Crank ground size vs new insert rod size

G

gogrannygo

Junior Member
Hi every one. We are new and I have been designated to post - hence - gogrannygo. Trying to figure out how to post. We have a 1928 tudor and the motor completely out and disassembled. The mechanic is going to re-bore the head for new .040 pistons. The crank is out of round where the connecting rods attach and he is going to grind it. We need to order new insert rods, but MAC's can't tell us the size of the journal bearings so he will know what size to grind the crank to. Can anyone give us the standard size that the crank should be ground to in order to fit the new rods? If it's .010 or .020 for the oversize rods, what should the crank be ground to in order to fit the new insert connecting rods? If we buy the rods and they are too small, we'll have to send them back. Is there some chart somewhere that will give this information? We are going to use the new insert connecting rods - twice as much $ as babbitt, but that was his suggestion. Thanks in advance. Gogrannygo
 
Standard throw size is 1.4995/1.5000 so -0.020 would be 1.4795/1.4800. That's the least of your problems! Grinding a Model A crank is a can of worms- there are more ways to wreck it than the the average crank grinder operator could ever know! Make sure your crank grinder has worked with Model A's before. A standard grinder stone will put the wrong fillet radius on an A crank- 1000 miles down the road and. . snap!
 
Crankshaft grinding shop have a number of stones with different radius on them to suit the most common modern cranks that they machine everyday and are redressed regularly but only as needed
the stones have a limited life and cost plenty so redressing has a cost and takes time not something most shops will do for a 1 off job normally they will use a stone that is dressed the closest not really what you want
Best is to find a shop that has the correct stone or be prepared to pay for the redress $$
Around me only 1 shop in the state has the correct stone and charges for the regrind plus the time to set it up and I pay happily just to get the correct job
 
Hey GGG, Welcome to Fordbarn! And if this is your first A, welcome to the hobby. OK, one crucial piece of advice for the crank grinder: fail to follow it and disaster will follow.
Do not use the factory centers for locating the crank on the grinder. These were "lost" many years ago during the truing (straightening and grinding) processes at the factory. If the only way the crank will mount in the grinder is between dead centers, then the centers must be re-cut to render a true crankshaft.
Here's what matters: the timing gear surface at the front end of the crankshaft must run true to 0.0002 (not a typo, ten-thousandths here!) on center when the crank is set-up for grinding. Similarly, the OD of the flywheel flange must run true to 0.0002 rotation at the rear end of the crankshaft when the crank is set up for grinding.
However the crankshaft is mounted in the grinder, these two specifications are imperative. Louse them up, and the performance of your engine will suffer accordingly... Good Luck, and Happy Motoring!
 
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Snyders sell the new rods and bearings for less. Snyders price is $471, when I checked Mac;s their price was over $600. Unless you are going to install a oil filter I would suggest using babbitt bearings instead of shell type inserts. Babbitt bearing rods in a non filtered environment are more forgiving to dirt and other matter in the oil.
 
Thank you everyone. It is our first time to work on a Model A. Helping our daughter with her 1928 Tudor. We have a 1930 pickup that's been in our barn for over 40 years. Figured we had better get with it, or time would run out. Now you have us scared. I just called BBB and I am really worried now. Seems like a little too much moving around for me. Says it's his shop, but not accredited with BBB and not his name on the business. He says he can do the re-bore for the pistons and just needs the pistons to make proper bore/clearance. When we dropped it off, he had motors everywhere. Does an exchange on rebuilt ones and seemed very knowledgeable abut the As. Anyone know of anyone in DFW/Fort area that does the crank that knows what they're doing.
Thanks. (P.S. - I love being listed as a Junior Member - haven't had the honor of being called a Junior in many years.)
 
contact the Ft Worth club, esp Logan.
too bad you don't have your PMs turned on you'd get more help that way. Many of us won't post in the open forum
 
Chris in CT said:
Do not use the factory centers for locating the crank on the grinder. These were "lost" many years ago during the truing (straightening and grinding) processes at the factory. If the only way the crank will mount in the grinder is between dead centers, then the centers must be re-cut to render a true crankshaft.

