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My father went flying a few weeks ago and told me the bottom 1/3 of the tach had filled up with oil. Several months back we had an issue with the needle jittering and getting stuck at a certain RPM and attributed it to the cable wearing out and binding. Now we have a leaky cable and a tach that needs reconditioning.
It looks nearly identical to this (Kollsman Centrifugal Tachometer):
Anyone have suggestions on a remedy? My first instinct is to replace the tach and cable, and send this one for O/H. Ideally I would like to have it fixed before Airventure ’21.
Wes
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Wes,
Per the L-5 Parts Catalog the historically correct tachometer for the L-5E is the Jaeger Type C-11 (Spec. 94-27343). It looks like this –
There’s nothing wrong with using the one you have if it hasn’t been damaged and you get it serviced after being oil-soaked. If you would like to install a C-11, contact club member John Seidts. He may still have some NOS tachs. They were used on many airplanes, including the P-40. His website is here: http://www.forgottenfield.com/amg/
Many people use recording tachometers instead. They aren’t correct from an authenticity standpoint but are useful for tracking engine time if you do not have a Hobbs meter. As delivered from the factory, the L-5’s didn’t have either and pilots simply recorded engine start and stop time from the clock.
If your cable is in good working order, no need to replace it. Do you have the original tach cable and housing assembly or an after-market replacement? If not, originals are not easy to find, but if you have the fittings from one any speedometer / tachometer repair shop should be able to build a new one for you. Unfortunately, since they were Government Furnished Equipment (GFE) along with the engine, there are no drawings available in the L-5 blueprint collection.
The tach cables generally don’t fail unless a wire strand breaks and the cable starts binding, or the tach itself fails and won’t turn up to speed. An oil-filled tack can cause that problem, as well as lack of lubrication. Periodic cleaning and lubrication of the cable is good practice and the tach should be cleaned and lubricated from time-to-time too.
As for the oil problem, there is a cork seal inside the tach drive housing about 1/2″ diameter and 1/4″ deep that is supposed to prevent oil from migrating into the drive cable and up to the instrument. Lycoming Part 60957. They are not easy to find, but it’s worth looking. I have a large number of them but cannot access my parts horde until I return to AZ from Alaska this fall. Sadly, I had some in my hands just a few days ago while on a visit to Phoenix. I may have sent John Griffin some extras a year or so ago, so you might ask him if he doesn’t see this post. You may substitute oil-proof O-rings and Sam Taber can help you with that. I’ve lost his info on part numbers but his Tabair phone # is (262) 642-4515.
Good luck,
Jim
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