mower stalls or dies when engage blades

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  #1  
Old 04-09-12, 09:53 AM
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mower stalls or dies when engage blades

Hello,
I inherited this mower from my dad because he was tired of throwing parts at it. It is a craftsman model 917.276826 mower LT3000 with 42inch cut and a Briggs and Stratton 20hp model 31P977 type 0635 E1 code 060517ZD.
The mower starts and runs fine, will pull a trailer fine and climb a hill fine. On level concrete with the engine at mowing speed you can engage the pto and the engine will bog down quite a bit, the blades will engage and the engine will try to get back up to speed. If you try to mow any grass the engine just continues to bog down until it either dies or you disengage the blades. This is a manual pto set up, not an electric clutch.
He has replaced the belts with factory part number belts, replaced the pulley stack that mounts to the engine crank with no change.
All I have done so far is a compression test which read 100psi. I did turn the blades with the pto engaged by hand while the spark plug was out and they turned freely.

Is this engine just worn out or am I missing something? Any ideas?
Thanks!
 
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  #2  
Old 04-09-12, 06:15 PM
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Kind of sounds like you have a worn down lobe on the camshaft. Have you had to adjust the valves frequently on this? Pull the valve cover and see if both valves move about the same amount, or if one has a good deal less travel when the engine turns.
 
  #3  
Old 04-10-12, 05:56 AM
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well cheese, you hit the pushrod on the head so to speak.

I pulled the valve cover this morning only to discover a broken pushrod. I called dad to ask when the last time any engine maintainence was done and he said 'never'. I downloaded the engine manual last night and read that valve adjustment is a yearly item so there you go...
Hopefully I can get away with just a new pushrod and adjustment?

Thanks for the starting point cheese....i'll update if anything goes other than planned.
Does anyone have instructions handy on the valve adjustment or is it just fully open intake, adjust exhaust and fully open exhaust and adjust intake? Slide feeler gauge between rocker and pushrod. 0.004 for intake and 0.006 for exhaust?
 
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Old 04-10-12, 09:52 AM
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Turn the engine clockwise from the top until it reaches TDC with both valves closed, then rotate it a tiny bit more (you want to bring the piston down 1/4" from TDC on the power stroke) and adjust both valves here. Otherwise you won't get them set right.

I'm pretty sure a new push rod and valve adjustment will get it going again. If the push rod was broken at the rocker arm, check the socket in the rocker arm for wear. The aluminum pushrod on these often wears thin in a spot where they rub on the plastic guides at the head until the spot gets so thin that it collapses into itself.
 
  #5  
Old 04-10-12, 12:54 PM
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I had a similar problem.

I have a mountfield lawnmower, it ran 100% onto one day i went to cut the lawn. I engaged the pto, the mower quickly stalled. Turned out to be a very cheep fix. When you engage the pto the mower revs up to prevent stalling, you don't usually notice it with the noise of the blades. However on my mower the cable which connected to the engine had came out of its housing. I would recommend for you to turn the mower on and engage the pto to see if the mechanism that revs the engine up is working correctly.
 
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Old 04-10-12, 05:10 PM
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Thanks all so far. Nathan, I wish I could get away with finding something like that cable but this was definately a valve problem.
The intake pushrod was broken right there at the plastic guide. I have a question about the adjusting of the valves though. I have to go get new feeler guages, mine had rusted and the only one I could read was a 0.004 that was close to what I need. My new problem is the adjusting 'nut' (briggs part 691986). I adjusted the intake to as close as I can get right now and locked it down I think. I did the same for the exhaust but the 'set screw' inside the adjusting nut bottoms out. There is a bottom inside this nut and it will not lock. I tightened it as much as I could but could still turn the adjusting nut by hand. The one for the intake seems to work fine and the set screw will screw all the way into the adjusting nut. Is that clear as mud? Is there a flaw in the exhaust adjusting nut to keep it from locking?
 
  #7  
Old 04-11-12, 08:52 AM
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question solved....
so i took off the adjusting nut for the exhaust and it turns out the end of the stud has broken off into the nut thereby stopping the lock down screw from doing anything but bottoming out on the stud end.
I'll have to get a new stud and new nut but i think the problem will be solved.
thanks everyone for the help!!!
it is a wonder this thing was running as well as it was.
 
  #8  
Old 04-11-12, 09:46 AM
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That's a first, I never saw a stud broken off inside the rocker arm nut. You can use the .004" feeler gauge. It won't hurt to set both valves at .004".
 
  #9  
Old 04-23-12, 05:51 AM
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well,
because I like to let everyone know how my adventures end for the sake of future searching I consider this one closed:
After replacing the broken pushrod, broken stud and non working adjusting nut as well as replacing the now missing valve stem cap and adjusting the valves the mower is running like a top and cutting grass like a champ.
Thanks everyone for the help.
Now if i just knew where that valve stem cap had run off to...
 
  #10  
Old 04-23-12, 10:27 AM
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Great! Thanks for the update. The little cap probably made its way into the oil sump or fell to the ground when you took the valve cover off. If it's in the engine sump, it probably will never hurt anything.
 
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