Talk about Tach

[Skydiver Scott]

OK, this may sound silly but My boat does not have a Tach and there is talk when people have a questions to troubleshoot with the basic tests including compression, spark and tach. I don't have one and go by feel with no basis to what I am getting in terms of RPM WOT and speed. If I wanted to add a Tach that is where my confusion starts. I am not un-mechanical and I do a lot of repairs and stuff but I am by no means an expert... There has been talk about about 12 Pole and 20 Pole, Tiny Tach and other options. If I wanted to add a tach to a 85HP S/N 856X7A, how would I figure out what I need?

Hey, this might be a Sticky directions chance

Thanks,
Scott

 

[huskerdaninva]

Re: Talk about Tach

The easiest way to determine the tach you need is to literally count the poles or individual windings on your stator under the flywheel. If you can find a picture of the proper replacment stator on line you can count the poles. (ie 12 or 20) Also any reputable seller should be able to tell you what type of tach you could run with your motor year, serial & model number. Hope this helps.

 

[roscoe]

Re: Talk about Tach

A tach helps in diagnosis, prop selection, determining correct idle speed, can alert you to sudden or gradual performance changes in your motor, etc.

You need a 20 pole tach for that motor.
Since the last remaining manufacturer has stopped making them, they are extremely difficult to find. All online and ebay sources have dried up. So you would need to check local Mercury dealers to see if they have one on the shelf. Or use an inductive TinyTach and deal with its shortcomings. They have short wires, and must be mounted near the engine, not on the dash.

Some guys were trying to engineer a converter, to let you use any outboard tach, but last I heard they were not successful yet.