A friend of mine with 502's is having problems with plugs popping the center porcelin (sp) out ! I think they are 43T's . Any idea why ? I remember something last year on this subject but can't find it .

Anybody ?? Thanks ,JOE

Overpressure in the cylinders can do that. He may be pre-detonating and causing it.

Boot, I have had this happen to me many times with AC plugs and I have several friends with the same problem.I switched to NGK BR6FS and have not had a problem since.

Kurt.

Boot,
It could be a combination of many things: High compression and bad fuel or low-octane fuel, early detonation like insptech mentioned or too early timing.

What kind of motor is this? Does it occurr repeatedly, different cylinders or the same one?

Try increasing the octane and start with the simple things first.

Cause is detontation. I had most problem with champions. After going to NKG plugs I only poped out pistons.

Motors are were stock 502 carb motors last year .It popped a couple plugs out then . Now it has a 250 super charger with single 1050 carb .It popped out # 2 plug twice and now # 8 . Put NGK's in ran for 2 hours with no problem but that doesn't mean much . Boat is running premium but that doesn't mean much when you buy it on the water . What should the timing be set at ? 28-30 ??
Turbojack , We don't want to be a piston popper !

Thanks everyone ! I will go over his motor better for him .Maybe something is off . Or maybe just those plugs ......

You may get away from it if you switch to some colder plugs, but more than likely your friend is going to have to adjust his boost level or run some racing fuel to keep it together. Make sure his water temp is staying down, and make sure the plug wires are serperated. Lean A/F mixture could also lead to more heat and the big "D". Fix it quick before the bearings or pistons go away. Good tuning!!!

Water temp is 100-110 ,oil is 230. Boost on previous boat was suposed to be 4-5 lbs. I haven't been able to convince him to put in boost gauges yet . After the bad time he had with buying this stuff from the previous guy , I wouldn't trust that it is only 4-5lbs. Plugs look good in color .
THanks for eveyones help ! JOE

Things to watch out for.
-Timming no more than 32 max
-water temp., l100-130 should be ok,
-boost pressure & compression ratio (both work hand in hand),
-air temp, if no intercooler, try to keep air going in engine cool as possible
-lean condition, not only at wot but also at part throttle ( last year messed motor up running only at 3500 rpms, did not notice knock sensor showing red)
-& the number 1 item to watch out for -
-GAS quality, I have distroyed more motors getting gas at marinas that I care to remember. You would think after I distroyed the first one I would have learned my lesson.