How to fit an engine speed or position sensor on heavy equipment

To fit an engine speed or position sensor on a machine, first work out how it mounts. A bracket or flange mounted sensor, like the Caterpillar 216-3446 used on 3054E, 3056E, C4.4 and C6.6 engines, has its gap fixed by the machining: oil the O-ring, push it fully home, check the flange sits flush, then tighten the bracket bolt. There is nothing to adjust. A threaded magnetic pickup with a lock nut is different: you set the gap yourself by turning a tooth under the hole, screwing the pickup in until it touches, backing it out by the amount your manual gives and locking the nut. Then plug it in, put the lead back in its clips and watch the engine speed reading on the first start. Most early failures come from treating one type like the other, a connector that is not fully latched, or a lead left near heat.

Which sensor do you have?

Our store has 70 heavy equipment sensors. Thirteen of them are speed sensors, two are crankshaft or camshaft position sensors and three are throttle position sensors. They do the same job, telling the controller how fast something is turning, but they go in two very different ways.

• Bracket or flange mount. A smooth plastic or metal body with an O-ring, held by one bolt through a bracket or flange. The Caterpillar 216-3446 position sensor (see current price) is this type: a Hall effect sensor with a bracket and an integral connector. The depth it sits at is set by the bore and the bracket, so the gap to the timing wheel is fixed.
• Threaded magnetic pickup. A threaded steel body with a lock nut, screwed into a tapped hole in the flywheel housing or gearbox. The Doosan 2547-1015 engine speed sensor (see current price) for Doosan DH, Solar and DX excavators is this type, as is the Cummins 4327233 dual output magnetic pickup for QSM11, M11, N14 and K19 engines. How far you screw it in decides the gap.

Look at the old part before you order and before you fit. If it has a lock nut and threads along the body, it is a threaded pickup. If it has a bracket ear or a flange with a bolt hole, it is a fixed gap sensor. Our heavy equipment sensors list each part with the machines it fits, and the part number on the old sensor is the surest match.

Before you start

• Check the new part against the old one. Same part number, same mounting style, same plug shape and pin count. Hold the two side by side and compare the body length below the bracket or the thread length. Some engines carry two speed sensors, one on the crankshaft and one on the camshaft or pump. Note which hole the old one came out of.
• Engine off, key out, and let it cool. MOTORTECH's pickup instructions say to install only with the engine shut down and warn that the sensor location gets hot. A flywheel housing sensor sits close to the exhaust on many machines.
• Photograph the lead. Take a picture of how the lead runs and where every clip and tie sits before you undo anything. You will put it back exactly that way.

Removing the old sensor

Press the latch and pull the connector apart before you move the sensor, so the lead does not take the strain. On a bracket sensor, take out the single bolt and twist the sensor gently as you pull it straight out. The O-ring often sticks in the bore. On a threaded pickup, slacken the lock nut and unscrew the body.

Look at the tip before you put the old one aside. Rub marks or a flattened face mean the tip touched the teeth. A coat of steel fuzz stuck to a magnetic tip means wear debris is reaching that housing, and it is worth finding out where it comes from. Wipe the bore and the seat face clean so the new sensor sits on bare metal.

Fitting a bracket or flange mounted sensor

Caterpillar's procedure for its bracket mounted speed and timing sensors is short and precise, and every point in it matters:

• One O-ring, undamaged, oiled. Check there is exactly one O-ring on the sensor and that it is not cut or twisted. Lubricate it with engine oil.
• Fully seated before the bolt is tightened. Push the sensor all the way into the bore by hand first. The bolt holds it in place. It is not there to pull it down.
• Flange flush, bracket straight. Caterpillar says the flange must sit flush against the engine for the sensor to work properly, and that the bracket cannot be replaced on its own. A bent bracket means a new sensor.
• Nothing to adjust. Do not add washers or shims, and do not leave it standing proud. Either one moves the tip away from the wheel and weakens the signal.

Tighten the bracket bolt to the figure in your engine manual, not by feel with a long bar.

One warning for 216-3446 owners: the fitting tip on our product page talks about screwing the sensor in until it touches the teeth. That applies to threaded pickups, not to this bracket mounted sensor. Fit 216-3446 as described here: seat it fully and bolt it.

