Mercruiser rotor don't fit right?

[Merc4ever]

Here's my latest dilemma, last year I bought a replacement rotor and ignition sensor because mine was rusty and I didn't want to get stranded if it failed. It was for my 1989 2bbl V6 Mercruiser. Well I just put it in and it works but the rotor bumps the sensor and makes it wiggle when I crank it by hand and watch it. Is it OK to run like this or will I be calling the Coast Guard to rescue me? You know the scenario 15 miles offshore the waves growing to over 8 foot and you can't get back to shore. Yikes!


18-5116-1 Ignition sensor
18-5432 Sierra Rotor

 

[boat127]

Re: Mercruiser rotor don't fit right?

that is not right it shouldnt be hitting. i would check for play in the distributor shaft and also to see if the fingers on the rotor wheel are bent

 

[Merc4ever]

Re: Mercruiser rotor don't fit right?

You can say that again, I took the cover off again to see if I could bend the arms and in the couple seconds I ran it the darn plastic sensor arm snapped off. The wires still hold it on, runs and doesn't hit anymore but now it's flopping in the wind. I sent an e-mail to Sierra tech support because there is no sense in buying another if it's going to do the same thing again. Everything is tight the shaft is solid yet the fingers on the rotor are just too far out in relation to the sensor arm location. I might have to get original Merc parts.

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser rotor don't fit right?

Does it look different from the old one? Compare them side by side and see. Maybe they shipped you the wrong one or the wrong one was placed in the package.

 

[Merc4ever]

Re: Mercruiser rotor don't fit right?

It is the correct part # I double checked. It looks different because it's Sierra not Mercury like the one I replaced but they seem to be spaced the same. Maybe the rotor was the wrong size but it had the right number on the bag.

 

[Merc4ever]

Re: Mercruiser rotor don't fit right?

Nope, the rotors are the same stacked on top of one another but after close examination the sensor is 50 thousandths closer to the rotor arms on the Sierra compared to the original Merc sensor.

 

[Merc4ever]

Re: Mercruiser rotor don't fit right?

UPDATE:

I didn't get an answer from my email yet so I called Sierra. They took my serial number and asked if it was a Thunderbolt IV. I checked and said "yes". They told me to go ahead and get a Mercury part because there is no sense sending me another one because it's going to do the same thing. They offered to buy it back if I can find my receipt but that's gonna be tough so I'll probably have to eat this one.

Lesson learned:

Anyone out there needing a new ignition sensor for a Thunderbolt IV stick with genuine Mercury parts. If not save your receipt and if it bumps the little sensor arm don't try to run it; send it back and get a MERCURY brand one.

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser rotor don't fit right?

Glad you figured it out!

 

[Merc4ever]

Re: Mercruiser rotor don't fit right?

Surprisingly, the new Mercury ignition sensor looks identical to the Sierra and it doesn't bolt the wires on it like my original unit. It comes with the same conversion to snap on the wires.

One big difference over the Sierra unit is there's lots of clearance for the rotor!