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B&S 16.5 Runs rough and hot under load


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07-31-09, 07:02 AM   #1  
B&S 16.5 Runs rough and hot under load

Murry Riding mower bought new in 2003. B&S 16.5 running really rough and hot. Runs even worse if you turn on the blades. Has gotten progressively worse over the last few uses, till now it it will start fine but does not have enough power to mow.

Gas flow from tank tested good, fuel solenoid closes when key is turned on, card has been cleaned, jets are clear and gaskets replaced. New Spark plug, fuel and air filters, tried new gas, oil level is good and no gas in oil.

Earlier this year I had fuel in the oil. don't know how long it was that way before I realized it. Someone suggested that it may have damaged the engine.

Any ideas of something I can try? How can I know if I have have engine damage? If I do can it be rebuilt?

Help,
Ken

 
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07-31-09, 07:47 AM   #2  
I wouldn't jump to the conclusion you have wrecked anything yet.

It sounds like a cam or valve lash. I don't know if that one has the hydraulic lifters. You can tell if it has a way adjust it though, when you get the covers off.

I would pull of the covers and see if the valves are moving and check for rocker clearance after the valve closes. It may just be a matter of adjusting the valve lash.

That'll get you started.

 
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07-31-09, 09:13 AM   #3  
Is there too little compression

I used to have a hard time getting it to turnover, but it would run fin afterward. It seems to crank easily now, but runs bad. Does that sound like a valve adjustment issue?

Never opened the valve cover but will give it a try. Are the clearances in the manual?

ken

 
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07-31-09, 07:27 PM   #4  
Just look up in the recent posts in this forum at the "Troybuilt that won't start". 31yeartech put a nice diagram in there on how to do what you need to do, too.

 
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07-31-09, 11:44 PM   #5  
While the valve cover is off, rotate the engine and see if both valves move much at all. I've been seeing a lot of wiped out camshafts lately, and if that is the problem, one or both valves will barely move.


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08-01-09, 09:07 AM   #6  
Tried to adjust the valves. It may have made some difference but certainly no fix. I found it kind of difficult to adjust the combination of screws. Also difficult to determine which feeler gauge would clear and which would not depending on how I wiggled the rocker arm.
Ran it for about3 or 4 minutes to test and it got extremely hot. Decided to remove the muffler and noticed that the short exhaust manifold pipe was thick with carbon.
Any other ideas as to what might cause this? Seem that I read somewhere to remove the head and clean the carbon with gumout? Any ideas?

 
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08-01-09, 11:41 AM   #7  
More info

I don't really know what to do next. Here is more info:
It is Briggs & Stratton 16.5 OHV Model 31C707 Type 0175 E1

I have attempted to set the valve gaps at 1/4" past dead center at .006 for exhaust and .003 for intake. Never done this before so there is always the question of how easily the feeler gauge should go in.

I pulled the head and took pics of the cylinder wall and the valves. Maybe from the pics someone can tell me if everything is ok or not internally.

Please let me know your thoughts.

Ken




 
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08-01-09, 08:46 PM   #8  
Well your cylinder is in great shape with no ring groove at all. So the rings are likely in good shape as well.

It would be pointless to say what you have with the valves from the picture. The question is are they moving and sealing. If you started out with the lash close to specs (that is - not a large amount of lash at the rocker to valve stem) and you just can't get it perfect, the performance problem with your engine isn't likely coming from the rocker clearance or the cam.

If you have it starting well and keeps running I would also discount the ignition coil as the problem.

Some possibilities are:

**The compression release is not letting the engine return to full compression.

** The valves are not sealing. Usually it would be the exhaust valve if one was burned. Either could have carbon at the seat. A compression test/leak down test would show up a compression fault, whatever the source.

** The carburetor needs cleaned and possibly a kit put in it.

 
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08-01-09, 08:48 PM   #9  
Your head and cylinder look great... like new. Is the choke sticking closed? And, you didn't say if the valves are opening much at all.


