Bent pushrods

[Qweaver]

My Bad Boy mower has a 27 hp BS engine with very low hours and it just bent a pushrod.  Repaired under warranty...got it home and after a few hours mowing...did it again. 50 miles round trip to take it to the repair shop and 50 more to pick it up.  I would fix it myself but that might void the warranty and what's to keep it from happening again.  I have no clue what would cause a pushrod to bend.  I built high rev racing engines for years and never bent a pushrod.  I don't know what RPMs the Briggs turns but I bet not over 3000.  Any clues?

Quinton

[giant splinter]

Is your mower a Zero - Turn JD 425 with hydrostatic drive? if so it should be set up at 2300 rpm and cut grass at 14 mph.
If the blades come into contact with a surface root from a tree or an old flush cut stump you can bent a rod very quickly as the blades are spinning right off the end of the crankshaft via a belt drive system and cant handle hitting anything but grass and a few weeds.

[Bibbyman]

 

 

Pushrods out of 18hp B&S.

Been there, done that.   Repair shop says it's ethanol in the gas not providing enough lubrication to the valve guides.  We've had a number of small engine problems until I swore off ethanol and now only run 94 octane non-ethanol gas. 

[Magicman]

I was not aware that could happen, but so far I have never put ethanol gas in any of my small engines.   :-\

[Al_Smith]

I researched this subject a little bit at work today .From what I gather some report problems with the valves "catching on compression .Could be carbon or soft valves or lack of lubrication .Others report the valve guides becoming loose in the head and "walking out " .

Evidently the push rod Briggs uses one aluminum push rod on the intake and a steel rod on exhaust .However there are reports of either one bending .

I only have two of the push rod style both 5 HP .They are on both a pressure washer and a leaf vacuum .Both are ran at full throttle so probabley that stops any carbon build up .So far so good .The only problem I've experianced was the diaphragm fuel pump on the vacuum engine .

I don't see in my pea brain how ethanol fuel would have a thing do with lubrication problems if that is suspect .Run a little mix gas if that's the worry .They won't smoke too much once they warm up .

[pineywoods]

Bibby got it right. I had a similar problem with the kawasaki on my mill. Called tec support, the first question was "are you using ethanol gas ?" Seems the problem isn't the alcohol itself, but the water that goes along with it. None of these small engines have valve guides, it"s a steel valve stem sliding up and down in a hole bored in an aluminum head. Add a little water and you get corrosion. When the valve seizes in the head, the weakest piece in the valve train will fail. If you're lucky, the pushrod bends, otherwise, camshaft gears strip, camshafts break, rocker arms bend, or the head casting busts. I was lucky, the pushrod jumped out of the socket on the rocker arm. Freed up the stuck valve (wasn't easy to do) and put everything back together..

[sawguy21]

Is your mower a Zero - Turn JD 425 with hydrostatic drive? if so it should be set up at 2300 rpm and cut grass at 14 mph.
If the blades come into contact with a surface root from a tree or an old flush cut stump you can bent a rod very quickly as the blades are spinning right off the end of the crankshaft via a belt drive system and cant handle hitting anything but grass and a few weeds.

It should be running 3300, 2300 is a high idle and will not allow adequate cooling especially under load. I am willing to bet the bent push rod is on the #2 (lower) cylinder. It receives it's cooling air from the top of the engine which is already heated by the #1 so runs hotter.
The main causes of bent push rods are over speeding (unlikely in your case), the valve seizing in the guide, or the valve guide 'walking' as Al suggested. This happens when the head over heats and the aluminum expands faster than the guide. The valve retainer hits the guide but the cam is still turning, the weakest link fails.
Ethanol is a real bugger. It is hydroscopic meaning it absorbs free water, remember gas line anti freeze, and the mixture is quite corrosive. The intake valve stem, being exposed to cool incoming mixture, gets coated and seizes in the guide. I work on the order desk for the Briggs distributor, we see this all the time. The best preventative is 94 octane(less ethanol), high quality oil of the proper viscosity, maintenance (keep the cooling fins clean) and use a good gas treatment with a corrosion inhibitor during off season storage.

[240b]

I just put saw gas mixed 50:1 fully syn in everything except the pickup now.  My honda generator has 3200+hrs on it with no problems. I can't find gas w/o ethanol in it. 

[Bibbyman]

Many of our gas stations display signs saying non-ethanol gas available or is stated on the pump "no ethanol" in their 94 octane pump.

[coxy]

Honda is good for bent push rods and broken rocker arms  ;D

[giant splinter]

After a closer look I see that the motor in my mower is a 23 horsepower OHV, Vtwin ,G4 Crankshaft High Performance Technology John Deere motor that was manufactured by Briggs&Stratton so I suspect the Motor in Queaver's Bad Boy Mower is quite different and much larger at 27 hp. I have had no problems with mine so far and sure hope you get your mower sorted out Queaver.