Originally Posted By: Astro14
Originally Posted By: 46Harry
The Model a engines may have speced .001" as a bearing clearance, but they have poured bearings and not inserts as original equipment and as a result, I have never seen a .001" clearance on any poured bearing. I still have my bearing knife that we used on the old Chevy and Ford engines with poured bearings to scrape off excess Babbitt material to get the proper clearance. In service the clearance usually runs more toward .003" and beyond so that is why I use a 30 or 40 grade oil in those engines.
Exactly. Plastigauge those bearings, which are very soft, and you'll find some pretty big clearances. 15w40 is a good year 'round choice....
Agree completely with those who recommend a multigrade. There's no advantage to a mono grade in the engine, just make certain that the engine is cleaned up inside before using the modern oil.
Also, with Babbitt bearings, you really have to watch your engine temp...the metal is soft and can degrade quickly with an overheat, leading to trashed rod or main bearings. Their softness should protect the crank from damage with a bearing failure, but if you get steel/steel contact, you're in trouble...
Do it right and the bearing is uniform, strong, and durable. You can most certainly keep to the .001 if you know what you're doing. Unfortunately, the old timers who did this in their sleep are dying out.