How to measure engine RPM?

[isaksp00]

for an 8HP 4 stroke Honda.

I have seen few posts of what type of test tach to get. I did find a few references to tinytach.com, however their site says the battery is good for 5 yrs (maybe more), and can not be replaced - don't like that idea.

I haven't found any other references anywhere to what type of test equipment would work.

Thanks, Peter

 

[Sea Rider]

Re: How to measure engine RPM?

Been using a Tiny Tach for more than 5 years and battery is still ok, with cutter and a bit of patience, you can open up the tach and change battery, will need to seal it again, for what is costs it's a excellent performer. No complicated wiring as they are inductive tachs, just wrap on any plug cable, will read rpm when engine is on and worked meterd hours when engine is off. Ideal for scheduled preventive/corrective maintenances and as prop selector wot reader.

Happy Boating

 

[isaksp00]

Re: How to measure engine RPM?

Thanks, SeaRider
I guess I can go with the TinyTach. Do you happen to know how many sparks a Honda BF8A (4 stroke, 2 cyl) has per revolution? That is, how to set (or translate with some simple math) the tach counter value? I have the shop manuals, and they don't seem to define this anywhere I can find.

 

[Sea Rider]

Re: How to measure engine RPM?

Thanks, SeaRider
I guess I can go with the TinyTach. Do you happen to know how many sparks a Honda BF8A (4 stroke, 2 cyl) has per revolution? That is, how to set (or translate with some simple math) the tach counter value? I have the shop manuals, and they don't seem to define this anywhere I can find.

There's a new TT Standard TT2A model, reads from 1 spark per 2 revolutions to 8 sparks per revolution. check ; http://www.tinytach.com/tinytach/gasoline.php

Will need the Honda spark info for adjusting, assume it's not a self spark/rev detecting tach.

Happy Boating

 

[TheInterestHunter]

Re: How to measure engine RPM?

This video helps people know how to use a Tiny Tach on an outboard engine:
http://www.youtube.com/watch?v=HMr7UTcmatY

 

[isaksp00]

Re: How to measure engine RPM?

I bought a "cheap" version of the TinyTach on ebay, see if this link works:
http://cgi.ebay.com/ebaymotors/ws/e...0726237258&viewitem=&sspagename=STRK:MEWNX:IT
It was titled "Tachometer Hour Meter DIRT BIKE ATV OUTBOARD MOTOR PWC" from seller "other_seller".

It was $18.99, free shipping. It seems to work OK, on my Honda 8HP BF8A. I think I left it at factory default, which I think was 1 spark/rev, as the Honda seems to have siamese plugs where the coil sparks both plugs at the same time. Of course, I have no way of knowing if it is accurate, other than when I adjust idle to what "feels" to be about the right speed, it does indicate about the factory recommended RPM, which if I recall is 1200. And it does ramp up as I throttle up, again if I recall to maybe 3000RPM in test tank (garbage can of water). So it basically seems to work.

 

[robert graham]

Re: How to measure engine RPM?

Just curious, but why are you needing to know the RPM's on that motor? Is it relevant to anything?

 

[Sea Rider]

Re: How to measure engine RPM?

Personally, if you like to play with props, is a must have to get the best final speed at wot at max factory recommended rpm, will help to calculate gas consumption knowing rpm at different cruising speeds, to adjust pilot idle speed, excellent for preventive/corrective maintenances if it's the dual rpm/hour meter. For what it costs and what it does, a superb naughty little instrument.

Happy Boating

 

[isaksp00]

Re: How to measure engine RPM?

I got it because after I disassembled and cleaned my carb, I wanted to be able to adjust the pilot screw and throttle stop to the recommended RPM.

 

[pvanv]

Re: How to measure engine RPM?

Tohatsu America also sells a tach, available from any dealer (including me) that we use in our shop. Very versatile -- can use it on anything from a 1-cyl chainsaw to a 12-cyl Jaguar, though a bit finicky in picking up stray signals. Also a bit pricey, but very accurate. Part # 99998STACH $209.18.