Briggs and Stratton 20 Hp Major Failure - Never Seen Like This

Hello All

I have a Snapper Lawn Tractor that was purchase in May of 2013 with a 20 Hp Briggs and Stratton Engine. Model 33M677 0110 G5 .

The Tractor has 150 Hours on the Engine Maximum. Every year the oil has been changed with new oil filter installed. So it has been well maintained. The Engine Ran fine with no issues all these years.

Then last fall the Engine had a Major Failure. It was running fine cutting lawn then like Sputtered and LOUD BANG. It Stopped. After lifting the hood it was seen the Whole Rear of Engine was Blown wide open. I mean the Whole Back at least 1” gap of Metal all the way across the whole rear of Engine. There where pieces of metal all over this area.

Looking at it you would think the Rod had failed somehow – the spark-plug was removed and it turns over by hand and still has compression so The Rod is not Broken as one would think.

The Engine is still installed in the tractor so it has not been taken apart yet to see what caused the failure.

Has anyone else seen this type of Briggs Failure and What is the cause?

Also does anyone know a Good Model Replacement for this Engine.

Thank you

Looks to me like the counterbalance let loose. Carefully look at the oil and see if you find shavings. Normally when I see a hole like that I see oil everywhere. Not to be a wise guy, the only time I’ve seen that is when the engine was run low on oil. When you pull it apart try to collect as much as possible and see if you have more than a quart. Also look for signs of over heating.

Like Rivits said.
Over reving will also cause the counterbalance to let go.

This failure is some what common on 28, 31 and 33 Series engines until they changed the counter weight system on later engines. On older 25 and 28 Series flat head engines you could get replacement parts for the counter balance Eccentrics which helped some. Might want to consider what kind of oil you are using and change more often than recommended even.

Walt Conner

All your pics don't show any oil blown out..

Could be if the engine suddenly locked there would be not a lot of oil splashed out? That blow out would sure ruin someone's day though.

Looking down the Big Hole I still see oil in the Bottom Sump. Will let you know how much when drained?

It was changed 5/18 with filter ( 4 months later was failure) so do not know where it would go. There was no leaks

Also does anyone know a Good Model Replacement for this Engine??

Maybe I'm looking at this wrong, but could it be the mounting bolts came lose? Continued slamming ripped it open.

What I see as disturbing is that at the blow out the inner case looks to be dry, if I'm seeing that right ?

Not sure what you mean Inner Case Dry??

This happen last fall so any oil would be in the bottom and I see oil down in the bottom.