Installing a model B crank into A have some ?'s

1

12secvx

Member
This is my first post so hello to all. I figured you guys are the ones to ask this question to. I have a good A block and a standard B crankshaft I am wanting to get turned down to fit into my A. I also have a good set of rebabbitted A rods.my question is has anyone ran insert bearings on the mains and Babbitt A rods on a turned down to fit Counter weighted B crankshaft with good results? Thanks Ben
 
I looked into this recently and asked a similar question here on the barn. I received some very sensible advice and decided in the long run to forget it and just go with a new Burlington crank shaft on inserts. I had pretty much decided on Suzuki G13A or Daihatsu ED10 bearings and thrust but decided any gain was not going to be worth the trouble reinventing this wheel. I have another motor with a Burlington crank which has been excellent so I decided to go the same way again, partly because when (if) a rebuild is ever needed, a good range of undersized inserts are readily available and it's all been done by someone else already.
 
I guess my way of looking at is the A motor has worn main babbitts which will need replaced or have inserts install anyways. And the B crank needs turned as well. I guess I need to see what the cost of machine work would be. Can a B crank safely be turned down to A sizes on the mains and rods? It is it just defeating the purpose because it increases the bearing speed? But doesn't a Burlington crank basically just that a B crank with A rods and mains? It is drilled for oil pressure also right?
 
The Burlington cranks are manufactured to the original Ford blue prints as far as journal size etc. The cranks were designed with the counter balancing as part of the design. We have Burlington cranks in our sedan and roadster and really have enjoyed how nice they work. I would suggest that rather than cutting down a B crank and then having to counter balance it install a new Burlington crank.
 
JohnLaVoy said:
The Burlington cranks are manufactured to the original Ford blue prints as far as journal size etc. The cranks were designed with the counter balancing as part of the design. We have Burlington cranks in our sedan and roadster and really have enjoyed how nice they work. I would suggest that rather than cutting down a B crank and then having to counter balance it install a new Burlington crank.
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His B crank is already counterweighted, so it would be fine money wise to turn it to fit your bearings.
 
Yes it is a late 33/34 counter weighted crank that has standard journals. I have 2 rough B blocks that are cracked badly. So my plan was to use a good A block that I have that has only been bored .0025 over. I was also thinking of using a modified V8 oil pump or model B instead of the A if If I will help keep the insert mains happy.
 
If you turn down both the mains and rods you have not gained anything except the counterweights, you have not gained any strength. Many C cranks were turned down to A main size in the old days but B rod size was retained, giving both counterweights, bigger rod bearings and more crank strength due to basic design. I have installed a C crank in an A block but turned down the mains half-way to A size, using babbitt throughout. If I were to do it again I would use inserts and turn the crank to 1.800" and use B rods. The V8 pump is a very good idea.
 
Jim Brierley said:
If you turn down both the mains and rods you have not gained anything except the counterweights, you have not gained any strength. Many C cranks were turned down to A main size in the old days but B rod size was retained, giving both counterweights, bigger rod bearings and more crank strength due to basic design. I have installed a C crank in an A block but turned down the mains half-way to A size, using babbitt throughout. If I were to do it again I would use inserts and turn the crank to 1.800" and use B rods. The V8 pump is a very good idea.[/QUOTE

I was hoping you would chime in Jim. Thanks for you and everyone else's advise. So what main bearings inserts would you recommend using in order to get the 1.800"? Also would you recommend using insert or rebabbitted B rod? Thanks Ben
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12secvx said:
I guess my way of looking at is the A motor has worn main babbitts which will need replaced or have inserts install anyways. And the B crank needs turned as well. I guess I need to see what the cost of machine work would be. Can a B crank safely be turned down to A sizes on the mains and rods? It is it just defeating the purpose because it increases the bearing speed? But doesn't a Burlington crank basically just that a B crank with A rods and mains? It is drilled for oil pressure also right?
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Actually, a smaller diameter reduces bearing speed, NOT increases it.
 
you are probably correct but I thought I remember reading somewhere that the strength and reduced bearing speed is why the model B engines had larger rod bearing journals.
 
