Crankshaft suddenly seized up

Clifford Pope · Post by **Clifford Pope** » Sun Jun 22, 2008 8:35 pm

Following on my post in Dohnut's thread, I thought I had exactly the same symptoms as his 40+.
However, prolonged attempts at starting have lead to a sudden new development - the crankshaft has gone very stiff to turn. It is impossible to spin the flywheel with the cord, and hardly possible with two hands.

What could have happened - does this point to a piston ring fault, broken perhaps? The compression had always been excellent before this.

Vic · Post by **Vic** » Sun Jun 22, 2008 11:36 pm

If its a piston or ring causing the trouble you should feel the crankshaft rather freer at TDC and BDC where the piston is not moving. If you can turn it to either of those points of course.

Waggles · Post by **Waggles** » Mon Jun 23, 2008 7:52 am

Could it be a problem down at the gearbox / prop end rather than the power head? does your have a clutch?

Have to confess I thought my dear old 40 was partially seized once only to look down and see the prop cutting into the lawn as I was holding motor at the wrong angle ......

Not suggesting you have done that of course but it could be a jam in the gears perhaps? partially engaged clutch? Separating the gearbox from the motor would prove it obviously.

I only mention it as it would be unusual for a motor to seize ( or partially so ) while not running assuming petrol / oil mix is ok. You could try putting some hot oil down the spark plug hole and see if that frees things up after some turning of the motor. Take great care of course.

Clifford Pope · Post by **Clifford Pope** » Mon Jun 23, 2008 8:18 am

No, it's stiff all the time, doesn't change at TDC. It's not the prop end, and there is no clutch. It looks like I'll have to open up the engine and look at the rigs and bearings.
It seems an odd coincidence that it has happened so suddenly but not while running, and hasn't run since it cut out. Can a crankshaft seal fail in a way that firstly it leaks, and then jams the shaft?

Waggles · Post by **Waggles** » Mon Jun 23, 2008 11:42 am

Only other thing I can think of is something loose in the magneto which has caused timing to slip / weak spark or both, and is now binding on the flywheel perhaps?

Do let us know what you find

Vic · Post by **Vic** » Mon Jun 23, 2008 2:30 pm

Can a crankshaft seal fail

. . . . . . . . . . . . . . . . . . . . . . . . . . Crankshaft seal?

Clifford Pope · Post by **Clifford Pope** » Tue Jun 24, 2008 11:32 am

I don't know the design in detail - I just assumed there must be some kind of seal stopping inlet gases leaking past the crankshaft bearings.

As luck would have it, I have just been given another identical model from someone's garage, and after cleaning up the plugs, points and fuel filter, it runs. I've had to pinch the bracket and carb from the first one, so I'll postpone the PM for a while.
Thanks for your suggestions.

CatiGull · Post by **CatiGull** » Sat Jul 05, 2008 10:42 am

I dont think you can seize an engine without runningit - I would guess some kind of mechanical obstruction is the order of the day.

No seals, just bushings. Lifting that flywheel would be my next step.