Cylinder Washout?

[83ATC185]

Ok, so i have a 1983 185s. Its been running like a dream since around june, when i first rebuilt it. Started on the first pull, every time i pulled it. but recently its been smoking a good bit, its smoking brown and bluish white(i know its oil). its gotten so bad that it will hardly start. ive checked for spark, nice blue spark, and checked ignition timing and cam timing, everything lines up. its getting plenty of gas, i believe its too much fuel, and compression has been on a steady drop since last month(ever since i rebuilt it, ive been keeping tabs on everything). I change the oil every other time i ride, but this time after i got out of the usual sunday mudhole, i checked the oil and it was dark, almost black. and it smells like gas. Someone(a buddy) told me that it was getting so much gas it was thinning out my oil and that was making it lose compression. can anyone back this up, and could this be the problem?

[dksix]

Gas is on top of the piston, the oil is under the piston. If gas is getting into your oil it just about has to be ring failure. I don't know much about engines but I don't think gas thinning the oil could have any effect on compression. Low compression is a leaking cylinder, either from the piston/ring or valves. Here's a easy check to see if your rings are going. Check the compression with a compression tester. If the pressure is low on the gauge put a little new engine oil into the spark plug hole ( not allot, a table spoon full or so, lust enough to coat the top of the piston and rings as a sealant ) then recheck. If the pressure increases 25psi or more, you need to rebuild your top end again. How long has it been since your rebuild (hours of riding)? If a rebuild and break-in was done correctly it should have lasted for a long long time, unless it's been abused.

[83ATC185]

i finished it up in july, i put new rings in, but did not hone the cylinder because i was told that had been done just before it quit(new cylinder, old piston and rings). but it just now started smoking. Will check compression again tomorrow

[Yamaha_Rules69]

Did you measure the cylinder and check piston to cylinder clearance, and ring end gap at least? Not measuring and just putting things together is bad news. If not, during teadown, follow the manuals motor specifications to ensure all the tolerances are correct, and nothing is worn. Also, gas in the oil could occur from a worn needle and seat in the carb. If you leave the petcock on "ON" and the nedle and seat are worn, fuel can pass by them, and keep filling until it has no where else to go, and finds its way into the oil. The needle and seat can be checked visually, or more effective is a very low pressure test. If you have any doubts, replace. Good luck, and hope this helps.

[83ATC185]

i went on hearsay, really. i was told it needed new rings, but the previous owner had gotten a new cylinder for it and had it running before it quit again. maybe there's a reason why it quit again. maybe its me lol i just need to tear it down and do it right anyway

[dksix]

Honing, rings and gaskets is the minimum when rebuilding. That's if the cylinder and head is measured/checked and they are still in spec. Most times you'll need to send the head in for leveling and the cylinder in for boring, then order the correct sized piston set to match the bored cylinder. It shouldn't take more than .005" to get the head level (maybe not always necessary but never a bad idea to have the engine shop check it). If your cylinder was never honed it's going to have to be rebuilt again.

[83ATC185]

well that brings us to a dillemma here. i wanted to ride it in the towns christmas parade, and im out of work right now so getting a rebuild done quickly is going to be difficult. Maybe i can get it started and take her on one last glory ride before i tear her down.