To File or not to File?

[KyCliff]

I am working on a '29 Model A engine and the front and rear mains are fine and within tolerance of .0015 clearance. The center main is at .004 with plastigage..... Is it acceptable to file the cap on a model A... seems I recall my dad doing that.
I queried it and find info on filing the Model T caps but nothing on an A.... even then there is a number of opposed to filing as well as approving of it..

This engine looks good, cylinders are nice and bored at .030 over. babbitt looks good on the caps.

Opinions on filing will be appreciated..

thnks, cliff

[Brian T]

Hello Cliff
I don't see any reason not to, instead of filing use some medium course wet and dry emery paper and a flat surface such as a table saw or flat plate glass to sand them down, it will not take much to remove a few thousandth, so recheck often ----- If you end up to close then you will need to use some shims available from the vendors.

[spectria]

I think crankshaft flex and position of the centerline are important.
If you simply file a cap to remove clearance, you are moving the centerline up .0025.
Will this cause the crank to flex too much?
Or will leaving .004 clearance let the crank wobble too much?
I know as a machinist that would not be acceptable in a modern engine, but in an AA with limited use and lower revs?

[Brady]

should not use plastigaue - use the "tin foil" method to set bearing clearances. Hunt for it....

[Neil Wilson]

Brady,
Why?

[spectria]

I use Plastigage when I know my crank is straight and true. If there is any doubt (as there might be with a heavy long throw 3 main journal A crank) I would use a method that would assure me that any flex is forced out during checking. Plastigage will give a false reading as it would compress before bending the crank straight on test measuring, especially if you happened to install it with the center bend up (with engine on stand upside down).
The foil or feeler gauge method will reveal the actual clearance used as described.
I posed my earlier question marks to garner others opinions...

[Brian T]

Spectria,
It seems to me to be rude to answer for others, especially with your opening statement, Brady is a go to person for usable info.

To answer your post it is a well known fact that the A engine crank flexes badly due to its small diameter, no counter weights and a very heavy flywheel 68# + pressure plate and disc, this causes most wear on the main cap bearing surfaces especially the center bearing ---- not on the block side, so raising the caps is not a problem, this as been performed for many years on these engines, and is an acceptable repair, I use both the platisgage and the foil method.
This A engine was robust and well designed for its time and was highly upgraded as time went on, I imagine they will last 3-4 times longer in todays world, modern engines are a totally different story.

[Warpspeed]

There are quite a few applications where the bearing loading is virtually all on a cap, not in the bearing half located in the main bed of a machine.
In that case, it is quite acceptable practice to skim the cap, to close up any excessive bearing clearance without effectively moving the bearing centerline.

I have done this many times on the cam bearing saddles of DOHC engines, where combined valve spring pressure is all upward, and only the caps wear. The lower bearing surface in the cylinder head when measured show that the bearing surfaces are all still dead in line, even though wear in some individual bearing caps may be 0.015 or more.

Just check that the bearing surfaces in the block are straight with a straight edge, its dead easy to do.
Any excessive clearance must therefore be in the cap. And you then know what to do.
Done intelligently and very carefully it is a perfectly legitimate method.
I use wet and dry paper coarse enough not to clog, backed with a sheet of plate glass.
Make figure of 8 movements with steady even downward pressure, be patient .... and go slow....

[KyCliff]

Let me clarify a little here... I have the engine upside down on an engine stand so no weight is on the cap of the main.. so being a newby at Model A's I don't understand how the center line would be affected by taking out some clearance...
On the tinfoil method... I have tried that and yes, I think it works fine but I grew up using plastigage on the old chevy's so find it familiar. I did use the tinfoil method on the rods as well as checking them with plastigage and came out fine either way.

thanks for all the opinions... all have their good points....

I will try the wet/dry sanding method on a cast saw table. Only have the one cap that is out of tolerance.

cliff

[Grand Valley Tractor]

Kycliff,

IMHE (in my humble experience)...when I did engine work early in my life, I trusted PlastiGage. That was in the 60's. The vintage iron I work on now is different, but I learned long ago to just use it as a quick reference.

Plastigage = probably
Micrometers + math = definitely

You'll learn a lot more about the "personality" of your parts using instruments.

Tim

[Warpspeed]

I think you need both if you are serious.

Good calipers, a micrometer, and plastigauge, plus some feeler gauges and a dial indicator are probably all you need to measure just about anything on an engine.
All have their unique uses.

[E.Moore]

When a Model A engine has begun to knock or loses excessive amounts of oil from the rear main bearing or has an excessive vibration when running, it is time to remove the engine to examine the crankshaft and babbitt bearings.

