Rod Babbit Failure

[Earle]

I mentioned, in an earlier post (related to a high-compression head discussion), the recent failure of the babbit (cracking and delamination) in all four of my connecting rods.

Here (I hope) are photos of the delaminated babbit. Cause?? - bad alloy?? - bad/cold pour?? - other workmanship issues?? - increased loading from a high-comp. head?? Too hard to tell now.

The babbitting work was done 25 years and 6500 miles ago. About 2500 miles ago the rods were visually inspected perfectly good when I had the engine rebuilt. So the rods were left alone. A 5.5:1 hi-comp. head was installed during the rebuild. This deterioration happened since then. Coincidence?? Can't tell.

I had the bad rods replaced with "new-insert" rods. We'll see how they hold up. (My wallet isn't holding up very well.)

(Ignore the blue tint to the photos. It's from a blue plastic tarp that was overhead when I shot the photos.)

Earle

 

[MikeK]

Definitely a grain size issue, if you look at the fractured structure above the "2010" on your second photo. Also internal gas porosity if you look at the collapse fracture pattern near the center of the oiling 'X'. Why? Absolutely inept melting and holding practice. NOT necessarily a temperature or 'too much remelt' issue as some may claim. Yes, temp and remelt may exacerbate porosity and large grain, but there are other melting practice faults that are the initiators.

I taught metal casting, mostly foundry and investment casting, for 28 years. My first questions to anyone with a babbitt pot are what alloy, how do you degas it, and what do you use as a grain refiner prior to pour, and how long do you hold it after the final degas and grain refinement? The answer to the last few Q's is inevitably "Huh?". That's why I will always use inserts and NEVER have anyone who does model A work do a babbitt job for anything I own. If you want to hear "Huh?" again, ask what their protocol is to degas, pig, and de-skull the melting pot between runs, and at what time interval?

If you like to gamble, go to Vegas, have castings made by someone with a backyard foundry, or get babbitt poured for a model "A". All bear possibility for a winning outcome.

 

[Kevin in NJ]

Mike,

You have me curious.

I know about using argon to de-gas (remove hydrogen if I remember correct) aluminum alloys.

In the considerable technical literature on babbitt I have not read about de-gassing the babbitt. I have run across keeping the pot clean, speed of melt, keeping the ratios in small pots and stirring the mix among the concerns with babbitt metal. I am in no way saying you are wrong, I have had a devil of a time just trying to find the stuff I have found so far and I am sure I have missed info along the way.

What gas are we trying to remove from babbitt and what would be the process for babbitt?

Do you have recommended reading on the subject?

Thanks!

 

[Earle]

Thanks, Mike. It's quite a science when done correctly. And it has to make you wonder - or stand in awe - at the folks who did it consistently-right 60 - 70 - -80 years ago without knowing all of the intricate science that metallurgists know today.

Makes me feel warmer about my "insert" decision.

Earle

 

[James Rogers]

Earle, your rods were not tinned properly, it's just that simple! If the forged rod saddle is tinned properly if the babbitt fails, the tinning will remain, no matter how the failure occurs. I have seen rods that had failures with the babbitt that the tinning was correct and the tinning was still in place (the babbitt didn't fail). Your rod in the picture has NO Tinning on the failed area. This is not rocket science just look at the result for the answer. Just try to peal some of the babbitt away from areas that did not fall off and you will see what I mean.

 

[Earle]

Appreciate your comments, James. Tinning would have kept the babbit adhered to the base rod metal?

On "Insert" bearings, like the ones in the new insert rods I just had installed ($$$), is there tinning on the base insert material before the thin layer of babbit was applied??

How thin is the babbit on inserts? It had better hold up way longer than this stuff did!

Earle

 

[allen]

Sorry for your rod failure, my question is do you think prolong sitting had anything to do with this, what i mean is after 25 years and only 6500 hundred miles or was this 65 thousand miles , If only 65 hounded would the oil run dry between runs just a thought

 

[James Rogers]

Appreciate your comments, James. Tinning would have kept the babbit adhered to the base rod metal?

On "Insert" bearings, like the ones in the new insert rods I just had installed ($$$), is there tinning on the base insert material before the thin layer of babbit was applied??

