I have a Sears gas powered snow blower and the blade is driven by a
chain. I tighten the chain by loosening the engine mounting plate
bolts, pull the chain tight and re-tighten the bolts. But after just
one season of a few uses, the chain is loose again. I keep
tightening it and it seem to get loose after a few uses.

Is the chain stretching or is something shifting so that the chain gets
loose again?

The chain is similar to a small bicycle chain.

thanks

Mark