1989 Merc 3.0 Sparl Plug Gap w/Pertronix?

[Condor1970]

I have an older 1989 Merc 3.0. I believe the plug gap is supposed to be 0.035" for the older engines running on points.

However, I just upgraded to the Pertronix Ignitor II, and was wondering if now I shouldn't set them at 0.045" like the newer engines do?

Anyone have ideas on this?

 

[eavega]

I did the conversion, and did not change the gap. I think if you read through the FAQs on Pertronix website, they do say some people have increased the gap to take advantage of the better spark. I'd be interested to hear what results people have gotten on changing the gap. I have a 1988 Mercruiser 3.0, so its the same vintage as yours.

Rgds

Eric

 

[Condor1970]

Well, I don't know if this guy just wanted to give me a quick answer, but.... I called Petronix Tech Support. The guy said that with the older engines, they recommend increasing the gap by an average of 0.007".

So, in my case, it would be 0.042".

Does this sound about right to you guys?

 

[Maclin]

A cross-firing problem inside the cap can be induced by widening the gap at the plug too much as the stock caps do not have the space between the contacts inside to support much more than the .035. Also the smaller diameter plug wires dielectric qualities can be overtaxed, this is why you see all those 8 and 8.8mm wires in hot rod shops. I think a gap of .040 is safe enough and should allow better starting in all conditions. Be aware that the wider gap at the plug will reveal all the weaker spots between the coil tower and the spark plug. Even the coil tower can leak spark to one of its' own terminals if the plug gap is too wide, path of least resistance, that kind of thing. Use new cap and rotor and plug wires if you go to .040 or higher, make sure the coil wire boot fits the coil tower. Think about using a dielectric grease to seal the boots to the plugs and the cap and coil.

 

[Maclin]

I meant to include this example regarding widened gaps. the HEI ignitions from GM that showed up in the late 70's last century could handle a .060 gap because their dist caps were larger in diameter and also allowed for larger diameter plug wires than before. By contrast, the same-era Chrysler electronic ignitiona were still limited to the .035 gap range because the location of their distributors did not allow for a wider diameter dist cap.