Autopsy of Broken "B" Engine

[George D]

What weight and type of oil were you using in that engine? Asking for a friend

 

[J Franklin]

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.

I bet you already know that the babbitt allows for a softer wear surface that can be easily renued. It protects the crankshaft and could be repaired on the side of the road if need be back in the day. I can't determine if this block had babbitt or insert bearings.

With proper oil clearance there is the proper oil film and cooling needed to not seize a rod and bust a hole in the block.

 

[Bob Bidonde]

I checked the oil feed to the rear main bearing and it is well open, so oil starvation is not the cause. The damage to the crankshaft journal was done during the connecting rod cap failure. Here are some pictures including the bearing cap.
1st & 2nd pictures are of the #4 Connecting Rod Cap. Note the broken stud trapped in the cap;
3rd picture is #3 Connecting Rod which was bent from collision with flailing #4 Connecting Rod;
4th picture is all piston assemblies;
5th picture shows damage to block from being slammed by the #4 Connecting Rod;
6th picture shows the deformation to the dip tray which is bent down about 3/8";
7th picture is the #4 Piston & Rod Assembly. The rod was so badly bent that it could not be removed from the block, so we bent it by prying it with a 2x3 stud until is straightened enough to get it out of the block.

 

[jack backer]

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.

Dan Iandola ran aluminum rods directly on a journal..but I bet you know that, you're just sandbagging us fact is the hydrodynamic principle doesnt care what the bearing or journal surface is, it only care about the clearance.. get .001 oil clearance per inch of journal diameter and you will ride on a film of oil.

 

[jack backer]

Along the lines of what jack said...my center main has a copper tube feeding oil to it now.

If you run the 'full flow'( as good as you can get) valve cover oil filter with that lube line from the oil pump body to the center main bearing you'll actually pressurize the bearing with pressure created by the oil filter restriction, not much,but its better than gravity.

there is a valid argument that the reduction of clearanced bearing area caused by the diameter of the lube feed hole diminishes the gain from the lube line trick.

 

[Benson]

From post #43:

"I checked the oil feed to the rear main bearing and it is well open, so oil starvation is not the cause."


I have no idea how the pressure feed to the rear main has ANYTHING to do with rod bearing #4 getting the oil from it's dipper that it needs!

Is this crank drilled for full oil pressure and we were not told about it.?

 

[johnneilson]

Dan Iandola ran aluminum rods directly on a journal..but I bet you know that, you're just sandbagging us fact is the hydrodynamic principle doesnt care what the bearing or journal surface is, it only care about the clearance.. get .001 oil clearance per inch of journal diameter and you will ride on a film of oil.

Jack,
I have heard stories about Dan and some of his ingenious work. The key to this is to have two dissimilar materials, this prevents molecular transfer from one side to the other. Remove the babbit and you have a problem.

Joe Gemsa ran steel valves directly on the aluminum heads, no seats.
Once the seat and valve settle, no issues.

And, just to clarify, if you burn the babbit out of the bearing, you will have too much clearance, on the rods I mod for inserts, you would have approximately .040-.050 clearance. That will not sustain a "hydrodynamic wedge" even with grease.

J

 

[johnneilson]

From post #43:

"I checked the oil feed to the rear main bearing and it is well open, so oil starvation is not the cause."


I have no idea how the pressure feed to the rear main has ANYTHING to do with rod bearing #4 getting the oil from it's dipper that it needs!

Is this crank drilled for full oil pressure and we were not told about it.?

Benson has a point, but beyond that, the mains shown in the pictures are not properly grooved for a drilled crank.

I have seen failures on newly built motors before where the inserts are not set up correctly. This usually results in a spun bearing insert. If the operator is diligent and shuts down the motor before too much damage occurs, it can be saved.

I also notice the broken stud and the other stud on #4 do not have cotter pins. HMMM

John

 

[McMimmcs]

Seems like there were lots of problems in addition to excessive speed!