How thin is the babbit on inserts? It had better hold up way longer than this stuff did!

Earle

Insert bearings are totally different in the way they are manufactured. I will say, if you lug the motor (as many do) it will destroy the new rods and inserts just like this did. The babbitt rods were bad to begin with since the babbitt might have been old or used and the tinning was inferior. I know of a builder in S. GA that has no idea how to tin the rods and main caps so, he drills the items and expects them to last, which they won't. You need to run the motor a little harder than you think it might need and it will be happier. As for the tinning, that's what helps the babbitt stay put. Once the babbitt fractures there is nothing to hold it. Kind of like painting your house after 25 years and not scraping the old paint off first.

BTW, the babbitt on the new inserts is in the neighborhood of .010 thick I do believe.

 

[Earle]

Allen,

Yep - 6500 - 6900 miles in 25 years!

Sadly, as my Dad's health and interest went down hill, only about 4000 miles were put on the car from the time of this engine rebuild & rod-pouring in about 1984 to his passing in 2001 (17 yesrs). I added the rest of the miles, up to today's 6900 after inheriting the car.

According to James, the lack of tinning was a major contributor to the failure. I understand his explanation that the base rod metal was NOT properly prepared before the babbit was poured. But I'd have to bow to the expertise of James and others here on the question of long times between running causing babbit failure. I could immagine momentarily-dry bearings showing bad scoring and smearing (but cracking and delamination too?) but the oil would be there after only a few revolutions of unloaded start-up wouldn't it? I vote for the lack-of-tinning explanation - so far.

During all those years in my Dad's garage, the engine was run briefly (~1/2 hour idle?) every 2-4 months. Just about as often, between those runs, the plugs were removed, a little oil was dropped into the cylinders, and a couple minutes of "fast" hand-cranking was done to try to keep things oiled up. Maybe that was not enough for any "splash action" to get into the rod babbits.

Oh well, the forensics are interesting and I do hope to eventually know the real "cause of death" but I'm down the road with my new set of inserts and I sure hope all this water is well under the bridge for a long, long time to come.

Thanks, Gents...

Earle

 

[Kevin in NJ]

James is right in that you should see tinning.

Try peeling off the rest of the babbitt and see if it was tinned anywhere else. Properly tinned, the babbitt will not want to come off too easy. BTW, when we talk tinning I mean tin, not lead. If you use lead tinning you can run in to problems since the lead melts at a lower temp. The babbitt could get hot enough to melt the lead tinning which would not be good for adhesion.

As far as inserts go, they can and do fail and they are not the end all save all many hope they will be. They tend to fail completely so you will need a tow home. While the rods you see in the picture may have been noisy, you could have driven for a while with them. In fact they probably were driven for a while in a bad state.

Some facts on bearings:
Either inserts or babbitt will give you 50,000 miles of use when done right.
Either will fail if they are not done right.
With inserts you are more likely to need a tow home and have a damaged crank/block.
Babbitt might be driven for another 100 miles in a failing state and the damage limited to needing new babbitt.

Always remember that the little 4 cyl engine we have in our A's is a precision built engine. Ford did not throw them together. Many parts were precision machined and balanced. A machine shop rebuilding the engine to the factory prints would be building to what they call race car standards.

 

[James Rogers]

Allen,

According to James, the lack of tinning was a major contributor to the failure. I understand his explanation that the base rod metal was NOT properly prepared before the babbit was poured. But I'd have to bow to the expertise of James and others here on the question of long times between running causing babbit failure. I could immagine momentarily-dry bearings showing bad scoring and smearing (but cracking and delamination too?) but the oil would be there after only a few revolutions of unloaded start-up wouldn't it? I vote for the lack-of-tinning explanation - so far.

During all those years in my Dad's garage, the engine was run briefly (~1/2 hour idle?) every 2-4 months. Just about as often, between those runs, the plugs were removed, a little oil was dropped into the cylinders, and a couple minutes of "fast" hand-cranking was done to try to keep things oiled up. Maybe that was not enough for any "splash action" to get into the rod babbits.



Thanks, Gents...

