Have a 6 yr old Cub with 18.5 single cylinder B&S. Need help getting it to run.

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Old 08-25-12, 06:21 PM
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Have a 6 yr old Cub with 18.5 single cylinder B&S. Need help getting it to run.

My 6 yr old Cub blew a head gasket to the inside back the first part of the summer. Smoked real bad and used about 3/4 pint oil each time I mowed. Then the gasket blew to the out side, quit using the oil and started losing power. Put a new head gasket on and it work fine for about an hour then would start losing power. Everyone said I needed to adjust the valves, so I did. The next time I mowed, same thing after about an hour, adjusted valves again. Then the last time I mowed it just completely lost power had to turn pto off and limp back to garage. Thought I had blown the head gasket again, open it up and gasket was still good, put it back together, adjusted valves and it fired right up BUT it runs like a sewing machine at idle speed but when I increase the throttle it chokes down and sounds like a thrashing machine. I have adjusted and readjusted the valves and it still does that. Have put a new fuel filter on it, took the fuel pump off and cleaned it out, sprayed carb cleaner in and through all the holes in the carb and it still does that. What could be my problem?? Sorry for the long post the first time on here.
 
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Old 08-26-12, 12:33 AM
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I'm going all in here, and am willing to bet you have a bad camshaft lobe. Take the valve cover off and look at the rocker arms. Watch how much they move and how far they push the valves down. One of them is not moving nearly as much as the other, right?
 
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Old 08-26-12, 10:01 AM
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what clearances are you doing the valves?
 
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Old 08-26-12, 02:06 PM
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I have had the clearance from .004 to .010. Right now they are on .005 clearance.
 
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Old 08-26-12, 02:12 PM
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cheese, you may have hit it on the head. It doesn't look to me like the valves move as far as they should and the top or exhaust valve I believe it is moves farther than the bottom valve does. How hard is it to fix, will it take a major over haul? Could I have done that by not having the push rods seated right when I put it back together?
 
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Old 08-26-12, 09:14 PM
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You'll have to replace the camshaft. It and the crankcase cover gasket will run close to $100 total. It's an easy fix. I have seen this happen several times, which is why I knew what it was by your description. I don't know what causes it... I believe running it too long with loose valves is the cause. It makes the cam lobe "slap" the lifter, and these cams are made of crappy soft metal that you can carve with a pocket knife. Make sure to clean the oil pan well since all that metal is going to be settled on the bottom of the pan. Lube the new cam lobes and lifters well before reassembly. This job only takes an hour or so for the pro who is used to doing it with air tools and all tools at hand, so expect it to be 2-3 hours to repair. You'll need to readjust the valves.
 
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Old 08-27-12, 08:59 AM
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Thanks cheese, I did mow one complete time with it after changing head gasket and then tried to mow two more times and would get about a little over half done when it would lose its power and the last time I didn't get a third done. I mow right at an acre. Thought I had the valves right but must not have. I will check around and see if I can get someone to fix it and how much it will cost. I may atempt the fix myself. I've never done anything like that but at 69 would be a good time to learn. LOL Thanks again and when and if I get it fixed I will post back the results.
 
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