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I don’t believe that I have ever written about watching out fordamaged as-cast reluctor rings, spark triggers or whatever other namesome manufacturer has given them to create their ownidentity/ownership. It’s not as bad as the variable displacementacronyms but still running a close second.  

ANYWAY. Before we talk about this issue you need to understand whythis area is so critical: it triggers the crankshaft position sensorused on engines with distributorless ignition systems. The crankshaftposition (CPS) sensor serves the same purpose as the ignition pickupand trigger wheel in an electronic distributor. It generates a signalthat the PCM needs to determine the position of the crankshaft and thenumber one cylinder.

This information is necessary to control ignition timing and theoperation of the fuel injectors. The signal from the crank sensor alsotells the PCM how fast the engine is running (engine rpm) so ignitiontiming can be advanced or retarded as needed. On some engines, aseparate camshaft position sensor is also used to help the PCMdetermine the correct firing order. The engine will not run withoutthis sensor’s input.

There are two basic types of crankshaft position sensors: Magnetic Field (Variable Reluctance) and Hall Effect (Figure 1).The magnetic type uses a magnet to sense notches in the crankshaft orharmonic balancer. As the notch passes underneath, it causes a changein the magnetic field that produces an alternating current signal. Thefrequency of the signal gives the PCM the information it needs tocontrol timing. The Hall Effect crank sensor uses notches or shutterblades on the crank, cam gear or balancer to disrupt a magnetic fieldin the Hall Effect sensor window. This causes the sensor to switch onand off, producing a digital signal that the PCM reads to determinecrank position and speed.

If a crank position sensor fails, the engine will die. The enginemay still crank but it will not start. Most problems can be traced tofaults in the sensor wiring harness. A disruption of the sensor supplyvoltage (Hall Effect types), ground or return circuits can cause a lossof the all-important timing signal, just as a crankshaft with a damagedor missing cog/tooth in the trigger wheel of the as cast Reluctor ring (Figure 2) will cause problems.

There are many crankshafts with as-cast reluctor rings that have one ofthe notches machined to identify number 1 cylinder at TDC. Because theyare part of the iron casting, these machined areas are very fragile.Remember, cast iron is brittle and has very little elasticity.

What you see here is indicative of many crankshafts that have Reluctorwheels to identify the number 1 cylinder.  If this small center lug issomehow broken off or damaged so that it no longer provides a goodsignal the engine will not run.  

I know this because of a course that I took in SHoKU (show’ coo)(School of Hard Knocks University) when an engine was sent out and itwould not fire. So pay close attention to the way that you handle anyand every crankshaft that has an “as cast” reluctor ring on it becausethe engine you may save could be the one that goes to a friend or a oneof your best customers.figure 1Figure 2

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Roy Berndt
Roy Berndt has decades of machine shop experience. He is the Program Manager for PROFormance Powertrain Products, a PER in Springfield, MO. You can reach Roy at [email protected]