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I know there are some inexpensive photo tachs on the market that read from the flywheel--but came across this one that takes info off sparkplug lead---do you think they are accurate ?

http://answers.northerntool.com/answers ... stions.htm

No reason it shouldn't be accurate... The spark (electrical pulse) travels through the lead, triggers a count by induction and then goes on to the plug where it ignites the mixture (gas and air) in the cylinder... Since any given plug will only spark once every 2 revolution (4 stroke engine) it's a simple matter of multiplying the result by two (will be done by the "chip" in the device)... Since they claim it's suitable for both 2 and 4 stroke engines I'm guessing that there's a setup for you to indicate whether you have a 2 or 4 stroke engine...

The internal battery powers the internal clock, "chip" and memory for the total hours... What would worry me is that in the somebody specifically asks "I want to use it in my boat and I'm wondering if it needs to be installed in a dry area." and the staff's answer is "This Tachometer/Hour Meter should only be used in dry conditions, getting this item wet would make it inoperable."...

So, if you want it for maintenance purposes and installed (permanently or temporarily) close to the engines (the leads provided aren't that long) this would be as good as any other non-marine tachometer... You could put it in some waterproof box... And, if it's going to an internal piloting station I guess it would be just fine... However, if you're thinking about installing this on a flybridge or open (to the elements) piloting station I think you're asking for trouble...

I am thinking for a temporary basis to check my analog tachs------problem would be distance to bridge--can the leads be extended----electronics is not one of my strong subjects------when I am testing the boat, just want to know the correct rpms and how it compares to my gauges---without having someone down at the motors using a hand held photo tach.

Craig Mac wrote:I am thinking for a temporary basis to check my analog tachs------problem would be distance to bridge--can the leads be extended----electronics is not one of my strong subjects------when I am testing the boat, just want to know the correct rpms and how it compares to my gauges---without having someone down at the motors using a hand held photo tach.

For that purpose you should be OK... The leads can be extended (or so it's claimed in one of the staff's answers...

Those type of tachs are potted in epoxy, so they are water resistant (i.e. you can hose them down, but not submerge). The problem is that since the battery is also potted in epoxy they are disposable when the battery dies (they claim 5 years, but who knows.). I had a Tiny Tach brand on a lawnmower. It worked fine until it died. The problem was that I lost the run time for maintenance purpose, as it doesn't give you a warning of its imminent death.

Is there a wireless option? That would make verifying tachs on the bridge easier.

Just bought one of these to try out.

http://www.amazon.com/Universal-Black-D ... B006M7GZ04

I assume i can use alligator clips to tap into pos and neg and sender wire under bridge panel. only need to test one engines instruments at a time.