Babbitt 4th main versus ball bearing

[ewdysar]

I've have heard many times here that ball bearing 4th mains are bad, "it'll break your crank!".

But why? Does a babbitt 4th main have more "give"? Is it more about alignment? If a babbitted ball cap is installed "cocked", does it just wear in with slightly less contact when done? When a pan flexes, does the babbitt just wear at the edges during the flex? The ball cap that came with my disassembled speedster has noticeable "wobble" placed dry on the drive plate shaft, but I can't feel axial play

It seems that installed correctly, the results from both types of bearings would be identical. There are reports of some folks with 1,000s of miles with ball bearing 4th mains with no problem.

So what is the engineering reason against ball bearing 4th mains? I would like to dig deeper than the anecdotal tribal knowledge.

Thanks,
Eric

[TXGOAT2]

In some applications, a sleeve type bearing or bushing will do a better job than a ball bearing. I think it's related to the better vibration damping of the sleeve/bushing type bearing. The Hyatt type roller bearings were sort of a hybrid, with a lot of load carrying surface area compared to the point contacts with a ball bearing. With a ball bearing under load, only some of the limited number of point contacts wold be carrying most of the load.

[Art M]

Ball bearings do not do well when lubricated with dirty oil such as engine oil or with rear axle oil. Babbit is much more forgiving with dirt and is better in vibration conditions. Ball bearings accommodate some misalignment depending on the internal clearance.

Art Mirtes

[kelly mt]

I'm running two ball bearing and two babbitt mains. They all run fine with lots of miles and hard pulls on them. Care in shaft alignment when building a motor is important.

[big2bird]

The pan MUST be straight.

The bearing needs to be dialed in when the engine is on a stand VERTICAL.

Cranks break when these two important steps are skipped.

[dykker5502]

Ball bearings do not do well when lubricated with dirty oil such as engine oil or with rear axle oil. Babbit is much more forgiving with dirt and is better in vibration conditions. Ball bearings accommodate some misalignment depending on the internal clearance.

The ball bearing 4th main offered by the vendors have sealed rollerbearing which not only seals the rear of the engine but also keeps the clean oil within the bearing and the dirty oil in the transmission/engine.

[ewdysar]

The pan MUST be straight.

The bearing needs to be dialed in when the engine is on a stand VERTICAL.

Cranks break when these two important steps are skipped.

Agreed. This seems important for both types of ball caps. Is there any reason that this process is easier or less critical with a Babbitt ball cap versus a ball bearing ball cap?

Eric

[ewdysar]

The ball bearing 4th main offered by the vendors have sealed rollerbearing which not only seals the rear of the engine but also keeps the clean oil within the bearing and the dirty oil in the transmission/engine.

To me, that sounds like a ball bearing 4th main is an improvement over the stock Babbitt ones.

Reducing oil leaks with modern solutions, i.e. cam shaft seal, pedal shaft seals, axle seals, etc. seems to be embraced by most of us, excepting the more hard-core originalists.

But if installed, a ball bearing ball cap should be removed as quickly as possible because “it’ll break your crankshaft”

Still wondering,
Eric

[TXGOAT2]

F-series Farmall tractors of the 1930s ran the crankshaft in two huge ball bearing mains. They were a very durable tractor.

[speedytinc]

Search "ball bearing 4th main"
This debate has been had.
Interesting take away - Herm Made a unit from modified original ball caps. No hacking of the DS ball.(Like)
He only sold to reputable builders only. I understand. You cant buy one, slap it on & expect success AS DESIGNED.
Anything but a dialed in output & straight crankcase will lead to problems such as a broken crank & the corresponding bad mouthing of the MFG.

There have been several versions available in the past. An example: A cast brass unit requiring a 3/8" hack off the DS ball.
I have seen/fixed the mess after one broke in the casting. Appears the rear end hit a good bump, slammed the cut DS into the brass body & broke.
Who would have thought a brass body wouldn't hold up like a steel body? There were also units made of aluminum.
I recall a recent post where the BB 4th main was re-installed & the flange wouldn't sit flat. More wrench Scottie!

