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Chamfering cylinder barrels.
Second Gear User
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April 5, 2020
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November 23, 2020 - 9:30 pm
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Hello folks,

I trust all is well with everybody and the enforced "house arrest" is not too bad.

I was out on the D1 GPO bantam the other day when a tinkling sound down the exhaust pipe caused some concern with a loss of power ( how does one notice a loss of power on a 1958 125cc bike?). I got home and took the head and barrel off to find half a piston ring had vanished, the piston damaged and a scarring near the exhaust port on the cylinder barrel.

I had been using the bike for a couple of weeks after fitting new piston rings so have no idea why it should do what it did then.

I am aware that new rings may catch on the "sharp" edges of the ports in the barrel and wonder if any body can point me in the right direction to "round them off".  Any suggestions as to the best way to do this, or even if anybody thinks it is a bad idea, will be much appreciated.

Ride safe, keep well.

Cheers Mick

Central France
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November 24, 2020 - 8:19 am
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Nasty. However, this is another problem that has been discussed 'to death' and is something that should have been done for you if the cylinder has been rebored. All the ports should have a slight chamfer on them - a needle file is OK - and the ring gaps should be towards the rear (about 5 O'Clock IIRC).

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Area Rep
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November 24, 2020 - 9:24 am
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Hi, I use very carefully I hasten to add a Dremel with a small stone just to take the sharp edge off the ports mostly top and bottom edges which are the likely ones to catch the rings. Regards Basil.

Second Gear User
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November 25, 2020 - 12:20 pm
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Many thanks, Cocorico and Basil,

I will get back in the shed.

Ride safe, Cheers Mick

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