Engine analyzer for one and two cylinder ?

[Mrwurm]

I gave away my old auto analyzer. It could only measure engine rpm's for 4,6, and 8 cylinders. I see that most of the new ones still are limited in the same way. I would like to find an analyzer that can read rpm's for 1,2,4,6, and 8 cylinders. Are there any out there?

 

[patrickg]

Yes, There are hand held tach/dwell meters that will work for 1, 2, or 3 cylinders. You might have seen meters made for 6 and 8 cylinders with instructions on how to use to read a 4 cyl engine. Similar compensation can be made for other numbers of cylinders. There are also optical (non-contact) tachs that don't care about number of cylinders. I've seen audio tachs that count the exhaust pulses.

Every time a 4 stroke engine makes one complete revolution, 1/2 of the cylinders fire. The ignition coil primary (if equipped) is switched once per firing. Counting the pulses digitally or via analog approximation gives the RPM. RPM equals the number of firings per minute divided by one half the number of cylinders. If you have a place to hook up your meter to get it to function then you are in buisness. Putting a meter made for 8 cyl on a 2 cyl engine is OK. The reading will be off by a factor of 4 (asuming 4 stroke, not a ringding, i.e. 2 stroke engine).

Each revolultion of a 2 cyl 4 stroke engine gives one firing pulse where an 8 cyl would give 4 pulses. A 2 cyl engine running at 4000RPM would have 2000 firing pulses per minute which in an 8 cyl engine would be 500RPM. So.... 2 cyl RPM is 4 times what the meter reads.

Anyway that is the basic idea. Undfortunately I don't do arithmetic all that well so check my work carefully.

pat

 

[MikePA]

Pat,

This is a timely post for me since I just received an Hour Meter/Tachometer for use on my twin cylinder, 4 cycle garden tractor.

The meter has a lead that is wrapped around one of the spark plug wires. Then the meter needs to be set for one of the following;

1. Plug fires twice per revolution
2. Plug fire once per revolution
3. Plug fires every other revolution

For my twin cylinder, 4 cycle engine I select Option 3 correct?

 

[Rowski]

We have one of those too. We can't even give it away /forums/images/graemlins/smile.gif. We call it the boat anchor.

Anyways, I use my inductive RPM probe for my fluke meter. It can be set for conventional ignition or DIS ignition.

I did see my chain saw guy use an inductive digital display tach. It was very small and did not have any leads. On my chain say he would just hold the tach near the spark plug with the cover on and read the max rpms. This way about 5 years ago when I saw him do this.

 

[AMP762]

</font><font color="blue" class="small">( Pat,

This is a timely post for me since I just received an Hour Meter/Tachometer for use on my twin cylinder, 4 cycle garden tractor.

The meter has a lead that is wrapped around one of the spark plug wires. Then the meter needs to be set for one of the following;

1. Plug fires twice per revolution
2. Plug fire once per revolution
3. Plug fires every other revolution

For my twin cylinder, 4 cycle engine I select Option 3 correct?

)</font>

Pat Ibelieve your's uses a waste spark sys. which means it fires twice per rev.

 

[patrickg]

Actually, I'm Pat and I was one of the folks answering the Q not posting it.

For a "standard" 4 stroke engine, all cylinders fire once every two revolutions of the crank so option 3 wold be correct.

Not sure about the "waste" thing but if the plug fires an extra time then you'd be off by a factor of two, with your readings being twice as high as they should be.

The tach held near a plug has an inductived pickup and so does the one with the wire wrapped around the plug lead with the latter being much less sensitive.

There used to be some fairly innexpensive optical tachs available. Hobby shops that cater to gas powered models used to carry them. They can be used to read the rpm of a shaft or other rotating device like a prop or... Sometimes you might have to put a white paint area on the moving part and let the tach measure how often it passes by.

Pat