Broken engine, oops

KevTrem

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Well while bashing the Baja yesterday my engine stopped suddenly, tried restarting it but had no compression. Pulled it apart this morning before work to see what was up.
Result is new piston, head and gaskets are on order.
I'm just happy its a cheap engine, rebuild will cost Β£30.
I was also informed that the piston was in back to front with the arrow facing the inlet.
20200629_115548.jpg 20200629_115557.jpg
 

Seandonato73

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The arrow is just for ring placement. Sometimes had to do with skirt length, but normally just ring position
 

KevTrem

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Where did all the metal come from πŸ€”
Z what looks like filings I think are impact marks from the floating piece of piston until it was pounded into the head. (fire away lol)

I was going to buy a piston and gasket set, but for Β£15 it seemed daft to pass up on the new head too.
The arrow is just for ring placement. Sometimes had to do with skirt length, but normally just ring position
So, arrow to exhaust and pin in the ring groove to inlet the other way? Google gives conflicting answers.
 

Z.hb71

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until it was pounded into the head. (fire away lol)
Think we need a 😏 reaction πŸ˜€πŸ€£
Z what looks like filings I think are impact marks from the floating piece of piston until it was pounded into the head. (fire away lol)

I was going to buy a piston and gasket set, but for Β£15 it seemed daft to pass up on the new head too.

So, arrow to exhaust and pin in the ring groove to inlet the other way? Google gives conflicting answers.
Think it varies from different engines (,correct me if I'm wrong) but normally I hear the arrow goes to the exhaust
 

KevTrem

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Think we need a 😏 reaction πŸ˜€πŸ€£

Think it varies from different engines (,correct me if I'm wrong) but normally I hear the arrow goes to the exhaust
I knew I'd get a reaction.

Anyways its just a KM 30.5cc engine, nothing special but its teaching me about 2 stroke, I'm fine with 4 stroke (bloody hell another opportunity lol).
 

TODD

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153
The ring breaking is from the piston being installed backwards. Take what is left of the engine and slide it together. See where the ring comes into the exhaust port. The ring opened and caught the exhaust port roof. Basically a guillotine effect. If you turn the piston around you should see where the ring should not be visable in the intake port roof. This keeps the ring in the piston and does not allow it to open and catch the roof of the port.
 
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You can see where the ring sheared and started bouncing inside the engine. Looks like the bottom end might still be good. Make sure to replace the WHOLE top end be careful of the crank aswell. Make sure to inspect that it didnt bend slightly and make sure no shavings got into the bearings otherwise you will be replacing an engine twice.
 

KevTrem

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132
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Newcastle, UK
So um did you have a bit of an issue removing the Kill switch. Normally the red and black wires have connectors attached to them . Hope you ordered a new one. Kill switches are kind of important on these stupid things.
Nope no issue, just bad soldering on my part, been having a lot of problems with broken wires on the kill switch of late, think the cable was a bit short, but I've now resolved that.

Had a good inspection of the engine this morning, can't see anything untoward, so just waiting on the piston, head and gaskets now.

I'll make sure I install it the right way and hopefully it'll last longer.
 

KevTrem

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