View Full Version : Spark Plug Gap

10-31-2008, 07:52 AM
My Moomba Mobius 2000 V has an Indmar Assault 5.7 MPFI engine.

I want to change the spark plugs this weekend as part of my winterization service.

The owners manual says the gap is 0.060"

Other boat forums state 0.045" gap.

Which is correct?

The O.E.M. plug is a AC Delco MR43LTS.

I have got 2 replacement types in my box to use....

NGK V-POWER TR5 (2238) from SKIDIM (gap is preset at 0.050")

NGK LASER PLATINUM PTR5D-13(6644) from my dealer. (gap is preset at 0.040" )

Am i supposed to set the gap myself or use the default gap on the plug?

Some plugs are ruined if you change the gap (the platinum for instance)

Any ideas?

10-31-2008, 08:16 AM
If the plug is built just for that application and is preset from the factory I NEVER change them. Some of the new types you cannot change due to the geometry. I think if it is possible you should check it to make sure it wasn't damaged during shipping and handling, again if this is possible.

10-31-2008, 06:22 PM
Go with the owner's manual. .060 is correct.

Sometimes the guy who designed your engine (an engineer) knows more that a poster online. Do check the gap on the plug, they are usually set, but they can get bent during shipping.

11-03-2008, 04:48 AM
I changed the plugs at the weekend, and opted to go with the NGK-LASER-PLATINUM version.

I didn't adjust the gap, and connected the cables back up, turned her over, and she sounds even better than before!?!?!?!

Should i just leave it......?

11-03-2008, 08:42 AM
Factory OEM plugs .060"
Aftermarket Plugs = what is recommended from the Plug Manufacturer for that application.

Engine Nut
11-27-2008, 09:41 AM
Here is the scoop on spark plugs for all Indmar 5.7L Vortec based engines (1996 or newer). If you have a 2006 or newer Assault 340 with catalyst exhaust, I recommend using the AC 41-932 or 41-993 platinum plugs gapped at .060". If your engine is not equipped with catalytic converters, I recommend using the AC MR43LTS conventional plugs gapped at .045".

Platinum or iridium plugs in an engine without catalysts are an un-necessary expense. Platinum plugs like to run HOT and LEAN. Our non-catalyst engines run relatively COOL and RICH. Save some money and use the MR43LTS plugs in those engines. The catalyst engines run a little warmer and a whole lot leaner, enough leaner in fact that they get better fuel economy, so the platinum plugs are much happier.

If you have an older, pre-vortec engine, use the AC MR43T plugs. The MR43T plugs are short reach plugs and the MR43LTS plugs and 41-932 or 41-993 are long reach plugs. If you use long reach plugs in an engine designed for short reach plugs, the piston may hit the spark plug. If you use short reach plugs in an engine designed for long reach plugs, you will experience incomplete combustion and poor performance.

I have no recommendations on aftermarket plugs. I know that the AC plugs that we use in the engines work, they are good plugs and the correct plugs for the engines and will not cause damage to the engine.