Packard Forum Index » Pre-War (1899-1942)

Thomas,

I noticed something mentioned at the start of this post that should be checked out. It was mentioned the mains were line honed. I hope this was not the case, and the mains were line bored.

Soft Babbitt type bearing should never be honed, only bored. The reason, abrasive particles from the hone will break off during the honing process and become embedded in the soft Babbitt.

Hard type bearings such as brass, bronze, steel, and cast iron can be honed because the material is not soft enough to allow the honing stone particles to embed into the bearing, and can be washed away with thorough cleaning.

Regarding the bearing clearances for your engine, data from a Motors manual listing '31 Packards is as follows:

Main bearing clearance - .001

Main bearing end play - .003
Thrust on main bearing #7

Rod bearing clearance - .0015
Rod bearing end play - .003

Plastigage is the best method for checking main & rod clearance because it measures the actual oil film clearance.

If one used a micrometer to measure the crankpin diameter and a bore gauge to measure the I.D. of the main bearing you could have a tight bearing even if you measured .001 clearance between the bearings. Why, if the crankshaft had a .001 bow in it, this bow would eliminate the .001 oil clearance that was measured.

Plastigauge can be purchased in .001 to .003 range. The bearing and crank should be clean before you make your measurement. Cut a length of plastigauge the full length of the bearing you want to measure.

You may want to check out:

http://www.plastigaugeusa.com/how.html

Torque the bearing caps to the correct torque, Motors lists 65-70 ft. lbs for the mains and 40-45 ft. lbs. for the rods.

The Motors data on the '31 only shows one value for the clearances, not the service limits.

Just as reference info Motors shows the following service limits for a '35 model 120:

Main bearing clearance - .001 to .003
Crankshaft endplay - .003 to .008

Rod bearing clearance - .0008 to .0028
Rod bearing endplay - .004 to .010

Good luck,

Dave

Dave and Dave,

Thanks for the information I really need to get an early Motors manual. Too bad they are so hard to find.

The bearings were line bored. Sorry about the mix up.

I also agree about the plastigauge, and that is the next step.

Regards,

Tom

Keep an eye out on eBay. I bought both a Motor's and Glenn's Repair manuals out there for less than $20 each.

Tom, perhaps the Internet isn't always the best place to find everything, I see old Motor's Manuals constantly and abundantly at automotive flea markets. One that is very useful though not in your case is the 12th Edition which covers 1935 to 1949. Another particularly useful volume is Chilton's Flat Manual, 11th Edition, which has extensive coverage for 1931 thru 1936 as well as some specs like tune-up data, front end alignment,and the like back into the mid 20s, and extensive coverage of carburetors including updrafts, generators, starters, voltage regulators, steering gear, automatic chokes, etc., plus a good dose of general info like interpreting vacuum readings, etc. Chilton's also has an abbreviated parts listing by year and model which is really helpful in quickly finding which other years and models used the same parts. Another really outstanding one though hard to find is the Standard Auto-Electrician's Manual. I have edition T covering 1931 thru 1935 which has VERY extensive coverage of automatic starting devices like Startix, headlamps and bulbs, Bendix drives, generators and regulators, ignition locks, lighting switches, starters, magnetos, and ignition timing. If a particular page or 2 from any of these is useful to you, send me a PM with you email address and I'll scan. And keep your eyes peeled at the larger flea markets.


Dave

I just talked to my engine guy. The plastigauge shows from .001 to .0025 across the mains. It was funny, at least to me, that he had to find an older guy in the shop that knew how to use plastiguage. I like this guy because he is willing to ask questions.

He is now going to do the same with the connecting rods.

Then it will be onto the camshaft. What do folks think about hard chroming the cam bearing journals to oversize them slightly. The bearings themselves are too worn to just take a little off the ends.

Thanks again.

Tom

If the cam bearings are worn and you aren't going to replace them which would be the best practice, I don't think I'd put a resurfaced cam against worn bearings. Wouldn't a better practice be to line-bore the cam bearings back to a uniform surface (assuming enough babbitt is present)and spray-metallize the cam journals and finish to proper clearance? I'd think hard-chrome is probably a bit of overkill. Good topic to hear Jack Vines' advice.

I have done a little research and looking, at it does not appear that the cam bearings are babbitt. Instead, they look like machined cast iron. Does that make any sense?

Nobody carries these bearings that I have been able to find.

One idea that I read about in Dykes is over sizing the bearings, then sleeving them with a brass bushing. Obviously, the sleeve would then have to be split to go over the cam. Not sure how this would work. Maybe press a sleeve into each half, then cut/grind off most of the excess, put the bearings back together for a final ream to size?

Probably wouldn't work, right?

Or, we can follow Dave's advice above and oversize the cam journals after bringing the old bearings to size; oversize with metalized spray (which I did not know about, thanks Dave) or hard chrome.

So, basically, I am up for ideas.

Thanks,

Tom

Tom, usually the bearing surfaces on camshafts wear very little, if any. The accepted way is to replace the cam bearings when doing a rebuild. This restores the proper fit and clearance. Have you measured your camshaft bearing journals? If the journals are worn, then I would look very carefully at the lobes which are more prone to wear.

Did you survive the rain? We are high and dry, but you are in a low area. Take care...

(o{I}o)

Sage advice from JW. And loose fit at the cam bearings is a classic for loss of oil pressure.

John,

Cam journals are not appreciably worn, but the bearings are. And, I would gladly replace them and have them line bored, but so far the usual folks don't have them for this engine (Terrel, Kanter, MM, etc.).

So, I either refurbish the current bearings, figure out some suitable substitute, or make new ones. Obviously, making new ones is a fairly daunting task (at least to this non-machinist). Making new ones is also probably out of my current budget, so that would stop the project for the foreseeable future.

Yup, we got wet over here. Westlake drive was closed this morning at 4am.

Cheers,

Thomas