Opinions about #8 Rod bearing failing on 39 320CI super 8

[Guest 39Super8]

I started to hear intermittent knocking, under hard fast acceleration sounded like possible detonation, mainly because it wasn?t consistent. I replaced all the rocker arm rollers and pins, exhaust manifold and whole exhaust system. Could hear this light knock, and then quickly hard knock. Listened with stethoscope, narrowed it down to #8 rod. Dropped pan, sure enough, bearing was flakey and coming apart. It did not spin. The crank journal measures exactly 2.157? The manual says it should be 2.1875 I assume this means the crank has been ground .030? under. I see bearings listed to .040? under. The crank journal looks perfect. The rod looks fine. My question is what happened? Are these engines hard on #8 rod? I have attached a picture of the bearing. It almost looks like someone had the steel shells re-babbited. I suppose along time ago they weren?t available. The engine is clean as a pin! Pistons look good from the underside. I guess the rocker arm rollers weren?t available when they built the engine, because they were far worse than the rest of the engine. Well guys, tell me what you know and think.

[Guest JT]

What do the rest of the bearings look like?

[Guest 39Super8]

Hi JT,

They are fine. I didn't know if there is any cronic issue with this era of engine and bearing used.

[Packard enthus.]

what happened is what usually happens, sooner or later, typically around the 2,500 mile mark, when most people try to re-pour babbit - dosnt matter whether they try it into the rod itself, or re-do a steel shell "insert".

If you are SURE your crank is prefectly round, then all you need to do is find an off-the-shelf modern "insert" and have your rod's "big end" machined to take it.

Your Packard rod bearing shells had a "lip" on one side for side thrust ("modern"...meaning post-war steel-shell "insert" type rod bearings do not have provision for side-thrust, because with shorter stroke engine designs it is unnecessary). Given how long your stroke is ( five inches ) I WOULD, for caution sake, make provision for side-thrust. I used to braze a little bronze "tit" to take the place of that "lip", so that I could use a off-the-shelf bearing. Problem is, I havnt worked on an eight cyl. Packard for nearly 50 years, so cant help you as to what modern bearing will work.

But it CAN be done and it is not rocket science. Any reasonably competent machinist should 1) know how to track down a bearing from the bearing spec. charts...and 2) bore out your rod big end to make it work.

Remember, your '39 Super Eight is actually a 320 cu. in STANDARD EIGHT - it was YOUR series engine that ran 25,000 miles, WIDE OPEN for the Worlds Fair Demonstration in late '34, to show how good your engine is with CORRECT rod bearings !.

[Guest 39Super8]

Good information. I think the bearing with lip is avaliable from a few sources again. I am very glad to know you think it is a bad babbit job, that is what I think too. I will see what I can find tomorrow. I am very happy to hear that these engines were solid. this is my first pre-war Packard, and I only have the distant memories my friend that worked for ECA used to tell. Thanks

[Dave Mitchell]

A well done babbit job will last far longer than 2500 miles. You just need to send it to the right shop. The best way to do this is to send the rod along with the crank dimensions and it will come back like new and ready to install, ready for long and reliable use, just as when Packard delivered the cars new. If you contact me, I will give you the names of a couple of good shops that can do this for you. I would look for underlying lubrication problems while you have the pan off.

[Owen_Dyneto]

If you look closely at the oil pump manifolding you'll note that the longest run is for #8 so all other things being equal, when one rod bearing begins to fail, its almost invariably #8. I've heard comments that the rod bearing shells for these 35-59 rods have been remanufactured recently, but for many years they were unavailable and all manner of attempts were made to keep the engines in service; these included installing pre-1935 rods that accepted babbitt, and trying to reline old bearing shells with new alloy. Some folks even tried shimming the shell from behind, or wiping the shell with silver solder; perhaps this is what was tried on your engine and I would think most attempts at these Goldberg fixes failed rather quickly; that said I understand that some of the prestige restoration shops have had success in applying new bearing alloy to old shells though I suspect it's a bit of an art and at the least requires that the steel shells have no pre-existing metal fatigue.

[Packard enthus.]

Owen - I disagree - I have worked on more than one eight cyl. Packard over the years of the 1924-1939 "separate crank-case and cyl block" type. I have seen an awful lot of these engines develop connecting rod problems. And, sad to say, not a few of them have the tell-tale signs of patching the aluminum crank-case where a rod went thru ! There was NO PATTERN as to which rod bearing would fail. Be assured Packard would have discovered it if the answer was that simple.

With the introduction of the U.S. Highway system in the late 1920's, road speeds really started to climb. The highway system was good enough by the early 1930's, that even a lowly Studebaker (forget what that particular "stunt" or test was called) was able to cross the continent in 3 days !

Low geared cars with long strokes suffer horribly from severe centrifugal "loads" on their rod journals when driven at what today would be ordinary suburban residential speeds ! The story of how Packard tried and failed to resolve the problem, until it finally gave up and went to an "insert" type connecting rod bearing in 1935, has been told elsewhere in this forum's threads.

Point is - it wasnt an oil starvation problem. It is possible I have seen and worked on as many Packards as you have over the years - be assured ANY rod bearing on a eight cyl. Packard can "go" if it is the "poured babbet" type.

My old friend Charly Last (you old hand Packard Twelve buffs will probably know that name) used to have a standing bet with anyone who could drive a Packard with post-war babbbet for more than 2,500 miles without wrecking the crank-shaft from a failed rod bearing. We never had a "taker" !

It is too easy to "do it right" and get a modern "precision" style insert in there.

If the primary purpose of your classic era Packard is to weigh down your trailer between car shows, to keep it from blowing away in the wind, then and only then would I say you MIGHT get away with poured babbet for a while.

Do it right, folks - car engineers who came up with, and without fail NOW USE EXCLUSIEVELY, "insert" type rod bearings, are smarter than us. Do it right, and get out of your Packard, the kind of service it is capable of.

[flackmaster]

Please keep the community informed as to whether you successfully (in current terms) re-babbit your existing shell, or have success identifying a modern insert and have your rod machined to accept.