Another problem with Craftsman lawn tractor

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  #1  
Old 07-21-12, 04:37 PM
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Another problem with Craftsman lawn tractor

I am having trouble with my Craftsman lawn tractor. The engine backfires through the muffler. The backfiring starts after the engine is run for a short period of time and is warmed up. The backfiring starts slowly at first (once/ 15 seconds) but increases to the point where there is a continuous, rapid-fire loud popping. I had this problem last year and I took the tractor to the repair shop; they said that it was water in the carburetor. The tractor ran good until 2 weeks ago and then the problem occurred again. I had the tractor for 10+ years and last year was the first this happened.

The engine is a Briggs & Stratton model 407777, type 0167-E1.

So far, I drained the gas, removed and cleaned the carburetor, replaced the fuel filter, air filter, pre-filter, and spark plugs, started using ethanol-free gas, and used Sea Foam to clean the cylinders. I did a compression test and both cylinders showed 135psi.

Nothing I have done seems to have any affect on the problem.
 
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Old 07-21-12, 09:06 PM
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Your description really sounds like a valve seat coming loose in the head. It can be hard to diagnose since the seat pops in and out of place. As the head warms up, it expands and lets the seat become looser, allowing it to pop out of place more and more often. Head removal would confirm. It definitely wouldn't hurt to put a new plug in and check for water before hand, just to be sure.
 
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Old 07-22-12, 07:02 AM
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That sounds like an unusual problem…

Once I remove the cylinder head, what do I look for? What are the indicators of a loose valve seat? Also, can it be repaired, a new valve seat pressed in or does the entire head assembly need replaced?
 
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Old 07-22-12, 10:52 AM
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Yes, it can be repaired. You can use a center punch to peen the aluminum around the valve seat once it is back in position.

Something else I just remembered that can cause this: Check the black wire that runs next to the starter. Make sure it is not stuck behind the starter. I've seen where this wire gets pinched between the starter and block, and as the engine heats up, the wire begins to short out against the block, making a lot of backfiring and irregular running.
 
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Old 07-22-12, 09:12 PM
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Hmmmmmmmmmmmmmmmmmmmmmmmmm,,,
 
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Old 07-22-12, 10:37 PM
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Hmmmmmmmmmmmmmmmmmmmmmmmmm
Yes, I deleted it. Read the forum rules that you said you read when you joined this site. This is not a classifieds site or place to look for financial gain.
 
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Old 07-23-12, 05:49 AM
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Ok that is fine,,,,,,,,,,,,,,like I said at the bottom of my post delete it if violates any rules. I'll reread the rules. Just trying to help the man out.
 
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Old 07-28-12, 12:10 PM
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It ain't that easy...

I removed the starter and looked at the black wire but found no damage.

I bought the Briggs repair manual and it seems that I will have to buy a few tools! My torque wrench is made for car and truck engines; not small engines and my supply of small feeler guages is limited.
 
  #9  
Old 07-28-12, 07:25 PM
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Your torque wrench should work fine. Just take the inch lb value and divide it by 12 to get your foot pound value for the bigger torque wrench.
 
  #10  
Old 07-29-12, 05:16 AM
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My torque wrench only goes down to 20 ft/lbs; that is 240 in/lbs, right? All of the settings are below this.

If this is the valve seats and I peen the heads, do you think that I will need to recondition the valve seats with a cutter?
 
  #11  
Old 07-29-12, 11:35 AM
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Correct about the torque wrench. If you peen the seat while the valve is still in the head with the spring holding it tight in the head, it will most likely settle back into a satisfactory position so that you don't have to re-cut or lap it.
 
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