Cleaning small sieze marks barrel and piston?

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eadmr04
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Thu Apr 06, 2017 8:21 pm

Just stripped the top end on my missus GP and it looks like it might have had a small nip up in the past, nothing too drastic. What's the best way to clean up the sides of the piston and few small marks in the barrel?

holty
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Thu Apr 06, 2017 8:32 pm

some fine wet and dry paper 400 grade, and wd40 or turps and just rub them out, on both barrel and piston, as recomended by dave webster in the lambretta tuning manual

mr oppinionated
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Mon Aug 07, 2017 5:22 pm

You could also drill some 1/2 to 1mm holes in the piston directly beneath the bottom ring on the part where the heart caused the siezure. I have done this many times, it's a trick I got from a dirt bike tuning manual. It helps to keep the piston cool at the very point where it gets hot.

Mike

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hungdog
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Mon Aug 07, 2017 8:03 pm

mr oppinionated wrote:
Mon Aug 07, 2017 5:22 pm
You could also drill some 1/2 to 1mm holes in the piston directly beneath the bottom ring on the part where the heart caused the siezure. I have done this many times, it's a trick I got from a dirt bike tuning manual. It helps to keep the piston cool at the very point where it gets hot.

Mike
Never heard of that before

mr oppinionated
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Wed Aug 09, 2017 5:16 pm

I had it published as a tip in Scooter Scene many years ago. Sticky added that you can also score hash marks with a file if you didn't want to drill the holes. However, I found that the holes are better at the job.

Mike

Martin20
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Wed Aug 09, 2017 5:24 pm

mr oppinionated wrote:
Mon Aug 07, 2017 5:22 pm
You could also drill some 1/2 to 1mm holes in the piston directly beneath the bottom ring on the part where the heart caused the siezure. I have done this many times, it's a trick I got from a dirt bike tuning manual. It helps to keep the piston cool at the very point where it gets hot.

Mike
How many holes Mike, and how far apart?

bristolmod
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Wed Aug 09, 2017 8:14 pm

jumping in- I've done this for many years as well. Generally 2 holes about 2 mm wide and I countersink them as well by a few twists of a larger drill. Make sure they are below the bottom ring, and not where the exhaust port is (mark the piston at BDC) Drill them either side of the exhaust port position.

Chris
Scootering since 1968.

bristolmod
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Wed Aug 09, 2017 8:28 pm

heres one I did earlier- this has 3 holes near the base of the piston on the exhaust side. When the piston is travelling up and down the holes do not enter the exhaust area.Image
Scootering since 1968.

mr oppinionated
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Wed Aug 16, 2017 5:03 pm

The method I follow is the one from the two stroke tuning manual. Usually, you would only need two holes, just beneath the piston rings. It really depends upon where your piston is over-heating.....you have to wait for that to happen (you don't need a siezure to see it) before you know where the piston is getting hot.
Pistons usually overheat towards the top, as that's closest to where all the heat from combustion occurs, causing the piston to expand a little (or a little too much !!) as well as the friction element.
I have found that it usually occurs on the exhaust side.
You really don't need anything larger than 1mm, but 1/2mm should do it. I agree with shallow counter-sinking, but only to remove any sharp 'edges'...you could also run a thin hack-saw blade across the holes to allow the fuel to move away from the holes easier.
I have never seen any holes drilled at the bottom of a piston before, so cannot comment on whether that method is of any value. I can only say that over heating pistons became a thing of the past for me....provided the engine was well setup of course.

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rosscla
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Mon Apr 30, 2018 12:25 am

Cleaned up a T5 barrel recently using spirit of salt to take the smearing off the barrel. Soak it into some sort of paper towel and let it rest on the smeared Aluminium then rinse off with water.

Odd rubs with fine emery to take the last of it off and a final rinse in petrol.
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