Just asking if there is any common knowledge of the performance / reliability difference of a Scat crankshaft vs the later Model A as used by many folk in their T's ?
Both crank shafts will require some modifications to the horse shoe rings of the inspection cover, dimpling the sides of the pan for clearance of the connecting rod bolts.
Scat crank is counter weighted
Model A is not but can have weights added
Scat is correct length and centers all piston rods in cylinders.
Model A, two of the rods are off center of the cylinders.
Your choice on how to address the off center rods issues.
Model A requires removing 0.125” from the inside of the block on the front and rear main
Model A needs to be shorten at the rear flange or run full length and move the pan apx. 5/8”, relocate front pan damn and build an extension adapter for the engine/hogshead fit.
Shorten Model A cranks that have had the flange modified have been known to break off. There are very capable sources of this service, choose wisely.
Haven't to date heard of a Scat Crank failure.
Bottom line, by the time you modified a Model A crank:
Shorten the overall length
Drilled for full oil pressure
Add counter weights
Located a good Model A crank
Ground the crank
Balance the crank
You are within a few hundred $$$$.$$ of a new crank shaft that was engineered for our needs.
Performance, by the seat of your paints you won't know the difference. Your choice of cranks, both give you more stroke, what you do with it on the engine build = performance!!!!!
You can get the SCAT crankshaft in either stock Model T stroke or longer Model A stroke. For comparison sake let's compare the SCAT Model A stroke crank to a stock Model A crank.
Cost of Model A crank:
Purchase price $200 used
Bead blast $20
Turn journals and polish $125
Cut off rear flange and rework $350
Cost of Scat Model T crank with Model A stroke
The SCAT crank has counterweights.
The Model A crank has no counterweights.
Both are forged steel.
Both require custom main caps, special main bolts, and modifications to the engine pan for clearance.
The Model A crank will require more work when balancing the rotating assembly. Maybe $300 more labor?
At the end of the day the SCAT crank costs a bit more.
Regarding reliability and performance there should be no difference.
Picture of a SCAT crank being fitted in Ross Lileker's shop:
LOL Mike types faster than me but we both agree.
The Scat crank is by far the better choice. Spend the money and don't look back.
I had a scat A crank put into my T and it IS counterbalanced and came ready to install. It was a little expensive but well worth it. I have 1,000 miles on it with no problem so far. I thought I was getting a Scat T crank but I guess I wasn't clear enough when I ordered it. I did have to do a little clearance work but not bad.
Perhaps you could consider the SCAT with the stock T specs.
You just drop it in and use the stock main bearing caps with no machining, no clearance issues, no probs.
I guess I am cheap and can do all the conversion work myself. For me the A is a good choice and the Ford C (with counterweight ) even better. I can pick them up easily for $100.00. My net out of pocket is about $200.00 over a T crank
I have spun them at 4000 rpm and 100 HP!!!
I have seen one broken model A crankshaft in a T block that failed like model T crankshafts often do. The other model A crankshafts that I have seen failed were due to the welded on flange breaking.
I have modified a 28 chev. crankshaft to fit in a model T block. It required the same amount of modifications to the block and pan as required in fitting in a model A crankshaft even though the chev. stroke is the same as the T crankshaft. I bored out the rear main and pressed in a model T transmission shaft which was welded on each end.
Thank you Gentlemen. A Scat Crank it is!
Having seen every welded on A crank flange fail, I now instal them using a heated and pressed on taper. No more failures and easy to do
Correction to my previous post. Today I talked with the shop that did the work and my car has a scat T crank with model A stroke. Just wanted to be correct.
I ended up with an unknown core engine that has a model A crank in it. How do I tell how the crank was modified to fit the T block?
It is still assembled with only the trans cover and dipper cover removed.
If there is a 5/8" spacer between the back of the block and the hogshead the crank is probably not modified at the rear flange. The block has been moved forward on the pan.
No spacer and the crank is probably shortened.
Look for non-stock plumbing to tell if it has pressure oiling.
I have a T engine with a model A counter balanced/drilled crankshaft that was shortened in the center main. I was told that Years ago, someone in the L.A. area shortened a number of A crankshafts by heating the center main and squeezing the crankshaft in a press during the heating process. This shortened the center main enough to allow keeping the original flange which was machined to fit the model T flywheel/transmission shaft.
I'm not recommending that others attempt this.....just sharing about another method.
Today, we are fortunate to be able to buy a good replacement crankshaft vice having to try and make something else work.
I am curious Alan. Have you broken the crank in the 10' or the 26' or working on another project? I hope the 10' and the 26' are fine. Good decision, Scat the same as Rob chose is the go! There is a Scat agent/distributor in Melbourne that has stock if you want the details.
Had a look, sure it is a shortened unit, no pressure oiling either. Has pretty robust main caps with what looks like DUC cast into them...
If all you are after is a "street engine", then the splash will be fine
The shortening job is a bit of a "crap shoot". It might be possible to determine if it was welded by close visual examination. If it was welded, then it will fail at some point. The failure is not usually dangerous, just darned inconvenient, as the flywheel spins freely! I have converted several welded ones with my taper/ press fit approach. Problem is I live about 2000 miles from you!!
Here is a main cap
Yea I am a little concerned about a welded up crank….
A bent transmission shaft or pan will place additional stress on the crankshaft flange. Make sure everything is in proper alignment to help a welded on flange survive. The model A crankshaft is strong....the welded on flange is the weak link. That's why I bored and pressed in a model T transmission shaft then welded both ends on the 28 chev shaft I modified. I once placed a bent transmission shaft in a 60 ton press to see what it took to break off the flange. It broke around 40 tons with one hell of a bang. That may not have been the smartest thing I have done but it did prove that the transmission shaft is very strong.
Has anyone broke a transmission shaft?
The engine sure looks filthy!!!
You are outlining the reasons I developed my "floating" transmission shaft. It still requires a straight pan, but eliminates all bending stress
Les Schubert: What ever happened with the floating Transmission shaft? I was waiting to hear more, did I miss it? Dan
Yes, I'd like to hear more about the floating transmission shaft also. I think such a design might largely eliminate crankshaft breakage.
I had two done using nice vintage main shafts the job was outstanding.
yes there was chipmunk home in the pan…we'll see how it goes.
Always wonder why an engine is not installed and running in a car.
Floating Trans shaft; 10 of them are being tested. So far so good
Gosh, Les. Maybe you'll need to make another run of them. So far mine are working well. Initial set-up was no more difficult than a standard transmission shaft with the engine standing on it's nose.
I will give it some thought. Maybe get some costs for a run of 50
I only have a couple thousand miles on the floating shaft in my pretty much stock 26 Coupe but it seems just fine. I am a fan of the concept and hope that they prove trouble free in both longer term and possibly higher performance engine usage.
Thank you for the update
With a scat crank installed and the rotating assembly balanced running a splash system, what is a safe top rpm for cruising?
I would say the RPM limit is dependent on the chassis and brakes. A Model T is a 40MPH design in the best of conditions, a more reasonable top speed / cruising speed is probably 35. I don't plan to go 40 MPH in low gear.
I do not enjoy driving my model T over 40 mph. Cruising speed around 35 or a little more is great. I run stock gears.