I have a 1961 Chevy C-10 LWB Step-side. When I purchased it, it came with the original engine. When I purchased it, I took some steps to restore it to driving condition after sitting idle for at least 10-15 years. After a few months of "overzealous" driving, it spun a main bearing in the heat of a July day. This was 3 years ago. A year and a half ago, I purchased a Craigslist engine of the same displacement (235cid) from 1957. Unfortunately, although it runs great, it has a slight knock at idle when warm. I'm trying to figure out if this could be silenced or quieted by a change in oil viscosity. I have noticed that STP helps a little bit, but it seems that when the oil is hot it begins to knock. Does anyone have any ideas on a good quality oil to use to relieve this problem, or any suggested additives?
Again, this knock occurs intermittently when idling and warm. Under load, it does not knock. Any help appreciated. Thanks!