Earle

Earle, I have dis-mantled many engines that were newly rebuilt or stored fresh and what I find is cause for failure of many that sit for long periods. The oil or assembly lube used in most engines will turn to putty after a time and block the oil holes. This can happen in as few as several months to a few years. Running it for short periods will not eliminate this problem. This is why any motor that has sat for a long time needs to be completely disassembled and cleaned with a petroleum solvent and all oil channels rodded out. To rod out the mains I use a 22 cal. gun cleaning brush and rod. The rods can be cleaned with a q tip or other suitable item.

Hope this clears up some of your questions and hope also the inserts last as long as you will need them.

I also agree with Kevin in his assessment of the tinning.

 

[MikeK]

Mike,

You have me curious.

I know about using argon to de-gas (remove hydrogen if I remember correct) aluminum alloys.

In the considerable technical literature on babbitt I have not read about de-gassing the babbitt. I have run across keeping the pot clean, speed of melt, keeping the ratios in small pots and stirring the mix among the concerns with babbitt metal. I am in no way saying you are wrong, I have had a devil of a time just trying to find the stuff I have found so far and I am sure I have missed info along the way.

What gas are we trying to remove from babbitt and what would be the process for babbitt?

Do you have recommended reading on the subject?

Thanks!

Kevin, you had to ask, so...

To start, you mentioned hydrogen gas. Hydrogen is a problem in many metals and alloys, but is not the only gas that can cause porosity. It is possible for dissolved oxides to reduce, liberating oxygen porosity in some alloys, notably those containing any percentage of copper or noble metals. I'm no Sn alloy expert, but early practice with tin/ antimony/ copper alloys relied on additions of a phosphorous-copper alloy inoculant to deoxidize and degas the melt.

No one hears about use of P/Cu alloy inoculation in field use of babbitt alloys today, but it's use in other non-ferrous alloy practice is currently commonplace, most notably in Cu based alloys. In certain Al alloys it also serves as a grain refiner. Alternative non-ferrous alloy degassing methods include: 1) Pigging an alloy in a long V shaped metal mold, encouraging the gas to erupt at the surface and away from the chill effect of the sides, then re-melting. (primitive, works!) 2) Stirred in additions of reactive halogen compounds. (AKA "fluxing", only works if vigorously introduced and well-mixed beneath the surface and into the melt) You can also directly flux with chlorine or florine gas bubbled through the melt. 3) Gas Disolution- bubbling a non-reactive gas (Argon, Nitrogen) through the melt, causing the offending gas in the alloy to go out of solution and into the inert gas. (common current practice) 4) Vacuum chamber degassing. Vaccuum degassing is a takeoff of #3, but the lack of an atmosphere above the melt causes the dissolved gas to diffuse from the surface. This method requires active stirring, often done by electrical induction of eddy currents, thus magnetic stirring. This happens in any conductive liquid, it does not meed to be 'magnetic'. (Highly effective, an industry standard best method if you can afford the induction melting and vacuum chamber equipment) 5) Hybrid approaches. One of my favorite tricks with aluminum alloy heats I ran was to combine #2 & #3. I used to bubble about 8 oz of Freon 12 (99 cents a can!) through a 60 lb heat of Al. just prior to casting of gas-sensitive and critical parts. The halogenated hydrocarbon would partially break down yielding chlorine and fluorine gas as a flux, and also would act as a disolution agent. (highly effective, but one of the R12 breakdown products was phosgene gas, a nerve gas used in WWI ) Did I say use positive ventilation??

Grain refining: This is accomplished by providing many nucleation points for crystalization to occur during solidification, resulting in more, thus finer grains. In non-lead babbitt alloys both iron and nickel intermetallics are candidates. One alloy, XXXX Nickel babbitt, was originally concocted to effect grain nucleation, although I doubt anybody currently selling Four-Ex really has any clue or tests for the effect. Iron (Fe), which is supposedly held low as a contaminant in 'new' babbitt, is responsible for the nucleation, or lack thereof, in most non-lead babbitt alloys. It is held low to begin with because it forms compounds that fall out of the melt to the bottom of the pot and fuse together into large particles that may result in objectionable inclusions. Iron will dissolve (like salt in water!) into alloys and metals from the ladle and pot. This provides the nucleation for fine grain, and this should occur just before casting. Unfortunately it also 'eats' the ladle and pot, shortening service life. As a result, dumb following dumber practice handed down has led to many iron pots and ladles purposely coated with a zircon ceramic wash, or 'seasoned' in other ways to prevent the metal from touching the iron. Good for an iron pot holding many metals/ alloys, but bad for babbitt if the iron is your only grain refinement source.

