Originally Posted By: mechtech2
Most engines even today are flat tappet type.
Maybe not pushrods, but buckets or lifters against cams.
Having 'flat' tappets is not a deal killer.
If the old car's engine is broken in, I see no reason why modern oils in the correct viscosity should not serve well.
But that 15-40 diesel oil would be a good choice for a bunch of reasons.
I agree with most of your statements (although I would prefer a 5w40 diesel oil like RTS), but I don't think that sliding cam-to-lifter or bucket contact exists in anywhere NEAR 1/10th of the engines being built today. Almost everything out there has roller cam followers now. Very few OHC engines still have "buckets" with shims following the cams, its all rockers or fingers with hydraulic lash adjusters and with roller followers on the cam side (and frequently roller tips on the valve side, too). American pushrod engines almost all went to roller lifters in the mid-1980s. The Jeep 4.0/2.5 was one of the very few exceptions. I'm most familiar with Chrysler engines, and the last sliding-contact cam engine they built (other than the aforementioned inherited Jeep engines) was probably the 2.2/2.5 SOHC 4-banger in the mid 90s. All the v8s and v6s went roller by circa 1985.
Woops, looks like the 2.2/2.5 went roller in 1988. So no slider cams at Chrysler any later than 1987. I'm pretty sure Ford and GM were about the same, if not sooner. I seem to remember that the Ford 302 (5.0) got rollers about a year before the Mopar 318, which would put it around 1984. Not sure about the smallblock Chevy.