National Aeronca Association Bulletin Board

Learned Aeroncateers,

On yesterday's flight, after about an hour of T/O and Landings, the tach started to jump up to about 2500 (from 2200) in the climb after a take off. It did this a couple more times during the remainder of the flight. No corresponding change in engine sound. I replaced the tach cable in the last 100 hours. Is it likely the instrument or cable?

Thanks for your thoughts on the matter.

Brad

Brad,

Have seen this with cables used on a speedometer so would focus on the cable first. Have you tried feeling the cable housing in flight? Might put your hand on the housing and see if you feel anything.

Just an idea...

Joe

Like Joe says if it is jumping up momentarily ,could be the cable but if it is staying up there for a period of time, probably the tach getting dirty. My SC is starting to do the same thing. Flew at 3000 rpm for a while this morning them 1500 rpm for a while then went back to normal.

I had that happen when I installed a new cable. I had to shorten the end that goes into the tach slightly.

My bet is it has too much lub. Remove the cable, clean and dry. Use a good general purpose grease, work into the cable then remove all excess
grease. That is all that is needed. It is a commen problem. In cold weather
the grease gets stiff and the cable acts like a rubber band--winds up then
lets go----you just over revved your engine! I had a simular problem
with my old VW coming from Fla. into -30F TN. winter. The speed-o-meter
would act up like the TAC. I used a rag soked in gas, squeezed the gas
into the housing-----presto, frozen hands, but it worked!
Best of luck,
Lowell

Lowell,

Can you give me instructions on how to clean and re-lube the cable? Think Texas Aggie when you respond <G>

Thanks,

Brad