The 'Skull": In metal casting the melting vessel, be it a metal 'pot' or of ceramic material, often a crucible, will accumulate deposits of insoluble compounds that are denser than the alloy. It is called a skull because in an empty, cold crucible it can often be popped out in one piece, looking like the top of a skull. (The lighter insolubles float to the top as 'dross', called slag in ferrous alloys, removed by skimming.) That stuff at the bottom of the pot serves two very negative functions. 1st, it serves as a base to promote crystallization of intermetallics necessary for the proper and desired physical properties of the alloy in the final part. In effect, it progressively screws up the composition of the alloy by removing them. 2nd, 'stirring the pot', necessary in babbitt to disperse the heavier grain nucleation intermetallics, will also stir up inclusions comprised of huge crystals that will provide internal stress risers weakening the part. If a babbitt pot is not drained into pigs and cleaned between runs, expect less than perfect results. Touring an engine rebuilder and seeing frozen metal in a holding pot is not best practice.

James Rogers also pointed out the lack of a tinning bond on the rod pictured by Earle in this thread, and he is absolutely correct, it should have been done. Keep in mind this is not the only cause of the failure. It just speeds up the process by increasing stress across grain boundaries in the babbitt while it is under compressive load. Main bearings in model A's are never tinned, as it is virtually impossible to physically 'tin' cast iron without first forming an inner bonding layer of another metal. Possible, but $$$.

 

[Earle]

Thanks again, Gents....

Earle

 

[Kevin in NJ]

I always like to ask interesting questions.

Thank you for taking the time to explain the process. You may have given me a couple clues how to tie together other stuff I have read. Not sure what all I will do with it all, but I am glad you took some time to write.

 

[James Rogers]

James Rogers also pointed out the lack of a tinning bond on the rod pictured by Earle in this thread, and he is absolutely correct, it should have been done. Keep in mind this is not the only cause of the failure. It just speeds up the process by increasing stress across grain boundaries in the babbitt while it is under compressive load. Main bearings in model A's are never tinned, as it is virtually impossible to physically 'tin' cast iron without first forming an inner bonding layer of another metal. Possible, but $$$.

Finally, someone agrees with me about tinning cast iron.The center and front caps are tinned the same as the rods since these caps are forged steel and will produce the same effect as shown on Earle's rod if improperly done.

 

[Stillrunners]

thanks...good read...gathering more info....and A-edumacation...

 

[Kurt in NJ]

I have an example of failed babbitt that was not due to lack of tinning, it was from my own car, it was a sudden total failure, all the babbitt crumbled at the same time, it was about 20 years ago, and being late for the parade I was going fast --not as fast as the car could go ,but well over 60, it felt like I drove over a telephone pole, then I heard the knock, I drove the last 3 miles to home much slower, with retarded spark.

The tinning saved the crankshaft, it was perfect, no marks at all, so I just replaced the rod --from the bottom.

 

[Dean Borchert]

Kurt: could you elaborate on taking the piston/rod "out the bottom"? I have never known one to come out past the crankshaft. TYVM DB

 

[Kurt in NJ]

I was being lazy, I didn't want to drain the cooling system, I pulled the rod & piston down as far as i could, rotated the crank for the best clearance, turned it about 45 degrees, took out the snap ring, then using 90 degree snap ring pliers in the hollow part of the wristpin , and moving both the rod and the pliers at the same time I slid the wristpin over enough to change the rod ---it won't work with a counterweighted crank, there is not enough room, it took a little wiggling of the piston, and the crank to find the best position.

I also proved how important balance is ---the replacement rod is 15 grams heavy, and I lost 5 mph top speed, the only change was the rod, and new oil, and some hylomar on the pan gasket, I do still have more vibration, but I do not push the car like I used to, I try to keep it under 55.