The Ford Barn

afuncar · 12-12-2012, 01:07 PM

what is the maximum allowable cut on acrankshaft

afuncar · 12-12-2012, 04:25 PM

have a model a crank counterbalanced and sized .030 main and .040 rods can anyone tell me if its o.k. thankyou.

Kohnke Rebabbitting · 12-12-2012, 05:43 PM

Quote:

Originally Posted by afuncar

have a model a crank counterbalanced and sized .030 main and .040 rods can anyone tell me if its o.k. thankyou.

If they ground it on center line, centering on the gear area, with out the gear, and on the out side surface of the rear flywheel flange, check rear flange for run out, and cracked checked it.

If they didn;t grind any tapor in the journals, and put in the propper Radis?

Should be good to go.

mach0415 · 12-12-2012, 06:56 PM

The other question is if the crankshaft is heat treated. On modern cars, cutting too much material starts to expose softer tempered steel/iron, and re-tempering is necessary to longevity - not so much because of heat build-up as much as tensile strength of the journals. Is this an issue applicable to our A's?

PC/SR · 12-12-2012, 07:09 PM

I had the same dimensions on a crank, the counterbalance guy said not to do it, because he would have to take .010 more off to true it up after welding on the counterweights. Just my experience.

Pete · 12-12-2012, 07:17 PM

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With babbit, if everything was done properly, there should be no issues.
With inserts, you have to size the crank to available bearings.
Sometimes not possible.

J and M Machine · 12-12-2012, 07:22 PM

Quote:

Originally Posted by mach0415

The other question is if the crankshaft is heat treated. On modern cars, cutting too much material starts to expose softer tempered steel/iron, and re-tempering is necessary to longevity - not so much because of heat build-up as much as tensile strength of the journals. Is this an issue applicable to our A's?

On Model A's that isn't the case for them to remove to much metal to affect the heat treating. You are correct about the modern day "Racing" where if you remove more than .010-015" then the crank would have to be case hardened again.
http://www.jandm-machine.com/crankshaftGrinding.html

afuncar · 12-12-2012, 09:17 PM

you guys have been very helpfull thank you. all input is appreciated; the size I stated are the finished sizes,

James Rogers · 12-13-2012, 06:21 AM

I never use cranks that are ground more than .030 in customer engines unless, the crank belongs to the customer and it is the one he wants. I did one once that the customer wanted ground .060 and inserts installed. I thought he was nuts and I wouldn't warranty the job but, it is still running and no problems. That was 2 years ago and the car gets run daily.

redmodelt · 12-13-2012, 11:56 AM

For Babbitt bearings: Depending on your mechanist, check with them first. Not all cranks need to be ground in .010 increments. Some guys are set up to use pre-set boring tools, other can adjust for what ever size you need. When Tom does cranks and rods he just has the crank ground to clean up. He then bores the mains to that size, same with the guy that does our rods.

afuncar · 12-13-2012, 03:00 PM

the crank was counterbalanced first and then machined to .030 mains and .040 rods which is the finished size ready to be used. If I didn't have so much into machining I would have used a different crank. I just wanted some experienced opinions, I am willing to eat the loss if its too risky. thanks to everyone for their input.

afuncar · 12-13-2012, 03:02 PM

also the engine will be fully inserted.

Tom Wesenberg · 12-13-2012, 04:18 PM

Standard is great, but you should be OK, especially since you have counterweights to help eliminate crankshaft flex.

12-12-2012, 01:07 PM	#1
afuncar Senior Member Join Date: Dec 2012 Location: coquitlam b.c. canada Posts: 130	safe size to machine crankshaft what is the maximum allowable cut on acrankshaft

12-12-2012, 04:25 PM	#2
afuncar Senior Member Join Date: Dec 2012 Location: coquitlam b.c. canada Posts: 130	Re: safe size to machine crankshaft have a model a crank counterbalanced and sized .030 main and .040 rods can anyone tell me if its o.k. thankyou.

12-12-2012, 06:56 PM	#4
mach0415 Senior Member Join Date: Jul 2011 Location: Chester, SC Posts: 162	Re: safe size to machine crankshaft The other question is if the crankshaft is heat treated. On modern cars, cutting too much material starts to expose softer tempered steel/iron, and re-tempering is necessary to longevity - not so much because of heat build-up as much as tensile strength of the journals. Is this an issue applicable to our A's? __________________ Thanks, Mark in SC "We the unwilling, led by the unknowing, are doing the impossible for the ungrateful." -- By society, who is still arguing over who said it.

12-12-2012, 07:09 PM	#5
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,279	Re: safe size to machine crankshaft I had the same dimensions on a crank, the counterbalance guy said not to do it, because he would have to take .010 more off to true it up after welding on the counterweights. Just my experience.

12-12-2012, 07:17 PM	#6
Pete Senior Member Join Date: May 2010 Location: Wa. Posts: 5,409	Re: safe size to machine crankshaft Sponsored Links (Register now to hide all advertisements) With babbit, if everything was done properly, there should be no issues. With inserts, you have to size the crank to available bearings. Sometimes not possible.

12-12-2012, 09:17 PM	#8
afuncar Senior Member Join Date: Dec 2012 Location: coquitlam b.c. canada Posts: 130	Re: safe size to machine crankshaft you guys have been very helpfull thank you. all input is appreciated; the size I stated are the finished sizes,

12-13-2012, 06:21 AM	#9
James Rogers Senior Member Join Date: May 2010 Location: Asheville,NC Posts: 3,104	Re: safe size to machine crankshaft I never use cranks that are ground more than .030 in customer engines unless, the crank belongs to the customer and it is the one he wants. I did one once that the customer wanted ground .060 and inserts installed. I thought he was nuts and I wouldn't warranty the job but, it is still running and no problems. That was 2 years ago and the car gets run daily. __________________ http://www.model-a-ford-4bangers.com/

12-13-2012, 11:56 AM	#10
redmodelt Senior Member Join Date: May 2010 Location: Portland OR Posts: 6,342	Re: safe size to machine crankshaft For Babbitt bearings: Depending on your mechanist, check with them first. Not all cranks need to be ground in .010 increments. Some guys are set up to use pre-set boring tools, other can adjust for what ever size you need. When Tom does cranks and rods he just has the crank ground to clean up. He then bores the mains to that size, same with the guy that does our rods.

12-13-2012, 03:00 PM	#11
afuncar Senior Member Join Date: Dec 2012 Location: coquitlam b.c. canada Posts: 130	Re: safe size to machine crankshaft the crank was counterbalanced first and then machined to .030 mains and .040 rods which is the finished size ready to be used. If I didn't have so much into machining I would have used a different crank. I just wanted some experienced opinions, I am willing to eat the loss if its too risky. thanks to everyone for their input.

12-13-2012, 03:02 PM	#12
afuncar Senior Member Join Date: Dec 2012 Location: coquitlam b.c. canada Posts: 130	Re: safe size to machine crankshaft also the engine will be fully inserted.

12-13-2012, 04:18 PM	#13
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: safe size to machine crankshaft Standard is great, but you should be OK, especially since you have counterweights to help eliminate crankshaft flex.