Autopsy of Broken "B" Engine

I drove my stock 1930 coupe with 3.78 rear end at 55 mph for years. Only once did I get to 65 and only for a few miles. (I was young.) Terry says that even with the Burtz block with modern bearings, pressure lubrication, and 2 inch journals, not to try and keep up with modern traffic. He says that is because of the aerodynamics of a brick and that air under the front fenders will lift the front end.
 
I don't know if he will weigh in here but I have been talking to Jim Brierley and he believes RPM's are a good thing and he has some evidence to support it. Jim? Got your ears on? I will be the first to say that I do not have enough experience with A or B motors to justify an opinion of my own.
 
Damn, sorry for your loss. Even if you already have another engine, it's still work and money that could've been saved.


What did your rebuilder say to such a failure after only 5000 mls? I'd have a long talk with him if I were in your situation.
 
I have two engines running new Burlington cranks running on inserts. BOTH of them have experienced rear main bearing failures because the lubrication was inadequate. Others have reported the same problem here. I know mine were to do with sustained highish revs and I suspect the others were too.
If anybody can put another engine together, it's Bob Bidonde but I bet he would rather not have to.
 
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The sad end of Bob Bidonde's Model B Engine
 
There is some evidence (anecdotal) that the center main journal on a stock model A crankshaft deviates up to .001 at high rpm due to torsional vibration, basically the dynamically balanced crankshaft vibrates like a tuning fork when spun hard. Automotive engineers developed the harmonic balancer to counteract this, but I dont have any proof that the ones available for an A are beneficial, other than sound theory.

The other reason for not driving fast is inherent in a model A.. even with everything on the chassis spot on you start to 'out run' the suspension.16" wheel tire widths help but the handling characteristics go to hell above 60 in my opinion..braking is not an issue..
 
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In my opinion, my road speed (63MPH) likely accelerated a fatigue crack in the broken connecting rod stud, but speed on that occasion was not the cause of the crack initiation. I will be posting pictures of the failed rod cap later today.
 
In addition to my model A I have a 42 Willys Jeep. There are some other owners who say that the rod bolts (which are replaceable in a Willys motor) should not be reused and can cite examples to support their belief. Don't shoot the messenger, I am only passing this along as an idea that would support the broken stud diagnosis.
 
Benson said:
I will not say anything about what my opinion of using too much RTV is as I have seen this problem too many times while taking apart used engines which had chunks of RTV floating around in the oil pan.
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The previous owner of my A had silicone subsitute as an oil pan gasket as well. Can someone explain to me why this is even done? :confused:


The gaskets are readily available and not even cheap. I would never even think about using RTV for this. If no gaskets were available I would at least use proper liquid gasket material and not silicone from a DIY market.:mad:
 
J Franklin said:
I noticed the overheated journal and agree it was overrunning the oiling capability.
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The journal damage was from steel on steel, no babbitt.
I suspect the stud on the rod broke after the initial problem, more of an interference problem with the block.

The fact of the matter is that journal ran long enough to displace all the babbitt and grind stl on stl. I would not be surprised if the cam shaft also has witness marks from the rod hitting before breaking.

And, FWIW, the orange silicone in the picture is a gasket, looks to be made from a sheet, probably 1/8" thick.

I wish Bob the best on this, but it is already expensive. J
 
johnneilson said:
The journal damage was from steel on steel, no babbitt. ...
I wish Bob the best on this, but it is already expensive. J
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The journal ran hot to look like that. once the babbit was gone there is plenty of room for cooling oil. Steel on steel would leave it shiny.
 
bavArian said:
The previous owner of my A had silicone subsitute as an oil pan gasket as well. Can someone explain to me why this is even done? :confused:


The gaskets are readily available and not even cheap. I would never even think about using RTV for this. If no gaskets were available I would at least use proper liquid gasket material and not silicone from a DIY market.:mad:
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I can only guess at why it's done. We are all bombarded many times a day with advertisements extolling the value of this or that product over its competitors. The total of all these claims is an accrued belief that newer is better. We Model A owners know that is not so but it's so ingrained in us that it's difficult to overcome.
Now, along comes silicone, a wonder new material that seems to be the answer to all of our problems. Now read the instructions on the tube. They tell us to apply a thick bead, fit the sump (pan), wait a while, then tighten. A ham fisted or impatient person will overdo it and end up with silicone where it shouldn't be. Viola! Another ruined engine.
When fitting a sump, I use no more than a dab of silicone at the four corners at the bearing caps. All four of those combined would be no ore than the size of a pea.
 
I personally would not drive a stock Model A chassis at a high speed, primarily for safety reasons. A destroyed Model A is cheap to replace compared to life and property. That is just me.
I know for a fact that some years, the Corvette owners manual states that if you race the car/engine for any length of time add an extra quart of oil. The theory is that prolong high revolutions tends to keep the oil in the upper part of the engine and will starve the oil pump. That particular 350 cubic in Corvette normally holds 7 quarts. Maybe the same theory would apply to a Model A?
Most of our A’s oil systems are gravity feed, oil pressure doesn’t mean much in this instance. A high output pump just might put more oil up in the valve chamber. Gravity system will lubricate/drain only so fast. The higher the pressure/volume the more the oil will stay up top.
 
J Franklin said:
The journal ran hot to look like that. once the babbit was gone there is plenty of room for cooling oil. Steel on steel would leave it shiny.
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Help me understand, if enough oil clearance is all that is required, then why do you need babbit or bearings? just run it stl on stl.
 
Post #35...I have often wondered about oil coming and going in an engine with susttained RPM?
 
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