Possible Leaking Exhaust Valve - Need Advice! - Snowblower Forum : Snow Blower Forums
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post #1 of 19 Old 02-01-2017, 12:02 PM Thread Starter
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Possible Leaking Exhaust Valve - Need Advice!

Tecumseh Snow King 4-Cycle, Horizontal Crankshaft, Air-Cooled, Model 31AE5HTG799
Craftsman 9 hp 28" snow thrower, model 247.887900 made by MTD in 2007.

At the beginning of the season it was starting rough and running rough. I replaced the 640349 fixed jet carb with a non-OEM fixed jet Everest carb. New NGK spark plug, fresh non-ethanol gas, with Seafoam added. It starts on one pull, runs great on full choke upon first starting, then as motor warms I turn a click at a time until fully open when machine is warm (about one minute total). It begins stuttering and running a bit rough in idle. Once augers turn, it still sputters but after running it for about 10 minutes under load, when auger is engaged, it begins to smooth out, but still sputters in idle. I had posted about this on another thread a month or so ago, but yesterday made a discovery...

It was dark outside and I could for the first time see the glowing orange inside the bottom of the muffler, with occasional hint of a small light flame coming out of muffler. The muffler doesn't turn bright orange on the outside, but I could see how hot it was on the bottom holes of the inside... glowing orange. When I shut it off, I pulled the cord with throttle all the way down and it does seem to pull very smooth... classic of this Donyboy video at 2:29

So now I'm suspecting a valve clearance problem or something of the sort, unless the carb is really just running that lean and it's starving for gas. Since this is not a diagnosis / repair I am comfortable doing myself, I could use some advice:
1) Is it ok to still run it for now? It does an excellent job at clearing snow and seems to run flawlessly when under a large load. What is the risk level of permanent damage by running it as is?
2) How big / expensive (ballpark) of a job should I expect this to be from a small engine repair shop?

Any/all thoughts and advice much appreciated!
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post #2 of 19 Old 02-01-2017, 01:20 PM
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I'd be looking at the carb first.

A couple of questions.

What RPM is the engine running at?
Can you perform a compression test?
What color is the spark plug?

It won't likely permanently damage the engine. The valve may need to be replaced worst case and the seat ground.

Last edited by AandPDan; 02-01-2017 at 01:22 PM.
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post #3 of 19 Old 02-01-2017, 01:23 PM
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Sounds like it. Flames come out into the muffler from the combustion chamber, which is where the explosion of gasoline takes place, piston, spark plug, valves, and if the exhaust valve is leaking it goes in to the muffler.

To fix it is not complicated but you need to buy some things, a suction cup lapper, valve grinding paste, maybe a new head gasket, and either build or buy a valve compressor.

You take the head off, take the small metal side plate off that covers the valve, install use the valve compressor to compress the valve so you are able to remove the valve key lock, it's in 2 pieces, two halves. Push the out slightly, put a little paste under the bottom slanted edge of the valve, put the lapper on the top of the valve head, and turn. You want to look and have a nice clean and same color and size edge all around without skipping on the underside of the valve on the slanted edge. Then you are done. Reverse the procedure. I would also do the intake valve.

Using non ethanol gas and adding a lead substitute to the gas will help for longevity. Lead is a lubricant. Newer equipment and cars have harden valves and seats.

Another thought, the valve seat could have lifted out. To fix that, push it back down and use a punch making indents around the valve to keep it there.

A compression gauge is $15 or so and is reliable to accurately tell you the compression. I can start and run engines at 40 lbs but it should be at least 50 if not 60-80. If the compression is low, remove the spark plug, put a tablespoon or two of oil in the spark plug hole and start the test again. If the compression rises 10 lbs or more, especially 20, the rings are leaking.

Last edited by JLawrence08648; 02-01-2017 at 01:34 PM.
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post #4 of 19 Old 02-01-2017, 02:23 PM
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Without Getting Overly Involved, You can First Remove the valve cover and breather. Using a large Screwdriver Compress the Valve spring and get a flat file between the Valve stem and Lifter. File Away until you get clearance. (You'll have to remove the 2 manifold screws and swing the carb out of the way.)
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post #5 of 19 Old 02-01-2017, 02:29 PM
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Well did it glow with your old carb on it?
If not I would say it's running lean.Start it up and leave the choke on at least one click.Then have a look at it.


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post #6 of 19 Old 02-01-2017, 03:46 PM Thread Starter
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Thank you for all the helpful tips so far! I don't know the RPMs when I noticed the glow, but it was running full throttle. I did pull the spark plug and it has some dry black residue on it, but it was dry and mostly white/tan... seemed normal. I don't recall ever seeing it glow with old carb, but part of the reason I noticed was that my headline bulb burnt out for the first time ever and it was particularly dark in the morning, so I was really able to see the glow by looking inside the muffler. I'll try 1/4 choke to see if there is any difference in regard to running lean. Would I be right in assuming that if glow goes away with choke that it's a lean condition from the carb and not exhaust valve? If so, should I just try running it 1/4 choke, since the carb is not adjustable? Maybe I should have bought OEM for $50 instead of the non-OEM for $17 - lol!
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post #7 of 19 Old 02-01-2017, 04:34 PM
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It's not unusual for a carb to be lean, not nowadays with the EPA regs and all.

Start with that. If you can perform a compression test you could do that too.

The plug doesn't sound bad.
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post #8 of 19 Old 02-01-2017, 04:50 PM
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You can buy adjustable carbs for $17 off Amazon. Buy one with an aluminium bowl.
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post #9 of 19 Old 02-19-2017, 02:51 PM
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If you occasionally get flames shooting out of the muffler, then it's likely an exhaust valve clearance issue. When the the clearance diminishes, the exhaust valve begins to open too soon letting the combustion leak by and shooting out the muffler. This tends to happen more after the engine begins to warm up, the exhaust valve stem clearance diminishes as it warms up due to it expanding, thus decreasing the valve clearance. Here we're talking thousands of an inch clearances and it only takes a few thousands to cause this issue.
~Ray

~Ray~
~1975 Canadiana 1026 Heavy Duty w/light & limited slip differential (& custom exhaust (need to fabricate manifold), customized impeller housing, removable chute in about 5 sec) (currently out of service)

~ Craftsman 8/25 Trac-Drive C950-52671 (mid 80's ???) (current user) (replaced blown engine with original, now in service again)

~ Craftsman 12/32 OHV 71-52112-1 (now in service)

~Noma GP 1028EL (repaired and serviced for daughter to use)
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post #10 of 19 Old 02-19-2017, 03:00 PM
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Quote:
Originally Posted by Jackmels View Post
Without Getting Overly Involved, You can First Remove the valve cover and breather. Using a large Screwdriver Compress the Valve spring and get a flat file between the Valve stem and Lifter. File Away until you get clearance. (You'll have to remove the 2 manifold screws and swing the carb out of the way.)
The problem I see with this method is some of the metal filings are most likely to get flushed into the crankcase and create another problem unless you can be certain to flush them all out before re-assembly.
~Ray

~Ray~
~1975 Canadiana 1026 Heavy Duty w/light & limited slip differential (& custom exhaust (need to fabricate manifold), customized impeller housing, removable chute in about 5 sec) (currently out of service)

~ Craftsman 8/25 Trac-Drive C950-52671 (mid 80's ???) (current user) (replaced blown engine with original, now in service again)

~ Craftsman 12/32 OHV 71-52112-1 (now in service)

~Noma GP 1028EL (repaired and serviced for daughter to use)
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