Question about Coleman Powermate Premium Plus 6250W Portable Generator
Wow, this could be so many different things. Here is a general procedure that I'd use to figure out what is going on, it's written with the Briggs engines used on Powermates in mind but more or less the same for any small engine.
First thing to do is eliminate the possibility of hydrostatic lock in the engine. This happens if there is a liquid (Fuel, Oil, Water) in the cylinder above the piston. You should probably do this outside ;-)
Take out the spark plug, make sure the ignition switch is in the off position, stand clear of the spark plug hole and gently pull on the starter rope. If there was liquid in the engine you'll see it come squirting out of the hole. Don't pull too hard on the rope, we don't want to break anything. You should also look at the end of the spark plug when you take it out, it may have evidence of liquid in the cylinder. It's also a good idea to visually inspect the cylinder as best you can. If you find fuel in the cylinder, you've probably got a carb problem, fuel fills the float bowl and runs down the intake if the carb is really dirty.
If you found the cylinder to be nice and dry, you need to check for bits of the engine stuck below the piston. Get a clean drain pan and drain all of the oil out of the engine. You want to make sure to get it really clean in there so use a spray can of brake cleaner to wash the crankcase by spraying thru the oil fill hole. Inspect the stuff that comes out looking for bits of metal, shreds of bearing, etc. If you've got any significant amount of metal in the crankcase you'll have to disassemble the engine further to see what's broken. This is a much more complicated thing.
If you didn't find any hydrostatic lock, and there aren't parts of engine in the crankcase it's time to check for broken valve parts. Carefully remove the valve cover (it's the thing that says OHV on it) be gentle so as not to break the gasket that seals it so the head. Check that the push rods are both in place and don't look bent, also check that the valves are in place. If both valves happen to be in the closed position at this point I usually do a leak down test - pressurize the cylinder with air and see how much leaks out where. It is best to do this with a real leakdown test rig, but it can be done with the hose from a compression tester and very careful use of an adjustable air supply. If everything looks good you can leave the valve cover off for the next part.
If you've gotten this far without finding anything seriously wrong with the engine this may be a case of stuck piston rings. When the engine isn't maintained well enough (and sometimes when it is) the piston rings can get goo behind them that makes them bind against the cylinder wall. Get a socket that will fit the flywheel nut, a chunk of pipe that will fit over the end of your ratchet handle (about 24 inches is long enough), and a supply of your favorite brand of penetrating lubricant (WD40, PB Blaster, Jigaloo). Spray the cylinder liberally with the lube and let it work for a few minutes. Then using the socket and cheater pipe gently try rocking the crank back and forth. Keep an eye on the rocker arms while you do this so you can get an idea of whether or not the camshaft is also turning. The camshaft not turning would be a Very Bad Thing.
With a bit of patience you should be able to free up the piston. It's better to have too much lube than too little. Try and move the piston just a little bit at a time down, then up. You need to listen to the engine while doing this to be able to hear any creaking or other bad noises from the bearings inside.
If you get the piston free, put in nice fresh oil, set the valve clearances and reassemble the valve cover, put in a new spark plug, reassemble the rest of what was taken apart and see if it will run. If it does you need to pay attention to rod knocking, bearing noises, and any other unexpected sounds. A fair amount of white smoke out of the exhaust is normal at first but if it continues you need to check for worn out or damaged rings/cylinder wall.
If you can't get the engine freed up with the above procedure you'll have to do a major teardown to find out what's wrong. Do yourself a favor and get the appropriate manual for your particular engine before you go any further.
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Posted on Dec 01, 2008
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Posted on Jan 02, 2017
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