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Briggs 11hp. Will it blow up?


msidan's Avatar
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06-21-07, 04:20 PM   #1  
Briggs 11hp. Will it blow up?

I have an old Craftsman LT4000 with a Briggs 11hp. It starts and runs great but I hear a rattling sound and a soft, internal hitting noise. Not too noticeable. And yet it is noticeable. Only does this at full throttle and after its been running a few minutes. Could this be what is referred to as "knocking"? Is my engine about to blow up or "throw a rod"?

I just changed the oil.

 
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06-21-07, 07:53 PM   #2  
We need the model numbers off the engine shroud. There are several things that can make the noise, from carbon deposits on the cylinder head and piston to connecting rods and counter balances. Make sure you are to the full mark on oil and use a straight 30 weight oil. Had a customer with a 11 hp Briggs in a John Deere tractor that said it was full of oil and since it did not have a dip stick, he was seeing the oil on the top of the drain plug. Put in 20 ounces of oil to get it to the top of the fill plug.

 
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06-22-07, 02:35 AM   #3  
The model number won't necessarily help us but I'm sure it is a 25 cubic inch Briggs just the same. This is a situation where sight unseen (unheard in this case) that it will be near impossible to help you. Possibilities include: Loose shrouding; Ignition coil airgap too tight to the flywheel; Crank bearings (bushings) sloppy; Worn connecting rod and crankpin; Excessive piston to cylinder clearance. If you suspect that the trouble is, indeed, inside the engine then the only way to verify is to tear it down and take some measurements. The first step I'd take is to grab ahold of the crank on the PTO end and feel if you have any side play and do the same on the magneto (flywheel) end by first removing the flywheel. If these feel good and tight then you'll want to tear into the engine.

 
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06-22-07, 05:50 AM   #4  
I may be able to post a video of the tractor running on Photobucket.
The rattling turned out to be the hood. This engine does not have a dipstick. Only an oil cap. I put in oil until the little hole was covered. (I'll post a picture of that too.)
Another thing is the bendix? gear on the starter is broken, but it still starts the engine.

 
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06-22-07, 04:39 PM   #5  
The oil is to be filled until it want to run out the fill hole, not the little hole below that point. Post back with the engine model, type and code numbers and I can give you a part number you'll need for the starter gear. How's the condition of the flywheel ring gear?

 
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06-22-07, 06:34 PM   #6  
Heres a video:
http://s187.photobucket.com/albums/x320/msidan/?action=view&current=100_1439.flv

Kind of hard to tell in the video but there is a faint clanking sort of noise. When I work the flywheel back and forth, there is sort of a loose sound inside. Flywheel is on good and tight.

The headlights work pretty good though...

I already have a gear for the starter from a junk tractor. Just haven't got around to installing it. Could the broken gear be harmful to the engine?

 
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06-24-07, 05:06 PM   #7  
The broken starter gear will only affect the starting of the engine, not the performance. Based on the vid, I'd say you do indeed have an internal knock and I believe it will be the connecting rod. Lets see what Cheese has to say too before you move on. Again, the engine ID numbers, please, so I can get you the part numbers for the starter gear and flywheel ring gear, if needed.

 
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06-24-07, 08:42 PM   #8  
Knocking sound could also be the counter weight if they get loose or the counterweight link breaks they can bust out the bottom side of the crankcase. They make a sound much like a bad rod. You would also have to tear down the engine to inspect and check tolerances on the weights, bearings and link .

 
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06-24-07, 11:15 PM   #9  
I agree that it sounds internal...I'm not sure, but I was thinking it sounds like the balancer or the rod...and at the age of that engine, it could be some of both. It sounded a little sporadic, not as noticeable during the accelleration as it is at full speed, and if I had to put my money on one part, it would be the balancer just because of that. If it's the rod...it's inevitable failure if you don't fix it. If it's the balancer, you might get away with running it for another 10 years, or it could break in the next 5 minutes. In either case, the crankshaft will probably also need attention or replacement if you intend to repair it. If the balancer is the problem, replacement of it and the crankshaft could exceed the value of the mower.

I think if it were mine, and I knew it was never run low on oil, and the oil is clean and there is no evidence of metal in it, then I'd run it, hoping for the best. If it gets worse in a short amount of time, you know to quit using it or expect failure. If it doesn't worsen, I'd chance it.


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

God bless!

 
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06-25-07, 06:19 AM   #10  
I can get a junk tractor with a good Briggs 12hp engine for around $40. That will put my costs in this tractor to $240. I have never replaced an engine before and I don't have all the fancy tools that you OPE shop owners do. Is there anything else besides the four bolts that hold it to the frame? (this probably sounds really stupid) Can a person simply pick up the engine without needing a crane or something?

I can't get those engine numbers until this afternoon.

 
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06-25-07, 01:09 PM   #11  
Usually thats all holding down the engine. Make sure you unplug all the electrical connections, fuel line, throttle cable and exhaust system. You may have to remove the stack pulley from the engine if it will not fit through the frame.

Yes, you can pick the engine up of one of these riders, but be careful not to hurt your back. It's better and easier if you have another person help as these engines are not all that heavy, but rather awkward to hold on to and somewhat difficult to lift out of the frame.

 
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06-25-07, 07:00 PM   #12  
I replaced the engine with a Briggs 12hp I/C today. I still have to hook up the fuel line, throttle, etc..., but all the heavy work is done. Looks like all I have to do is fill it with oil and blow out the cooling fins. I'll let you know how it turns out.

Lets see, $40 for the engine and $20 for someone to help. Sounds like a deal to me! (plus about $6 for carb cleaner and oil.) That carb and choke cleaner cleans the grime off the frame pretty good.

Cheese, if I new I was going to keep this tractor I would "chance it". But I plan on selling it. I could probably "hustle" it and let it break for someone else, but I don't want to be known for that.

 
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06-26-07, 12:00 AM   #13  
Good man. I didn't know you were selling it. I've seen briggs engines with balancer noises run for years. The trouble is you never know when it's going to let loose.


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

God bless!

 
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06-29-07, 08:30 AM   #14  
Got that engine all hooked up and its actually already sold! Thanks for all your help guys.

 
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06-30-07, 01:27 AM   #15  
Glad you got it fixed and sold! Are you going to have a look into the 11hp and see what the noise is?


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

God bless!

 
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06-30-07, 07:30 AM   #16  
Probably not, but if I do I'm sure you'll here about it.

 
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07-08-07, 09:25 AM   #17  
Guess I'll tear this 11hp apart and take a look. If it is the rod or something like that, will a rod from a 10hp work? Where should I start?

 
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07-08-07, 12:35 PM   #18  
I'd start with taking the engine apart and checking it out. Then, after determining what parts are needed, use the model# to get part numbers for those needed parts.

Some parts are used in more than one engine, but the only way to tell for sure if the rod from a 10hp will work for the 11hp is to look up the part numbers for each and see if they match, or measure them carefully at several critical spots. I reccomend using part #s.


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07-08-07, 01:05 PM   #19  
I took the bottom off and looked into the crankshaft area. I didn't really see anything wrong. But I don't know what to look for either. I turned the shaft by hand and the rod doesn't hit anything inside

 
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07-08-07, 09:15 PM   #20  
The knock would be caused by too much play between the crankshaft and the rod, and/or between the balancer bushings and the crank.


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

God bless!

 
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