B&S Intek 20hp wont crank

Hi guys i got a question for you i was mowing yesterday and went to start the mower and it ran fine till i turned the blades on and the motor didn’t sound like it had much power so I turned the blades off and mower was still running but when I turned the blades on again it did the same thing but when i moved forward it made a loud bang and the motor wouldn’t spin at all. Since then i can move the motor by hand but only to a certain point and it won’t move any further also sounds like something is rattling when i turn the flywheel by hand. If anyone could steer me in the right direction of what blew on this motor. I would appreciate it. Thanks.

My uneducated guess would be a connecting rod.
Take the spark plug out and put long screwdriver or rod in the hole until you hit the piston, then spin the flywheel and see if the screwdriver moves with the piston.

First of all don't keep trying to force the engine to rotate.
Drain the oil and see what comes out, run it through a sieve but make sure SWMBO does not catch you in the kitchen.
If you find alloy or steel in the oil than it is pull down time
If you find no oil then it is new engine time
If you find too much oil which feels a bit thin smells a bit like fuel then it is 50:50
If you find little bits of steel then it is new governor time.

If it all appears in order, pull the spark plugs and rotate the engine by hand and listen very carefully.
If the sound seems to be coming hig in the engine, then pull the flywheel and check for something stuck in the magnets jambing the flywheel
If the sound comes form one of the cylinders then it is pull it out & pull it down time

Scrubcadet10 said:

My uneducated guess would be a connecting rod.
Take the spark plug out and put long screwdriver or rod in the hole until you hit the piston, then spin the flywheel and see if the screwdriver moves with the piston.

Click to expand...

How can the connecting rod blow if it had oil in it

Fatigue
Loose bolt
Fuel diluted oil
failed oil pump
Overheating
Piston separation
Mowing across a slope
If I try hard enough I could probably make a list better than 20 items long.

There is a bit of a system that works really well.
First you find what has failed then you work out why it failed then you make a repair.

IT works a lot better if we ask you to do things , you do what is asked then post your findings from which we can make educated deductions.

You post screams out OIL SEIZURE , classic symptoms
However a dropped push rod also has similar symptoms.
I now have a really good bore-o-scope so in a case like yours it is dump the oil then shove the camera inside & take some unhappy snaps.
This saves the customers having to pay me to pull the engine out then pull it apart to tell them the engine is trashed.

Naturally we are more than happy to go into the why nitty gritties but for right now what is important is the What.
IT takes about 10 minutes to drain the oil into a container so it can be measured at a latter date.
While the oil is draining you can pull the rocker covers off & check that there are 4 pushrods.

If you are willing to go back & forth you mower could be diagnosed today, although not by me as it is beddy bies time for this little wrench spinner.

One last thing before the sleepy dus does it job.
If you decide to pull the engine, remove the flywheel before you pull it out of the mower.
It is a lot easier to do in situ than on a bench or the floor

bertsmobile1 said:

Fatigue
Loose bolt
Fuel diluted oil
failed oil pump
Overheating
Piston separation
Mowing across a slope
If I try hard enough I could probably make a list better than 20 items long.

There is a bit of a system that works really well.
First you find what has failed then you work out why it failed then you make a repair.

IT works a lot better s we ask you to do things , you do what is asked then post your findings from which we can make educated deductions.

You post screams out OIL SEIZURE , classic symptoms
However a dropped push rod also has similar symptoms.
I now have a really good bore-o-scope so in a case like yours it is dump the oil then shove the camera inside & take some unhappy snaps.
This saves the customers having to pay me to pull the engine out then pull it apart to tell them the engine is trashed.

Click to expand...

So you think it is the connecting rod because the flywheel only spins part way then stops also when you rotate it before it stops you can hear like a clanging of metal moving around before it stops. Does this help you. Also motor had oil in it before it blew

What helps is you doing what was asked.
So start with dumping the oil & checking for metal
Pull the rocker covers off and count the pushrods
Then if necessary pull the flywheel.
If you have read what was posted it could also be something stuck under the flywheel.
I don't make guesses if it can be avoided.
In the time you have been sitting there quering what has been posted, the oil & rockers could have been done and you could be getting some useful answers.
Otherwise it is just a guessing game that can go on for months and show no useful outcome.
A blown out lower oil seal can empty an engine in about 5 to 10 minutes.

Now nitty nite , good luck & hopefully you have gotten to the bottom of it before I am having my rolled outs & coffee in the morning.

Take the spark plug out and put long screwdriver or rod in the hole until you hit the piston, then spin the flywheel and see if the screwdriver moves with the piston.

Click to expand...

Do this and you can rule out the rod. even though it stops while you spin it over, if the crank is moving the piston should be moving too.
and do what Bert says, smart guy :thumbsup:

Scrubcadet10 said:

Do this and you can rule out the rod. even though it stops while you spin it over, if the crank is moving the piston should be moving too.
and do what Bert says, smart guy :thumbsup:

Click to expand...

The crank only moves slightly. Do you think it is the rod

not now that you said slightly... more than likely a dropped pushrod like bert said...
If you would post your engine model numbers so we can get specifics on it, https://www.youtube.com/watch?v=tAA55bq8yrY