 

[Flathead]

This integral rod bolt design was not one of Ford's better ideas, at least not for the long haul. I have torqued up rod bolts and had this stud pop right off of the rod before even getting up to torque. There is a lot of stress at the root of the stud and no radius to protect it, over time they often fail. These rods have to be magnifluxed with the cap OFF so that the stud can be seen and checked. This is a different design than other engines with replaceable rod bolts and most machine shops will mag the rod with the cap still on. You will not spot any rod stud cracks if the cap is on.
I suggest that your stud was compromised and finally let go, once that happens the rest is history.

 

[Gene F]

If you run the 'full flow'( as good as you can get) valve cover oil filter with that lube line from the oil pump body to the center main bearing you'll actually pressurize the bearing with pressure created by the oil filter restriction, not much,but its better than gravity.

there is a valid argument that the reduction of clearanced bearing area caused by the diameter of the lube feed hole diminishes the gain from the lube line trick.

Interesting thought. I'll ponder that. The shop I used for my engine always puts that little line on there. The I.D. of the thing is not that big.

 

[jack backer]

Got one on mine too..positive flow to the bearing helps.

 

[Synchro909]

I accept that there is merit in that argument, I think it is overcome by the increased oil flow through the bearing by pressurising it. I drilled the middle main bearing cap and put an oil line from the pump to it in my touring engine. That engine has done more work than an unmodified bearing would have allowed and it's still going. If it weren't so fiddley to do, I'd pressure feed all of the main bearings from the top.

 

[Stingray70]

Bob, very sorry about your misfortune but glad you posted this. Interesting discussion. I am curious what oil you were using in this engine and how often you ran at (for a Model A) those high speeds?

 

[Benson]

...

 

[daveymc29]

Not to one up anyone, but I have a crack near the bottom of number three bore into the water jacket and am looking for some type fix for that. It is an "A" block with incerts and has less than 2000 miles since it was built. The crack can be felt with finger nail running up and down the bore with the piston all the way bdc. I believe the crack to be about one inch long. Engine ran great, just sent a cloud of steam out the tail pipe. Am I day dreaming that somewhere there is someone that can repair this? The bore is .060 over. Any idea are welcome, including going back to the builder.

Dave Mc Arthur

 

[Kurt in NJ]

It must have made a lot of noise before the big noise
What are the threads like in the nut that came off? It coming off broke the other stud off the rod.
What does the Babbitt in the pan look like, melted, or chunks?

 

[jack backer]

Not to one up anyone, but I have a crack near the bottom of number three bore into the water jacket and am looking for some type fix for that. It is an "A" block with incerts and has less than 2000 miles since it was built. The crack can be felt with finger nail running up and down the bore with the piston all the way bdc. I believe the crack to be about one inch long. Engine ran great, just sent a cloud of steam out the tail pipe. Am I day dreaming that somewhere there is someone that can repair this? The bore is .060 over. Any idea are welcome, including going back to the builder.

Dave Mc Arthur

Sleeve the one bore is a solution if I'm reading this right, the crack is in the cylinder bore.Any scoring in the cylinder itself?

 

[Bob Bidonde]

Here is the info about the motor oil I use. It's Mobil 1 10W30 which is a synthetic blend. Oil starvation at the #4 Connecting Rod was not the case. If it was, this engine would have failed long ago.

The rod stud failed from fatigue which initiated at the last thread in the stud. As the rod cap bent away from the crankshaft journal, the babbitt failed. As the rod flailed around, the castle nut on the remaining stud stripped-off. That's when the rod was thrown off of the crankshaft and was rammed until it punched through the block.

Benson, I will answer your questions. Regarding my comment about the rear main bearing, you are correct, it has no bearing on the failure. The crankshaft is a stock Model B with counterweights.

 

[jack backer]

Failure analysis is interesting work and a good way to avoid repeating a mistake, if one occurred .If I may rebut your statement, its highly unlikely a catastrophic rod stud failure would result the bluing and scoring of the crankshaft journal (as shown in your pictures) and the total removal of the babbit (it appears it occurred by friction) on the rod side bearing. In most cases little friction heat evidence is shown during a rod cap catastrophic failure, during which within the next few engine revolutions major damage occurs.