Why do these crankshafts fail? There are several reasons for failure.
1. Aged Failure - Let's face it, these parts are 60-80 years old.
2. Improper weld - If the crank is not welded correctly, porosity or voids can form in the journal, weakening the crankshaft.
3. Improper engine tuning - Having the timing wrong, fuel mixture wrong, miscalculating the compression ratio, etc. can cause unnaturally high forces inside the engine. It can typically be heard as a "knock".
4. It just failed - Fatigue failure - due to the nature of the design, a fair portion of the crankpin is actually weld, not the original crank. The pictures below show the anatomy of a welded crankshaft.
This guy wasn't so lucky. When the crankshaft failed, it also damaged the Block, Connecting Rods, Camshaft, and even the Tractor Crankcase itself.
This crankshaft was in a running tractor. When you tried to roll the flywheel over, the engine had a "hard spot" that was very difficult to roll thru. The most common place for them to crack is in the radius. This one is cracked all the way thru the journal into the arms. Fortunately, this was discovered before the crankshaft separated and failed completely. This crank likely failed from improper tuning - timing was advanced too far.
Crankshafts
Increasing the stroke adds Cubic Inches and most importantly TORQUE and HORSEPOWER!!! One of the most effective changes you can make to your engine is to increase the stroke. The downside to the conventional stroker crankshaft is that it is inherently weak and prone to failure.
NOTE: THE FOLLOWING PICTURES OF BROKEN CRANKS ARE NOT EXTREME TRACTOR PARTS CRANKSHAFTS
Extreme Tractor Parts is committed to providing Superior Quality products that outperform the competition. Failure rates on Extreme Tractor Parts Welded Crankshafts have been very low (only 1 known failure to date).
Even though failure rates of welded crankshafts from ETP have been very low, we are always looking for better ways to do things. ETP will no longer supply the typical Welded Crankshaft. There are now 2 options available from ETP.
For a John Deere 2 Cylinder, we can do what we call a "Half-Billet". What the %^*#$$ is a "Half-Billet Crankshaft?" This is a lower cost version of a full billet crankshaft, but much stronger than a "welded" crankshaft. The center section of the stock crank is removed and a solid piece of billet steel (hence the term "half-billet") is welded to the flanks of the crank, away from the rod journals. This is then CNC machined to shape and ground like a traditional welded crankshaft. The result is a very strong crankshaft free of welds in the journal of the crank.
9.50" John Deere G "Half-Billet" crankshaft.
8 inch John Deere B Billet Crankshaft
If you have a Farmall, Moline, AC, Oliver, Massey, or anything else, including a John Deere, Full Billet Crankshafts are available. The Billet Crankshaft is made from a steel alloy nearly double the strength of the original Crankshafts. Prices vary depending on the model.