Adjusting bearings on 42 Chev engine

Has anyone adjusted the bearing clearance on a babbitt bearing Chev? I understand it is possible by removing shims and this used to be a regular part of an overhaul.

I just bought a 42 Chev with 77700 miles on it and was thinking of taking off the oil pan and scraping out any sludge. Wonder if I should get some Plastigage and check the bearings.

Rusty;

I've never adjusted the bearings on my 48 Chevy 216, but, the shop manuals will tell you how to do it with the shims. Be careful with the oil pan and don't move the oil troughs for the rod dippers, or, the aim of the 6 oil nozzles. It requires some special gauges to reset this stuff. You might want to pull the valve cover as well, and, make sure the valve gear is oiling OK as well. These engines like thin oil at high volume - I use 10W-30 in mine. Normal hot oil pressure at speed is 14 psi, hot idle on my car is about 4 psi. The 216 is a solid lifter engine - so make sure the valve clearance isn't set too tight. I do a lot of interstate running with my 48 so mine are set at top of spec, and, tap pretty good at idle. I also suggest you get on the VCCA forum. Lots of expert advice there.

Regards:

Oldengineer

1948 Chevrolet Fleetmaster Town Sedan

Is it possible to remove and clean the pan and pickup screen without disturbing the nozzles and dippers? Maybe it would be better left alone? I am an experienced mechanic and my first car was a 48 Chev in 1964. This engine has 77700 miles on the clock and has no oil filter. It has been sitting in a garage for at least 8 years. I am thinking I should clean out the pan and valve cover and install a filter then run detergent 10W30 oil.

Bearings should be set at .001 per inch of diameter of the pin. Your crank when standard is 2.311, to 2.312. Clearance in the book says .00005, to .002-60.

If you set the rods to .00005, to .001, the motor will be seized. You will smear the babbitt, or burn the rods out in 5 minutes.

The shaft clearance should be set from .002-30, minimum, to .002-80 maximum, that is 1/2 thousandths difference.

30 Wt. detergent should be used in summer, and 20 weight when colder.

10w30 is OK for pressure fed rods, but not a splash system, and there is not enough cushion.

Herm.

Rusty:

If you're careful, you should be ok with the pan removal. Just don't bend the troughs or move the nozzles while cleaning. My 48 doesn't have an oil filter either, but, I only put a couple of 100miles on the car between changes.

Regards:

Oldengineer

As usual Herm is right.

You can't run the close clearances of a pressure system in a splash system oiling environment.

There is a good explanation there >>> http://chevy.oldcarmanualproject.com/shop/1942_47/4247csm619.htm

Sounds like fitting bearings is part of a rebuild. Is there any way of knowing when to do this or do you keep driving until the rod is sticking through the block?

Unfortunately you have to drop the pan to find out since engine oil pressure won't be affected by loose rod bearings on THAT engine.

If you have a good ear you can listen for knocking but that's hardly a good way to determine when to take up bearings.

On the other if it ISN'T knocking you're probably safe anyway so........ :confused:

After 77K miles I think you'd be well advised to drop the pan anyway as it's probably loaded with crud.

I'd drop a quart of Marvel Mystery oil in there and drive it some before dropping anything.......get her cleaned out really well!