How much better is a B block than an A?
 

I've had my 3 Model A engines for a while, but haven't done anything with them yet. I have recently obtained a B block and counterweighted crankshaft. My intentions were to put the B crank in one of my A blocks, that is until I saw the difference in main journal diameters.


Now for the big question...


Is it better to machine an A block for the B crank, or clean up the B block and use my extra A stuff to finish it up?

Re: How much better is a B block than an A?
 

Use the A block. The B blocks are well known for their ability to develop cracks for no good reason.

Re: How much better is a B block than an A?
 

Better to machine the B crank to fit the A mains than to do it the other way round. (or so I've been told by the master mechanic in our club.)

Re: How much better is a B block than an A?
 

I go along with that. To take this thread to the next stage, what would you use for bearings. I believe there are a few options for inserts that will go in with a slight relief at the bolts or is it better to just buy a new counter weighted crank shaft and be done with it?
I ask because I have a B crank here but as expected, the block was cracked. I have plenty of decent A blocks though.

Re: How much better is a B block than an A?
 

Thinking about this, would it not be perfectly fine to run poured babits? The whole idea of running a counterbalanced crank is to 1) reduce vibration, which will 2) lessen the dynamic load on the bearings. Obviously, inserts would be optimal, but I would think poured bearings would hold up just fine in a street/touring A-banger.

Thoughts???

Re: How much better is a B block than an A?
 

Why not have the B block crack tested ,Let that be the decider .
Get a copy of Jim Brieleys book "4 bangers and Me"
Lots of good info in there also see what he has acheived with Babitt.

Re: How much better is a B block than an A?
 

As far as I can see, the ratio of cracked B blocks to sound ones is about 10 to 1 and if it's not cracked now, it probably will be soon.
Babbit has a lot going for it. I think many opt for inserts because A, they have had some bad work done with babbit in the past or B, they have heard stories and imagine that inserts must be better. It ain't necessarily so!

Re: How much better is a B block than an A?
 

Six of one half dozen of the other. Both have their pluses and minuses. Pick the one in the best overall condition and start from there.

Re: How much better is a B block than an A?
 

Re: How much better is a B block than an A?
 

Also have it Pressure Tested.
I am in the process of building a B with a Yapp Riley OHV. The much larger bearing size is the plus I can't ignore. After all the larger bearings were Ford's idea.
Cracking comes from overheating. During the last eighty some odd years cars were used and abused. These days owners of our fine Fords don't subject them to the abuse they suffered in the past. Better cooling systems kept clean and rust free help a lot.

Re: How much better is a B block than an A?
 

Inserts are definitely better if you are running a high compression head. Babbitt was designed when engines had 4 to 1 compression.

Re: How much better is a B block than an A?
 

Cracks around the valve seats can be easily fixed.

Re: How much better is a B block than an A?
 

If I try to go with the B block, will I have to use the B bellhousing/transmission/oil pan? Or can I use my A parts?


(Showing my ignorance...sorry)

Re: How much better is a B block than an A?
 

Brett,

good question, you can use the "A" trans, bell housing and pan but the pan will require a little work. You see, the rear main is larger on the "B" motor so the radius at the rear will need to be opened up, also, the "B" rod nuts will hit the side next to the rail edge. This can, and should be corrected by using APR rod nuts which are smaller OD and much stronger.
Or, you can cut the bell housing extension off the "B" pan.

OK, you mentioned the "B" block is cracked, where? Valve seats can be replaced/installed but it must be done correctly. Otherwise you will have leaks at the seats. This applies to "A" motors as well. One of the biggest problems I have seen are the head studs and repairs that someone has attempted. From drilling off center to butchering the holes down through the boss etc.

A friend of mine always mentions that perfect blocks do not exist, it is a matter of your persistence to use old junk. Do not despair though, keep looking, there are many good serviceable blocks around.

J

Re: How much better is a B block than an A?
 

John,


Thanks for the reply! First off, I have no idea of the condition of my block, so questions concerning my use of the B block are purely hypothetical. As I get closer to discerning my direction, I'll be more thorough in my inspections.


Secondly, will the B crank accept A rods? I'm guessing , since I must turn down the main journals, that I would be required to turn the rod journals as well to use A rods. Would that not eliminate the rod nuts and rail edge from occupying the same real estate?


Finally, thanks to all that have commented here! I'm still learning and want to make good decisions when I finally start assembling my banger.

Re: How much better is a B block than an A?
 

Brett,

OK, understand, you are doing some worst case investigation prior to the surgery.
Kind of like getting the second opinion before the primary care appointment.

You have to ask yourself truthfully the intended use of the motor/car.
If stock configuration for enjoyment, some modifications are beneficial and some just overkill.
That said, "B" block allows for more HP and has a pressure fed oiling system to mains with larger journals. This along with drilling the crank to feed oil to rods and some compression will yield a nice motor that will last a long time.

I do not recommend drilling the "A" crank for oil to the rods as the journal is so small the potential to break increases substantially.

I have put the "B" crank in the "A" block before, not recommended in my opinion.

Either Babbit or inserts if done correctly are satisfactory, since I do not have access to a good Babbit facility, I use inserts.

Of course you have to understand that these opinions are just that, my opinions. YMMV

Best of Luck, Mr. Brierleys book is very good, you may hear opinions that do not agree with him but I doubt that those opinions have as much experience.

John

Re: How much better is a B block than an A?
 

Again, I say thanks John.


My intent is for a nice peppy banger for my '31 Tudor. Its going to be a little hot-roddish for this site, but since you asked....


The car will be basically a stock sedan with '40 juice brakes and a dropped front axle. Not much else done mechanically, except for the motor. I'd like to lighten the flywheel and adapt a V8 pressure plate.


As for the engine, I have a police head as well as the "C" head from the B. I also have an alloy aftermarket downdraft intake and an assortment of Ford/Holley 94s. The only other "trick" part I have is a Mallory distributor.


At some point, I have a Halibrand 201 center section that I would like to stuff my '40 rear parts into. That would give me tunable gearing for my style driving.


Thanks again for all the answers and opinions...and keep 'em coming!

Re: How much better is a B block than an A?
 

With the weaknesses of the "B" Block known I am hoping that someone will start reproducing them with the weakness upgraded.

Re: How much better is a B block than an A?
 

There would probably be a better market for an A block with the improvements that were made to the B block. I have 2 Model B vehicles but can't put my finger on any more (except for a few that show up at meets).

Charlie Stephens

Re: How much better is a B block than an A?
 

see this thread https://www.jalopyjournal.com/forum/...-works.616056/

John