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Could it be the tach?

B

bluesflyer

Member
Engine recently started showing only 2200 on the tach at full power. Starts fine. Plugs not fouled. Mag drop is between 50-75, both mags. Carb heat shows minor drop and then back up again when closed. SOUNDS like it's making full power, but tach doesn't show it as such. I tried to use a digital tach that uses a laser, but I cannot seem to get a reading. I probably have too much light. Might have to do it at night. Lycoming O-360 180 hp. Approx 450 SMOH. Mechanical tach. I have heard that where the square cable enters the back, the area can become worn and the cable starts to slip. Any thoughts? This is in a 50 year old Beechcraft.
Any help is appreciated.
 
bluesflyer said:
Engine recently started showing only 2200 on the tach at full power. Starts fine. Plugs not fouled. Mag drop is between 50-75, both mags. Carb heat shows minor drop and then back up again when closed. SOUNDS like it's making full power, but tach doesn't show it as such. I tried to use a digital tach that uses a laser, but I cannot seem to get a reading. I probably have too much light. Might have to do it at night. Lycoming O-360 180 hp. Approx 450 SMOH. Mechanical tach. I have heard that where the square cable enters the back, the area can become worn and the cable starts to slip. Any thoughts? This is in a 50 year old Beechcraft.
Any help is appreciated.
Click to expand...
Also, it never showed above 2500-2550 since I bought it in 2024.
 
Find a good optical tach to see what RPM you really have. Then you'll know if you need to troubleshoot or not.
 
bluesflyer said:
Can you provide some more info on an optical tach, please. Sad to say, not sure what it is. Similar to a timing light? Thank you.
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I think that's the laser light device I have. Just need some better light conditions. Right now I've been trying to do that in daylight. Probably not the best condition for that.
 
The least expensive types will likely have a piece of reflective tape you put on one blade and read via laser. There are other types that you can put inside the aircraft and they'll read the RPM of a 2 or 3 blade prop. That type may be more expensive, though.
 
D-Dubya said:
The least expensive types will likely have a piece of reflective tape you put on one blade and read via laser. There are other types that you can put inside the aircraft and they'll read the RPM of a 2 or 3 blade prop. That type may be more expensive, though.
Click to expand...
 
I had an old optical tach that I used for model RC airplanes. I had someone point it at the prop while I was inside my plane, with the engine running. The optical tach reading matched the tach display of the engine monitor.

My $.02 this afternoon.
Steve
 
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