Tach cable: lay right or left.

[Martinho]

What could be the problem (or could be the consequences) if you install a tach cable lay left instead lay right?
Tks
Martinho

 

[Steve Pierce]

I don't understand your question.

 

[Martinho]

Sir,
There are two types of internal cables for driving the tachometers, with the wires twisted to the left or right (photo below). The question is whether there will be a problem if I use the cable with the opposite twist to the original cable.

 

[Steve Pierce]

Interesting, I did not know that.

 

[irishfield]

Using the opposite twist than required, the instance there is any resistance to turning it will swell open and ruin your day !!

 

[Charlie Longley]

Buy an electronic tach.

 

[TR Dunn]

What could be the problem (or could be the consequences) if you install a tach cable lay left instead lay right?
Tks
Martinho

The left lay is intended for CCW rotation, the right lay is intended for CW rotation. Using the opposite rotation than designed, will most likely end in a failure at some unpredictable time. Match the appropriate cable and tachometer rotation to your engine tach drive by observing its rotation (the tach drive) while turning the crankshaft in is intended operational direction. There are radial engine designs that incorporate two mechanical drives, one being CW, the other CCW based on their location on the accessory case. Important to visually confirm rotational direction and use the correct cable and tach.

TR

 

[Martinho]

The tachometer inner cable of my PA-18 is,certainly, CW but, here in Brasília-BR, I only got CCW cable. In order not to run out of flying, I'm considering using this cable, even though I know it's not the right one, until I import a new one. However, what worries me is, eventually, damaging the tachometer.

Martinho.

 

[skywagon8a]

From long ago experience, the cable will just unwind and break inside the conduit. No harm will be done to the tachometer, it will just stop working. Just speculating here, if you have it well lubricated with some very slippery lubricant you may get some life out of it.

 

[Martinho]

Your considerations are quite reasonable. I expect to use the incorrect inner cable for a short time until I get the proper cable. Thank you for your attention

 

[flyguysr5]

In the Stearman radial engine world there is a poor oil seal where the cable is driven by the engine and the wrong lay tends to draw oil up into the tach, ends up ruining the tach vs pushing it back toward the drive.

 

[Martinho]

The mechanic who made the inner cable warned that if the cable was excessively greased, the grease could penetrate the tachometer. The same could happen if oil passed from the engine socket to the cable. My engine is a Lycoming O-290D and I did not identify any excess oil that could be piped into the instrument. Anyway, thanks for the alert.

 

[skywagon8a]

There is a pressed in cup seal around the tach drive in the engine which is supposed to prevent engine oil from getting into the drive. The engine can be run without the tach drive installed without any oil leaking out of the drive. Don't use an excessive amount of lubricant, just a slippery type of lubricant.

 

[Martinho]

Well observed. I think the only concern will be with the integrity of the internal cable, which I hope to replace as soon as possible. Thank you.