Spark Plugs & tune up ?

[mike456]

1992 Merc 5.7L Thunderbolt V8 S/N OD709044. I've owned boat 2 years.
I plan to do a full tune up and would like advice on plugs to use. Engine currenlty has AC 43T plugs. At the end of last year while running at full throttle one of the plugs blew out (the porcelaine part came right out of metal part). The noise was crazy and I was sure the engine had blown. Amazingly I fixed the problem for $2! Needless to say I'm not keen on using AC plugs again. Can I get some recommendations another good brand and can you tell me the part number for my engine?
I have all the repair manuals so I'm sure I can look it up but what is the gap for my engine?
As understand it I have Thunderbolt IV ingnition and will be replacing the roter, cap and wires. Any recommmendations on those? I know that OEM Merc are best but are the Searra parts OK? How about any good sites that offer good prices?
Advice on anything else I should look out for is appreciated. I have a recent post from Don S on how to do the timing.
This forum is the best!
Thanks

 

[Don S]

Re: Spark Plugs & tune up ?

I've seen the porcelins on Champion plugs blow out many times. First i've heard of an AC doing it. Merc recommends an NGK plug, BR6FS.
The gap should be on a tag on the plastic cover over your carb, near the SN you posted. But it's .035.

 

[Bondo]

Re: Spark Plugs & tune up ?

Engine currenlty has AC 43T plugs.

That Should be MR43T.......
The R43T is the Auto Equivalent, with a Steel body instead of the Alloy bodied Marine plugs......

I run Nothing but the AC Delcos...... Never had an Issue like Your's.....

 

[mike456]

Re: Spark Plugs & tune up ?

Don and Bond-o, Thanks for the reply.
I know I currently have AC R43T and NOT MR 43T. I wonder if the fact that they are auto plugs and not the alloy type that is supposed to be in there is what casused one to blow out? I have no idea how long they were in use.

 

[Bondo]

Re: Spark Plugs & tune up ?

Anything is Possible,......

But like I said,........ I firmly believe that AC Delco's Belong in Chevy motors......