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Briggs 31P977-1066-E1 Very Strange Problem - need advice


jl66redcpe's Avatar
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10-23-15, 08:09 AM   #1  
Briggs 31P977-1066-E1 Very Strange Problem - need advice

This came in on a Craftsman DLS-3500 Lawn Tractor. It would not start. Customer said they were cutting grass with it and it started making noise and blowing smoke. I checked valves, flywheel key, spark, even ran an auxillary gas tank -- all the normal stuff. I did a leak down test this morning and seemed like I heard air escaping at the head. I removed the head and found the head and the top of the piston all banged up like someone had dropped a ball bearing in the cylinder.
I have called the customer to come and take a look at it before I proceed.
I think the piston is probably ok however the head is questionable. I can either order a new head or try to file any high spots on the current head and put a new head gasket and try it -- or maybe a double head gasket.
Any thoughts would be appreciated. I have never seen one like this before.

 
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10-23-15, 09:01 AM   #2  
While you are checking, look for where a screw is missing. Choke butterfly, throttle plate, carb screw, air cleaner fastener, etc.
Your description points to the engine ingesting a fastener and chewing on it before spitting it into muffler.

RR

 
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10-23-15, 10:05 AM   #3  
I agree with RR... usually a screw from the throttle butterfly is the culprit.


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God bless!

 
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10-23-15, 10:35 AM   #4  
What do you folks think about filing the high spots on the head or a double head gasket.

 
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10-23-15, 02:29 PM   #5  
Head needs to be lapped, not filed.
A piece of emery paper taped to a sheet of glass works for me. Move it in a figure 8.
No way on the double gasket!.
I agree with the other posters, I had a screw fall out of the choke plate and got lucky, it got stuck under the valve and held it open so it stopped with no damage.
I had a brand new Honda pressure washer that the engine ran so hot it melted the spark plug and the electrode fell into the combustion chamber.

 
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10-23-15, 05:23 PM   #6  
I'd grind off the high spots and leave the gasket mating surface alone and you won't have to worry with the sandpaper and glass. Do the same to the top of the piston and reassemble with one new head gasket. If it didn't smash the top of the piston so much that it squeezed the top ring, it should be fine.


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

God bless!

 
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10-24-15, 06:07 AM   #7  
I saw the electrode from a Spark Plug do that once on a automobile engine.

The culprit projectile was never found; but it was clear as to where it came from.

 
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10-26-15, 02:55 PM   #8  
Well, I put the engine back together and got it running however it was not easy. I have a friend that is a Briggs dealer and he put the head on a machine that made sure it was flat. I used my air grinder to smooth out the high and rough spots inside the combustion chamber. I left the piston alone. Installed a new head gasket and torqued the head down. I set the valves to 005 and 005. Connected the exhaust and intake manifold. Next, I removed the carburetor to make sure there was not any more foreign objects inside. I also noted that all the butterfly screws were in place. Reconnected everything and tried to start it -- no luck. Checked the valves again. Removed the coil and cleaned it and re-gapped it. Wire brushed the flywheel magnets. Actually checked the valves several more times. No luck. My gut was telling me that the engine just was not getting gas properly. I removed the manifold again and reset the o-ring. Then I noticed that the long thin governor spring was not attached. I reconnected the manifold and the spring and tried again -- this time it started and ran. I was kind of in shock at this point in time that it ran. I cant believe the governor spring caused it to not start however I do think that resetting the o-ring in the manifold did. Since all the carburetor screws were intact, I have to believe that the Sears guy that was there less than two weeks ago had to have dropped the ball bearing into the carburetor when he installed the new air cleaner. I don't criticize other mechanics however I cant think of any other way that ball bearing got in the cylinder. Tomorrow, I will install a new valve cover gasket, the blower housing, clean up all the oil on the exhaust and drive it around the yard before I return it to the customer. This has been a real adventure for me. Again I would like to thank everyone for their input.

 
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10-26-15, 04:38 PM   #9  
Posted By: jl66redcpe ". . . I have to believe that the Sears guy that was there less than two weeks ago had to have dropped the ball bearing into the carburetor when he installed the new air cleaner . . ."
Do you mean intentionally . . . . like in sabotage ?

A ball bearing that originated where ?

 
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10-27-15, 03:00 AM   #10  
It sure appears to be something that may have been intentional. How else could a ball bearing get inside the cylinder. When I removed the head I found the object laying on the ground. It was way too big to be a screw. Looked to be 3/16" diameter. The object fit perfectly in the holes created in the head and piston. As I mentioned in the title -- "Very Strange Problem"

 
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