Curious About Grinding Crankshaft on 2 Litre

[ace124]

I have new in box genuine fiat o/s crank bearings here somewhere too.
I think if the grinder does his job and keeps the fillet radius correct it wont be a problem for road use....
I know a few guys that track their cars on reground 2l cranks without an issue either.
Here is a solution you might not agree with...
When i was at Uni many moons ago i rebuilt my 1st 2l Super Brava engine. One of the journals had a factory undersize of 0.005'' The crank was otherwise like new. I was going to reuse the original bearings on that journal but they were a little scored. So i used one new standard bearing shell and one 0.010, shell. Plastiguage showed correct clearence and crank spun nicely without any tight spots.
I did 3 years of Uni and over 60k km on that engine before selling the car....and never had an issue.
Bad engineering maybe??? It worked though.

[timinator]

but is it really fair to say that a machined crank will fail in a gently-driven street car just because some racing engine "experts" have had machined cranks regularly fail in severely tortured race engines?

Maybe not, except Kingme2 said he couldn't wait to get his engine tuned so he could go race it. Just a street car you know.

And right there you have hit the nail on the head!

I have no idea what nail you are trying to hit.The crank makes metal to metal contract with the bearing every time you start it. Crankshafts bend, flex, twist, vibrate, and oscillate the entire time they are running while suspended between bearings. Are you sure the don't make contact? Ever seen a bulkhead broken completely out of a small block Ford or Chevy?

and then (and ONLY then) will the nitriding make the tiniest bit of difference.

Like the cheapest car company going, Chevy,is going to tufftride cranks for the tiniest bit of difference.

A chevSB crank isn't forged as std (well not sure about the LS series as it's been 20 years since I built a SB) or nitrided, It's a nodular cast crank, and one that's been twisted to achieve the 90 crank pin offset.

All sbc built from 55-62 had forged cranks. In 63-67 the only cast cranks were 283's in the cheapest model chevys because forged cranks were expensive. By 68 cast cranks started to appear in everything except high horsepower units. Forged cranks remained available in Z28, Vette, and trucks up through 85. They were also had one piece rear main seal forged cranks through 97. Gen III engines come with cast and forged cranks.

maybe if you compared a forged flat plane crank...but that would be a specialised racing only part, not a production mass produced item like we are talking about.

Chevy marine 153 four cylinder flat crank engines had forged cranks from 62-89. So did the stroked version 181 4 starting in 76-89. Oh, they made alot of them.

Will a cast iron cam work, it sure will. Is the nitriding a nice feature, yes it is as it provides a very hard lobe...will the lobe fail if the assembly isn't right, damn right it will, with or without the nitriding.

Not sure what this means. Did you mean that cast cams are nitrided? Anyway who cares, we were talking about cranks.

a specialist crank manufacturer in the USA would just not have that sort of expertise available

Aircraft Specialists will grind and re-nitride a crank and then certify it. Seen any certification on your Fiat crank?

ne of the journals had a factory undersize of 0.05' The crank was otherwise like new. I was going to reuse the original bearings on that journal but they were a little scored. So i used one new standard bearing shell and one 0.010,

Are these metric sizes. As in 0.05mm equal to 0.00197in and .01mm equals 0.00039in. So you changed the clearance by 0.0015in. That sounds risky.

[ace124]

Correction: 0.005' not 0.05'.
Ill correct it in my original post above.
Fiat bearings are sold in imperial o/s so 0.010', 0.020', 0.030' and 0.040'
On the factory undersize journal of 0.005' i used one original bearing shell in the cap side and one 0.010' shell in the block side.
Clearence thus works out at 0.005' according to my logic in my late teens.
Now thinking about it....the 0.010' bearing shell should have been tight on the crank and the standard shell loose thus slightly distorting the crank but it spun freely and plastigauge showed good.
Can't remember if we did anything else to make it work but it worked for 60k km +