spark plug help with new head

[Fishermark]

The head I received for the engine rebuild (early 70's vintage Mercruiser 165 - Chevy inline six 250) is different than the one I took off. The new head has provisions for smog control (pipe plugs covering exhaust port area) and a hole for an in-head temp sender - which I have plugged with a brass pipe plug.

I should have asked the head shop for a spark plug recommendation, but forgot to do so. I already have the head installed, but here are some casting numbers and pictures in case anyone can help. The old plugs were NGK BR6ES - the style that has a washer. I don't know if they are correct for the new head or not. Help!

 

[Bondo]

Re: spark plug help with new head

Ayuh,.........

Over the years, there used to be some inline motors that used an 18mm thread,......
Over than That,......
Chevies Love the R43T plugs, which of course the automotive equivalent of the AC MR43T.....
Which is My sparkplug of Choice.......

 

[Don S]

Re: spark plug help with new head

The later models (by Serial number) went to an AC #R43T.

Oops, I had it backwards, not the CR43N, but the R43T (as Bondo said)

 

[Fishermark]

Re: spark plug help with new head

AC R43T it is. Thanks!

 

[Bondo]

Re: spark plug help with new head

AC MR43T Mark,.......
It's got the Alloy body,......
The R43T is the Steel body,+ Will Rust solid..........

Same Plugs except for the Alloy body with the Marine plugs.......

 

[Fishermark]

Re: spark plug help with new head

Thanks for clarifying.