In Reply to: More on oil posted by Larry on December 21, 2017 at 06:43:38:
The recommended oil is fine. The technical information provided is not.
Engine oils in the late 50's and early 60's did not contain levels of zinc or phosphorous anywhere near the levels contained in current oils. That is pure myth. Well known experts like Bob Olree (chief engineer of the lubricants division at GM and now deceased) have explained time and time again that the zinc and phosphorous (ZDDP) levels started to increase in the late 80s and early 90's for reasons other than wear protection. Prior to that ZDDP treat rates were quite low by modern standards. When fellow N-board member JMOR told me he had a large quantity of premium engine oil from the early 60's I asked him to send a sample to Richard Widman at Widman Oil. Mr Widman is a resident expert over on Bob Is The Oil Guy forum and very knowledgeable wrt engine oil additive technology. I was curious what he might find and what his reaction might be. The analysis confirmed what Mr Olree and the other REAL experts at API had been saying:
The unopened can of oil sampled was labeled as an API service category MM-MS-DG oil - the highest performance category at the time. It contained 510 PPM zinc and 480 PPM phosphorous - roughly HALF of the MINIMUM levels required in a modern engine oil. This sample is exactly the oil Ford and most other motor companies were specifying for use in ALL of their engines.
The flat tappet valve spring pressures in your 1940-50 tractor are very low by any standards and it does not need nor will it benefit from zinc/phosphorous (ZDDP) levels above 800 PPM. The same is true of virtually all production flat tappet engines up through the late 80's. There are exceptions. Some high performance engines with higher than normal valve spring pressures require higher levels of zinc for flat tappet anti-wear protection. They are the exception not the rule.
The hot running engines of the early 90's is what drove the increase in the ZDDP treat rate. In addition to being an excellent anti-wear compound ZDDP is also an excellent anti-oxidant. ZDDP treat rates were increased primarily to provide better ant-oxidation protection.
ZDDP is not the only anti-wear/anti-oxidant compound that can be used. It just happened to be the cheapest and most readily available. Starting 20+ years ago more expensive but just as effective compounds began replacing ZDDP. The motivation for that was to extend the life of catalytic converters which are damaged by phosphorous. So unless you are building a high performance race engine you don't need a high ZDDP oil. And even that is a bit of a canard because lower ZDDP treat rates coupled with advanced anti-wear/anti-oxidant compounds can be just as effective at preventing flat tappet lifter wear and oil oxidation as high ZDDP only treat rate formulations. There are thousands of controlled flat tappet engine tests demonstrating that fact.
Here is a link to Richard Widman's monograph on engine oil additives. It opens with a page one discussion of the analysis of the sample oil JMOR sent him...
Engine Oil Additve Technolgy by Richard Wodman