You are correct Griff...it is either 250 or 300 hours. I have noticed one other tid bit, Merc has changed the type of plug being used. I'm going to pull out a new AC 41-983 and compare the heat range to the original Denso plug.

A direct replacement would be AC41-983. But please let me know if I'm wrong.....

That is the number that merc gives in the parts catalog and thats what we use in all of them.

and plugs werent designed to last for ever.....

I would think a max interval of 5 years/ 500 hours. I did mine and found them pretty rusty. Leave it much longer and they won't come out properly. They showed some wear on the electrode also. Plus it gives you a look at whats going on.

I couldn't find a service interval in the service manual.

I was able to find the ac delco 41-983 plug at Oreilys - $5.88, GM dealership was $12.15. Scared to check with Mercruiser.

THe ones I pulled out were gapped at 1/16", seemed to be a huge gap. So wide I could check it with a caliper!

What is the correct plug gap for these in a 496??

Good price...I bought mine from Summit Racing @ $5.95/each

i got mine from napa 6.25 ea

What is the correct gap?