Rev counter

apshutt · 23 May 2015, 10:55

Hi all. Can anyone send me a link to a rev counter to buy as I want to check out my engine. 8hp Mariner 8b. I have looked on ebay and can't find a test one.
Thank you

Andy

dave3235 · 23 May 2015, 12:47

Not sure how to link but Digital Tach Hour Metre,should come straight up.

chipko · 23 May 2015, 17:46

Cheap one
http://pages.ebay.com/link/?nav=item...d=221770858676
Better one
http://pages.ebay.com/link/?nav=item...d=200875873269

apshutt · 23 May 2015, 19:00

Thanks to you both. Liked the "better one" though.

chipko · 23 May 2015, 21:00

Don't blame you. I have both, both work, but the better one has a much clearer display. Factor in some import tax if considering though.

Roflhat · 25 May 2015, 08:27

LCD Digital Engine Tach Tachometer Hour Meter Gauge for Racing Motorcycle UK | eBay
These are not bad either, pretty much a copy of a tiny tach

kestrel452 · 29 May 2015, 03:16

I tried for a couple hours to find a spot on my Merc 15's spark plug wires that'd make my trail tech tto portable tach work. I couldn't get it to read reliably. I would get a stable reading, but then it'd just start going all over the place again. Tried switching the sensitivity as well.

Those portable tachs are nothing more than a digital display with a long wire antenna attached to them, anything electrical going on in the motor will interfere. I found that even if I somehow managed to get a somewhat reliable reading, placing the cowl back on the motor ruined it. I resigned to the fact that messing around with it any further was a fool's errand, especially since the cowl seems to be like reflecting the interfering signals back inwards (which the trail tech tach would pick up).

dave3235 · 29 May 2015, 09:04

Quote:

Originally Posted by kestrel452

I tried for a couple hours to find a spot on my Merc 15's spark plug wires that'd make my trail tech tto portable tach work. I couldn't get it to read reliably. I would get a stable reading, but then it'd just start going all over the place again. Tried switching the sensitivity as well.

Those portable tachs are nothing more than a digital display with a long wire antenna attached to them, anything electrical going on in the motor will interfere. I found that even if I somehow managed to get a somewhat reliable reading, placing the cowl back on the motor ruined it. I resigned to the fact that messing around with it any further was a fool's errand, especially since the cowl seems to be like reflecting the interfering signals back inwards (which the trail tech tach would pick up).

Hi

What about once connected to the HT lead, try covering the rest of the lead with insulation tape just a thought.Also have the lead running directly outside of the engine cowl.

Max... · 29 May 2015, 10:26

Quote:

Originally Posted by kestrel452

I tried for a couple hours to find a spot on my Merc 15's spark plug wires that'd make my trail tech tto portable tach work. I couldn't get it to read reliably. I would get a stable reading, but then it'd just start going all over the place again. Tried switching the sensitivity as well.

Those portable tachs are nothing more than a digital display with a long wire antenna attached to them, anything electrical going on in the motor will interfere. I found that even if I somehow managed to get a somewhat reliable reading, placing the cowl back on the motor ruined it. I resigned to the fact that messing around with it any further was a fool's errand, especially since the cowl seems to be like reflecting the interfering signals back inwards (which the trail tech tach would pick up).

I found the opposite on my Merc 15, worked perfectly (£10 Chinese job) - just wound the wire around the HT lead next to the plug, fed the wire out under the cowl seal and worked great.

dave3235 · 29 May 2015, 10:33

Same with mine,just the display is angle sensitive.

Roflhat · 29 May 2015, 13:36

I've not had any problems like that with the tachs. Just be careful of how many times you wrap the wire around the HT lead, once should do, maybe twice. If you put too many it will break (not sure why, thats the reply I got from tinytach!)

Last Tango · 31 May 2015, 05:24

I've got one of Chipko's "cheep ones" on my 6hp merc and it works perfectly. It's fitted under the cowl because I only really wanted it for "hours". The wire was cut short, wrapped round the HT lead 4 or 5 times and taped to it. Strangely it had to be set to "firing twice per revolution" to get the correct reading (1300-6000rpm) on a single cylinder 4 stroke. Didn't make sense to me but........if it ain't broke, don't fix it.

Roflhat · 01 June 2015, 10:51

that could be down to the number of wraps around the HT lead as well

Last Tango · 02 June 2015, 17:22

Quote:

Originally Posted by Roflhat

that could be down to the number of wraps around the HT lead as well

Wouldn't have though so. The number of turns will only vary the amplitude of the induced pulse and the digital tach won't use a "diode charge pump" type input because it has to be able to cope with different HT voltages from Kettering to electronic.... about 28KV to 40KV+. To be honest I didn't really give it much more thought, the 1300 idle speed was bang on and the rev limiter cut in at 6100 so that was good enough for me. I know some ignition systems fire redundantly at the end of the exhaust stroke just for simplicity but I'm only really looking to record hours so it had as much time spent on it as I was going to give it.

Roflhat · 03 June 2015, 08:37

sounds like you know much more about than I do! haha
Think somebody on the thundercat forum mentioned the number of wraps could have an effect