Briggs & Stratton - bad rings, breather, other?


Old 07-24-05, 02:23 AM
Motor Hugger
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Briggs & Stratton - bad rings, breather, other?

Hi, great forum - I'm glad I found this place. I've got a 6.5 hp Briggs & Stratton Intek-powered lawn mower, 4 years old. The engine quite suddenly began having problems this summer. It burns oil like mad to leave a haze of bluish white smoke hanging over the yard after a few passes. Starting is nearly impossible, and sometimes the engine "catches" and rips the starter cord out of my hands, but strong pulling gets it to turn over. Only starter fluid and marathon pulling will start this engine. Motor oil covers the inside of the air filter and the air intake.

First I checked the compression by turning the engine over with the starter cord; ~20 PSI dry (very bottom of compression gauge scale), and ~35 PSI wet. I figured this low compression is the problem, but I've read that compression testing these small engines is difficult and unreliable, and it doesn't help that I cannot find the compression specs for this engine anywhere. I also tried holding my thumb over the spark plug opening while hand cranking the engine, and the pressure seems to bleed on the upstroke, and I feel a vacuum on the downstroke. I can even hear what sounds like air squeezing past the rings.

I checked the breather valve as well. Blowing and sucking on it (not what you're thinking) revealed a functional diaphragm, letting air pass easily while flapping shut with the least bit of suction. A 0.45" feeler gauge wasn't even close to slipping between the diaphragm and the valve body. The tube connecting the breather to the intake housing is also clear. Is this a thorough test of the breather?

The cylinder head and valve cover both seem secure, but I haven't removed them to check for a bad head gasket. Rather than do any major work on this engine, I prefer to buy a new one. I found a Honda GCV160 cheap, and it only cost a bit more than doing a ring job on this BS engine, since I'd have to buy the tools for compressing rings. I've no experience on replacing/adjusting valves, so without help such a repair is out of the question.

So, is low compression is the problem? What else could I do to pinpoint the problem? Thanks in advance for your help. Sorry about the long posting but I didn't want to leave anything out.
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Old 07-24-05, 09:35 AM
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Insure the oil level is correct, also smell it for evidence of gas. Also b4 starting remove the spark plug and turn the engine over several times to allow any accumulated oil/fuel above the rings to escape.
Ur compresion check using your thumb should be valid. The briggs manuals I have say to rotate the engine reverse normal direction by hand, when resistance is felt release and the engine should kick back. I have not seen nor do I know of any specs.
You may also check the muffler for restriction. You can remove it and start the engine to see if the symptoms dissapear, if so clean or replace it.
Other internal problems are possible however I am not experienced with the internals on theese overhead valve engines.
Old 07-24-05, 07:22 PM
Join Date: Jan 2005
Location: 5353'57.39" N 12244'13.58" W
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I think the first thing you should check would be your air filter. If oil in it you probably have a leaking head gasket and it is blowing oil from the crankcase into the carb.

If not check the flywheel key--may be sheared and timing way off. I don't always read the forum so send me a private email for a reply.

Old 07-24-05, 07:25 PM
Join Date: Jan 2005
Location: 5353'57.39" N 12244'13.58" W
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oh yeah--check the head bolts first--they work loose and you can sometimes cure a leaky gasket by tightening the bolts. Definitely sound like your problem after re-reading your post.

Old 07-25-05, 12:06 AM
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Hello Motor Hugger!

It does indeed sound like you may have a blown head gasket. The gasket can blow between the cylinder and the chamber where the pushrods pass through. This will pressurize the crankcase and cause oil to blow out of the breather into the carb and air filter. This is a simple repair we can help walk you through. It shouldn't cost you more than 10 bucks and an hour or two. Removal of the head would be the first order of procedure and will show the condition of the gasket.

I don't reccomend just tightening the head bolts. If the gasket has leaked, then the damage is done and tightening the bolts would not be a lasting repair and also risks warping the head.

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