Originally Posted by
mountaindave
Looks like you have semi horizontal dropouts, so not a lot of room to take up slack in the chain. That’s probably why there was still a rear derailleur on there. If you can’t grt the chain tensioned properly, you may need a bolt-on tensioner.
Thet crank lists its spindle length requirement. Check what you have already. There are some pretty cheap black cranksets on eBay too. You may just have to experiment since this is a MTB, not a road bike.
And if that front hub is original, OE date code indicates 1990.
Hard Rocks of this vintage have a real weird dropout. It looks like a semi-horizontal when there's a wheel skewered in there, but they left a bridge when machining the dropout to act as a stop.
Hard to describe, so here's a picture I found on the internet:
