crankshafts

[spidernut]

Fiat used two crankshaft designs - one for a manual transmission with a clutch shaft pilot bearing and one for an automatic transmission without the milling for a clutch shaft pilot bearing.

It is obvious that the crankshaft for use with an automatic transmission cannot be used for a manual transmission since there is nowhere for the clutch shaft to fit into the rear of the crankshaft, but what about the other way around?

Can the crankshaft designed for a car with a manual transmission be used with an automatic transmission?


John G
Lincoln, CA

[seabeelt]

John, are you sure about the crank nut. Seems almost counter intuitive from an assembly line perspective, and isn't the flywheel and ring gear mounted before/ in between the motor and tranny, or are those different as well?

[DanD]

It doesn't make sense that they would make special cranks just for automatic models.

Have you verified this ?

[spidernut]

100% absolutely guaranteed that they made two crankshafts - one for manual and one for automatic. The auto crankshaft does not have the milling for a pilot shaft bearing. Also, the flywheels are different since the manual must handle the clutch and pressure plate assembly. The auto uses a different flywheel with a torque converter bolted to it.

A mechanic whom seems quite trustworthy said the pilot shaft bearing on the back of the flywheel is only used on front wheel drive cars...the cranks can therefore be exchanged between auto and manual on all rear wheel drive cars. I am looking for a second expert opinion on the subject (not that I don't trust him, but like Reagan ... trust but verify).

[TX82FIAT]

Learn something new everyday. Looking forward to hearing the answer on this one as well. Alway knew guys with automatic transmission would have problems with the cranks!

[spidernut]

so far the consensus is that the cranks are interchangeable on all rear wheel drive cars. The input shaft bearing in the read of the crankshaft is not used on rear wheel drive cars. I have the motor out of one of my cars with an auto and the trans out of one of my cars with a manual. Since they're apart, i think I'll try mating them up to see how it goes.

[engineerted]

John, You are mostly correct. All rear wheel drive vehicals with a manual transmission gets the pilot bearing, automatics do not. The crankshaft is machined for a bearing in either case so you can interchange the crankshafts.

[spidernut]

Thanks Ted...what I wrote didn't come across the way I intended.

Manual transmission = pilot bearing in the crankshaft
Automatic transmission = no pilot bearing in the crankshaft
Rear wheel drive cars = interchangeable crankshafts because the manual transmission doesn't use the milling for the pilot bearing, nor does the automatic transmission
Front wheel drive cars = not interchangeable since the manual requires the milling for the pilot bearing and the automatic does not.

Does that sound more accurate? I hope so.

John

[FiatMac]

Thanks Ted...what I wrote didn't come across the way I intended.


Rear wheel drive cars = interchangeable crankshafts because the manual transmission doesn't use the milling for the pilot bearing, nor does the automatic transmission

John

Not correct. On rear wheel drive cars, both the manual transmission version and the auto version have the machining for the pilot bearing in the crank. The bearing is just not installed on a car with the automatic since it is not needed. Therefore, an crank from a rear wheel drive can be used universally in any rear wheel drive application.

[FiatMac]

Just want to share additional info from this topic as was posted on the Mirafiori.com forum. Apparently some of the later model auto transmission cranks had a shallower clearance hole behind the pilot bearing that will cause interference where the manual transmission input shaft extends through the pilot bearing.

http://forum.mirafiori.com/mirafiorum/m ... ener.Gener

[spidernut]

Stan,

Incorrect. I have three 79 Spiders and two are automatics and one a manual transmission. There is no milling for a pilot bearing and no installed pilot bearing in the tail end of the crankshaft on the automatic crankshafts. I can even take pictures to prove it. Both cranks are original to the engines. The manual transmission cranks have the milling and the bearing. I'll post photos tonight when I get home.

[spidernut]

My good camera got broken at a car show yesterday, but I think these photos are clear enough to see the milling in the back of the crankshaft used for automatic transmissions. Note that there is no milling for the pilot shaft bearing.

I took a close look at the transmissions side by side. With the automatic transmission, the input shaft is recessed from the leading edge of the bell housing by about 2 inches. On the manual transmission, the tip of the input shaft is flush with the bell housing.

I also looked closely at two manual transmissions and it is obvious that the input shaft rides inside the pilot shaft roller bearing in the back of the crankshaft (which makes sense to support the shaft from flopping around). There is no pilot bearing or milling for a pilot shaft bearing on the cranks used with the automatic transmissions so even if they mate, the leading edge of the input shaft on a manual transmission has nowhere to ride and would flop around (the pilot bearing serves this purpose).

Therefore, I do not see any way that a manual transmission could be mated to a motor with the crankshaft installed on automatic transmissions. However, I know the crankshafts used with manual transmission with the milling for a pilot bearing can be used with an automatic transmission because that's what is on the car that I'm driving right now and all is well. The pilot shaft roller bearing had to be removed from the end of the crank for the auto transmission to be mated with the motor.

So where does that leave me? It still makes no sense to mill a special crankshaft for cars with an automatic if the crank used with a manual transmission will work. I can't confirm where the 1995cc was used in a front wheel drive car, so I can't speak to that issue.

Any experts who have been there and done that before? I could use a good professional opinion - BTW, this is a 1979 1995cc motor bone stock, one car purchased with 31,000 original miles, the other with 89,000 original miles.

[spidernut]

Fiat did not use two different crankshafts. I was misinformed which explains why the shop manual only shows one style. They are one in the same design as verified using a micrometer. A friend who has a spare crankshaft was kind enough to compare the measurements with me via telephone. Mystery solved. Thanks to those who weighed in on this. Now I feel stupid. Well, live and learn.

I guess my expert wasn't an expert afterall. Those of you who said the cranks are one in the same win the prize of being right. You may say "I told you so."

[Dawgme85]

The reason the input shaft of the automatic transmission is shorter is that it engages with the torque converter, not the crankshaft. On automatic cars there is a flex plate that bolts to the end of the crankshaft in place of the flywheel and incorporates the gear which engages the starter. The torque converter (which acts as the flywheel, due to it's mass) is then attached to the flex plate with 4 bolts and has a boss, which is approximately the same diameter as the bearing used on manual transmission applications, that mates with the crankshaft for alignment purposes. This is why the same crank is used for both manual and automatic cars.

Hope this helps.

[BEEK]

i am going to start an argument here but so what!

there were 2 different crankshafts in the 2.0 in the US. not inclusive of the pinnifarina, which used 2 totaly different crankshafts.

95% of all the fiat badged USA cars used the same crankshaft, But i have seen with my own eyes a few crankshafts that came from an automatic car that were not machined for a pilot bearing.