I've always thought these were the neatest engines I ever saw when they came out. That's why I put one in my 36 pontiac sedan a couple years ago. Unfortunately it hasn't worked out quite as planned. I have had nothing but trouble with it.
I bought one from a guy in Tennessee who had it in a 66 Tempest convertible. He had it rebuilt by a machine shop there. The cam went flat in a short time and it burned oil. They put a reground cam in it and replaced all the valve guides. They used a reground cam because he could not find a new Sprint cam. Three lobes went flat and he gave up and put a V8 in it. He said he had spent $3000.00 on the motor all told and it had less than 1000 miles on it. I bought it for $1000.00 and got a NEW Sprint cam from Jerry in Utah. I put it and all new followers in and put it in my car. Looked great, but when I got it running all the lifters (lash adjusters) were rattling. I talked to Tom Langdon, Jerry and anyone else I could find who knows anything about these engines. Unfortunately, although I did every thing they told me to do, nothing worked.
After about 3000 miles, the problem solved itself. I was running down the highway when the #2 exhaust valve head decided to part company with the valve stem. It broke the block, head, #2 piston, and bent the rod. No more noisy lifters.
I found another engine in good shape and rebuilt it. My cam, crank, lifters, and followers were still good, so I rebuilt this engine and put it in. The lifters don't rattle, but it has used oil from day one -- a quart every 200 to 500 miles. I thought the rings might seat, but I've got about 4500 miles on it and it hasn't improved any. Now it has developed a dry rod knock when I start it. Lasts anywhere from a few seconds to a couple of minutes. Not lack of oil pressure -- it comes up quickly and is good. I have some new rings and gaskets. I'm trying to decide to try it one more time or just go with a 250 or 292. I have spent about 4 or 5 times as much money on this as I've ever spent on any engine and I've never had trouble like this. That's my sad story.
BTW I have been a mechanic for 42 years, so I do sorta know what i'm doing. Joe