Spark Plug Gap

[BrentP]

So, MP340 2007. The book says a gap of 0.60. My dad and I have been sitting here talking about it. We can’t find another motor running a gap this big... do any of the dealers that sold this motor/ work on it gap that big? I’ll do it if it’s right but it smells fishy.

There are a number of threads on this I know. But it may drive a lively debate.


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[sandm]

not sure on the gap size BUT when I replaced the plugs many years ago in my '06 supra with the indmar ext340 cat motor I was told to buy the iridium plugs for that block and do NOT change the gap setting. leave them as they come from the manuf.
this was from both the dealer and the local checker auto parts where I bought them.

iirc they were in the .055-.060 range. boat ran fine and never missed a beat.

this is straight from an indmar engine tech off another forum I belong to:

Here is the straight spark plug scoop! If your 5.7L engine does not have catalytic converter exhaust, use the MR43LTS spark plugs gapped at .045" even though the engine may have come from the factory with 41-932 plugs.

If you have an engine with catalytic converters us the 41-932 or 41-101 plugs gapped at .060".

[BrentP]

Yah, I think that's where the mess up is.. mine has no cats on it. We spoke to the guy who did the super charger on another boat in the family circle and he said the 0,60 gap will put a lot of strain on the ignition system... Hmm

0.45 it is! Although I went double platnimum vs iridium...

[chpthril]

With the amount of juice a modern elec ign puts out, jumping a .060 is a piece of cake. With that said, GM issued a TSB a number of years back for some v8's changing the gap from 060 to 040. But, I would not apply that TSB to a marine engine, even if it was the same block as the street version V8. Theres a good chance that GM worked with the boat engine marinizer to determine if their plug gap needed to change also, and then the marinizer would issue their own TSB. I would also never trust the gap out of the box. I always double check them to make sure are correct and one did not get bumped.

[sandm]

I would also never trust the gap out of the box. I always double check them to make sure are correct and one did not get bumped.

I agree with ya 100% on this hence the reason I checked them but both told me that anymore most plug models are vendor/block specific and are gapped as such. most of the major spark plug manufacturers say not to gap iridium/platinum/dual tip.

interesting on the tsb on gm engines. wonder what drove that.

[chpthril]

I agree with ya 100% on this hence the reason I checked them but both told me that anymore most plug models are vendor/block specific and are gapped as such. most of the major spark plug manufacturers say not to gap iridium/platinum/dual tip.

interesting on the tsb on gm engines. wonder what drove that.

I think the message they tried to conveigh was to not alter the designed gap. An example would be if you bought plugs intended for an engine with a .060 gap but your application called for .040, dont pinch them down, get the proper plug. Same with the converse, dont stretch the gap beyond its intended use. However, checking the gap and making an adjustment to put it back to its intended gap, I would not call "changing" the gap.

In brent's scenario, he would not want a plug for a .060, then pinch it down to .045 if thats the gap he wanted. But, if he wanted .060 and one in the box was .055, yeah, im going to correct that, and move on.

[BrentP]

Yah, but the stock gap on those plugs was .45, not .6.


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[flyboy]

Geee, new out of the box my AC 933 Plugs are well above .60mm? Well above!?

Vortec 5700

[flyboy]

I dont have gauges in inches...therein lays my problem :-)