Spark Plug Gaps and Base Timing Mode

[problem child]

I will be changing plugs/wires and making some carb adjustments as part of winter lay-up this year and I need clarification on two things. Engine is 1997 5.7 LX, 4 barrel Weber carb, Thunderbolt V Ignition, old style heads (non Gen +).

There is not a specific tune up spec for the 5.7 LX engine listed in the Merc manual (#17), go figure. I am sure the plugs are NGK BR6FS. The engine plate says gap to .035. The manual also states the same in the tune up specs for all non Gen + engines, however the Ignition section says to gap to .040. What is the correct gap?

To do the carb adjustments (idle is a little high, and may be running rich even after warm up), I know I need to place the ignition in base timing mode. Where is the best place to ground lead #13? (I.e. engine block, negative post of battery, etc.) I would appreciate some advice if anybody has ever done this procedure.

 

[Don S]

Re: Spark Plug Gaps and Base Timing Mode

Just out of curiosity, what is the Merc SN for your engine?

 

[problem child]

Re: Spark Plug Gaps and Base Timing Mode

Engine Serial # OK167850

From Merc Site: (457L100KS)


Sorry Don, should have posted that earlier

 

[Don S]

Re: Spark Plug Gaps and Base Timing Mode

The specs in the manual was a change. Some how the LX didn't get added. If you still have the timing, rpm and timing specs on the flame arrestor decal, go by that. That is Mercruisers default "Place to go" for any engine info. If the decal and information in it were changed, there would be a service bulletin with the change and the new decal number. There isn't one for your engine.
If the decal was missing altogether, I guess it would be a good time to call Mercruiser Customer service for the tuneup info.

 

[problem child]

Re: Spark Plug Gaps and Base Timing Mode

Got it...Thanks Don.

Flame arrestor cover decal is on the boat and in good shape.

Gap listed is .035. I know for sure the engine is a not a Gen + (i.e. 12 bolts total on the intake manifold), so the correct plug would be NGK BR6FS

Any advice on where to ground the base timing lead to ensure that I have it properly grounded?

 

[Don S]

Re: Spark Plug Gaps and Base Timing Mode

About anything that isn't painted.
If you aren't sure, just make a long jumper and hook it directly to the negative battery terminal and to the purple white wire. That ought to get it done.

 

[ChrisCraftJohnny]

Re: Spark Plug Gaps and Base Timing Mode

NGK (Japanese) plugs on a GM-made engine?

I don't think that was original. AC's were original.

No problem using NGK though. But not original.

Johnny

 

[problem child]

Re: Spark Plug Gaps and Base Timing Mode

10-4 Don. I will get in there and have a look see. I may just run it back to the battery to be sure. I have plenty of wire laying around and the lead is sitting right on top of the manifold.

Johnny..............Merc says I can use NGK and I will. I have been around engines my whole life and I swear by NGK's. I Always thought AC's were junk.....just my opinion though.

 

[Don S]

Re: Spark Plug Gaps and Base Timing Mode

Mercruiser doesn't sell AC plugs, if you order plugs by the Mercruiser PN, you will receive NGK plugs.

Anything is better than Champion. (shouldn't say that, I have fixed a lot of engines that wouldn't run right, only because the owner installed Champions, I replace them, it runs fine)

 

[ChrisCraftJohnny]

Re: Spark Plug Gaps and Base Timing Mode

You can use any plug you wish. That's why there are many manufacturers out there making the same product.

As far as AC's being junk. Well then, I guess GM and their products are all junk. In manufacturing, one does not make quality over here, and crap over there. It's called QC. (Quality Control)

Everything is made to a standard. To meet or exceed.

You may not like AC plugs for what ever reason. But by saying they are crap, is the same as saying your engine is crap. Do you really think GM can make a good engine but not a good spark plug? This is the problem with America.

20 Years in Precision Manufacturing.

Johnny

 

[Don S]

Re: Spark Plug Gaps and Base Timing Mode

Don't go off the deep end there Johnny.
Probably 99% of the posters here recommend AC, and also have no problem with NGK on the GM engines.

 

[ChrisCraftJohnny]

Re: Spark Plug Gaps and Base Timing Mode

Don ,

No deep end here. Just head injuries.

 

[bruceb58]

Re: Spark Plug Gaps and Base Timing Mode

deleted

 

[TilliamWe]

Re: Spark Plug Gaps and Base Timing Mode

wrong pictures

 

[Don S]

Re: Spark Plug Gaps and Base Timing Mode

Tilliam, he has a carbed engine. That picture is for EFI engines.

 

[TilliamWe]

Re: Spark Plug Gaps and Base Timing Mode

I see, I thought the plug was the same. My bad.