O-200 tach reads about 200 rpm during take-off

[gcgilpin]

During take-off the tach shows about 200 RPM lower than it should (ie it shows about 2250 but should show about 2450). I've verified the engine actually turns 2450 with a hand-held electronic unit.

After a couple minutes the tach always starts reading the proper value.

The tachometer is new, the tach cable is new and the engine is new.

Saw this same thing last winter so I put a new tach cable in and the problem went away, thought I had fixed the problem. Now the exact same problem is back.

Anyone have any ideas?

 

[aalexander]

(ie it shows about 2250 but should show about 2450). I've verified this with an hand-held electronic unit.

You've verified what? that the engine actually turns 2450, or that it turns 2250? could be read either way, and makes a world of difference in the discussion

 

[gcgilpin]

(ie it shows about 2250 but should show about 2450). I've verified this with an hand-held electronic unit.

You've verified what? that the engine actually turns 2450, or that it turns 2250? could be read either way, and makes a world of difference in the discussion

Verified that the engine turns 2450 while the tach shows 2250.

 

[stevensonjr]

I had several problems with the stock mechanical tach and cable so I went with a Horizon electronic tach. No more problems and more information too. Bill

 

[garyh]

I had trouble with my tac also. like my mechanic said " the only way to know if the tac is reading correctly is to use electronic tac " so i bought an Electronics international (2-1/4"). trouble gone forever and i love it.

 

[R. JOHNSON]

You might want to pull the tach cable off at the tach and check for oil coming through the cable into the tach. This just happened to me and it unfortunately voids the warranty on the tach when they've got oil in them.
The tach worked but it would "lag" behind similar to what you described.

 

[RobL]

It's also possible that the tach cable has the incorrect "lay". They are designed to rotate one way only. If it's rotating the other way, it might tend to unwind, showing as a lag in the reading.

 

[gcgilpin]

The tach cable was ordered with the correct 'lay' for an O-200. I checked this.

 

[gcgilpin]

The 'oil in the tach' theory seems to make sense. I've heard the same thing on the Aeronca site. Probably got oil in it when I was running with the 'old / ancient' cable.

Has anyone used the new UMA electronic tachs?

 

[gcgilpin]

The 'oil in the tach' theory seems to make sense. I've heard the same thing on the Aeronca site. Probably got oil in it when I was running with the 'old / ancient' cable.

Has anyone used the new UMA electronic tachs?

 

[Mathew Sharp]

See the Pierce's group buy on tachs from EI on shortwingpipers.org

 

[NimpoCub]

Still looking for a new(er) tach cable. Mine broke. I've not been pursuing this as dilligently as possible, so if someone can make this easy for me, that'd be great. (Oh, about 22-24" would be perfect)
I've got so many things going on right now it's almost confusing.