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08-03-09, 06:53 AM   #10  
Posted By: cheese Your head and cylinder look great... like new. Is the choke sticking closed? And, you didn't say if the valves are opening much at all.
The choke is not closed, I checked. I really don't know how much the valves open. I was hoping that cleaning the carbon build up on the valves might help my problem. I read on the B&S Q&A that an engine that runs worse under a load can be attributed to carbon build up on the piston and valves.
Ken

 
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08-03-09, 09:30 AM   #11  
Sounds like you are going for the hardest things first. Engines run hot for many reasons.
1). Cooling fins clogged up with grass.
2). Ignition timing off. Did you hit a rock or another object while mowing in the past? This could cause the flywheel key to be sheared causing hard starting and running hot due to timing being off.
3). Dirty Carb. I did read that you cleaned the carb, but did you soak it? A carb running lean will cause your problems.

 
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08-03-09, 10:46 PM   #12  
As of now, with no more info than what we have so far, I am going to put my money on a bad camshaft.


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08-04-09, 08:02 AM   #13  
I will try soaking the carb, valves, and head and cleaning the top of the piston. If I still have a prob, I will pull the engine and look at the camshaft.


Last edited by lemonmower; 08-04-09 at 08:18 AM. Reason: delete post
 
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08-04-09, 10:06 AM   #14  
Posted By: cheese As of now, with no more info than what we have so far, I am going to put my money on a bad camshaft.
If the camshaft is bad, I am guessing that means that the valves are not opening fully. Would that cause the engine to run hot?

 
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08-04-09, 07:59 PM   #15  
If the exhaust lobe is shot it could theoretically cause some overheating, but you'd have a backwash of exhaust through the intake so your symptom would likely be more in the area of performance.

But why are you saying the engine is running hot? What does the plug look like? Is it light brown or chalky white?

 
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08-05-09, 09:32 AM   #16  
Posted By: marbobj If the exhaust lobe is shot it could theoretically cause some overheating, but you'd have a backwash of exhaust through the intake so your symptom would likely be more in the area of performance.

But why are you saying the engine is running hot? What does the plug look like? Is it light brown or chalky white?
I am definitely having performance issues, but the engine also gets very hot very quickly. The 2 month old plug is black on the end. Replaced it and ran the new one for about 4 minutes and it is already beginning to get brown on the end. Can't say much more other than is just radiates a lot more heat than it used to. The last couple of times it worked well enough to mow, as it started radiating more heat the engine performance got worse.

 
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08-05-09, 08:54 PM   #17  
I don't know about the extra heat you have. The blackened plug could be carburetor, poor ignition, or low compression (back to the valves).

Considering the condition of the cylinder, I would have to lean towards the valves still being OK.

It would help if you could post a picture/pictures that would show both valves at fully closed and fully open. It would tell us a lot about the cam.

 
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08-09-09, 03:44 PM   #18  
OK. I soaked and cleaned the card, valves, and head. Reinstalled them and adjusted the valve clearances. Still runs rough and hot.

More info I learned in the process. The intake valve looks like it moves about 5/16 of an inch and the exhaust valve looks like it move about 3/16 of an inch. Also, when I cranked it back up, seems like it idled pretty good at med to low throttle but ran really bad on full throttle.

I'm thinking of taking the engine apart and getting to the cam shaft. Can anyone provide or point me to so direction on that?

Any other thoughts are appreciated.

One more thing. Either my torque wrench is shot or the numbers on the B&S Chart are absurd. Says 220/lbs for head bolt torque but I broke a bolt at about 130.

 
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08-09-09, 04:51 PM   #19  
Your head bolt torque is in inch lbs not foot lbs. Were you able to get the bolt back out?

 
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08-09-09, 05:59 PM   #20  
As Cheese thought, the cam is bad. Watch the torque settings (obviously).

 
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08-09-09, 08:36 PM   #21  
The cam swap is pretty easy. Make sure you replace the lifters as well (comes with the cam...~$90). Pull the engine, remove the sump cover, replace the cam, replace the sump cover gasket, put blue locktite on the sump cover bolt threads, then reassemble making sure to adjust the valves properly.


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