The Stovebolt Site Forums The Shop Area Engine Shop Babbit mains on chevrolet 216 engines

Hello;
Can anyone tell me when Chevrolet quit using poured mains on their 216 engines? I had a discussion with a friend
and we would both like to know.

Thank you 59shortfleet

I'm not sure the 216 ever had poured mains. Only the rods were poured.

Roy is correct: 1937 216 - removable steel-backed babbitt main bearings

In 1948 Chevrolet changed the process of the mains to allow "precision fit" bearings to be used. Before that the bearing inserts needed to be line bored once installed in the block.

So it would be safe to say that '47 and earlier had poured babbit, steel-backed insert bearings? If they were designed to be line bored, then there had to be a significant amount of babbit bearing material on them.

That is correct Carl!

Thanks to all for the information on the 216 main bearings.

much obliged, 59shortfleet

The general term for this type of bearing is "semi-finished". Back when crankshaft grinding equipment was not as accurate or repeatable as today's high-precision machines, bearings had to be custom-fitted by boring and/or hand-scraping to get an acceptable fit and clearance. Another advantage to semi finished bearings was that a reground crankshaft could use the same bearing set as a standard-diameter one- - - -just bore the bearings to a smaller diameter. Cam bearings were also supplied as semi-finished for some engines.
Jerry

Can the later precision fit bearings be used in the earlier blocks?

Possibly- - - -if the outside diameter is the same. It would be a situation of trial fitting and maybe shimming for the correct oil clearance, or maybe installing the bearings without the crankshaft in place, measuring to see if they're round, and grinding the crankshaft to fit the bearings. More than one way to skin a cat! It also might be possible to line bore the block for the precision bearings, if the OD is different.
Jerry

I do not know how they were going to do it. Though the machine shop that was going to rebuild my 1946 235 was going to convert it to bearing inserts. Though I got a free 1954 235 at that time and had that one rebuilt. Jeffrey

They were probably going to convert the rods, not the main bearings. That's been done pretty regularly for many years. Currently, I'm working on a procedure to salvage "worn out" 216 and 235 crankshafts by using Massey-Ferguson rod bearings in rebored rods.
Jerry

Starting in about 1948 Chev sold "precision fit" bearings to fit the 1947 and earlier engines, but cam to crank gear backlash could be a problem, because of the imprecise main line placement.

That's also something to consider when line boring a stovebolt engine. If it's done incorrectly the cam and crank gears bottom out. An engine with a timing chain instead of gears can end up with a loose chain and late cam timing.
Jerry

This is the information from 1948 that Dave refers to.
https://www.flickr.com/photos/advance-design_parts_co/albums/72157652194902731

So are the pre-48 blocks basically obsolete?

Just be ready to check everything and spend plenty of money.

I definitely learned something today.

I knew about the Babbitt connecting rod issue with 216s, but thought the main bearings were all replaceable across all years

Be glad we're not addicted to Model A's or Model T's! Both of them have poured main bearings!
Jerry