Tag engines have been developed and refined over the years to a high level of performance and reliability. But to keep that high performance and reliability, the crankshaft demands respect. The crank rod assembly is one of the most highly stressed components in the engine.
It is asked to spin at up to 17000 rpm while exerting huge acceleration and combustion forces on the rod bearing and main bearings. Surprisingly it survives this bedlam, but only if it is well aligned and not wobbling. Wobbling is called crankshaft runout in technical terms. Runout occurs when the two crank halves are not in perfect alignment on the crank pin linking them together. A wobbling crankshaft has at least 2 detrimental effects: first is increased bearing friction on both the main bearings and the lower rod bearing, and second is shortened bearing and seal life.
Very few crankshafts will achieve perfect alignment even from the factory. Most TAG crankshafts have some measurable wobble. But within certain limits it is OK because the clearances designed into the bearings will accommodate small misalignments. However, beyond that limit increasing wobble rapidly increases bearing heat and stress and the horsepower lost due to friction. The best policy is to keep wobble to the minimum by observing a few simple rules.
The common denominator for all these “don’t”s is avoid shocking the shaft. Although the crankshafts are pressed together with many tons of force, and the friction holding the parts together is therefore great, a sharp blow with a hammer or other object can duplicate those many tons of force for a very small instant and move the crank halves relative to one another. Any small movement like that is likely to increase run out and decrease performance.
It is asked to spin at up to 17000 rpm while exerting huge acceleration and combustion forces on the rod bearing and main bearings. Surprisingly it survives this bedlam, but only if it is well aligned and not wobbling. Wobbling is called crankshaft runout in technical terms. Runout occurs when the two crank halves are not in perfect alignment on the crank pin linking them together. A wobbling crankshaft has at least 2 detrimental effects: first is increased bearing friction on both the main bearings and the lower rod bearing, and second is shortened bearing and seal life.
Very few crankshafts will achieve perfect alignment even from the factory. Most TAG crankshafts have some measurable wobble. But within certain limits it is OK because the clearances designed into the bearings will accommodate small misalignments. However, beyond that limit increasing wobble rapidly increases bearing heat and stress and the horsepower lost due to friction. The best policy is to keep wobble to the minimum by observing a few simple rules.
- Do not use impact wrenches to tighten nuts on the crankshaft. Use a holder to stabilize what ever you may be tightening on the shaft.
- Do not strike the crankshaft with a hammer. EVER.
- Also try to limit the number of times ignition rotors and clutches are popped off of the engine’s tapered shafts.
- When shipping an engine, pack it so that the crank is protected from the bumps and drops that can occur in transit.
The common denominator for all these “don’t”s is avoid shocking the shaft. Although the crankshafts are pressed together with many tons of force, and the friction holding the parts together is therefore great, a sharp blow with a hammer or other object can duplicate those many tons of force for a very small instant and move the crank halves relative to one another. Any small movement like that is likely to increase run out and decrease performance.
