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Platinum spark plugs for 4.3

S

settimo velo

Contributing Member
My 4.3 LX V6 (4 bbl) engines arrived yesterday, so I am just starting to go through them.

They have Bosch HR9BPX platinum plugs fitted, rather than the NGK BR6FS as specified by Mercruiser. Also the Bosch plugs are gapped at around 60 thou whereas the NGK gap is specified at 35 thou ... Anyone know if the Bosch platinum plugs are a recommended replacement for the NGK and is it normal to open the gap on a platinum plug ... ?

I guess I need to get hold a really good engine service manual that will give me this kind of information, so if anyone could recommend a publication that would be great!
 
First off Platinum plugs are PRE GAPPED, No re gapping!!! They typically are a larger gap due to there superior performance.
Is .060" too much? I am not sure. Is platinum plug ok to use? I am not sure of that either...

Most likely that motor was designed for EFI and not carberator. That may explain the platinum plugs.

If you are running a carb change back to the NGKBR6FS and gap at .035". You know that will work....

Maybe someone else will add to this but that is my take on it...

Should you have a service manual? YES!!!!!
 
Ayuh,... My guess is the PO "Thought" he'd get some sorta performance gain outa 'em, which just isn't so...

I run the ole standard plugs for marine Chevys,...
AC Delco, MR43T plugs in mine...
 
The engines are carb so maybe I should ditch the platinum plugs as I'm doing a full service. However, I did go the other way on my 1969 MGB, as the plugs would foul - causing a slight misfire - if the engine had to stay on tickover for any length of time. The platinum plugs have stopped that happening ...

My engines were manufactured 1993 - 1995. Would anyone recommend a Seloc or a Clymer manual for engines of that vintage, or is there little difference beween either publication?
 
I have the V6 Merc manual (printed in 1999) in pdf format. it is 11 mb in size.

I am not sure how to send you a copy....if someone can suggest a way I will gladly send a copy to you

I think it may be to large for regular email.

If you know how let me know
 
I went to your face book page and got a email address and sent the V6 manual as a zip file, 8.8mb in size. Hope you receive it.
 
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i don't like bosch period. Get rid of them pronto. I just don't have enough time to describe all that i have seen go wrong with them.

Consider this a chevy motor chevy plugs.

I have never had a problem with ac, i also recommend what bond-o posted. MR 43T napa has them a little over 2 dollars a plug.

Want a tip from a old school kinda guy, a very small drop of oil or grease on the threads, even if you leave them in for 10 years they will just screw out easy.

And your not torquing down a head bolt so bottom out the plug and just a little more.
 
I know it isn't a boat engine, but my Harley was eating the standard plugs every 1000 miles. Switched to NGK Irridiums and haven't needed to change them in last 15,000 miles. Just a thought.
 
Yup...... I was wondering about your sig. Figured there was only 1 kghost in this world and you were one in the same..........
 
You can really mess up an engine by trying to outsmart the factory test labs. They have millions in that facility, to give us a reliable product. If it serves us well we will buy another engine from them. They are in business to sell engines not spark plugs. Think about it.
TB
 
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