The Ford Barn

pooch · 06-23-2017, 05:21 PM

I think I may need a crank grind.

Will do some measuring this morning.

I bought some std bearings and they say to suit 2,138.

I see on the van pelt site that the size is 2.139.

I think i have come across a size of 2.138 - 2.139 allowing a 1 thou tolerance.

If I grind .010 under what should I aim for with modern oils , as these sizes were original specs back then.

I think a grinder can do .0005 tolerances ?

I know some say . go ask your machinist, but I like to be forearmed first, so I can state what I want.

Lawrie · 06-23-2017, 05:33 PM

Make sure you have the bearings first,sometimes they are hard to get,barnfind 08 should have them,
the crank grinder should know the size from his master books,but a copy of the ford service bulletins page wont go amiss.
lawrie

pooch · 06-23-2017, 06:15 PM

Lawrie, mine are locked bigends, 8BA rods, double drilled crank, C69 A .

GOSFAST · 06-24-2017, 08:08 AM

Hi "pooch", the ONLY correct way to get the desired clearances (rods or mains) when grinding a crank for any undersize is to mount the brgs in position, measure the inside i.d. (vertical) and subtract the desired clearance and cut the crank to that specific size. Your clearances will be "dead-on".

There are some variables to check beforehand, you need to confirm the actual rod and main bore numbers for a start! These should be within specs before proceeding forward.

When machining any parts with "tolerances" you can end up with numbers that aren't the best to use?? These "tolerances" can end up being "stacked" one way or the other. If you have absolutely no accurate way to get these numbers you are always safer cutting the crank to the "low" dimensions. For example, on an 8BA with a 10/10 cut this would be 2.488" on the mains and
2.128" on the rods, both these numbers are considered "low".

Thanks, Gary in N.Y.

P.S. Under ideal conditions you want to be very close to .002" on both the rods and mains. Slightly larger is better than smaller. You should also measure the cam brg clearances as well, but not too many options there for any corrections. We've been using "Teflon" coated cam brgs to help make things just a bit tighter in this area.

pooch · 06-24-2017, 05:22 PM

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Ok thanks for info Gary,

Will measure the best I can and ring the machinist .

06-23-2017, 05:21 PM	#1
pooch Senior Member Join Date: Sep 2010 Location: South Coast NSW Australia Posts: 2,596	46 239 crank bigend size. I think I may need a crank grind. Will do some measuring this morning. I bought some std bearings and they say to suit 2,138. I see on the van pelt site that the size is 2.139. I think i have come across a size of 2.138 - 2.139 allowing a 1 thou tolerance. If I grind .010 under what should I aim for with modern oils , as these sizes were original specs back then. I think a grinder can do .0005 tolerances ? I know some say . go ask your machinist, but I like to be forearmed first, so I can state what I want.

06-23-2017, 05:33 PM	#2
Lawrie Senior Member Join Date: May 2010 Location: Qld, Australia Posts: 4,215	Re: 46 239 crank bigend size. Make sure you have the bearings first,sometimes they are hard to get,barnfind 08 should have them, the crank grinder should know the size from his master books,but a copy of the ford service bulletins page wont go amiss. lawrie

06-23-2017, 06:15 PM	#3
pooch Senior Member Join Date: Sep 2010 Location: South Coast NSW Australia Posts: 2,596	Re: 46 239 crank bigend size. Lawrie, mine are locked bigends, 8BA rods, double drilled crank, C69 A .

06-24-2017, 08:08 AM	#4
GOSFAST Senior Member Join Date: May 2010 Location: Long Island, NY Posts: 1,052	Re: 46 239 crank bigend size. Hi "pooch", the ONLY correct way to get the desired clearances (rods or mains) when grinding a crank for any undersize is to mount the brgs in position, measure the inside i.d. (vertical) and subtract the desired clearance and cut the crank to that specific size. Your clearances will be "dead-on". There are some variables to check beforehand, you need to confirm the actual rod and main bore numbers for a start! These should be within specs before proceeding forward. When machining any parts with "tolerances" you can end up with numbers that aren't the best to use?? These "tolerances" can end up being "stacked" one way or the other. If you have absolutely no accurate way to get these numbers you are always safer cutting the crank to the "low" dimensions. For example, on an 8BA with a 10/10 cut this would be 2.488" on the mains and 2.128" on the rods, both these numbers are considered "low". Thanks, Gary in N.Y. P.S. Under ideal conditions you want to be very close to .002" on both the rods and mains. Slightly larger is better than smaller. You should also measure the cam brg clearances as well, but not too many options there for any corrections. We've been using "Teflon" coated cam brgs to help make things just a bit tighter in this area. __________________ http://www.stromberg-bulletin.com/me...berg-equipped/

06-24-2017, 05:22 PM	#5
pooch Senior Member Join Date: Sep 2010 Location: South Coast NSW Australia Posts: 2,596	Re: 46 239 crank bigend size. Sponsored Links (Register now to hide all advertisements) Ok thanks for info Gary, Will measure the best I can and ring the machinist . Last edited by pooch; 06-24-2017 at 05:28 PM.