Babbitt is comprised of several soft metals - copper, tin and antimony. There are other metals that are added or substituted to the mixture, but Ford Motor Company used 85% Tin, 7% copper & 7% Antimony. Lead is a common substitute for tin because lead is less expensive than tin. Metal companies that sell babbitt sell much more lead based babbitt than tin based babbitt due to the difference in price.

Lead based babbitt is softer than tin based babbitt, so the main and rod bearings that are made from lead based babbitt will not last as long as bearings made from tin based babbitt.

Babbitt is best poured around 850 to 900 degrees F. Antimony is used to make other metals harder and stronger, but will become brittle and lose some of its properties if heated too high.

Copper is a good conductor of heat and is ductile. Copper in babbitt helps to transfer heat to the block and into the oil that surrounds the crankshaft. Copper and antimony help to prevent excessive babbitt wear during engine start up.

Tin is the best alloy for babbitt because of it’s ductile ability with copper to withstand the pressures of crankshafts during the power stroke. It rarely cracks at the rear main bearing unlike lead based babbitt that often cracks at the rear thrust. Tin based babbitt resists squeezing out of the center main bearing unlike lead based babbitt that does.

Other alloys like nickel are used to increase the strength of the machined bearing, but other alloys can cool at different rates after being poured and can cause hard spots in the bearing surface. Hard spots show up during align boring of the babbitt.

Model A crankshafts have often been machined by people unfamiliar with the metals of the Model A crankshaft. Ford used Vanadium in the chassis and crankshafts of the Model T & A , which allowed the steel to be more malleable and not brittle. Vanadium is the primaary reason that the Model A crankshaft flexes but does not crack or break.

Machinists do not know that when a Model A crankshaft is installed in a crankshaft grinding machine, the crankshaft flexes slightly when the live end of the lathe is tightened against the end of the crankshaft. The machinist unknowingly puts a slight bow in the crankshaft.

The crankshaft is machined to the next smaller standard diameter in order to remove existing scoring and it is then returned to the customer or sold to a parts supplier.

The Model A crankshaft needs to be checked for alignment. A simple fixture can be used to support the crankshaft on the rear main bearing surface and the front bearing surface and a dial indicator is used to measure the run out at the center main bearing surface.

I’ve measured Model A crankshafts right from a crankshaft machine ship and found center mains over .060 out of round. It does no good to try to straighten it, because the crook was ground into the crankshaft. Most of the time, a crankshaft measures more than .030 out of round right from the crankshaft grinder. The measurement I want is .000 and no more than .002

Unknowing customers who purchase a crankshaft ground poorly and install it, find they have a bad engine vibration.

If the bent crankshaft were straightened at the center main, then the flywheel flange would be out of lateral specs.

KRW made a tool to mount to the crankshaft flange to measure the crankshaft flywheel mounting flange run out against the rear of the engine’s flywheel flange. There should be no more than .006” all the way around. Less is better.

If this is not verified, an out of round crankshaft flywheel flange will let the flywheel wobble, adding to the engine vibration.

This can cause the transmission pilot bearing to be out of alignment with the transmission input shaft, and can result in the transmission input shaft bearing and pilot bearing to wear prematurely and can cause the clutch to chatter during gear shifting.

Many Model A’s and AA’s have cracked flywheel housings that will add to mis-alignment of the transmission to the engine and make matters worse for clutch chatter and transmission bearing & pilot bearing wear.

There is a reason that there are .010 shims used at the accelerator mounting ears, because the original engine to flywheel housing gasket was .010 thick. I have original NOS flywheel housing to block gaskets with Ford Script stamped into them and they all measure .010. Most every modern aftermarket gasket is no where near .010. Instalation of a thicker gasket at the block to flywheel housing, then installing the .010 shim at the accelerator mount will instantly cause warpage and a huge flywheel housing runout problem.

A Model A crankshaft that is poorly machined will cause the rear main bearing to crack at the thrusts and will beat the center main bearing out of the block and cap and can cause a knock.

Adjusting the main bearing caps on a crankshaft that is warped is of no use because the out of round crankshaft will continue to beat the babbit out of the block and caps.

Some people have their crankshaft welded up and ground down to standard specifications. Others do not like doing that.

Some will have a crankshaft built up with chromium and machined down, but sometimes chromium plating comes loose.

It is possible to use a Model B cankshaft and have it ground to standard Model A specs, but the oil slinger on the Model B has to be machined as well and machine shops unfamiliar with the Model A oil slinger can screw it up.

A modern rear seal would be best when using a Model B crankshaft that has been machined to Model A specs.

I am not a final authority on this issue. There are many others who are knowledgeable about this problem. Any crankshaft to be used in the Model A engine should be inspected, measured and balanced before installing it.

[spectria]

Yes...