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When installing AC or PS a person might want to have the option of driving those systems direct from the Crankshaft. A few very expensive options from the AC manufacturers are available but not a lot of attention to this problem has lead to a decent solution. Chevrolet's solution for the large trucks of the day was to use the two bolts on the standard single pulley balancer to bolt a second pulley to the front of your existing one. That is my favorite solution but sadly, they are very rare and very hard to find.
http://devestechnet.com/Images/Resto...50b00495lg.jpg
Another solution is to use a small block Chevy V8 balancer with NO pulley and have your machine shop machine it for your 216/235/261. then purchase a tin dual pulley that bolts to the balancer in three places. It was suggested on another forum to do this, so I tried it myself. The problem with this idea is the 3 bolts are not self centering and it is very likely your pulleys will 'wobble' and cause unnecessary vibrations. I do not recommend this.
http://devestechnet.com/Images/Resto...50b00493lg.jpg
Another solution has come to light recently and credit for this one goes to Tom Langdon. This idea uses the 292's Dual Pulley Harmonic Balancer but requires you to machine a little over 1/2" off the back of it so it will allow for the 216/235/261's timing cover. This can be easily done at any machine shop and the 292 solution is more likely since they are not nearly as rare. The Damper used is a 1986 292 Chev 6 it will need to be trimmed .530†on the rear edge to clear the timing cover . The machine work to the front of the crank to retain it is drill and tap a 7/16-20 x 1-1/2" for the bolt. Drilling a 7/16" fine thread hole through the crank is a good idea anyway to hold your current HB on. The idea of pressing it on turned out to be a bad idea over time.
http://devestechnet.com/Images/Resto...50b00495lg.jpg
Another solution is to use a small block Chevy V8 balancer with NO pulley and have your machine shop machine it for your 216/235/261. then purchase a tin dual pulley that bolts to the balancer in three places. It was suggested on another forum to do this, so I tried it myself. The problem with this idea is the 3 bolts are not self centering and it is very likely your pulleys will 'wobble' and cause unnecessary vibrations. I do not recommend this.
http://devestechnet.com/Images/Resto...50b00493lg.jpg
Another solution has come to light recently and credit for this one goes to Tom Langdon. This idea uses the 292's Dual Pulley Harmonic Balancer but requires you to machine a little over 1/2" off the back of it so it will allow for the 216/235/261's timing cover. This can be easily done at any machine shop and the 292 solution is more likely since they are not nearly as rare. The Damper used is a 1986 292 Chev 6 it will need to be trimmed .530†on the rear edge to clear the timing cover . The machine work to the front of the crank to retain it is drill and tap a 7/16-20 x 1-1/2" for the bolt. Drilling a 7/16" fine thread hole through the crank is a good idea anyway to hold your current HB on. The idea of pressing it on turned out to be a bad idea over time.