SeaDogAK
Senior Member
- Joined
- Aug 9, 2021
- Messages
- 386
- Vessel Name
- Sea Dog
- Vessel Make
- 1991 DeFever 49 RPH
I have twin Perkins T6.3544 engines, approximately 1991 vintage. Currently my tachometers run from the Balmar voltage regulator. I’m thinking of switching to mechanical tachometers using the tach drive on the front of the engines.
The current tachs work intermittently. As far as I can tell, they quit working when the alternators aren’t charging. When they do work, they always read 500 rpms or so high at cruising speed. I’ve gotten to where I go down to the engine room with a laser tach when I need to know rpm’s, because the tachs are pretty well useless.
I’ve checked all the contacts, and I’ve had a tech look at the situation, but I’m not sure what else to do to try to make the existing tachs work. There isn’t really anyone in Juneau that I can have look at the problem. I’m thinking the solution is to just switch to mechanical tachs.
I’ve seen a lot of threads with people complaining about alternator tachs not working, but not a lot of solutions. I suppose there’s a reason why people switched from mechanical to alternator tachs years ago, but I’m not sure if there are any disadvantages to going back to a mechanical tach.
There is what I think is a tach port on the front of the engine (picture below). I’m thinking I can put a mechanical sender like an Aetna Engineering 8901on there. I’m not quite sure, though, about the gear ratios; I don’t know if the tach port turns at the same rpm’s as the engine, or if it’s geared differently, and how to deal with that. The Aetna says it gives 8 pulses per rotation, but I don’t know if that corresponds to one rotation of the engine.
Has anyone done this? Does anyone have a recommendation for a tach to use?
The current tachs work intermittently. As far as I can tell, they quit working when the alternators aren’t charging. When they do work, they always read 500 rpms or so high at cruising speed. I’ve gotten to where I go down to the engine room with a laser tach when I need to know rpm’s, because the tachs are pretty well useless.
I’ve checked all the contacts, and I’ve had a tech look at the situation, but I’m not sure what else to do to try to make the existing tachs work. There isn’t really anyone in Juneau that I can have look at the problem. I’m thinking the solution is to just switch to mechanical tachs.
I’ve seen a lot of threads with people complaining about alternator tachs not working, but not a lot of solutions. I suppose there’s a reason why people switched from mechanical to alternator tachs years ago, but I’m not sure if there are any disadvantages to going back to a mechanical tach.
There is what I think is a tach port on the front of the engine (picture below). I’m thinking I can put a mechanical sender like an Aetna Engineering 8901on there. I’m not quite sure, though, about the gear ratios; I don’t know if the tach port turns at the same rpm’s as the engine, or if it’s geared differently, and how to deal with that. The Aetna says it gives 8 pulses per rotation, but I don’t know if that corresponds to one rotation of the engine.
Has anyone done this? Does anyone have a recommendation for a tach to use?