Troy Bilt Pony 17.5 sounds like machine gun!

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  #1  
Old 09-03-13, 06:04 PM
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Troy Bilt Pony 17.5 sounds like machine gun!

Hello all,

I really dont know how to describe it any better than that- my Pony 17.5 sounds like a machine gun! It'll start up fine by it just pops consistently and loudly. Upon taking the air intake cover off (the engine is a Briggs, btw) I noticed that white smoke was coming OUT of the air intake, along with a sputtering of gasoline. This doesn't remedy the machine gun fire sound, just makes it louder and at a quicker rate. White smoke is also coming out of the exhaust.

This issue happened almost instantly. Was running fine, then it started sounding like this. This is what I've looked at/tried.

-Changed spark plug
-changed oil
-Adjusted valve clearance (1/4 past compression TDC 0.04 for intake, 0.06 for exhaust)
-Fresh gas
-Disassembled and cleaned the carburetor (this carburetor is less than 4 months old, it was perfectly clean)
-Checked all the safety switches

So now I'm not sure what to look at or potentially double check. Any thoughts?
 
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  #2  
Old 09-03-13, 06:20 PM
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Take off the valve cover and make sure both rockers are moving. It sounds like the exhaust valve pushrod may be out of place.
 
  #3  
Old 09-03-13, 06:27 PM
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Both of the rockers do move. I've went through a full cycle a few times, the push rods are not broken, the rockers move and the valves do as well. I don't know how MUCH they're supposed to move, but I know that they are moving.
 
  #4  
Old 09-03-13, 06:37 PM
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That type of thing is often when the exhaust valve isn't opening to let the exhaust out. Then the intake opens and it all comes back into the carb with a pop.

Might want to double check that one. Sometimes the pushrod comes out of the block at the bottom.
 
  #5  
Old 09-04-13, 12:24 AM
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This also happens when the camshaft wipes a lobe off, or when a valve seat comes loose. Since it happened suddenly, I;d go with the valve seat coming out or other problem keeping the valve open. Possibly the valve guide slipped and is holding it open.
 
  #6  
Old 09-04-13, 12:56 PM
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So what should I do? I'm no really sure how to proceed at this point. I've got the valve cover off. I've checked to make sure the push rods are in the correct spot. When I move the flywheel clockwise and watch the movement of the valves/rocker arm/push rods, I see everything move. There seems to be good movement in the bottom valve, but not much in the top valve. Should they move equally the same? What do I need to open/replace/look at?
 
  #7  
Old 09-04-13, 01:11 PM
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Look at the bottom of the pushrod. Is it seated in a pocket on the the cam rider? When you rotate the flywheel does the valve stem/rocker come around to a point of having space between the two (valve lash)?

They should move roughly the same amount. The valve not moving is the problem.

Did you set the valve lash before and after this started or just after, trying to fix it?
 
  #8  
Old 09-04-13, 04:15 PM
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It seems to be seated firmly in a pocket, yes. As I turn the flywheel there are points in which the rocker arms are loose, but they seem to always connect the round magnet connected the the valve (not sure the terminology)

I've had to adjust the valve clearance before (I'm assuming this is the same as the valve lash?) I adjusted it due to a hard start issue, I also had a broke pushrod, though I don't remember which one it was. The mower worked well for a good four months until now.

Is it safe for the motor to push on the valves with my hand to see if they are bound up in some way? cheese mentioned something about valve seating; how is that fixed.
 
  #9  
Old 09-04-13, 05:12 PM
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In terms of a valve seat getting dislodged, you would pull the head, put the seat in place and peen around the seat with a sharp punch to swell the aluminum in on the seat to hold it in place.

When you lost a pushrod, did you have an exact replacement for it? And what happened when you lost it? Did the mower start acting up and you looked at the valves and found a bent pushrod. If so there may well be something with the cam or valve guides that has gotten progressively worse. You may be looking at the end result of something that started months ago.
 
  #10  
Old 09-04-13, 08:00 PM
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The pushrod broke in half. I always felt it was caused by me, however. When I first started messing with the valve clearance, I was still learning the process. One day after I thought I set it, I pulled the cover and found that the nut that held the rocker arm came off. I think I discovered the broken pushrod shortly afterward. (Youll have to forgive me, it's been a few months). I ordered an exact replacement from Jacks? Small Engines.

Is there anything else I should check before doing a tear down? I'm not really sure if I'm qualified to reseat the valve.
 
  #11  
Old 09-04-13, 09:23 PM
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It's either the valve seat that came out, or the camshaft is wiped out. Pull the head off and see. If the valve seat fell out, you will see it. if the cam is wiped, it may have been run with too much clearance for too long.
 
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