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Old 26 September 2014, 08:51   #1
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Mariner/Yam 30 hp 2s pistons

Oh mighty and all knowing gurus, please would it be possible to offer an opinion on these pistons?

Some light scoring is visible but nothing that is detectable by the back of a fingernail.

The cylinders look fine apart from a little darkening round the exhaust ports.

Thanks
Hugh



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Old 26 September 2014, 14:39   #2
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Replace them!
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Old 26 September 2014, 15:25   #3
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I will add one to my black museum of broken pistons, s-shaped valve stems and bent cams....

Thanks
Hugh
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Old 26 September 2014, 16:24   #4
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FWIW
If they are as you describe, and they were mine, I would remove the rings, then give the pistons a good clean removing all the carbon build up, then give them a good polish with the likes of brasso.

Push the top ring squarely down the bore about 1/2" down on its own and check the gap against the spec, if in spec then I would order new rings same size, give the bore a quick hone so that the new rings will bed in and all should be good.

Just my opinion
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Old 26 September 2014, 19:02   #5
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Hi all.

I second that, you do seem to have a hot spot on the ring's.May be give the top of the piston a bit of a clean with some wet and dry and the ports.
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Old 26 September 2014, 21:44   #6
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They may be too far gone. What you can do is find someone with a glass blaster. An armature winder is a good place to begin. Cleaning with really fine glass beads will take them up beautifully. For those who don't think this will work, I did it for years to the pistons and cylinder heads, for some reason it made the surfaces almost anti-stick and left them cleaner at each annual rebuild (approx 750 hours). You must use a gentle bead though so test on another bit if alloy first. You must replace the piston pin clips though, do not reuse. Count all of the little ends so you don't miss ant putting them back and from memory the curved side of the thrust washers face the bearings. Grease the bearings into the con rod to assist you with install. A marine grease is fine. If you can't save them at least post a picture of the quality the glass blaster produces, you will be surprised.
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Old 27 September 2014, 03:50   #7
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Thanks chaps, I'll see what options are available locally.

I'd taken it apart because of a tapping noise, expecting either the top-end bearing or a little end bearing to have gone - or even a badly scored piston. All bearings seem good.
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