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Old 10-04-16, 08:44 AM   #1
Appletop
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Default +30 Riston Pings

Am in the process of rebuilding my Spec 18 D and I need a set of rings (don't think a 3mm ring gap is right somehow) but the piston is +30 thou, |I've had a look on tinterweb and can get standard rings but found some that are +40, my question is, even though they are to big would they gap down and be ok on a +30 piston? I can't see that it would make that much difference to the rings themselves...

Thankys kindly.
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Old 10-04-16, 08:51 AM   #2
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Ignore that, found some +30!!!
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Old 10-04-16, 09:05 AM   #3
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Am in the process of rebuilding my Spec 18 D and I need a set of rings (don't think a 3mm ring gap is right somehow) but the piston is +30 thou, |I've had a look on tinterweb and can get standard rings but found some that are +40, my question is, even though they are to big would they gap down and be ok on a +30 piston? I can't see that it would make that much difference to the rings themselves...

Thankys kindly.
Good news you found some

The rings would have the wrong radius/diameter therefore would be under stress in the bore even though you gapped them.....
Its not something I'd advocate.....

Any one else wish to comment?
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Old 10-04-16, 11:01 AM   #4
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I did wonder if that was the case but as they say, "needs must" sometimes
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Old 10-04-16, 11:38 AM   #5
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I did wonder if that was the case but as they say, "needs must" sometimes
I thought you might have pondered......

I remember the case of the rattling Bantam.....my dad had a BSA Bantam that had a rebore, we got the barrel and piston assy. back from the engine place, re-assembled the engine then wondered why it wouldnt start on the kick start.....
Tried several attempts at bump starting it down the street, but all the while all we could here was this incessant rattle from the cylinder.....
Took the head off and barrel, it then became apparent.......The rebore service had supplied us with a +30 piston and rings but bored the cylinder + 40........
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Old 10-04-16, 12:48 PM   #6
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That was handy then!!!!

Most of the time the answer is fairly obvious just sometimes it isn't!!!
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Old 13-04-16, 09:42 PM   #7
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+30 thou rings came today, now the rebuild and paintwork can start ....
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Old 15-04-16, 11:27 AM   #8
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+30 thou rings came today, now the rebuild and paintwork can start ....
Were they any good? What make were they? and where did you get them from, as I may also need a set myself in the near future.
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Old 15-04-16, 05:40 PM   #9
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Were they any good? What make were they? and where did you get them from, as I may also need a set myself in the near future.
They are NOS wellworthy ring and I got them off ebay. Haven't had a chance to fit them as yet tho.
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Old 15-04-16, 07:05 PM   #10
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I had to over hone the bore on my BSA 420 a little more than wanted, the piston still feels snug with very little slap, but the original rings were rendered useless, so fitted a set of 20 thou oversize rings and gapped them back to size, runs fine and zero smoke at last and great compression which will hopefully get better as they bed in, should be ok Rob
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