Jump to content
Strawberry Orange Banana Lime Leaf Slate Sky Blueberry Grape Watermelon Chocolate Marble
Strawberry Orange Banana Lime Leaf Slate Sky Blueberry Grape Watermelon Chocolate Marble
wullie

set rev counter for m4 Vetus.

Featured Posts

Just fitted new control panel for engine, M4 Vetus, the taco has to be set but even though i have looked at instructions,it shows placing a small rod into choice of  two holes in the back of taco to adjust RPM it doesn't say what to use,looked at all instructions but defiantly no screws in either hole, one for increase  and one to lower RPM. Totally confused.

Share this post


Link to post
Share on other sites
5 minutes ago, wullie said:

Just fitted new control panel for engine, M4 Vetus, the taco has to be set but even though i have looked at instructions,it shows placing a small rod into choice of  two holes in the back of taco to adjust RPM it doesn't say what to use,looked at all instructions but defiantly no screws in either hole, one for increase  and one to lower RPM. Totally confused.

 

They are not screws. they are push buttons that you need a thin rod (perhaps a bit of wire?) to push.  One increases the setting, one decreases the setting.  You need a mark and a separate, handheld tachometer to set it correctly.

 

The other version of the Vetus tachometer can only be set at exactly 2600 rpm by pressing a button on the back of the unit, but you still need a separate tachometer to get the revs to the correct level before you press the set button.

Share this post


Link to post
Share on other sites

It's all pretty arbitrary what speed the engine is turning at anyway, so not the end of the day if you don't get it right.  As long as you have a fairly good idea of what three mph sounds like you don't need much else.

  • Greenie 1

Share this post


Link to post
Share on other sites

There are suitable apps available for phones and tablets that use the sound of the engine so you can work out the speed. I've used one to set up a rev counter successfully.

Look for oscilloscope apps. Find an app that gives a graph of frequency against strength. They are prone to errors at low revs, sometimes showing double the actual engine speed, due to the frequency response of the mic, but at 2600rpm should work OK. There will be peaks showing that relate to the engine speed and harmonics of speed. Multiply by 60 to go from Hz to revs per minute. 2600rpm should give a sharp frequency peak at 43.3Hz, Your microphone should pick this up, but if not, the next peak will be 86.7Hz (double).

Jen

Share this post


Link to post
Share on other sites
16 minutes ago, Jen-in-Wellies said:

Multiply by 60 to go from Hz to revs per minute. 2600rpm should give a sharp frequency peak at 43.3Hz, Your microphone should pick this up, but if not, the next peak will be 86.7Hz (double).

You know, I read this and thought to myself “What’s so magical about 60?”  It took a while for the penny to drop. Not enough coffee I think ;)

  • Haha 1

Share this post


Link to post
Share on other sites
11 minutes ago, WotEver said:

You know, I read this and thought to myself “What’s so magical about 60?”  It took a while for the penny to drop. Not enough coffee I think ;)

 

It is the total number of days in June and September, or April & November, but if you add all 4 together you will need to divide by 2

  • Greenie 1

Share this post


Link to post
Share on other sites
15 minutes ago, Alan de Enfield said:

 

It is the total number of days in June and September, or April & November, but if you add all 4 together you will need to divide by 2

Gotcha. 
 

Or I could take the days in a year, subtract 5 (or 6) and divide by six...

Share this post


Link to post
Share on other sites
46 minutes ago, WotEver said:

You know, I read this and thought to myself “What’s so magical about 60?”  It took a while for the penny to drop. Not enough coffee I think ;)

 

 

For a minute I laughed so hard it Hertz ...

  • Haha 1

Share this post


Link to post
Share on other sites
53 minutes ago, TheBiscuits said:

 

 

For a minute I laughed so hard it Hertz ...

 

What's car rental got to do with it?

Share this post


Link to post
Share on other sites
7 hours ago, dor said:

>>It's all pretty arbitrary what speed the engine is turning at anyway<<

 

Agreed. So long as the tacho can give you reference points for idle, slow ahead/astern and normal cruising speed, it doesn't actually matter what the numbers are.  One engine's 900rev/min may be another's 1100rev/min, but what does that matter?

I suggest the OP uses a suck-it-and-see approach before faffing about to get the "right" readings.

It would be my bet that the tacho isn't all that far out when it leaves the factory.

Share this post


Link to post
Share on other sites

I bought a cheap handheld laser tacho from eBay to calibrate mine. Cost about a tenner. The boat tacho was way out. I guess it doesn't really matter but if you have a rev counter it may as well read correctly. For years I'd wondered why my engine didn't rev according to the engine specs and I finally found out. In gear it was over-propped and I gained some revs by having the prop repitched so that was part of it, but it was also due to the tacho being so out of calibration.

 

Even a cheap handheld laser tacho is likely to give a reasonably accurate reading.

  • Greenie 1

Share this post


Link to post
Share on other sites

I've used the G string app to measure rpm. The formula above is I think correct for a two cylinder four stroke engine (one bang per revolution). A four cylinder engine will (should!) do two bangs a revolution, so 1500 RPM is 50 Hz (divide by 30). 

 

My tacho has not worked for over 20 years.

Edited by Scholar Gypsy
  • Greenie 1

Share this post


Link to post
Share on other sites
2 hours ago, Scholar Gypsy said:

I've used the G string app to measure rpm. The formula above is I think correct for a two cylinder four stroke engine (one bang per revolution). A four cylinder engine will (should!) do two bangs a revolution, so 1500 RPM is 50 Hz (divide by 30). 

 

My tacho has not worked for over 20 years.

Theoretically yes. I was expecting two bangs per revolution on the four cyl four stroke engine I tried it on, but the biggest peak was at one per revolution, then a second peak at two per rev. It will depend on the engine and what is making the most noise, but you should have a good idea where the peaks will be and at what rpm. On a typical non vintage 4 cyl 4 stroke, idle will be around 800 to 1000rpm and absolute max will be maybe 4000 to 4500rpm, so you'll have at least a rough idea of what ball park main and harmonic pitches to expect be for any throttle opening.

Jen

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.