For longevity, re-hardening is recommended. If it were my car, I would have to take a hard look at the cost. I could be wrong, but the cranks in the earlier cars (1600) were not hardened and mine is holding up fine.

How deep is your crankshaft scored? If you only need to grind it 0.010" under size, will that exceed the depth of the original hardening? More questions than answers but one of the engine experts should be able to provide a definitive answer.

 

Hi,

After heat treating you also will have to have the straightness checked and corrected if required. The last guy I trusted a heat treatment to couldn't detect the bend let alone straighten it. For another shop it was no problem.

I found the bend when I noticed a tightness during trial fitment to the block.
The repair shop said there were actually 2 bends. Their method of correction was to heat the crank slightly, load it and let it slowly bend back over time.
When this expert retires, and he's an old guy now, an art form will likely be lost to this part of the planet.

That being said the 1300, 1600 and 1750 cranks were not hardened. They get hardened these days for race applications and by fussy owners.

However I have not personally run a cut 2 litre crank but do not see why not to for a daily driver.

FWIW

Ken

 

Alfa factory hardening is quite good, and intentionally, not very deep. Some tell me .015 or so. If you grind and polish .010, you might, or might not be OK. Crankshafts were nitrated for racing with the GTA's, though there might have been some earlier. I understand by the advent of the 2L, all were nitrated.
The job done by a shop that specializes in racing crankshafts is not very expensive, and it should considerably extend the life of a rebuild. I now do all crankshafts, particularly those for the older engines used in restorations.
My fear would be that you might be at the edge of the surface hardened with a .010 grind, and have hard areas, and not as hard areas subject to wear. Seems like a sure recipe for oval journals over time. On the other hand, I'm sure many shops just grind and polish to whatever undersize they go for, do not re-harden, and get away with it, for a while at least. Do you plan to keep your car? Just some thoughts.

 

The quote I got was $45 for the grind and $160 for heat treating. When I built my chevy big blocks and needed cranks done, heat treating was never considered, and running high compression and nitrous never broke any cranks. Maybe Alfa cranks are just fragile and need it? Regardless, it just seems like insurance that I'll probably never need. Anyone have a horror story?

 

When I built my chevy big blocks and needed cranks done, heat treating was never considered, and running high compression and nitrous never broke any cranks. Maybe Alfa cranks are just fragile and need it?

Nitriding is done with the crank hot, hence the word heat treating but this is not the same as tempering, forging or other heat treats that harden the whole crank.

The surface hardening treatment is to increase wear resistance, over time, while the softer, forged inner core can still withstand twisting forces, much like a spring.

This is what nitriding does. It's surface hardening to decrease wear and no more. It's done by heating the crank to around 1050 F and then flowing ammonia gas which form some hard nitrides on the surface of the steel making it much more wear resistant. Most modern crank nitriding is now done with a nitrogen plasma. More expensive but more controlable.

 

Make sure that when a crank is ground under size that the shop doing the grinding is well aware that the radii of the journals MUST be maintained. He may charge more, grinding wheels are expensive and dressing radii on the wheels wear them down. Pay the price, broken cranks from sharp or too small radii are not uncommon.

 

I have a nice picture of that failure, as well as a shop that left "chatter-marks" around the journal radii of a (now ruined) 750 Veloce crank.
Alfa cranks are very high quality forged components, but this is a long stroke engine, and the crank is not as massive as a forged Chevy crank. It also turns at a considerably higher engine speed in normal use. The surface hardening treatment is to increase wear resistance, over time, while the softer, forged inner core can still withstand twisting forces, much like a spring.

 

Fortunatly my shop did know about the radii, they charged me for it on top of the .010, was happy to pay. Did not reharden and have had no problems and many, many, miles.

 

Thanks VML! I send cranks out to have this work done, use a VERY good shop, never costs me much. I wondered how they do it. You have explained it in few words, and very well!

 

I thought good 2L cranks were easy to get. I would say just get a good used crank and spend the cash on getting the oil plugs replaced with threaded inserts. And a good balance.