Piston problems Model C

pictures (or stories) of hideous injuries sustained by your ariel
M.Bagshaw
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Piston problems Model C

Postby M.Bagshaw » Sun Sep 15, 2019 8:23 pm

Rebuilt bike a couple of years ago, set of this morning on a run 18 miles in piston nipped up! Been running great, plenty of oil?
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JohnnyBeckett
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Re: Piston problems Model C

Postby JohnnyBeckett » Sun Sep 15, 2019 9:45 pm

is it Runing to rich and washing the oil off the boor or is the timeing out

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brenton.roy
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Re: Piston problems Model C

Postby brenton.roy » Sun Sep 15, 2019 10:56 pm

The pitting on the crown suggests it was burning really hot. Lean?
It's not easy to jet the mains as we tend not to ride at big throttle openings.
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Re: Piston problems Model C

Postby nevhunter » Mon Sep 16, 2019 12:29 am

Insufficient clearance It looks like. Perhaps the day was a bit warmer or your riding a bit more enthusiastic than normal. It takes thousands of miles to wear a bit of extra clearance on the piston and sometimes a piston will "grow " slightly. Don't file off the "heavily"dragged areas, they will already be undersize most likely. It's also a good idea to relieve under the lower ring and drill a few holes at an angle through the skirt. (NOT in the ring groove). A bit of two stroke in the fuel, doesn't hurt either. An egg cup to a tank of fuel is enough. Nev

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Re: Piston problems Model C

Postby john.whiting » Mon Sep 16, 2019 3:24 am

Insufficient,or deficient cam relief,if you ask me .....in fact it looks like the piston is just plain round ,with no taper,and no cam.....there was similar one pictured a few weeks ago,and I thought the same thing then........if you are going to use a round piston,give it plenty of clearance...like .006-.008........are both sides the same?.....the rod may be bossing in the piston and forcing it over.....ie crank not centred.

M.Bagshaw
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Re: Piston problems Model C

Postby M.Bagshaw » Thu Sep 26, 2019 9:26 pm

Thanks for your suggestions, but its none of the above, with the exception of perhaps being a little too enthusiastic!
Barrel being lightly honed then its back together for another go.

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Karol Burger
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Re: Piston problems Model C

Postby Karol Burger » Fri Apr 23, 2021 6:48 pm

it also happened to me with my original piston. I couldn't find the cause. I sanded the damaged area, and the error did not happen again I think I adjusted the mixture in the carburetor a bit
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Re: Piston problems Model C

Postby tony.barnett » Mon Apr 26, 2021 9:14 am

A wise man once told me that original Black Ariel pistons had a habit of expanding, but not contracting. His advice if it nipped up was to clean up the high spots on the piston (file not emery) and try again.
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Re: Piston problems Model C

Postby nevhunter » Mon Apr 26, 2021 9:36 am

What looks like high spots has become low spots due seizing and shrinking the metal. Check with bearing blue or a micrometer. Most just hone a bit out and try again. It makes the ring gap wider though.. Filing a piston skirt all over takes skill and time. It was more common with two strokes that have NO ovality or crankcase compression disappears . Nev


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