Autopsy of Broken "B" Engine

[Bob Bidonde]

While returning home from a fall foliage run last year, the #4 connecting rod punched a hole in the side of my Model "B" engine. At the time, I was on a highway going 63 MPH in my Victoria.
The 1st indication that something was going wrong was a whirring noise like a turbine spooling down Then in a few seconds, the whirring turned into a violent banging. After a ping noise, the banging subsided a bit, and the engine kept running. I pulled to the side of the road and found a large hole in the block alongside of the starter motor.

The failed engine is now out of the car, completely dismantled and this is what I found:
>One of the studs in the #4 connecting rod failed, the cap loosened, the babbitt overheated and spun out of the rod & cap. The rod cap bent from being slammed by the spinning crankshaft, and the bent cap pried the 2nd nut off. Then the cap departed altogether and wound up in the dip tray;
>Examination of the failed stud looks like a fatigue crack started, and when there was insufficient material to carry the cap loading, the stud completely failed in tension;
>While flailing around, the #4 connecting rod bent severely, and turned the piston 90 degrees. The rod scrubbed a chunk out of the #4 piston and bashed-up the bottom of the #4 cylinder bore;
>Also while flailing around, the #4 rod slammed into the #3 rod and bent #3 just below its piston;
>The is metal debris babbitt and shims throughout the engine;
>The #4 piston came close to but did not hit the cylinder head.

Fortunately, the career of the broken "B" cylinder block is not over. A fellow club member is going to make an educational cutaway of it.

 

[Jemelton#]

Ouch! bet that won't buff out. Sorry for your loss.

 

[jack backer]

That looks like a fresh build, sorry for your loss. I respectfully contend with your failure analysis, the rod bolt failure could have been a result of the catastrophe, not a cause. I feel that a bearing failure as indicated by the galling and heat evidence on the crankshaft journal was the root cause of the event, the rod bolt failure occurring afterward the bearing seize, most likely from impact.

as we used to say in the shop "that's a lousy place for a window"..that block could be repaired.

 

[Bob Bidonde]

My failed engine story has some bright spots. I met Jersey Mike and bought a ready to run rebuilt Model "B" engine from him. I am having fun "Play Dates" with my friends in the Model A Ford Club of Long Island to change engines in my Victoria.
Also, having the transmission out of the car provided an opportunity to inspect the needle roller bearings in it. I am happy that in my opinion, the bearings I bought from Bratton's are as robust as the original factory parts. However, I did see evidence that the transmission input shaft was spinning in the pilot bearing. The shaft's journal measures about 0.030" less in diameter than the pilot 0.668" diameter pilot bearing ID. So I am again experimenting with a fix of the shaft. Over the years, an undercut developed in the shaft. Theoretically, the shaft should not spin in the pilot bearing. I have filled the slight undercut with J B Weld that I will abrade for a line fit into the bearing.

 

[Bob Bidonde]

Jack,
Your analysis is also rational, and I will keep it. The babbitts in the other 3 connecting rods had spec clearances and no indication of damage. This engine was professionally rebuilt and had about 5000 miles on it.

 

[rotorwrench]

One thing that a lot of rebuilders may need to do if they don't already, is to perform some form of non-destructive testing on the connecting rods and crankshaft. Whether magniflux, dye penetrant, or eddy current, it dosen't matter as much as just doing something to detect small fatigue cracks before they can become broken parts. That is about all a person can do to lessen the possibility of catastrophic failure.

Sorry for your loss. Good B engines are getting fewer and farther between.

The pilot bearing should be a loose fit but I agree that .030" is way too loose. .0015 or maybe a bit more would be better. A lot depends on how frequently the clutch is disengaged and how long an interval before it is either re-engaged or shifted to neutral and re-engaged.

 

[Ray in La Mesa]

OUCH! Been there, done that. My. "B" lost #4 also but I saved the block & a patch was braised over the hole of the crank case. It's running great now with inserts. When it develops the dreaded piston-valve cracks I'll be switching back to an "A" block.

 

[chrs1961815]

That's why inserts are better imo. But there are many people running engines with babbit fine.

 

[J Franklin]

Your story helps to explain why a lot of old car owners don't drive at peak MPH.

 

[jack backer]

OUCH! Been there, done that. My. "B" lost #4 also but I saved the block & a patch was braised over the hole of the crank case. It's running great now with inserts. When it develops the dreaded piston-valve cracks I'll be switching back to an "A" block.

