MTFCA Forum

I have been thinking of building an engine using a stock Model A crank and to have the crank ground to standard T size for the mains and rods then using stock main caps. This would be going in my 21 Huckster or 25 cut down pickup. I will be using 26/27 block, hogs head and 4 dip pan.
Have been toying with the which would be better joining two pans to stretch or move the block forward. Right now I thinking more along the lines of moving the block forward, would eliminate the need to modify the driveshaft/radius rods and other parts to keep distances to the rear the same as stock and lined up (such as also the parking brake lever)
I am thinking that instead of moving the dam in front I would cut the clearance for the timing gear in the original dam and mount an extension to the front to mount the timing cover and seal.
Not going to build a speed car, just a little stronger bottom end. I want to keep stock stroke and stock pistons which may require grinding the rod journals off center of stock A, don't know on that one yet may not be needed. I plan on using the heavy type T rods which would be closer to A rods in weight anyway. Because the center line to bore of the A crank number 2 and 3 rods are different then T, adding thicker babbitt thrust left or right depending on location to those 2 rods so they stay in line with the center of the T cylinders and same with 1 and 4 to keep the weight the same and centered as need to the bore. This will be hogs head/internal supplied splash lube and want to keep the magnets/magneto.
This would be a slow as money allows job and at some point in the process would think about using a Model A cam. Parts of course would be balanced as the project goes along.
Right now this is early thinking, nothing set in stone yet and am trying to keep cost in prospective of my income and except for moved block, looking stock and no SCAT crank type stuff. At some point it would get my Chevrolet over head conversion put on.
Am I on the right track? Any critiques of my ideas so far?

Hi Mark,

I think turning that crank down that much would be counter productive. It would weaken its properties especially near the webs and and at #2 main bearing. Some have used 28 Chevy cranks, rods, with modified wrist pins. There are specifics in dynamic/stress test that formulate crankshaft journal size to its rotating mass. Then there is metallurgy to support these findings. Your Idea I applause but sometimes reality sets in. If you notice on a stock Model T the flywheel is very heavy as a rotating mass (somewhat balanced), this equals to low RPM torque and inertia. I do not believe the stock Model T bearing caps could handle the excess pressure generated. The G forces with a working load would require more lubrication as well.

Sliding the engine forward 3/4" has its own issues with the water neck alignment, fan clearance, and so on. Not to criticize but to assist.

Hope this Helps!

All the Best,

Hank

Why not use the complete model A engine? Way way back when Bill&Jean Barth were still in the mitten they showed up on a short tour with a late 20" coupe and a V-8 60 HP. Really nice car and nice people! Bud.

Keep it coming The Chevrolet crank and rods are not out of the picture, except I sold the conversion pistons thinking I would never do it.
I have given some thought to the angle of the water outlet and fan.
When guys install the V8 clutch in an A, the weight of the flywheel is about the same as the T with magnets. Not all those conversions get counter balanced cranks.
I think I understand what you are saying about the main caps. What about reducing the diameter of the mains to approx 1.4995 and use the heavy duty caps with thicker babbitt? I am not seeing a lot of meat in that area in the block to remove.
If I was going to transplant an engine it would be the 26-28 Chevrolet, that has been done too.

If you study the old “speed manuals” apparently over size cranks were made featuring 1-7/16” mains and 1/3/8” rods based on the concept that the stock main caps and stock rods could be used. I have tried the idea and it works okay.
A alternative to moving the block ahead is to shorten the back of the A crank using my taper and shrink fit approach. It does require shortening the rear main by 3/4”at the back

Hello, Steve here,
I'm not an engine builder but here is a picture of my 1926 Model T block with a Model A crank.
I'm having it build by a good friend. Hope this will help someone.

Thank you Steve.
I got to thinking about the moving of the flange last night. What about threading it on, then using locktite and pins?

The WW2 Tank and landing craft engines used a shorter flange with I believe a 40 spline to drive the clutch plate.
After the war there were a lot of these engines sold new in the crate. They used a lot of Continental W-670 aircraft engine parts.
As I understand it the airplane guys used these engines with a 20 spline shaft attached with a taper arrangement to the 40 spline stub.
I myself used a set of tank engine cylinders when I rebuilt the engine on my Waco cabin oh so many years ago.

That is a nice way of doing it Les!

Mark Gregush wrote: ↑

Wed Jan 08, 2020 12:35 pm

What about reducing the diameter of the mains to approx 1.4995 and use the heavy duty caps with thicker babbitt? I am not seeing a lot of meat in that area in the block to remove.

Some blocks do end up pretty thin. If my rememberer is workin right... the center main tends to get the thinnest. Grinding the crank down to 1.500” would certainly help keep some meat in the block. But thicker babbit is not a good option. I’m probably going to open a can of worms here... but babbit should be about .040” - .050” radial thickness.

I’ve done 3 A crank conversions. I’ve always kept the mains stock A size and used custom main caps. I line bore the block right to the edge of the bolt holes. Then I use bolt dowel sleeves to have precision fit of the caps. I agree with Kevin on thin babbit

Kevin and Les,

That's the way we do it too!

Hank

I want to thank everyone for the information provided so far. This started out as a way to just get a stronger crankshaft in the car I tour with, without going to something like the SCAT crank which is WAY outside my budget and keeping as many stock parts as possible. The babbitt in my block has less then 2000 miles on it and is bored for .020 or .030 undersized crank so was thinking about boring back to standard.
For my application and thoughts, less then a 1/16" of babbitt and pressed on flange just do not fit with where I want to go on this. While there are no sure things when it comes to breakage, what I do now more or less will have to last the rest of my T owning life. To tell the truth, I have not been driving the 21 as much this past year as in the past because if the crank breaks or other major issues I am not really sure what my next step will be.
Thanks again, I hope everything posted so far helps someone in the future.
MarkG