Tach Cable

Cross Reference Reference only: Please verify the product is eligible for your aircraft before adding to your cart. OEM Part Number McFarlane Part Number Comment S1605-5 MCS2550-8 S1605-6 MCS2550-8 S2550-8 MCS2550-8

Approval: FAA PMA (DocumentNumber: PMA-MCA-219) SupersedesPartNumber: S1605-5 (Manufacturer: Textron) SupersedesPartNumber: S1605-6 (Manufacturer: Textron) SupersedesPartNumber: S2550-8 (Manufacturer: Textron)

We recommend replacing the full tach cable assembly instead of only replacing the core. The old casing will have wear, and sometimes this wear will be enough to prevent a brand-new core from rotating smoothly when used with the old casing. We do not offer replacement cores; however, our full tach cable assemblies are an affordable alternative with better strength and reliability

1) Tach cable should be installed as straight as possible. The installed cable should be free of kinks, dents, and sharp bends, with no bends on a radius shorter than six inches and no bends within three inches of either terminal. Any deviation from these instructions is very likely to cause binding/jerking of the tach cable as it rotates, which will prevent the tachometer from reading accurately.2) It’s unlikely to be an issue but ensuring that the hole in the engine ferrule is pointed downward when installing may help with oil drainage if the oil seal in the tach drive housing ever fails for any reason. If that seal fails in flight, and the oil can’t drain out of the drainage hole in the ferrule, it may travel up the tach cable into the tachometer and leak out of the instrument panel into the cabin.

A noisy and/or inconsistent tach needle is a sign that something is likely wrong with the tach cable. If the cable is new, the problem is more than likely either in the installation or the lubrication of the assembly. In which case:1) check the housing for kinks, dents, or sharp bends. Ensure it is routed as straight as possible. The more bends in the assembly, the more likely the tach cable will have issues rotating smoothly, especially as those bends get sharper or get nearer to one or both ends.2) Disconnect your cable at the tach, hold it vertically by one end, and slowly rotate the core terminal by hand to check for smooth rotation. Any jerking may be an indication of wear spots, kinks, or breaks in either the core or conduit. Damaged spots on the core will snag on the inside of the conduit when rotating (or vice versa), causing the jerkiness in the tach needle.3) Re-lubricate the assembly. Re-install per the maintenance manual instructions. Check the tach needle for steady and accurate reading.4) If the problem persists, the cause is less clear. If the tach cable has been in service for some time, it may have become too worn to work correctly. Even if the core didn’t have obvious worn spots, kinks, or breaks during the earlier troubleshooting, the inside of the conduit/casing may have accumulated enough wear over time to prevent smooth rotation. A replacement will fix that. It may also be an issue with the tachometer itself if the normal troubleshooting steps don’t fix the issue.