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AR125 Gone BANG :(

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tshort2007
Scooby Slapper



Joined: 07 Jun 2009
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PostPosted: 20:41 - 07 Jun 2009    Post subject: AR125 Gone BANG :( Reply with quote
Sad Finally fixed the problem with my AR running rich and misfiring, the coil pickup was loose!
So decided to take it out for a run
5 miles of gentle riding got the engine nice and warm, so decided to kick it a notch on the dual carriageway.

about 5 seconds later, a thud and a rattling noise occured, resulting in the bike not idleing, but still fine at high RPM (apart from the quiet rattling)

Got back to the garage, and pulled the plug, looked perfect, nice mocha coffee brown colour. Fearing shattered bearings, i proceeded to strip the top end. Took the exhaust off, and out fell a chunk of piston, and a bit of ring. Images attatched (hopefully)

It appears the piston caught the exhaust port on the way down, as the piston has been burred over the bottom ring, just below the missing chunk.

The ar125 engine uses a rotary valve, with the injection port at the side of the block, so the piston has no holes for the inlet port. However, where the split is in the rings has been installed to the wider exhaust port. Is this correct? as the piston has no markings for inlet

What would cause this to happen?
And does my barrel look ok to you?

Thanks for all your help today
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ms51ves3
Super Spammer



Joined: 07 Jun 2007
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PostPosted: 20:47 - 07 Jun 2009    Post subject: Reply with quote
If there are no deep scores in the barrel you may get away with just cleaning up the exhaust port with a dremel and putting a chamfer on it.
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bmwsport
Nitrous Nuisance



Joined: 25 Oct 2008
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PostPosted: 20:50 - 07 Jun 2009    Post subject: Reply with quote
Shocked wow at least you did it properly lol, err the barrell doesn't look very good to me, is that a bit of plating missing just below the exhaust port? does the ar have a powervalve? is that ok? Check out the mikata thread in general, couple of us going through the top end rebuild phase at the mo lol
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tshort2007
Scooby Slapper



Joined: 07 Jun 2009
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PostPosted: 20:50 - 07 Jun 2009    Post subject: Reply with quote
ms51ves3 wrote:
If there are no deep scores in the barrel you may get away with just cleaning up the exhaust port with a dremel and putting a chamfer on it.


That was my thought. barrel isnt scored, and head has NO chunks taken out. luckly it was a clean break, with all the bits going strait into the exhaust. What would cause the piston to go like this?
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tshort2007
Scooby Slapper



Joined: 07 Jun 2009
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PostPosted: 20:54 - 07 Jun 2009    Post subject: Reply with quote
bmwsport wrote:
Shocked wow at least you did it properly lol, err the barrell doesn't look very good to me, is that a bit of plating missing just below the exhaust port? does the ar have a powervalve? is that ok? Check out the mikata thread in general, couple of us going through the top end rebuild phase at the mo lol


No powervalve on the AR, and that is just a mark/lip on the btm of the exhaust port. the AR barrels were never plated, so they do wear easily. As the compression doesnt start till after the top of the exhaust port on the upstroke, i wouldnt see any problems in smoothing out the burr and chamfering it back. I bought the bike 6 weeks ago, and only just got legal on it, so i dont know the history of the bike i'm afraid. Showing 12500 on the clock, and spent 4 years in a blokes garage. thats all i know!
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 21:34 - 07 Jun 2009    Post subject: Re: AR125 Gone BANG :( Reply with quote
tshort2007 wrote:
However, where the split is in the rings has been installed to the wider exhaust port. Is this correct? as the piston has no markings for inlet


Not sure with the AR, but none of the 2 strokes I have had to do rebuilds on have had the ring gaps over the exhaust port.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing
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tshort2007
Scooby Slapper



Joined: 07 Jun 2009
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PostPosted: 21:38 - 07 Jun 2009    Post subject: Re: AR125 Gone BANG :( Reply with quote
Kickstart wrote:
tshort2007 wrote:
However, where the split is in the rings has been installed to the wider exhaust port. Is this correct? as the piston has no markings for inlet


Not sure with the AR, but none of the 2 strokes I have had to do rebuilds on have had the ring gaps over the exhaust port.

All the best

Keith


Do you rebuild engines then mate? Do you think my block will be ok, orshould i send it for re-boring?
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 21:49 - 07 Jun 2009    Post subject: Reply with quote
Hi

Just my own! With the small amount of damage you would be best off reboring it, but could probably get away with a new piston.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing
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tshort2007
Scooby Slapper



Joined: 07 Jun 2009
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PostPosted: 22:30 - 07 Jun 2009    Post subject: Reply with quote
TBH, i bought a cheap 125 to learn on, with the intention of getting a cbr600 later this year, so if the AR will last 1000 miles with just a piston, i'm gonna do it on the cheap!
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welshlad25
Two Stroke Sniffer



Joined: 27 May 2009
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PostPosted: 08:43 - 08 Jun 2009    Post subject: Reply with quote
this exact thing happend to my honda mtx m8 .i got told if barrel is not to bad the rub down with very fine wet and dry to take high points of were damaged and fit new piston and rings m8

i did that and fitted new piston and now bikes up and running spot on if u look in show and tell i think theres pics of my piston and looks like yours
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The last post was made 15 years, 355 days ago. Instead of replying here, would creating a new thread be more useful?
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