need suggestions- 426 smokes on cold start after new piston

a big hose clamp works just as good as ring compressor

Problem solved (I think). I'm fairly sure it was the end gap in the oil rings, but I could possibly have put the second comp ring in upside down, I'll never know for sure. I took it out this evening after I got it back together and ran it, no smoke. I let it sit for 1 1/2 hours and started it back up, no smoke. I rode it up and down the street with a penlight in my teeth for about 1/2 hour and it's still good. Me and the boy will go out tomorrow evening for a good long test run unless it rains. Thanks again for your help guys...

make sure you use race gas[not octane booster].especially while breaking in new topend.i always use race gas to break in new motors.even when im breaking in stock motor first tank i use 104 oct.the higher the octane the cooler your engine will run and better your rings will seat.

Race fuel, in iteslf, will not make an engine run cooler. That is one of the oldest misconceptions around.


Remember one thing (Might have been cause of first problem). When breaking in a engine (2 0r 4-stroke, car, anything) ALWAYS use a petrolium based oil for the first tank of gas. Bean oil isn't a good break-in oil. Go buy some Kendall GT-1, Yamalube, or anything like that and run it for a tank of gas, then switch to whatever you normally run. If you get a glaze built up your rings will never seat if running improper break-in oil, and thus will smoke all the time and cause engine damage.

Some people said it could be the gas, only thing gas has to do with it is if its too low octane you can have pre-mature detination (Won't cause it to really smoke, just break a rod). I am a Pro ATV racer and am always running my YZF wide-open in a quad and I've run 92 octain pump gas at times and never had any problems. I broke-in my engine on Kendall GT-1 and then switched to Amsoil and mine never smokes.

Hope this helps,


[ January 31, 2002: Message edited by: Sickman80 ]

By the way- it's still going strong.

I bumped this in response to GlenT's question...


Glad its together. You mentioned the smoke was grayish. My bet is your rings were fine. The smoke may have been coolant from the reused gasket. This can run from white to gray and can go away with expansion.

We'll never know.


Originally posted by MikeOK:

Anyway, I have re-built the top end on several 2 smokers, and with the new cylinder plating I have always been under the impression that all you do is check your ring end gap, slap everything together and go ride. Maybe the tolerances are not as critical but that's how everyone I know does their 2 strokers...

Yeah know I rebuilt all of the 2-smokes I've owned over the last 10 years this way. I thought one of the benefits of nickel plating/electrofusion was the durability of the cylinder wall outlasting the piston. I had a 93 YZ 250 that I rode for over 4 years frequently riding 50-75 hard desert miles a weekend (year round) and never replaced the cylinder. I put 3 different top ends in it during that time. Ditto with the last 2 KX's I had prior to buying my 426. I too thought that if you inspected the cylinder walls and there were no abraisions, visible flaking of the coating, etc than you were good? Is there something different about 4 strokes that require a new cylinder every time you replace the piston (if it costs more to bore/replate than a new cylinder than we're talking about buying a new cylinder with a new top end).

Thanks in advance, I'm really curious about some of the stuff in this thread.

Are you sure you did not break a ring putting the top on. White smoke is Oil its sucking it from somewhere.

Alot of info here overload overload overload

Tear the top off and chk everything with a fine tooth comb.

You will often see white smoke coming out of ME when my bike is warming up.

Mike if you got the second ring in upside down, that was your smoking problem for sure. A lot of people dont know this but the second ring isn't really for compression. Its not square on the "sealing" edge either, thats why it has a top and a bottom. The second ring is an oil wiper. It may help with compression, but that isnt why its there. The oil ring is for oiling, the second is for clean up. If your relying on the second ring to help the first, youve lost the battle at the top ring.

Smell the smoke. Be one with the smoke. Put a wet towel under the garage door a....

If the smoke is blue. No question. Oil. Gasket, ring or valve seal.

If smoke is black, it is probably soot. Fuel/Air problem or ignition problem.

If smoke is white, it is steam (coolant), gasket or cracked head.

If gray, that's a gray area. Smell the smoke. If you smell antifreeze (assuming you use antifreeze) it is coolant. If you smell oil, it is oil.


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