I believe A properly designed, built & installed BB cap could be a good thing. With proper alignment, A BB cap is no more likely to break a crank than a babbited unit. I believe perceived damage goes back to alignment. How many "assemblers", other than professional motor builders, indicate the output shaft before finish assembly? How many reading this don't know it's necessary?

As a side note regarding the use of a bronze bushing.
More clearance than for a babbit bushing is required to not seize. That makes for extra oil washing out the U-joints grease.
I have tried O-ring seals, but not successful long term. I am back to babbit.

[ewdysar]

Search "ball bearing 4th main"
This debate has been had.
Interesting take away - Herm Made a unit from modified original ball caps. No hacking of the DS ball.(Like)
He only sold to reputable builders only. I understand. You cant buy one, slap it on & expect success AS DESIGNED.
Anything but a dialed in output & straight crankcase will lead to problems such as a broken crank & the corresponding bad mouthing of the MFG.

I believe A properly designed, built & installed BB cap could be a good thing. With proper alignment, A BB cap is no more likely to break a crank than a babbited unit. I believe perceived damage goes back to alignment. How many "assemblers", other than professional motor builders, indicate the output shaft before finish assembly? How many reading this don't know it's necessary?

I've done the search and noticed that almost all of it refers to "somebody told me..." The forum discussions have gotten to the point that if a BB cap is visible in a photo about something else, folks cant say "get rid of that BB ball cap" fast enough. In a recent thread about someone's very damaged triple gears, one suggestion started with "First issue I see is that accessory 4th main bearing !" which has nothing to do with the triple gears, of course.

Given your second paragraph, are you also saying that if one cannot (or choses not to) align the output shaft appropriately, then a babbitt ball cap is safer, less likely to break a crank? If so, why? I would surmise that most broken crankshafts came from engines with babbitt 4th mains because over 15 million were installed.

Apparently, not all BB ball caps result in broken cranks and not all broken cranks come from BB ball caps. So why do we believe that there is a causal relationship between the two? Is insufficient alignment a more determining cause of broken cranks, regardless of the ball cap type? Perhaps some folks are replacing a babbitt cap that was damaged by mis-alignment or excessive flex, thinking that the BB cap would "fix" it.

I'm just trying to find out if there is a practical difference in using either type of ball cap. If so, there should be a reason. If not, is this more of an old wives tale or superstition?

And I agree about hacking the DS ball, in my case, the ball cap will covered by an auxiliary transmission, no modification of the DS ball needed.

Eric

[RajoRacer]

One needs to specifically view the LACK OFF lateral movement of the B.B. 4th main - it is secured to the transmission output shaft with 0 lateral. Ford designed lateral movement between the driven plate & clutch drum w/steel washers, which we all realize, when up to operating oil temperatures, some of that lateral clearance goes away. With the B.B. 4th main cap "fixed" to the driven plate, whether a press fit or "glued", even more lateral is lost - IMO.

I had a conversation with Herman many years ago regarding such lateral movement being achieved with the driven plate shaft being broached for at least one keyway, if not two opposite keyways with a bushing slotted internal to the bearing.

[speedytinc]

I am not saying a babbitted cap will prevent a broken crank or cure a misalignment.
In fact, a worn/chewed up babbit 4th main is a quick sign of a serious misalignment. Seen this many times.
A perfectly made BB cap would not cause a problem. However, many past & present examples fall way short.
As far as some claiming a BB cap must be removed - you dont believe everything you read here do you?

Rajo makes a point about lateral movement. If I read it correctly, Herms units are not glued or press fit, but allow some forward & aft movement.

[TXGOAT2]

Ball or roller bearings are commonly used at the rear of the mainshaft in later transmissions. It's common to see a babbit lined bushing at the rear tailshaft when it also serves to support a sliding driveshaft yoke. I don't think a ball or roller 4th main on a T could contribute to crankshaft problems as long as it was properly engineered AND properly installed. It is absolutely essential with the Model T to have the "4th main" correctly aligned with the other 3 main bearings. A straight crankshaft, crankshaft flange, and transmission shaft are also critical.