broken and part of it escaped without damaging the cylinder wall... are the top compression ring gaps and piston / bore clearance within spec? No blue smoke or fouled plug, just white smoke and low compression from a broken oil scraper ring.

Is this a 750/4? Pics would be interesting...

I made a suggestion on the 81 KZ 440 thread above this one. I suggest it be done in this case as well.
Steve

As I was pulling the cylinder off the piece of the oil ring fell down did not happen when it was running. I do not know bore spec. Everything looked tightas I was disassembling. Here are pics of what I have done

That looks like a secondary ring. Do the bore test and with new rings if within spec you should be good to go. A small piece in the pan shouldn't be a problem. The strainer and filter (if you have one) should keep it out of the oil galleys.
Steve

Am wondering since you have it that far if you should pull the pan and look for that piece .... you could clean all the sludge and gasket material you probably dropped out at the same time..... and then you can wonder about doing something to the head.... I swear its never ending !! :laugh:

KZB2 650 wrote: Am wondering since you have it that far if you should pull the pan and look for that piece .... you could clean all the sludge and gasket material you probably dropped out at the same time.....

big +1 on cleaning the pan. You won't believe how much sludge will be in there. And you can "hose upwards" with brake cleaner spray and clean the underside of the internals while the pan is off.

You will want to get the valves turned and replace the seals while you are doing this, also the O rings on the oil feed pipes going up to the head. Guess how I learned that...... :ohmy: