external tach

[Don O'Gorman]

I have a MerCruiser 3.0 (older one...1992) and am in need of an external tach so I can adjust idle and mixture when needed. Will a contactless one work if I just point it at the large pully in the front of the engine with a piece of reflective tape on it? Thanks for any help.

Don

 

[BillK2632]

Yes, I have one and it works great, very accurate.

 

[Don O'Gorman]

But is that how you use it....do you put a piece of the reflective tape on the big pully on the front of the engine?
Also I read somewhere that whatever it reads you have to divide by 2 if its a four-cylinder engine.....something about there being two revolutions to each cylinder.....or is whatever the tach reads is simply your rpms?

 

[techmitch]

But is that how you use it....do you put a piece of the reflective tape on the big pully on the front of the engine?
Also I read somewhere that whatever it reads you have to divide by 2 if its a four-cylinder engine.....something about there being two revolutions to each cylinder.....or is whatever the tach reads is simply your rpms?

Get an inductive timing light with tachometer. It will be money well spent.
There are cheaper ones and far more expensive ones than this one with adjustable advance.
https://www.amazon.com/KZYEE-KT60-I...mzn1.fos.18ed3cb5-28d5-4975-8bc7-93deae8f9840

 

[Don O'Gorman]

Hey Techmitch...we're neighbors....just around the corner coming out of Harewood Park off the gunpowder River. Small world. ok so a few questions......How do I know if I have a 2 or 4 cycle engine....its four cylinder mercruiser 3.0 like an old GM straight four so I am assuming its a 4 cycle right? Also if I put the induction thing around spark wire number 1 is that how I get the rpm reading? And are their instructions that come with it for checking my timing?

Don

 

[BillK2632]

A 3.0 is a 4 cylinder. Like mentioned an induction timing light with advance and a tachometer is a good tool to have. But for $20 the tachometers that use a reflective tape are handy too. Yes you would connect your timing light to the #1 spark plug wire. You need to find the procedure for checking / setting the timing on your engine. Most Mercruisers that have Thunderbolt IV or V ignition must be put in “base timing mode” to properly set the timing. It’s not hard, but I would find a manual for your engine to be sure you are doing it correctly.

 

[Don O'Gorman]

Do you put the reflective tape right on the large pully that's on the front of my engine? If not where is the best place to put it?

 

[BillK2632]

Yes, just stick it on the large (crankshaft pully) in a position so you can easily shine the tach light on it. For my old boat, Merc 4.3 v6 that’s exactly what I did, then put the ignition in base timing mode and timed it with an old fashion timing light I have. Locate the timing marks in the crank pully, timing is usually something like 10deg BTDC @650rpm, which means the spark plug fires when the piston is 10 deg before it reaches the top of the compression stroke. Like I mentioned earlier, find a manual for your engine and understand how to set the timing, it’s a simple process but if the timing is set wrong, long term it can cause damage to the engine, in addition to it running bad.

 

[Don O'Gorman]

Wow...thanks for the detailed instructions.....I appreciate it.

Don