Stiga mower won’t run

[MattyF]

I’ve got a stiga park compact 16 with a Briggs 155 engine.

last night I was cutting the grass and it sounded like the exhaust baffles where falling out ! Then like it was running out of fuel. So I stopped and re fuelled.

on starting it back fired a few times and then went dead.

it has fuel.

it has a spark 

I’ve checked the fly wheel key and it seems intact.

any other thoughts ? It seems to have a different note turning over so I’m thinking either a valve is stuck or is dropped a valve. 

[Muddy42]

I think you are on the right track.  I would remove the valve cover, check the valve clearances and see what the moment looks like when you turn the engine over. Are the push rods moving in and out at all.  Its best to do this with the spark plugs removed, for safety but also so you can check whats happening to the pistons.

[MattyF]

9 minutes ago, Muddy42 said:

I think you are on the right track.  I would remove the valve cover, check the valve clearances and see what the moment looks like when you turn the engine over. Are the push rods moving in and out at all.  Its best to do this with the spark plugs removed, for safety but also so you can check whats happening to the pistons.

I know nothing about valves so it will be time to learn I guess then ! The engine is turning over it seems with less compression but I’m hoping the pistons are ok.. this mower was supposed to outlast me 😂

[Muddy42]

Post a video here of the valve movement if you want?

[MattyF]

This is what I can see … so obviously not right , should the long thing be at that angle 😂

[Muddy42]

Yes, something is not right!

 

When you move the engine, that bent rod should be moved in and out by a lifter which is pushed in and out by the camshaft. Thus it opens each valve in turn.

 

- Is the exhaust rocker and valve still moving OK?

- Can you move the intake valve in and out (that thing with the spring around it)?

- Can you confirm that the intake lifter is still moving inside? maybe just unbend the bent rod and use it as a feeler.

 

Was the oil level OK?

 

penetrating oil can unstick valves. then gentle tapping

[AHPP]

What causes a valve to stick in the first place? Bad AFR? Moisture?

[AHPP]

You’d think the channels the push rods slide in wouldn’t be much bigger than the push rods themselves so they can’t bend. Unless they’re designed to bend sacrificially, rather than a valve stem snapping or punching a hole through the valve face? Or the rocker pivot threads pulling out. 

[Muddy42]

20 minutes ago, AHPP said:

You’d think the channels the push rods slide in wouldn’t be much bigger than the push rods themselves so they can’t bend. Unless they’re designed to bend sacrificially, rather than a valve stem snapping or punching a hole through the valve face? Or the rocker pivot threads pulling out. 

Yes that's my understanding, the rods and rockers are designed to be the weak point.

 

Yes, there is quite a lot of space around the rods. Maybe to allow oil to move around?

Edited Tuesday at 12:11 by Muddy42

[Mick Jones]

1 hour ago, MattyF said:

This is what I can see … so obviously not right , should the long thing be at that angle 😂

Matty, did you move the rocker arm over to one side to get the bent pushrod out or was the rocker arm like that when you took the valve cover off?