bolens MTD engine will not spin beyond two rotations.

[Dchurch]

Bolens MTD
502CC 15.5 HP
Briggs and Stratton
Model 31A607 Type 0458-E1

The motor will not spin beyond two rotations before stopping.

Battery and solenoid were bypassed.

Used charged car battery. used jumper cables with negative connected to mower battery (assumed mower battery negative is connected to frame of mower) and the positive touched to starter motor. engine rotated about two rotations (maybe until compression stroke).

I can turn engine by hand through all four strokes; engine not physically seized. there is a compression stroke.

Seat was up, blades disengaged, starter switch on, gearing in neutral, brake on.

I did not expect engine to fire (as electrical power merely applied to starter mower). But I did expect the engine to spin while starter motor energized.

Any suggestions?

 

[dana a]

Take the spark plug out and see if it will spin more than 2 turns.

 

[Mike_Goad]

Dana does have a good suggestion. There could be one or more issues at the same time. If the combustion chamber has a lot of carbon build up, that would raise the compression too much for the starter to handle. The only real way to fix that is to pull the head off and decarbonize the top end.
Another possibility is that the compression release is no longer working. To fix that would require a complete engine disassemble and replace the cam shaft.
another possibility is that the starter itself is weak and just will not spin the engine when a load (compression) is present.

I would start by doing a compression test. if the ACR is working properly, the compression should be fairly low (less than 100psi) if it is not working, it will be well over 100psi.
if all that is good, try shinning a light through the spark plug hole and see if it is all black inside. if so, a good cleaning may be required.
If those are good, try to do an AMP draw test on the starter and see if it drawing too many amps. this would indicate a bad starter.

I will probably get more flack for this but I once again will warn, DO NOT use a car battery on a lawn equipment. In a perfect world, nothing will happen, but if there is a wiring issue somewhere, the extra amps can fry an entire electrical system.

Get your engine model number and spec and search online for the service manual that will walk you through any of the above steps.
I hope this helps.
Mike

 

[bertsmobile1]

Firstly the ignition is self powering so every time the magnets spin past the coil the engine can spark.
Lots of mechanics short a digit or two because they did not understand this.
Also the reason why you are instructed to pull the spark plug wire whenever you play with the blades.

Now you have a 4 stroke engine which compresses and fires on every second rotation.
Your engine does 2 revolutions and stops.

Sound like the starter can not overcome the compression ?

In order to protect the crankshaft & con rod the starters on mowers are only just strong enough to overcome full compression when new.
To allow this weak starter to spin the engine fast enough to start they all have decompression mechanisms fitted.
In order to work the decompressors rely on the valve lash being set acurately.
Too tight and there is nothing in the cylinder to burn
Too loose and no decompression.

 

[Tyy]

Gotta love these Briggs Eh Bert !