crankshaft minimum specs

[beast_3]

What are the minimum bearing sizes for a Model A crankshaft? I'm planning a engine rebuild & want to see if my crank is worth rebuilding.

Also, what is involved in straightening a bent crank? If it worth doing or just better looking for a straight one or a Burlington crank?
Many thanks!
Bob

 

[James Rogers]

I generally don't use a crank for babbitt that is less than .030 under. With that said, I have done a couple of motors that were .040 and .060 under with inserts. I thought the customer was nuts to do this but I do what thew customer wants, I just don't have to warranty it. Those are both still running and both are touring motors. Inserts are available in undersizes up to .060 under standard.

Straightening a crank is something best left up to the grinder. I don't do them but, my crank grinder does and I am very happy with his work.

 

[George Miller]

What are the minimum bearing sizes for a Model A crankshaft? I'm planning a engine rebuild & want to see if my crank is worth rebuilding.

Also, what is involved in straightening a bent crank? If it worth doing or just better looking for a straight one or a Burlington crank?
Many thanks!
Bob

I would go for the Burlington crank. A lot of grinders grind the cranks with out the radius at the journals. That is not good but lots of them do it because they do not want to waist there wheel by putting a radius on them. If you grind your old crank send it to some one that does A cranks all the time.

 

[Kevin in NJ]

How do you know the crank is bent?

The crank wears at the opposites sides from the ends to the center.

There is a lot to consider with the crank and only a few places have a clue how to deal cranks, let alone the A crank.
When dealing with the A engine you need to understand it was a precision built machine built to what is considered racing specs today (no I am not kidding).

Here is a little thing on crank grinding I wrote up: Crankgrinding

I would contact J&M Machine and Kohnke Babbiting, both are present on this board and understand the A engine for further information about crank grinding.

 

[Chris in CT]

Hi Beast, You have some very good information and advice posted above. I would double what James said above and not go below 0.030 in. on the regrind. You can check for runnout (bent crank) by mounting the crank on Vee-blocks on the front and rear main, and then setting your dial indicator on the center main. Runnout should not exceed 0.002 in. (If you think Kevin above was exaggerating, consider that the runnout spec for a small block Chevy is 0.006 !!!) Use someone who is experienced for straightening and grinding your crank. Happy motoring.

Chris

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www.burlingtoncrankshaft.com

 

[mach0415]

How do you know the crank is bent?

The crank wears at the opposites sides from the ends to the center.

There is a lot to consider with the crank and only a few places have a clue how to deal cranks, let alone the A crank.
When dealing with the A engine you need to understand it was a precision built machine built to what is considered racing specs today (no I am not kidding).

Here is a little thing on crank grinding I wrote up: Crankgrinding

I would contact J&M Machine and Kohnke Babbiting, both are present on this board and understand the A engine for further information about crank grinding.

Amen to you brother on the racing specs comment. When I started out in these old cars 5 years ago (cars > 60 yrs. old), my eyes popped out of my head when I started to read some of the specs. Modern non-race engines' specs, for the most part seem to have more clearance between moving parts, when compared to these old engines. Its pretty sweet to think of the precision that was built into these things back in the day, especially given the type of technology available to make that happen. I think we do not give enough credit to our pioneers. Modern diesel engines require the builder to get within .0001" clearance on certain items, so that finesse is still a part of modern diesel production engine building to that degree today.

 

[MikeK]

There is another alternative, should you decide to go new rather than risk counterweight welding and regrind. The SCAT crank, 100% machined in the USA. Everything, including the counterweights, is machined. Available drilled if you wish to run pressure. I believe they require use of a (Terry) Burtz rear seal. That requires an accurate align-bore when the babbitt is done or the block is prepped for insert bearings. Here's a catalog link, look on the second page. SCAT Link

 

[J and M Machine]

Straightening a crank sometimes is very interesting to say the least.
After cleaning and magnafluxing the crank you have to place the crank on the vblocks and then indicate to find the bend. after straightening then you move to the outers and correct those, then move back to center and you may have to start all over. The radius of the crankshaft is where it's strength is.Most of the cranks we see unless original have the radii ground off due to the prior crankgrinder not willing to redress a bigger radius in his wheel.
Once the radius is gone then crank strength is reduced.
Shown is a Model T crank radius at 1.25" there's not much of a journal so all the more to have a stout radius.
We installed the Burlington cranks with great success but as of yet we haven't used the Scat ones.

Can anyone reply and tell us if the Scat Model A cranks are actually machined here as I thought they were machined and forged offshore.?

www.jandm-machine.com

 

[Chris in CT]

Straightening a crank sometimes is very interesting to say the least.

We installed the Burlington cranks with great success but as of yet we haven't used the Scat ones.

Can anyone reply and tell us if the Scat Model A cranks are actually machined here as I thought they were machined and forged offshore.?

www.jandm-machine.com

Hi John (Mike?), The Scat cranks are a very good product, rough forged in India. Because Scat has the facility to do so, the cranks are machined here in the USA pretty much on a custom basis. They will cost you $500. more than the Burlington unit, however. Hope you folks are busy up there in Mass!

Chris

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www.burlingtoncrankshaft.com

 

[James Rogers]

I have installed 2 Scat cranks and like them. They compare to the Burlington, which I also use exclusively for Model A's and the Scat for Model T's because Chris doesn't have one for a T. If he did I wouldn't use the Scat because I like the Burlington.