Spark plug loosening, but I don't think its detonation or lean

[racin69z]

I have an issue with mainly if not always the left spark plug loosening on my banshee.  I have a set of cheap Chinese 19cc cool head domes on it.  The spark plug threads seemed a little loose to me right out of the box.   I probably should have sent them back, or not ordered cheap crap at all, but I don't seem to learn.  Here is some info about the build just to make sure its not detonation or lean.

 

Pro X stock replacement pistons 1st oversize.   FMF fattys.  MX/dune port,  I cannot find my notes on port specs, but I think the exhaust was at 195, cannot remember the transfer.  19cc domes.  With throttle open kicking until it stops, I have 170 psi of cranking compression.  Timing is advance 4 degrees.  Stock carbs with 340 mains(largest in my kit.).  I cannot remember the pilot jetting.  K&N style pod filters.  32:1 gas to oil ratio.  Currently running 93 octane fuel with 1 quart of VP madditive per 10 gallons of fuel, but I have tried vp113 with no change in symptoms with the plug.  The piston top seems to have the right coloration, plug ground strap timing mark doesn't show too high of timing.

 

Could the cheap domes with poor thread engagement be causing this?  I can convince myself either way when I think of it.  They tighten up without stripping, so I would say even though the thread engagement is poor, it probably should stay tight unless stripped.  But if the thread engagement is bad, then as it heats up, it gets looser and then shakes out from vibration.  

I will say these banshees shake like a dog shitting fish hooks.  Its hard to keep things tight.  The vibration is nuts.

 

Any suggestions are appreciated.

Thanks

Lyn

[Jereme6655]

Still sounds like a deto issue to me if you’re shaking plugs loose. Just because you tried a higher octane doesn’t mean that the knockoff domes are cut correctly. The squish could be way off, the dome angle could be off….. it could have a wicked ridge creating a hot spot……

and 170psi is no joke…. That’s right on the ragged edge of 93 to the point that everything has to be perfect to not have problems….

 Point is …When you’re squeezing things that hard….. things get weird. Shit look at diesel….. it’s essentially a fuel oil…. But runs in an engine with enough squeeze

 

 You know that you don’t trust those Chinese domes….. so just go the right way and call your builder and get some quality domes in that machine

[racin69z]

Thanks for the reply.  I built the motor, so no builder to contact lol.  I did forget to mention the squish is .045 measured with a piece of solder in a few places.  

[skeeter86]

Anytime my plugs tried coming out, a trick racing plug lock fixed issue.  But usually ended up blowing up soon after, probably not related 

[racin69z]

Skeeter, is that sarcasm lol?

 

[ClaudeMachining]

Squish and uccr test then report back.

Envoyé de mon SM-S908W en utilisant Tapatalk

[skeeter86]

9 hours ago, racin69z said:

Skeeter, is that sarcasm lol?

 

No, I have no sense of humor. 

[Qliphoth]

there you have it. "cheap chinese" you can't fix this. throw it away or try it with Loctite one time 😄

[Jereme6655]

Did you do the porting yourself? I have a VERY similar setup as you described. I had a site sponsor do the port work for me and sent me domes (I told him I wanted to stay on 93 pump fuel)….he originally sent me 19cc domes BUT….he wanted me to let him know the compression levels. When I called him back (if I remember right) I was around 170ish…..and he immediately sent me different domes to get my compression down to about 155. He said it MIGHT run okay at 170 on pump….. but that number was too high for his comfort on pump fuel. 
 

for reference I am running a dune/play port, fmf fattys, k&n pods, +4 timing, and a cool head. 
 

I’ve never backed a plug out or had any shake loose. In fact I’ve only seen them back out because of deto on two different machines. 

[racin69z]

I did the porting myself.  I had notes on it, but cannot seem to find them.  Pretty basic. Maintained the same angles in the transfer, raised and widened the transfers, widened and raised the exhaust.  Only number I can remember is 195 or so on the exhaust which I think is a pretty aggressive dune/mx port.  It makes poor low end good mid range but seems to peter out at high rpm.  I am going to pull the head and measure the durations and then re-evaluate it.  Probably get some larger quality made domes.