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#1
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K301 Smoking After Rebuild
Acquired a Cub 1250 with K301 motor that was losing power when hot. Figured the motor needed a rebuild, so tearing down the motor found that the exhaust valve was burnt. So I checked all clearances and found that a standard rod and piston were needed plus gasket set, valves etc. I followed the vendors info for ring placement and completed the rebuild. On first startup it smoked quite a bit for 30 to 40 seconds and quit, running motor at 3400 rpm. Shut down and restarted 10 minutes later required no choke, started right up with no smoke. Waited about 2 hours and restarted requiring little choke but smoked again for 20 seconds. The next day startup was the same with smoke for 20 seconds then quit, also worked the motor and run at governed speed. Additional startups with little time between refire produced no smoke. This motor has a little over 1 hour run time after rebuild. How much wear in time is required for rings to set and this motor quits smoking. Should I be patient with this or am I missing something. Your thoughts and suggestions are welcome.
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#2
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Run it a while to break it in, before you worry too much.
How much choke are you having to apply? Could you be flooding it? I have a 16 hp cast iron Kohler here that I KNOW is tired. Starts good and runs alright, better now that I have replaced the valves, lapped them in (seats were great) and set the clearances. I can see more of the top ring than I like with the head off. Exh valve was also bad like yours was, stem was stretched and "necked", quite a bit of slop within the guide. Much better now. I know that this engine could use a rebuild, to include a rebore. When I had the head off, the top of the Piston was soaked in oil as was the exhaust valve stem. All that said, it doesn't smoke nearly as bad as I would expect, other than when starting up when cold. And that is less now that I have gotten rid of the excess guide clearance. Is yours smoking out of the exhaust or the breather/ valve cover? Is the breather assembled right and right side up? How's the carb settings? These are other things that can cause these engines to smoke. |
#3
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Will check the breather tonight, followed the service manual for assembly but you never know. As for the carb, its brand new and runs a little rich but wanted to give the motor more break in time before adjusting. Very little choke needed for cold start, surprised at how quickly it starts when warm. Thanks for the help, will keep informed.
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#4
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If you just re ringed the motor and not rebored it oversize, it is expected to use some oil as a used bore is always tapered and egg shaped somewhat.
Normally they will get better over time as the rings take the shape of the bore, but never be like a new bore. Also you make no mention if valve guides were worn, that can cause oil consumption. How did you measure the bore? with a dial-bore indicator or telescoping gauge/mike. Or a caliper which is useless? The ring end gaps are normally staggered 120* What was your new ring end gap? within specks? Did you deglaze the block with the proper cross hatch pattern, are you using a chrome ring set? If you deglazed it, did you thoroughly wash the block with hot soapy water? If not, change the oil several times in the next 10 hours At this point prolly use it as you built it, and accept any short comings. If it is starting with little choke that is best as it is not lean for a new engine. |
#5
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Actually the bore, piston & valve guides were in really good shape considering the age, the exhaust valve edge was burnt (lack of power when hot). Used set of inside mikes for bore and used new standard piston and rings. Honed cylinder to achieve proper cross hatching and checked compression ring and oil control ring at top and bottom of stroke bore, all within tolerance. Cleaned bore, set rings at 120 deg and used 30 weight detergent oil. Will change after five hours. It only smokes when cold start for 20 to 30 seconds and then clears up, does not smoke on warm start up. I know "be patient"...........
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#6
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Is the smoke from using the choke when cold? Is the smoke black?
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Richard 1979 IH Cub Cadet 782 w/CH20, dual hydraulics, power steering and Cat 0 three point |
#7
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Quote:
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Cooperino 100, 104,125, 126, 2x129's, 804, 1211, 1641 |
#8
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Problem solved, but here's the long and short of it. Been in the business of designing and building machinery as an engineer for 40 years and follow manufactures spec's to a tee, the instructions provide by this ebay seller (which I questioned) for installing the rings were wrong. There are many different styles for the second ring (compression/oil scraper), the supplied instructions indicated chrome ring top inside bevel up, second ring inside bevel down and then the three piece oil ring. The only problem is the ring supplied was a "Torsional Twist Taper Face" ring, which means the inside bevel goes up and the taper face points down. If he would of supplied me with a Reverse Torsional Taper Face his instructions would be correct, inside bevel down taper facing down. After 5 hours of work removing the motor from the 1250, honing the cylinder again and reinstalling with new rings and head gasket (supplied by local cub dealer) started up without a trace of blue smoke. Job complete, this 1250 will now outlive me.
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#9
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Glad to hear you discovered the problem and got it fixed.
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Roland Bedell CC Models: 100, 105, 1450, 782, (2) 784, & 2072 Buy: Made in the USA |
#10
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Quote:
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2072 w/60" Haban 982 with 3 pt and 60" Haban 1811 with ags and 50C 124 w/hydraulic lift 782 w/mounted sprayer 2284 w/54" mowing deck |
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