Here's what matters: the timing gear surface at the front end of the crankshaft must run true to 0.0002 (not a typo, ten-thousandths here!) on center when the crank is set-up for grinding. Similarly, the OD of the flywheel flange must run true to 0.0002 rotation at the rear end of the crankshaft when the crank is set up for grinding.
However the crankshaft is mounted in the grinder, these two specifications are imperative. Louse them up, and the performance of your engine will suffer accordingly... Good Luck, and Happy Motoring!
Click to expand...


Two things/thoughts here.

1st) I often hear people say "Take it to someone who has worked on Model-As before "( ...and I think Mike's advice here is spot-on ) however, it also gets mentioned with frequency here how there are quite a few professional, -yet substandard Model-A engine builders out there. Therefore, if all of the above is true, then just because it is taken to someone who does many Model-A engines, how does this ensure someone is getting a "good job"?? :confused:


2nd), Chris with regard to what you are saying about crankshafts being turned on centers vs. chucks, I am not sure I am following your logic or wisdom. Most machine I have been looking at have interchangeable chucks and centers on the heads. Correct me if I am wrong but the chucks are non-adjustable as far as run-out ( -as is centers ) however the heads on each end are adjustable in 4 directions to compensate for this. Therefore if this is fact, then a machinist who has the proper indicator for the machine that can measure 10 thousandths should surely have 100% capability to set-up the crank to those tolerances using centers. What am I missing?

.
 
It must be something I am not allowed to do even though I am registered. I can find nothing under my name on right hand side that says PM or Private Message.
 
Go to USER CP at the top of this page, click on that.
Then on the LH Side under Control Panel, click Settings & Options, then Edit Options.
Now on the RH side of the page under Messaging & Notifications, about half way down there is a check box "Enable Private Messaging". Check that box and you should be under way.

And while you are there, might as well fill in your location. :)
 
Got it fixed. Thank you very much. Also, found a place in Denton, TX (gonna skin us alive for the money), but at least they are experienced with As and they know what they are doing. I think we are going to have the crank ground, head re-bored and cleaned up, then put everything back together ourselves. I am sure we will be begging for help from all you experienced guys before we are done. Thank you again. GGG
 
Any time an expensive part gets out of my sight I always take a picture of a marked identification on the part. Some times parts get "misplaced or mixed up" - just saying.
 
MikeK said:
Standard throw size is 1.4995/1.5000 so -0.020 would be 1.4795/1.4800. That's the least of your problems! Grinding a Model A crank is a can of worms- there are more ways to wreck it than the the average crank grinder operator could ever know! Make sure your crank grinder has worked with Model A's before. A standard grinder stone will put the wrong fillet radius on an A crank- 1000 miles down the road and. . snap!
Click to expand...

Mike, Standard Model A Rod Pins are 1.498, to 1.499.

1.499 is to tight, you are going to smear some babbitt, so we always grind from 1.448 to 1.448-50.

The Standard Ford Rod Hole was cut to 1.500.

Thanks,

Herm.
 
Most crank grinder operators, do not like radiusing their stones, as stated here.

Having different stones, with different sizes of radius, would be very rare, indeed, as the last time I had heard about stone pricing was 750.00, and that was a long time ago.

All that you can do is ask, or look at a guys work.

Just remember that there are many more that don't know how to grind a crank, then do!

Many grind up to the old Radius, and stop, very bad, weak place.

Many put in the wrong size Radius. If to large, the rod has to be fit in that area.

If to small, it leaves a weak place in your crank.

Herm.
 
There's been plenty of talk about getting the correct radius in the corners of the journals. I understand why they are there etc but WHAT IS THE CORRECT RADIUS??:rolleyes::confused:
 
gogrannygo;
Unless I miss read it, sounds like you were talking about trading your block for one that was done? If your block matches the car then it will have it's serial number that matches your paper work. make sure you get your block back.
 
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