MTFCA Forum

Hi
I've seem lots of references of fitting a Model A camshaft to a Model T for improved performance.

Could someone explain how this is achieved. The cam bearing sizes between the two are noticeably different.

John from Perth WA

I machined an A camshaft to fit a T block. I simply machined the cam bearing journals (correction) to about 1" diameter and machined the front for a T cam gear. It took some wiggling and turning to get the cams to go through the bearing holes in the block, but it worked.

Here are photos of it. I had planned to make bronze cam bushings to slide in place.

My approach is different. I machine the center and front bearing to run directly in the block (just like on the model A). Then I filed slots for the lobes to slide through. I will try to post some pictures

I'm surprised it can be done. I thought the length and distance of the lobes would be different. Also the A has a different firing order so if you use the timer, you will need to change the order of the wires between the timer and coils.
Norm

Model A fires 1-2-4-3 just like a T.

There is so much to consider if you do this. If you machine the A cam to fit the bores thrust control must be addressed. Also the front of the cam should have a T nose. Also I feel you should use A tappits, otherwise the duration will change, but lift will increase over a T. The inside of the block will need to be machined on both ends for clearance. This not a job for the weak of heart. I'm sure I forgot to mention something

Joe, the Model A fires 1,3,4,2 The Model T fires 1,2,4,3. However the top centers would be the same except that the exhaust stroke and intake stroke would be different. same position of the piston however. If I were looking for performance I would rather buy a new cam designed for higher performance but is made to fit a Model T block. I do not like to do anything which changes the Model T block except to bore out cylinders or re grind valves or insert valve seats.
Norm

The Model A is 1243 same as the T, not 1342.

Rich Eagle, You wrote, intended to use bronze bushings, what did you end up with? Thank you, Dave in Bellingham

I built my first one of these in 1978!
Ran the cam directly in the block cam bores just like the model A. To control the end float i brazed up some spots on the front cover and carefully fitted them to run on the cam gear nut. Installed a VW oil pump on the back of the camshaft and went full pressure. Ultimately a Sherman head and a Stromberg V8 carburetor. In a speedster capable of 100 mph. And a Vega distributor which provides automatic ignition advance. The car is still being driven by a new owner.

Dave, I didn't ever use the A cam. The machining of it was a great challenge, but I moved on to other projects. It would have been fun to try it in my Roof 8 engine. Perhaps a future task.
Rich

On using A tappets: They are too large to be used in the T tappet bosses. You would have to grind the shanks down in order to make them useable in a T block. Using T or A tappets will not have any effect on cam duration- duration is totally controlled by the cam profile and nothing else.

FWIW...

Rich Eagle, Thank you, Dave.

You guys really need to listen to the "old timers" - Dan, Les - they don't guess, they KNOW.

The last picture shows my latest version and the gear drives a flathead V8 oil pump

Thanks for the photos, Les.

I think I'll go that way.

The Model A cam being thicker is not as flexible as the Model T so I can increase my valve spring pressure if needed.

John from Perth WA.

I don’t go with heavier springs on a flathead T engine. Even with a radical cam grind the valves don’t start to float till over 4,000 rpm. I like it as a built in rev limiter!

You don't need a T nose if you run a side drive mag. The A cam rides bearing less in a T block. The notches required for fitting can be set using a plug and long drill bit st at about 90 degrees.

Les, what was your transmission shaft that was discussed many years ago? To reduce vibration?

With regards to this current discussion I am looking to use the Model A cam with an OHV conversion head ie a Rajo BB. So spring pressures may need to be increased.

John from Perth WA

John: Here is a thread about the Floating Transmission Shaft.
http://www.mtfca.com/discus/messages/50 ... 1438120257

I'm surprised no one has mentioned this problem. The foot of Model A lifters is larger, 1 1/8 inch or 1 3/16, for a reason. The contact point will be off the edge of a 1" lifter. You might get by with that for at least a while, but it's not considered a good idea.

CamMan wrote: ↑

Wed Nov 01, 2023 12:41 pm

I'm surprised no one has mentioned this problem. The foot of Model A lifters is larger, 1 1/8 inch or 1 3/16, for a reason. The contact point will be off the edge of a 1" lifter. You might get by with that for at least a while, but it's not considered a good idea.

What's your idea "a while"? Mine has been running almost 45 years and as many can attest the previous owner "tested" most everything on the car to the breaking point. . .

Lots of folks have done the A cam conversion, especially for hopped up motors. Lifter head isnt an issue.
Why go to the trouble of such a conversion? You get a higher lift with a heavier "stick" that doesnt bend & flex.

All I can tell you is that an A cam (unless the lobe is reground) will run off the edge of the lifter. Ford and other cam designers don't think that is a good idea. That's why they used a larger diameter lifter in the model A. Your certainly free to do whatever you want.

This has nothing to do with lift. Flathead V8 cams had more lift but would run on a 1" lifter, because,they had an entirely different grind profile,

I wonder if that I ran a significantly reground profile (.325 lift) managed this