Why do the push rods on my John Deere X300 lawn mower keep getting bent?

I purchased the mower in May of 2007. It ran beautifully for half the summer. Then it became harder to start and didn't run as smoothly and seemed to lose power while going up inclines.

In April of 2008, it wouldn't start at all. Luckily, it was still under warranty. John Deere fixed the mower and said the push rod was out of place and the valves were loose. It ran beautifully again.

After 2 mowings, it started acting up again. John Deere says it is bent push rods, probably due to old gas (the gas was about a month old), and that I should only use new gas and drain the mower completely after each use. What a pain! This never used to happen before. What's going on? Is it a bad mower or has gas really changed that much?

Comments

3 Responses to “Why do the push rods on my John Deere X300 lawn mower keep getting bent?”

Ron G says:

June 28, 2009 at 5:31 pm

My guess is that the push rods were bent from the first go round. The adjusting nuts were not tight and allowed the valve train to loosen and slightly bend the rods. The mechanic reinstalled the slightly bent rods and adjusted the valves. You ran it again and really bent the rods. Old gas will not bend rods. There is no reason to drain gas except to piss you off. The mechanic is probably getting a good laugh over that one every time he tells it. To go on with the mower now, it has been run with a loose valve train for so long that some care is needed to insure that you get all the use out of this engine. I would insist on a competent mechanic to begin with and ALL of the parts of the valve train be replaced that were affected by the loose adjustment. Push rods, rocker arm, adjusting nuts. They were loose long enough not to trust to give good service. After all, you did buy a new mower. I also assume that you treat the mower well. Like changing oil, correct oil per manufacturer, gas treatment, winterizing.
gary o says:

June 28, 2009 at 5:31 pm

Another way push rods can be bent is from carbon buildup inside the cylinder or excessive moisture in the fuel as neither is compressible so as the valve tries to open due the action of the push rod this will result in bent push rods. Caused by old gas? that’s a stretch, as if the gas is old the engine will be hard to start and will run poorly. Normally John Deere makes quality equipment. I would discuss your claim with the dealer and if no satisfaction go to the manufacture for help.
David T says:

June 28, 2009 at 5:31 pm

It is possible that the valves are sticking in the guides in the heads/head. This will cause push rods to bend. All may be well for a time, and then they stick and cause bending. Of course, adjustment could be a problem. I highly doubt that a lot of parts need to be replaced, but most engines carry a two year warranty. The reason I mention the guide problem is, I work for a lawn and garden dealer and we had the same thing happen to a Briggs and Stratton engine, we were able to get this covered under factory warranty. Old gas could cause the problem, but it would usually take more than the short time you have owned this machine. I can’t see draining the gas every time, maybe at the end of mowing season.
I would take it back to the dealer or a dealer for the brand of engine that is on the mower and get them to check it out. Push rods don’t just get out of place unless something is loose.