Tach question

[ronward]

I've been following the post by Rookie456 about a tach for his '72 Johnson 50 but didn't want to hijack his post. I also want to add a tach as well, but on three different motors. A '77 Evinrude 25 (25702H), a '74 Johnson 50 (50ESL74M), and a '70 Johnson 33 (33E70M). There were two people giving different answers on Rookie"s post. One said a 6p tach and one said a 5p. What does 5p and 6p actually mean? And how does someone know which type to use for any given motor?

 

[boobie]

Re: Tach question

You have to have a battery charging system on your motor for a tach to work. It runs off of the stator. On the smaller mtrs you set the tach to 5 P due to having 5 magnets in the flywheel. The bigger mtrs have 6 magnets in the flywheel therefore 6 P position. No charging system, no tach. Unless it's a "Tiny Tach".

 

[ronward]

Re: Tach question

So what I get is you have to count the number of magnets on your particular flywheel to know what tach to use, 5p or 6p. Do all marine tachs have a switch for 5p or 6p or do you have to get a specific tach? how do you know since they don't list 5p or 6p in the description?

 

[boobie]

Re: Tach question

All good tachs have a switch on the back where you set the pole position. Usually you get instructions with the tach to find out what mtr you have and the pole position to set it on.