Freestyle Front spark plug coming loose during riding - DASA 1100

[Waldbjoern]

I have an issue with the front spark plug coming loose on my DASA1100, 10mil, PFP, FS49's jetted by Ed for the specific engine.

I am running OEM ignition.. And flywheel is installed as per Yamaha instructions! I am running shell v-power octane 99 EU (RON) comparable (I presume) to your octane 95 US (MON).. Domes are 48cc, aprox 185 psi.

Thought i resolved the issue, cause the PW hit the connections of the waterline, but that didn't fix the issue.


Pulled head to check condition, and signs of detonation.. Non were found. Pictures of front cylinder / dome.



Pictures of back cylinder / dome.



Tried installing new o-rings, after the removal of the head.. Still same issue.

Tried both NGK-BR8EG(3992) and NGK-BR8ES(3961) - dont feel like tightening the spark plugs anymore, afraid to strip the threads!

Any inputs would be much appreciated.

Thanks in advance

 

[Waldbjoern]

@Christian_83 @Stefan!BOB!

 

[jo5hi3]

If a plug is backing out, the cause is almost always deto. On a second note, your domes look a little milky...

 

[Waldbjoern]

But after inspection there's no sign of detonation?! Milky??


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[jo5hi3]

With forged pistons you wont' see it on the piston face for a long time. Do you have pictures of the plugs? The liquid that's on your domes looks like oil that is mixed with water.

 

[SmittySX]

I had a plug that was doing the same thing. It was a squish issue for me.

 

[Waldbjoern]

Too many failed flip attempts may be the cause of the water ingestion, combined with a broken o-ring on the front dome.. That's changed now, but still the same issue. The engine is straight out of Thrust´s workshop, no modifications of any kind done "at home", so I dont think there's a squish issue.

Do you have pictures of the plugs? .

Ill see what i can do with a pic of the plugs.

 

[jo5hi3]

I had a plug that was doing the same thing. It was a squish issue for me.

If you're squish was too tight then that was causing deto, which was backing the plug out.

Too many failed flip attempts may be the cause of the water ingestion, combined with a broken o-ring on the front dome.. That's changed now, but still the same issue. The engine is straight out of Thrust´s workshop, no modifications of any kind done "at home", so I dont think there's a squish issue.

I would check the squish to be sure. I have seen them come straight from dasa and the squish was way too tight.

 

[augustaf]

Twenty- five years ago- the early days for aftermarket heads- a certain manufacturer, now defunct, seemed to have problems with the dome to head shell clearance. It seems that was never acknowledged, but the plugs vibrated enough to loosen no matter how tight you made them. Sure enough, after that, Riva, then MRD Dave came out with heads which did not have replaceable domes. After awhile, others started to manufacture heads with separate domes with great success.

 

[jo5hi3]

Twenty- five years ago- the early days for aftermarket heads- a certain manufacturer, now defunct, seemed to have problems with the dome to head shell clearance. It seems that was never acknowledged, but the plugs vibrated enough to loosen no matter how tight you made them. Sure enough, after that, Riva, then MRD Dave came out with heads which did not have replaceable domes. After awhile, others started to manufacture heads with separate domes with great success.

It's funny you say that. The 1000 I had, the domes fit super tight in the head shell. I had to use ice or something cold to shrink the domes enough to get them in and out, which could cause them not to seat if you are unaware of that.

 

[SmittySX]

If you're squish was too tight then that was causing deto, which was backing the plug out.

Correct. Although, my plugs werent backing out. The white part of the plug was actually separating from the rest of the plug threaded into the head..

 

[jo5hi3]

Correct. Although, my plugs werent backing out. The white part of the plug was actually separating from the rest of the plug threaded into the head..

I have seen it happen both ways.

 

[Waldbjoern]

Thanks for inputs - ill be checking squish asap. Ill get back with results. Anyone know the precise squish? Pref in metrics.

 

[tor*p*do]

Poorly developed piston wash; looks lean to me.

 

[jo5hi3]

Poorly developed piston wash; looks lean to me.

Going by the amount of goop on the domes, piston wash isn't something that you can read. Water in the combustion chamber steam cleans parts.

 

[Philip Clemmons]

What is your jetting?


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[augustaf]

Thanks for inputs - ill be checking squish asap. Ill get back with results. Anyone know the precise squish? Pref in metrics.

Usually 1.3mm. Can vary

 

[cookn]

I would agree and say 1.3mm would be as tight as you want it on pump gas

 

[sneds]

I just checked my motor and Kyle from Dasa told me anywhere between 0.050"-0.060" is good.

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[Waldbjoern]

I Will check up on jetting - kyle offered me a replacement set of domes free of charge to rule out loose thread tap on the dome. Will also check squish ASAP. Will post when there's any news. Thanks


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