Well, imagine a shaft diameter of say, 2.5 inches. That is a circumference of about 7.854 inches. So if we put a dot on the shaft and rotate it exactly one revolution, our dot has traveled 7.854 inches. If the engine is turning 2,000 RPM, bearing speed is 1309 feet per minute. If we reduce the shaft diameter to 2 inches, the circumference is now about 6.283 inches. So our dot now travels only about 6.283 inches per revolution. So at 2,000 RPM, bearing speed is down to 1047 feet per minute (assuming my calculations are correct).
This is why big block Pro Stock drag race engines often use Honda rod bearings with a diameter of 1.88 inches, for less friction due to lower bearing speed.
 
If it was me I would not turn the rod dia to the A size. The weak part of the crank is number 4 rod journal. That is where they like to break. For a stock engine it would probably be ok. But why take a chance. The extra material would also help to take some of the twist out of the crank.

I would also keep the mains as big as I could. Sounds like Jim has the answer on that.
 
I had a B block which cracked when valve seat inserts were fitted. That left me with a counter weighted B crank and all the new parts I had purchased to overhaul the B engine. I also had an A block so decided to reduce the B crank mains diameter to standard A size and use A insert bearings. On the big ends I used the new insert B rods I had which were 20 under standard. The engine has done over 5000 miles now and runs nicely. My only issue is oil seep from the one piece rear main seal.

Cheers ,
Gavin
 
Gavin said:
I had a B block which cracked when valve seat inserts were fitted...
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That happened to me, only on my A block. Only mine didn't show up until I had everything assembled and installed back in the vehicle. Less than 50 miles and it was to do all over again. I also have a whole raft of new (well with 50 miles on them) parts that I can't use. (inserted rods, pistons, rings, valves, and what have you.)

I guess it's somewhat comforting to know that I am not the only one this has happened to.
 
IMHO, retaining the larger big end journals will improve the rigidity of the crank shaft and for that reason, I'd keep them but the standard Model A size would be fine for durability. I've never seen the rod bearings give trouble, even in babbit.
 
I have a B crank in my A block and I use a bearing from a older Mini cooper. I would have to look for the part number. I had no problem finding replacement inserts but I think the crank was originally mistakenly turned down to A size main journal diameter so I think if I were to do it again I would grind to larger size although I have stressed this crank quite a bit and it is still going !/4 mile or 1/10 mile at a time.
 
tbirdtbird said:
"I had a B block which cracked when valve seat inserts were fitted"
This happens more often than not. There is a shop not far from me that has ruined more B blocks because they don't get it.
B blocks are thinner in the valve area and I try to avoid them altogether.
You try not to use valve seats in an A either, but they will hold up better in an A.
THis comes up all the time. There is one poster that says he has never had a failure in his shop. Do not let that fool you....that is not commonplace.
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I don't put hardened seats in any A or B motor. I see no sense in removing good, solid cast iron (thus weakening the block) for the sake of a harder seat. Even an A block is prone to cracking from the exhaust valves to the cylinder (especially on Nos 2 and 3) if the motor gets hot. It is a flaw in Henry's design.
 
There is a Saturn rod bearing that is 1.850 ID and fits between the main bolts in the "A" block without relieving.
Works very well, especially with full pressure oiling. I just cannot imagine putting in inserts and NOT pressure oiling.
As for bearing speeds, yes, larger diameter equals more surface speed. Assuming that the bearing is properly lubricated, at our speeds is a non issue. My race motor has 2.500 dia bearings and spins much faster than 2k. I want to see a Mod "A" or "B" turn "ProStock" revolutions, from a distance I might add!
Valve seats, yep do those also, you just have to select the proper size and be careful at assembly.

Scat made some cranks to fit "B" blocks and uses "A" rods. For most people this is a fantastic combination and the machine work is Top Notch. Unfortunately, the combination doesn't handle high output very well and I have seen a couple broken cranks. Everything here on the "A", "B" is a compromise. Be realistic and you will have good results. Go past the edge and your wallet will remind you.

J
 
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