Small Engines (Lawn Mowers, etc.): B&S Firing Early, vertical shaft, coil assembly

Question
Hi,
I pulled a B&S 3.5hp engine from a bin yesterday - it is a vertical crank 40 series I think.

It had a sheared con-rod (a fairly clean break) so I replaced it and attempted to start it.

The engine fires well before TDC resulting it some serious kick-back on the rope - I have double checked timing, carb mix - everything I can think of. The flywheel key is intact and the coil assembly is also properly in place.

Before I scrap this engine for parts, is there anything else it could be apart from a bent crankshaft?

Many thanks,
Tim


Answer
If it is a vertical shaft engine intended for a lawn mower then the flywheel should be aluminum.  You will need to install a blade to test the engine.  The blade acts as flywheel weight.  Without the blade the rope will jerk out of your hand and usually the flywheel key will shear.
Also, by installing a blade you can usually tell if the crankshaft is bent.

The other option is to use a cast iron flywheel but these are faily difficult to source.

Let me know if this helps.
Eric