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I had a broken rod and piston and messed up camshaft in an BRIGGS INTEK 2 CYLINDER...I did the honing...replaced the rod..piston and cam...set the valve clearance..and the engine runs very well..(maybe some slight backfiring at idle) but at high throttle it smokes...is there a break in for the new piston and rings??...would they naturally smoke for a while?...how long??..or have I screwed something up!..also...what if I got the valve clearances wrong?..would that cause some smoke?...I would really appreciate any help
 

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New rings need time to seal properly. But it shouldn't be smoking! Just when you first start it up to get rid of the residuals you got in the combustion chamber when assembled. Did you make sure the gaps in the rings were not in line when you installed the piston? Did you take material off the cylinder walls when you honed it? The stock rings might be undersized and will never seal! Are the valve seals in good shape! The oil is either coming from the crankcase or the valve seals. Do a compression test see what you get! If the ring gaps are in line your compression will be low. Make sure the crankcase vent is not clogged. It shouldn't be backfiring either even at idle. Do you mean missing or popping? Popping on deceleration it's just leaned out. Having the valves too tight will leave them open causing low compression ,rough idling, but not blue smoke. I'm taking for granted that the smoke is blue!! I'd throw a compression guage on it first. If it's low pour some motor oil in the cylinder, check it again if the compression comes up your rings are not sealing! If it doesn't you probably have a valve not closing. Good Luck!!!!!!
 

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I would look at the plugs to see if one or both cylinders are burning oil. Is it possible you installed one or both of the scraper rings upside down?
 

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The scraper is the second ring on the piston. Many of them are directional. If installed incorrectly, it will actually pump oil up to the combustion chamber as opposed to pushing it down to the crankcase.
 

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Ericwest,

Yes there is typically a "break-in" period for any engine after an overhaul.Try putting some hours on the engine, smoking should reduce then disappear. Some times you can accelerate break-in by lightly sprinkling powdered Ajax or Comet down the carburetor with the engine running at about 3/4 throttle. (this is an old mechanics trick to speed break-in) Also, check the breather (disconnect from intake to see if pressure is excessive) Breather should not be pushing oil vapor or oil droplets from hose, this would possibly indicate "blow by" (compression into crankcase) from non-seated rings. Sometimes the breather itself (original) cannot control crankcase pressure and needs replaced. There is a lot of possibilities, don't panic, check systematically. Good Luck

Roosamaster:fing32:
 

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"you can accelerate break-in by lightly sprinkling powdered Ajax or Comet down the carburetor with the engine running at about 3/4 throttle. (this is an old mechanics trick to speed break-in)"

And best left to "an old mechanic"

A blow down test will give you a better picture of what is going on. Did you check the ring end gap before installing them to make sure they were not near or at the reject spec? By the way, rings travel, they do not stay where placed even though carefully staggered when installing.

Walt Conner
 

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If his rings aren't undersized he shouldn't have any blue smoke he can run it for six months it's only gonna get worst. And you can take off a few thou running a hone too long. I've recut alot off of coupling bolts due to overenthused techs running a sunnen on a rotor coupling, even a light one. And that metals harder than a cylinder wall.
 
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