Piston & Head Damage (Detonation???)

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Frautzi
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I have recently bought a complete engine which i knew was suffering from a plug eating disorder. I got it for a fair price and had rode it before i bought it, it ran like a dream lots of power plenty of torque just kept pulling, and it sounded crisp.

Spec
Mugello 225 Cylinder (Touring Tune) 238.63cc
Asso 70mm Piston
Chiselspeed Modified Head
Casings/Manifolds matched to cylinder
62mm Full Circle Crank - 107mm Rod
GP200 Gear Box
19x46 Sprockets
12v Electronic Ignition
BGM 80 Watt Stator
Italian Regulator
Ducati CDI Unit
Ancillotti Exhaust
6 Plate Clutch
Dellorto PHBH 30mm Carb
Ram Air Filter

The plan was to drop it in my GP to see if i could iron out the plug issue. I read up on the possible causes ,Poor ignition,over heating,wrong plug temp and detonation. I decided to check the obvious fly wheel rubbing pickup and dodgy stator wires. When i rotated the fly wheel i noticed some resistance at TDC, pulled the fly wheel of expecting to evidence of the fly wheel rubbing something....nothing. i rotated the crank by hand and notice the resistance was still there.
Head off time.....now I've read a little about the causes of detonation but i never expected to see this


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The bore looks ok put is polished in places,

So hows this happened, whats the cause and more importantly how would you set up the replacement head.

Any suggestions and thoughts will be appreciated

Cheers

Jay
Better to keep quiet and be thought of as a D!ck Head, than to open your mouth and remove all doubt.
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Muppet
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Main scooter: SX 150 running in

Looks like mine when it ate a bigend bearing.

Might be detonation, but could just be a metal on metal sandwich.
C’est la vie
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Frautzi
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crank seems fine, but ive yet to strip it out and have a look.
Better to keep quiet and be thought of as a D!ck Head, than to open your mouth and remove all doubt.
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bristolmod
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Main scooter: Lambretta TV175 S3- what else!
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doesn't look like detonation IMO

Looks like somethings been eaten, and the top ends been quickly "rebuilt" prior to selling it.....

Ring broken up? Something ingested?

Chris
Scootering since 1968.
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Frautzi
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taking on some suggestions that it may be an end of an electrode that may of caused the damage, but it looks like its run that way for a bit as metioned.

So do we think this is the cause of the plug eating problem?
Better to keep quiet and be thought of as a D!ck Head, than to open your mouth and remove all doubt.
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bristolmod
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Main scooter: Lambretta TV175 S3- what else!
Location: Bali-Hai bar, Locarno Ballroom Bristol, 1967!- mines a Brown Split!!
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If it was running as you said in that condition, I'd be inclined to clean it up, put it back together and carry on!

Chris
Scootering since 1968.
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Frautzi
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bristolmod wrote:If it was running as you said in that condition, I'd be inclined to clean it up, put it back together and carry on!

Chris
Now i know its like it is, i'll have to sort it, it can't be ridden for long like that.
Better to keep quiet and be thought of as a D!ck Head, than to open your mouth and remove all doubt.
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fairspares
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its more than likely a broken ring been eaten up , you will find the indents the same size as the rings , it was probably stripped and just rings replaced without cleaning up the head etc.
Fairspares Lambretta workshop.
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Frautzi
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fairspares wrote:its more than likely a broken ring been eaten up , you will find the indents the same size as the rings , it was probably stripped and just rings replaced without cleaning up the head etc.

its a fair point i have spoken to the seller and he tells me there has never been any issues like you suggested, I know him and i'm as sure as i can be about anyone he's on the level, but somethings happen which is becoming a mystery. :roll:
Better to keep quiet and be thought of as a D!ck Head, than to open your mouth and remove all doubt.
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fred
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looks like piston hitting head to me. what was squish clearance?
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