Hey guys, kind of a strange situation, but I have had my left side cylinder spark plug back out of the head 3 times over the past 1100kms of riding. I guess what I'm wondering is if any of you guys have experienced something similar? I'm running a '17 AXYS with a Silber turbo at 7lbs on 100% 100LL. I've tightened it to spec each time, even tried putting in a new plug, but it doesn't seem to have changed. Any insights or suggestions would be greatly appreciated.
Spark plug comes out
- Thread starter jockdoc
- Start date
zal
Active VIP Member
How are the threads in the head? Do they look damaged or "thin" compared to the other spark plug hole or normal internal threads?
Pistonbroke
Active VIP Member
Any signs of detonation? Plugs backing out is a classic symptom of det.
pfi572
Active VIP Member
^^^^^
What PB said .
What PB said .
If I didn’t see it I wouldn’t believe. Friend in our group has an 850 with a Silber, he was WOT trying to wiggle the sled out on a side hill and it started popping. We could keep it running but barely, concerned it was a major issue we turned for the trucks while we still could ride. Made it down by supper. Next morning started looking and the PTO side plug was backed way out. Pulled the plug, replaced with new and off we went for a flawless day of riding.
I was amazed it doesn’t blow the head gasket or something else - impressive to think what it would take for forces to back that plug out.
I was amazed it doesn’t blow the head gasket or something else - impressive to think what it would take for forces to back that plug out.
I had the same issue with my '13 pro. Unfortunately for me by the 3rd time (even with new plugs) it wouldn't stay in at all as the threads were shot.
Go to Canadian tire and they have a spark plug thread kit. It's not a helicoil, it's a thread-sert.
You can take off the head but what I did was tap it with heavy grease and no shavings fall down. Takes 20 minutes to do and I havnt had single issue since I did it last season.
Hope this helps ya
Teth-Air
Active VIP Member
Usually always detonation doing this. It can back out bolts and cause piston ring retaining pins to fall out too. Fix the cause not just the effect.
- Thread starter
- #9
No real indication of detonation that I can tell. No codes. Plugs are white-ish, not the classic coffee colour that I like to see on a 2 smoke.
I switched to VP C12 to see if that has any effect. Ridden hard for 2 days now and it seems good.
I'm honestly thinking AV 100LL may be part of the problem.
I switched to VP C12 to see if that has any effect. Ridden hard for 2 days now and it seems good.
I'm honestly thinking AV 100LL may be part of the problem.
CrankShop910
Active VIP Member
It’s detonation,the squish is too tight for western Canada. Even with 100LL
Lund
Active VIP Member
Definitely detonation, seen it many time's among home tuner's. Your lucky the little squirrel loosened your spark plug. Many don't get that little warning till its too late. That's usually a hole in the center of the piston.
If your having to run c12 to avoid detonation at all cost as you posted, your asking for trouble. What is the squish on that motor ? I know i would be changing up, way to finicky for recreational use. Only good for the track a motor like that.
moyiesledhead
Active VIP Member
Less timing, less boost, less compression. Maybe all three. You're lucky you got the spark plug warning. Detonation damage gets expensive quick. 
Dazzler
Active VIP Member
The plugs will be white/grey color from running av gas. My guess is it's most likely timing, if you are not running a timing key, or maybe a lean spot in fuel program or maybe fuel filter?. 7lbs boost should run fine with 50/50 av and a good premium gas let alone 100% av, unless you changed the top end on your motor to a higher compression?
I'm running 10lbs on my Axy and 12lbs on my 15 Pro on 100% av with no issues.
sick1
Active VIP Member
From my past history if the thing is popping plugs from one hole all the time its on borrowed time. Crank could be out of phase just a bit from you detonating or over revving.
Similar threads
