James H. wrote:
The blade on horizontal small engine lawnmowers acts as the flywheel. It provides the inertia to keep the motor turning. It's almost impossible to hand start the engine without the blade or if the blade is loose and spins on the crankshaft. The small engines that don't use the blade for the flywheel have a heavier flywheel. The aluminum key is actually there only to align the flywheel on the shaft, the crankshaft is tapered and the flywheel is held tight by the nut or starter mechanism. The blade, if it's not bent and there is enough left to sharpen, then sharpen and balance it. Don't worry about getting all the nicks out of it. I usually use the body grinder when I sharpen one, using a file can take a long time, always balance the blade. Ask the local mower shop what they charge to sharpen a blade, and they will have replacement blades and contrary to what the manual says you can usually get replacement at many box stores that will work just fine. Make sure the replacement is EXACTLY the same as the old one. There are 6 point star holes and 4 point and square ones and diamond shaped ones and some have three holes, mulching, non mulching and of course the proper length. I'd stay away from the blades that use inserts to correct for the main bolt hole size. The last blade I bought was made in France and needed balancing even though it was brand new. The last trimmer string feed bump head I bought was made in Italy and is a flimsy POS. Have fun, tell your neighbors, friends, and co-workers you will take their old mowers and weed trimmers, you should have a collection by the end of summer to fix. Surprising how many of them just need a carb cleaning, spark plug, starter rope, cable etc. and they are good for another couple years. Some aren't worth fixing but many have a lot of good hours left in them. Oh yeah, speaking of cables, the one that pulls back the safety brake and kills the engine when you release it, make sure it's in good shape and pulls the safety brake completely back. It will cause a drag on the engine if it doesn't and makes it hard to pull start. It's a good hobby fixing old mowers and weed trimmers, keeps you in shape pulling the starter ropes on those old dogs.