Some believe cracking relieves internal stress,that pinning and seats/sleeves are a good repair

 

[BRENT in 10-uh-C]

That's why inserts are better imo. But there are many people running engines with babbit fine.

Many MORE stock connecting rods that have been converted to inserts have come apart causing damage (...such as above) than what refurbished cast-bearings in rods have. That damage on Bob's engine is likely more of a result where the rebuilder failed to inspect and Magnaflux the connecting rod BEFORE the rod was ever reconditioned (-repoured). I do this routinely even on stock Model-A rods, and I have failed more than a few core rods when I was repouring due to suspect areas around the rod stud. I don't take a chance.

While some might argue this is yet another valid reason to use aftermarket connecting rods, I feel the brutal reality is that there are WAY more (by percentages) original connecting rods that are successfully restored/refurbished which never experience any form of failure which refutes that theory that new replacement rods are necessary for reliability and longevity.

Also, from my perspective as a Model-A engine rebuilder (-both stock and hi-performance), there really is not any truth to stating one style of bearing (inserts vs. cast/poured) is superior to the other based on facts. Just as in the instance of Bob's failed rod, this was likely due to the rebuilder's poor craftsmanship than by the design of the component that failed, ...and whether the rebuilder chooses to cast a bearing or install an insert, poor craftsmanship can cause failures in either.

 

[jack backer]

This one "stumped the chump" (not hard to do) this is new babbit on an engine I have that was under construction by a master machinist at Aerojet. Its not a high lead based babbit,its very hard,like tin (unscientific scratch testing)...but the color you see is actual,just wonder if anyone has seen it before

 

[DJ S]

This one "stumped the chump" (not hard to do) this is new babbit on an engine I have that was under construction by a master machinist at Aerojet. Its not a high lead based babbit,its very hard,like tin (unscientific scratch testing)...but the color you see is actual,just wonder if anyone has seen it before

Never seen that color babbitt... looks like that cap is missing oil wells.

 

[Big hammer]

Insufficient oil will cause any bearing to fail. The bearing side of the broken stud is worn more than the other side, that rod was spinning for a while wearing the bearing down. Secondly there is a hot spot on the bottom side of the piston, that engine wasn’t happy and finally said I’ve had enough. Looking at what’s in the oil pan would be interesting

 

[jack backer]

Never seen that color babbitt... looks like that cap is missing oil wells.

It’s a main cap

 

[goodcar]

Your story helps to explain why a lot of old car owners don't drive at peak MPH.

Bingo!!

 

[Ed in Maine]

Hello Bob, sorry to see such a fatal end to the B motor. I have just one question? Why on earth were you driving at 63 mph? Were you leading a line of cars on the interstate?

I hope you have a good project day installing the new B engine. Ed

 

[Synchro909]

When I read that you where travelling at 63 mph, I thought to myself "I hope he was in overdrive. That motor won't last at those revs."
It was only about 3 weeks ago that I was driving a friend from the US to one of our club's events in my '29 Tourer. I had just exited a tunnel and was still going up hill at 50 mph in O/D when he commented that we seem to lug our cars more than they do. I wondered what sort of revs they cruise at because to me, 50 mph, even in O/D is no where near lugging. I've read on here many times, people saying that a Model A should be able to run at 60+ mph all day. I don't believe that and the likes of Bob's experience is why.
Bob, were you using O/D when it happened? What is the diff ratio?

 

[McMimmcs]

Hello Bob, sorry to see such a fatal end to the B motor. I have just one question? Why on earth were you driving at 63 mph? Were you leading a line of cars on the interstate?

I hope you have a good project day installing the new B engine. Ed

If you do the crime you do the time. Bingo twice !

 

[4bangerbob]

I lost a rod bearing many (50?) years ago. It was #3 rod bearing, original babbit bearing set to .0015" clearance. Driving to fast for a prolonged period on a hot summer's day was source of the problem IMO. As soon as I heard the engine start knocking I shutt it off and coasted to a stop in neutral. I got lucky in that only damage was loss of babbit on the con rod.

I had the rod rebabbited, polished the crank journal with some fine emery paper, reinstalled and ran the engine for several thousand miles after that. Just drove a slower.

I felt I was lucky when I see ventilated blocks and bent con rods.