Well,

After a weekends racing we were pulling down the ski and found that the plugs BR8ES 11 on # 3 & #2 cylinder had cracked off the insulator around where you gap the plugs. It looks like #17 here http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html which is good, but missing bits.

I am runnig the RIVA Billet Head & Girdle with 35cc domes, 180 psi, 182 psi, 180 psi compresion.

I run 100% AV Gas at 40:1 premix. The ski still runs fine, the plugs had 2 maybe 3 hours total run time and were put in new with the heads.

Should I be running a different plug? if so what?

Thanks in advanvce for any advice offered.

Cheers

Peter

If your plugs truly look like the example in your link and there's no signs of detonation you should be fine. Is this the first time this has happened? How many hours on the engine since last rebuild?

A broken insulator is often due to over-tightening the plug or placing lateral stress (not bracing socket when pulling on ratchet) on the plug as you tighten it. This can happen whether or not the rubber insert in a plug socket is removed.

Porcelain is strong, but brittle as well...

[ 01-20-2002: Message edited by: RIVA CREW ]

Riva Crew,

This is on the insulator that is on the inside of the dome !!!!!! not the out side where the plug cap clicks on too.

Where the spark thingy is ... (highly technical term here).

Never been rebuilt, 80 hours total, only 3 - 4 in total with 35cc domes.

Cheers

Top.

That is exactly the part I'm referring to. When you torque the plug and put a lateral load on it at the same time you can stress and even crack the core. The area the spark plug socket comes in contact with on the plug is just above the area you're referring to. The porcelain is one piece and hollow so it doesn't take to well to the lateral stress. Yes, the top is more likely to break, but I've seen this happen at the bottom of the plug as well.

http://www.machv.com/broksparplug.html

What gap were you running???
Which plugs? Are you sure they were the -11??

Check your compression
Remove your head and check top of piston for detonation nicks also check your power valves. If they dropped you will detonate.

[ 01-21-2002: Message edited by: Fercho ]

[ 01-21-2002: Message edited by: Fercho ]