The Ford Barn

RHD · 01-04-2025, 01:24 AM

You take possession of your brand new 1929 Model 'A' directly from the dealership.
Getting it home, you remove the distributor cap and check the backlash in the drive by rotating the distributor cam with the cam screw locked in place. How much backlash do I have?

mercman from oz · 01-04-2025, 04:37 AM

Joe K · 01-04-2025, 10:08 AM

Backlash here is the "free motion" between camshaft drive gear and the oilpump/drive gear AND the slot/groove in two different shaft connections. It can be considerable.

You may also be helical gear "turning" the oil pump/distributor drive gear "up" out of its position and compressing the gear/drive retaining spring. But this take considerable UMPH and possibly even a pair of vice grips torque arm to do it.

One of the challenges in timing the Model A engine is to time the engine ALWAYS keeping in mind the rotation of the engine and taking up that lost motion. As I say the lost motion can be considerable, but even half a turn of lost motion can be compensated for.

One engine disassembly of mine found "leather pads" placed in the vertical shaft coupling "forks" in attempt to reduce this lost motion. Functional in its effect but IMHO would make the actual engine timing "sketchy." Another engine found the "extended distributor shaft" option which is another way to reduce lost motion by reducing the number of actual slotted connections.

Nice he has the cam retaining screw with the "hole" (for oiling.) This means the distributor shaft is likely "drilled" for lubrication of the upper bearing - which is not original but a "nice to have."

Joe K

butch chase · 01-04-2025, 11:55 AM

When new a few degrees. Now they can be worn pretty sloppy. A new oil pump drive gear with oversize teeth, new upper and lower distributor shafts can remove much of the slack. 1 degree at the points is 2 degrees at the crankshaft.

There's 2 schools of thought on timing to account for this slack/sloppiness. one says use the distributor cam wrench to hold pressure clock wise while tightening the point cam will work.
The other is to use a timing light with the engine running, which takes up the slack, and a pointer or NuRex timing strip next to the front pulley.

yes I know Ford didn't use a timing light, because they weren't invented until 1937.
the choice is up to the owner

Kurt in NJ · 01-04-2025, 02:50 PM

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I just looked at my car, while it is not new both the cam and drive gear are functionally new, the distributor shaft was new original Ford and the backlash is 1/2 the width of the rotor tip.
I also found that oiling the distributor as the owners instructions say will oil the upper bushing, most distributors it is recommended to give it a few drops, Ford said to fill it.

01-04-2025, 04:37 AM	#2
mercman from oz Senior Member Join Date: May 2012 Location: Queensland, Australia Posts: 12,009	Re: Imagination required.

01-04-2025, 10:08 AM	#3
Joe K Senior Member Join Date: Jul 2010 Location: Cow Hampshire Posts: 4,610	Re: Imagination required. Backlash here is the "free motion" between camshaft drive gear and the oilpump/drive gear AND the slot/groove in two different shaft connections. It can be considerable. You may also be helical gear "turning" the oil pump/distributor drive gear "up" out of its position and compressing the gear/drive retaining spring. But this take considerable UMPH and possibly even a pair of vice grips torque arm to do it. One of the challenges in timing the Model A engine is to time the engine ALWAYS keeping in mind the rotation of the engine and taking up that lost motion. As I say the lost motion can be considerable, but even half a turn of lost motion can be compensated for. One engine disassembly of mine found "leather pads" placed in the vertical shaft coupling "forks" in attempt to reduce this lost motion. Functional in its effect but IMHO would make the actual engine timing "sketchy." Another engine found the "extended distributor shaft" option which is another way to reduce lost motion by reducing the number of actual slotted connections. Nice he has the cam retaining screw with the "hole" (for oiling.) This means the distributor shaft is likely "drilled" for lubrication of the upper bearing - which is not original but a "nice to have." Joe K __________________ Shudda kept the horse. Last edited by Joe K; 01-04-2025 at 10:18 AM.

01-04-2025, 11:55 AM	#4
butch chase Member Join Date: Feb 2019 Location: Polk County Mssouri Posts: 42	Re: Imagination required. When new a few degrees. Now they can be worn pretty sloppy. A new oil pump drive gear with oversize teeth, new upper and lower distributor shafts can remove much of the slack. 1 degree at the points is 2 degrees at the crankshaft. There's 2 schools of thought on timing to account for this slack/sloppiness. one says use the distributor cam wrench to hold pressure clock wise while tightening the point cam will work. The other is to use a timing light with the engine running, which takes up the slack, and a pointer or NuRex timing strip next to the front pulley. yes I know Ford didn't use a timing light, because they weren't invented until 1937. the choice is up to the owner Last edited by butch chase; 01-04-2025 at 12:04 PM.

01-04-2025, 02:50 PM	#5
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,555	Re: Imagination required. Sponsored Links (Register now to hide all advertisements) I just looked at my car, while it is not new both the cam and drive gear are functionally new, the distributor shaft was new original Ford and the backlash is 1/2 the width of the rotor tip. I also found that oiling the distributor as the owners instructions say will oil the upper bushing, most distributors it is recommended to give it a few drops, Ford said to fill it.