MTFCA Forum

I am in the process of installing a chevy crankshaft into a model T block.
So far in this project I have modified the crankshaft flange as well as the front end of the crank.

This particular engine had been rebuilt not long before I acquired it. When I opened it there were a number of issues, however the pistons and cylinders are great, so my intention is to use the Chevy crank and T pistons and rods if I can.
Not looking to build race engine, rather just want to have bit more robust crankshaft than the stock T .

I understand that main bearing journals on the T block can be opened up to 1 7/16" while the rods can be upsized to 1 3/8".
One concern is with the width of the chevy rod journal bearing surface which is close to 1 7/8" while the T rod bearing is 1 7/16" wide, this will allow for a lot of endplay in the connecting rod, has any one out there dealt with issue and what was the end result?

I understand the easiest thing (if not the smartest) thing to do is buy a Scatt crank, but I have a well equipped machine shop and like doing this stuff.

Dave Eddie

Dave, I don't know if the extra big end bearing journal width would be a problem on its own, but you would need to centralise the Ford rod in the piston. That is done with internal circlips in some applications, while others use a teflon cup on the ends of the piston pin.
Others with more experience may have a better idea.

Allan from down under.

Modified Model A cranks are fairly common in T engines. 1-5/8” mains diameter and 1-1/2” rods. At this main diameter the babbit is extended right up to the main bolts, and so might be wise to bring the chebby crank to 1-5/8” mains at the largest. The stock Model A rods are a tight fit as well inside the block, but this could be due to the additional 1/4” stroke of the Model A crank.

The rod width issue could be resolved by screwing/welding thrust plates to the sides of the rods. But I’m sure there were plenty of ol timers that just ran em loose back in the day…

Here is a block being roughed out for an A crank with 1-5/8” journals

When using a Chevy crankshaft in a Model T block, where is the crank thrust bearing surface? In the Chevy engine it is taken on the center main and on the rear main for the Model T engine.

Shannon, the thrust bearing will be the centre one, this will be part of the modifications to the T block to accept the chevy crank.

Dave

Dave, so you just machine the center web of the block to accept the bronze shells from the Chevy engine? Which main caps are used? How did you
modify the rear flange on the crankshaft?

Here is a discussion from years past of various methods for handling the rear flange modification:

http://www.mtfca.com/discus/messages/25 ... 1326874054

Dave1 wrote: ↑

Fri Mar 10, 2023 12:55 pm

Shannon, the thrust bearing will be the centre one, this will be part of the modifications to the T block to accept the chevy crank.

Dave

Is that the excepted standard modification?
Does the Chev crank not grow like a T crank?
If It grows, how does that effect field coil clearance or are field coils/magnets left out normally?
Been a long time since I heard of this once very popular conversion.

Yes, the reasurch I have done using the centre main is the standard, the thrust surfaces on the Chevy crankshaft are on the centre main not the rear as in the model T.
I used a combination of a taper and heat shrink to install the rear flange.

If it were me, I would not cut the center main back to add thrust. I would leave it at the rear and go with adding babbitt to the block, not just the cap. The center main takes a lot of beating as it is and would be cutting a lot away to add thrust for the Chevrolet center journal.
I would have to look at the shells I have out of a 28, the thrust as I recall was the bronze shell itself, not poured babbitt, so the journal was running on the full length of the shell.
I could be wrong, but when I set my Chevrolet crank on the T block, the rod journals did not look to be centered with the cylinders so adding ring clips or the nylon buttons would be needed to keep the wrist pins from scoring the cylinder walls if they moved over too far using the T piston and rod setup.
Wish now I had kept the set of pistons that were made so could use the Chevrolet rods.

I imagine the chebby bronze shells would get too big fast. The minimum spacing between the T main bolts is 1.750”. Might work out for the front main, but the center and rear main bearing shells are waaaay too big to fit between the bolts. I’ve heard about folks notching the main bolts tho…

Took some photos of the T and Chevrolet crankshaft for comparison. Hope they show a little bit of the differences between the two.

Couple more. While maybe not the best shots, the difference between the Ford center main and Chevrolet amount to quite a bit of the center saddle being cut away, especially in my opinion if you were going to use it for thrust. Note that in the photo of the flange, that to get things close to lining up, the flange on the Chevrolet would need to be moved. For the rods, looks to me like would either need to let them just float on the journal or would need to build up the thrust on one side only, something like, two to the front and two to the rear.
Anyway, for what it is worth, doing a quick look see, that is what I am seeing.

I wonder how many old timers would have gone down this track if Scat crankshafts were available? It requires a deal of machining and some compromises. Sure, it was done, and with some success no doubt, but it was done then because there was little alternative. We are more fortunate.

Allan from down under.

IF YOU HAVE the skill and tools, then doing the A of Chevy crank conversion is comparatively cheap! You learn and have a rewarding experience. When the special pistons were available it had minimal incremental cost.