Im working on my 6th in a row Craftsman LT1000 tractor and this time its got a 21hp Briggs V-twin Intek motor. Customer complaint was, hard starting, no power, smoke, and loud popping sound.

So I investigated and found on the right cylinder, the intake push rod was bent, the exhaust push rod was no where to be found and im guessing it fell into the crankcase through the oil passageway... Finally just to top things off the left cylinder had a blown head gasket! :)

Anything specific to look for as the cause of the bent push rods? The only thing i noted was that there was a mouse nest in the cooling fins of the right cylinder, but could that have been the cause?

Take a look at the valve guides on that head with the bent rods, the intake guide is more then likely out of place, slight bend or galled.one other cause could have been stale fuel caused the intake valve to stick with varnish and allowed the rod to bend.

when you get all back together again and running properly make sure the engine is running at correct high speed RPM. Over speeding could cause the rods to bend.

Most likely cause is simple neglect or lack of maintenance. As I know you are aware of these engines with solid lifters, need periodic adjustment of the valves. The valves can get loose over time and with excessive clearances the push rods just fall off the rocker arms and can become misaligned and easily bent.

In addition to old fuel as mentioned by rotti, dirty and old oil can also contribute to a seizure of a valve in the valve guide, as well as dirty or plugged cooling passages around the valve guides. Overheating can also be the cause of a blown head gasket.

This is why regular maintenance is important to keep the engine from having these types of issues during the season. You should use this to talk your customers into regular spring maintenance.

Thanks everyone, i look a look at the valve guides and they look fine and don't have any excessive play for the hours on the motor. Im going to go with 30years lack of maintenance, because the guy did change his oil, plugs and filters but never adjusted his valves.

Just some food for thought.........I see a lot of engines that have that happen,and along with all the mentioned things,when the cooling fins get plugged and the heads get overheated,the guides start migrating down towards the tulip,and stick them,resulting in the bent rods.I work on mostly Kawasakis,but maybe this could happen on B&S also?
Steve