What type of plugs are recommended for Merc motors
 

I have a 502 mag efi with a super charger on it. I would like to change my plugs (175 hours). I know of two poeple that have used ac delco plugs in their motors and both have had the electrodes drop into the cylinders. One bent a valve and the other destroyed his rings and piston in one cylinder. Is this common with those plugs? I would think ac delco would be the best replacement but after those horror stories I would like to try something different. Any ideas or part numbers would be helpful.

Re: What type of plugs are recommended for Merc motors
 

I run ac delco plugs in my blower motor,never had one fall apart yet. I would figure any plug would burn if too lean for too long, the porcelein and metal used has got to be near identical in most garden variety brands. 175 hours between plug changes!!!! THATS something else,your motor must be tuned perfect,most these blower motors have some spot in the fuel curve(mine is at about 1-2 psi boost) where they run a little rich,i change plugs when i change oil,every 25 hours,i could probably get 50,maybe 75 out of them but i like to see whats going on in the cylinders and once there out,why bother reusing them. Just out of curiousity,what kind of blower,how much boost,Smitty

Re: What type of plugs are recommended for Merc motors
 

The only electrodes I've ever heard of dropping into engines are ones that were gapped carelessly cracking or causing fatigue at the electrode that later led to failure.

Re: What type of plugs are recommended for Merc motors
 

You are probably right about the running lean part because both the guys I know that broke the plugs had carburrated motors.
What ever the reason they fell apart I do know that on one of the motors GM stood behind the damage and paid to have the repairs done, so they did admit it was defective. I don't know how much complaining the guy did to get it fixed or who he complained to but it must have been to the right person.
As far a my motor goes it was stock with the exception of headers and an air cleaner until about five hours ago. I just had AZ speed and Marine put a Vortech Super charger on it and I thought I would get some new plugs and wires. I had no idea that you were supposed to change plugs that often.
I guess I could have changed the plugs but I never really thought about it before, I guess I'm just used to newer cars where you can go 70,000 miles before you have change plugs. I do have an intermittent miss though that they could not locate, we thought we had fixed the problem and it came back this weekend at high rpm (5200 and above) and then once at idle for a while. I thought while I was changing the plug wires I would do the plugs as well.

Re: What type of plugs are recommended for Merc motors
 

I had one "burn out" on a relatively tame, carbed 350. I had recently switched carbs and was running lean. I adjusted the carb, following Edlebrock's guides, and it ran like a top for the rest of its well used life. I, too, changed the plugs every 50-75 hours. I used MR43T, and MR43TS, the "S", they say, is for Stainless Steel. I guess it has less of a chance of freezing itself into the head.....with my frequent changes, the 43T's are fine (and they cost less). Last thought: How's the cam fit for the set-up? Do the cam, carb and timing "fit" together? I ,also, once used a wrong (inappropriate) cam, with similar results.