Crankshafts

By Dave Nicoll
May 2012

I did a little exercise to see what replacement cranks cost.

Brown and Gammons and Moss are, of course, distributors.
Manley is a supplier of race TD parts.
Moldex and Farndon are both crankshaft manufacturers.

Interesting to see a swing of 25% from lowest to highest.

I (Webmaster) asked for more information. Dave Nicoll added the following:

There are three common manufacturing processes for crankshafts.

1) Casting. This pours molten metal into a mould then the crankshaft is machined. The oldest method and perhaps the worst. Not used much anymore. Castings tend to be more brittle.

2) Forging, Excellent for internal strength and the best possible method with modern materials. Only viable on longer production runs. Forgings tend to be tough.

3) Billet. This method machines an entire crankshaft from a solid bar. Very expensive, but very accurate using modern methods. Short run production only. Machined all over gives excellent finish and balance.

ANY new crankshaft, be it forged or cut from a billet is many times superior to the old OEM cast cranks. This is just a fact with new steels and new heat treating methods. A new crank will no longer be the weakest link in the XPAG engine.

EN40B and 4340 are just the identification of two steel alloys one US and one UK that fit this application.

AISI 4340 is a heat treatable, low alloy steel containing nickel, chromium and molybdenum. It is known for its toughness and capability of developing high strength in the heat treated condition while retaining good fatigue strength.

EN40B is a chromium-molybdenum nitriding steel usually supplied in the hardened and tempered condition, which offers high wear resistance together with good toughness and ductility. It is characterised by its suitability for nitriding, which can give a hard wear resistant core in the range of 61-65Rc. The relatively low temperature of the nitriding process produces components with a scale free surface, and minimum distortion.

Ion nitriding is a process to harden the top layer of a finished product such as a crankshaft or a camshaft. Bob Gruneau ran a nitrided cam in his race TC. When you consider wear in an engine, say between the cam shaft and the tappets, it is normal to design the most expensive or hard to change part dominant. That is to say the tappets are designed to be softer and slightly sacrificial to the cam so they carry the wear load, thus extending the life of the camshaft. This is also one reason why bearing shells are used on the crankshaft bearing surfaces.

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Last revision: 31-May-2012