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rebuilding briggs 15hp motor


panteramatt's Avatar
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04-06-09, 06:44 PM   #1  
rebuilding briggs 15hp motor

My craftsman lawn mower has been smoking for the last 2 years and keeps getting worse and now fouls plugs. Took the head off and cylinder and head and piston looks fine. I want to put new rings in but how do I get to the piston since the cylinder doesnt come off?

 
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04-06-09, 08:35 PM   #2  
Replacing just the rings is a band aid solution that may or may not solve the problem. If they are that worn, valve guides, seals and other internal parts are likely done too. Replacing them means removing the engine and stripping it down.

 
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04-06-09, 08:47 PM   #3  
Before going that far, look at the section of head gasket between the cylinder and push rod chamber. If it looks like it may have been leaking, or letting air get past it, that is probably the problem and a new gasket should fix it up. If that isn't the problem, then you have to remove the engine and take the bottom sump cover off to get the piston out.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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04-07-09, 05:35 AM   #4  
In addition to what Cheese advises take a look at the following articles. The leakdown test, IMO, is the definitive test.

What compression should my engine be reading?

Building and Using a Cylinder Leakdown Tester

- Harbor Freight Tools - Quality Tools at the Lowest Prices

PER Notebook - Those Messy Oil Leaks

 
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04-07-09, 09:00 AM   #5  
On a somewhat related question, is it generally cost effective to rebuild small engines these days? If an engine is in otherwise good shape, I could see spending $15-$20 on rings but if the motor needs the bore cut, guides machined, crank turned, etc I could see the cost of the machining work quickly approaching the cost of a new engine.

What's the general rule these days? Are small engines just replaced (or short blocked if they're larger and/or more expensive) if they need machine shop work?

Thanks,

- Joe

 
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04-07-09, 01:35 PM   #6  
Head gasket is fine. It just startede smoking last year after winter storage and has ever since.

 
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04-07-09, 10:52 PM   #7  
Just suddenly started smoking after storage? Doesn't sound like rings to me.

To answer the other question... I build common inexpensive engines that have a good usable bore, crankshaft, and other internal parts. I don't get into boring cylinders, turning cranks, replacing valve guides and seats, etc... Just not worth it.


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04-08-09, 11:44 AM   #8  
Than what could it be? Should I put the head back on and do a leak down? I did a compression test and it was low. It eats oil and leaves the spark plug completely fouled in a couple of mows. Where can I find torque specs?

 
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04-09-09, 12:45 PM   #9  
Forgot to also add that it backfires pretty loud when shutting it down.

 
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04-09-09, 06:26 PM   #10  
What is the model, type and code number of this engine?

I would not be overly concerned about the backfiring until you determine the cause of the low compression.

Low compression may be a result of defects in piston, rings, cylinder wall, head gaskets or valves. One way of determining if compression loss is in cylinder or valves when performing a compression test is to place about an ounce of engine oil in the cylinder just prior to performing the compression test. If compression increases the rings and/or the cylinder is the problem. If no change in readings, the valves most likely are the problem. A leakdown test is a better method of locating problems.

In my opinion, most Briggs & Stratton engines are not cost effective to re-ring or install a short block.

What causes engine backfire out of the carburetor or muffler?

http://www4.briggsandstratton.com/mi...art_ms3992.pdf

Torque Specifications for Briggs and Stratton

 
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04-09-09, 07:26 PM   #11  
briggs vanguard 28q777-0129-01

So your saying once these motors have a problem, you need to throw them away? I think Ill throw the head back on a do a leak down test.

 
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04-10-09, 06:40 AM   #12  
Posted By: panteramatt briggs vanguard 28q777-0129-01

So your saying once these motors have a problem, you need to throw them away? I think Ill throw the head back on a do a leak down test.

No that is not what I said!


I said, In my opinion, most Briggs & Stratton engines are not cost effective to re-ring or install a short block.

My statement is implied to engines repaired by a repair shop and takes into consideration shop rates, machining, etc. As an owner, you may not consider your time so it may be feasible for you. When you tally up the cost of outside labor and parts, you may not find it practical.

Since there is, no short block available for this engine and Briggs & Stratton does not list an engine replacement repair is the only option. Before you do anything, you need to learn what is causing the compression loss. Up to this point we are all giving you possibilities. It is time for you to find the problem. You may just need a simple valve job or a head gasket.

The 496412 cylinder is available, if it comes to that.

 
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04-10-09, 03:42 PM   #13  
Cylinder and headgasket are fine.

 
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04-10-09, 04:52 PM   #14  
Airman, lighten up, don't get so tense you will bust a vessel;

After checking the IPL, I vote Head Gasket. Have a good one. Geo

 
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04-11-09, 10:03 AM   #15  
The gasket looked good. Im going to put the head back on and do a leakdown test when my tester gets here.

 
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04-12-09, 10:13 PM   #16  
Just suddenly started smoking after storage? Doesn't sound like rings to me.

 
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04-13-09, 08:01 AM   #17  
Yea. And it just started eating oil and fouling plugs. Heads gasket looks good.

 
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