Fitting a threaded magnetic pickup

The gap is the distance between the pickup tip and the top of a tooth. Too wide and the signal the controller sees is weak. Too close and the tip can strike the teeth. The usual way to set it, which Seaboard Marine gives for the Cummins dual output pickup, is:

• Centre a tooth under the hole. Bar the engine over until you can see one tooth sitting squarely in the middle of the hole, not the gap between two teeth.
• Grease the threads lightly so the pickup turns smoothly and comes out next time.
• Screw it in by hand until it bottoms out on that tooth. Stop as soon as you feel it touch. Do not force it.
• Back it out. Seaboard gives exactly half a turn for that pickup. Use the figure in your own manual if it gives one.
• Hold the body and tighten the lock nut. If the body turns with the nut, the gap changes.

What half a turn means depends on the thread. MOTORTECH's magnetic pickup uses a 5/8-18 UNF thread, and its instructions state that one turn moves the tip 1.4 mm. Half a turn is about 0.7 mm, inside the 0.5 to 1 mm air gap MOTORTECH specifies for that pickup. A pickup with a different thread pitch moves a different distance per turn, so count turns against the pitch, not by habit.

Never crank the engine with the pickup screwed down onto a tooth. The first tooth that comes round will hit it.

Connector and lead routing

A lot of sensors that seem faulty are really connectors that are not fully latched or leads that have rubbed through. Caterpillar's procedure asks for the connector to be latched on both sides and the harness to be secured with the ties in their correct places.

• Clean, dry pins. Look into both halves of the plug. Green corrosion, bent pins or water mean the harness side needs attention before a new sensor will read properly.
• Push until it clicks. Then pull gently on the plug body, not the wires, to confirm the latch holds.
• Back into every clip. Follow your photograph. A loose lead near the flywheel housing, alternator or belt will be cut through in time.
• Keep it off hot metal. MOTORTECH's instructions also say to protect the lead and to keep the sensor clear of mechanical damage. Route it away from the exhaust and turbo.
• No tight bends right where the lead leaves the sensor body. That is where the wires break inside the insulation.

First start checks

• Watch the engine speed while cranking. On machines with a monitor or a diagnostic tool, an engine speed reading should appear as soon as the starter turns. No reading at all points to the plug, the gap on a threaded pickup, or a sensor in the wrong hole.
• Steady idle. The reading should be stable at idle and follow the throttle smoothly.
• Clear the old codes once the engine runs, then run it up and back down and check that no speed or timing code returns.
• Calibration. On the Caterpillar engines its procedure covers, timing calibration is only needed after replacing an ECM that will not communicate, not after fitting a sensor. Other engines and machines differ, so follow your manual. Throttle position sensors such as the Hitachi 4614912 and Caterpillar 227-7658 do need the throttle calibrated after fitting, as the machine manual describes.
• Recheck after the first hours. MOTORTECH recommends checking regularly that a pickup is still tight. Look at the lock nut and the bracket bolt at the next service.

If the new sensor gives the same fault as the old one, the sensor was probably never the problem. Look at the harness, the plug and the timing wheel before you order another. For part numbers you cannot find in our heavy equipment engine parts, send us the number from the old sensor through our quote request page.

Frequently asked questions

Do I need to set an air gap on the Caterpillar 216-3446?
No. It is a bracket mounted sensor. The gap is fixed by the bore and the bracket. Oil the O-ring, push it fully home, check the flange is flush and tighten the bolt.

How far do I back out a threaded speed sensor?
Use the figure in your machine manual. Half a turn after touching a tooth is a common figure, for example for the Cummins dual output pickup. On a 5/8-18 UNF thread that is about 0.7 mm.

Should I put thread sealant on a magnetic pickup?
The instructions we use for Cummins pickups call for a light coat of grease on the threads, not sealant. The lock nut holds the setting.

The new sensor shows the same fault code. Is it faulty?
Check the plug for corrosion and a full latch, the lead for chafe, and on a threaded pickup the gap. A fault that survives a new sensor usually lives in the harness or connector.

Can I reuse the old O-ring?
Fit the sensor with one undamaged O-ring, oiled. If the old one is flattened, cut or stuck in the bore, use the one on the new sensor and make sure the old one is out of the hole first.