counterbalanced B crank in model A

T

trctrdr

Member
I just bought a model B crank with counterweights (not the ones that have to be removed to grind crank) I want to install it in mt 29 A coupe. What's involved in this swap?
Thanks M&M
 
What you have is commonly called a 'c' crank. Calling them that may be incorrect but everyone knows what that is and it saves time explaining it. In the old days most people just turned the C crank down to A size, B rods must be used. I recently did what you are asking about and turned the crank half way between A & B size, I then had the block babbitted but if I were to do it again I would turn to 1.800" and use Corvair inserts, other bearings may be available at that size too??? The mains on the A are 2" between bolts, 1.800" leaves enough room for inserts without hitting the bolts when line boring. Have fun!
 
Jim Brierley said:
What you have is commonly called a 'c' crank. Calling them that may be incorrect but everyone knows what that is and it saves time explaining it. In the old days most people just turned the C crank down to A size, B rods must be used. I recently did what you are asking about and turned the crank half way between A & B size, I then had the block babbitted but if I were to do it again I would turn to 1.800" and use Corvair inserts, other bearings may be available at that size too??? The mains on the A are 2" between bolts, 1.800" leaves enough room for inserts without hitting the bolts when line boring. Have fun!
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I have thought about using a B crank and offset grinding it to Model A size and build a stroker motor. I would have to make or find some pistons to use to keep the piston from hitting the head. Got any ideas Jim?
 
James Rogers said:
I have thought about using a B crank and offset grinding it to Model A size and build a stroker motor. I would have to make or find some pistons to use to keep the piston from hitting the head. Got any ideas Jim?
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I'm not Jim but I have a "B" crank with the rod journals ground offset .157" giving a total stroke of 4.564". Mains are stock "A" dia. I'm using "Skokie" rods modified to use different inserts. I'm using J and E pistons with a corrected compression height of 1 .750. There might be a SBC piston with correct height. I have a 4.000" bore.
 
I've used a B crank in an A block that was off set ground .187 for a total stroke of 4.625. Mains ground to A size. I used stock A rods with custom 4" Ross pistons. In fact, I have 2 of them. Both are broken. I would not recommend that much offset!!!!!!

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I have a "B" crank in my car. Just have the mains ground to stock "A" size. Use the "B" rods which have a larger bearing, which is a good thing.

To use the "B" rods, you will need to "bump" out the "A" pan to give the larger "B" rods the needed clearance. If you look at a "B" pan you'll see what I mean.

You can use a "B" pan but you will have to splice in part of a "A" pan to make the rear of the "B" pan to make it fit the rear mains area.
 
I just had a C crank off-set ground 1/8" FOR A 1/4" longer stroke, am going to build it for my speedster. I had large radius ground into the crank for strength. Most guys go to .187" but I decided .125" was enough. I think the radius is the secret for strength.
 
Crazydaddyo said:
Looks like I'm in for a race next year at the Antique nationals. ;)

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Yes, I believe you will be. After all of the griping this year I will probably have to run my car in the same class as you and Jim if I can find a driver. My grandson drove last year but now is away in college studying beer drinking.
 
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