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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Nip up Comet
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<blockquote data-quote="Tony Wilkinson" data-source="post: 111901" data-attributes="member: 4387"><p>I bought my 1950 Comet a few months ago from a Dealer. After some running problems I fitted an electronic ignition as the mag was weak.</p><p>I then had the engine nip up on me on a long straight. I was doing about 60mph, whipped the clutch in sharpish for a few seconds, let out and it started and ran ok since.</p><p>Now although the bike has loads of compression and runs really well, it smokes when hot, mainly on down gear changes.</p><p>I got with it a load of receipts for new parts bought a couple of years ago, including a new exhaust valve and lower valve guide.</p><p>I only assumed these had been fitted by the previous owner.</p><p>Cutting a long story short, I managed to get hold of the last owner who informed me he had indeed fitted the new valve and guide but had not investigated further as the piston looked new.</p><p>I bought a little endoscope thingy off ebay to look down the plug hole. The bore looks recently rebored and piston does look new and has no carbon on it. However I can see a faint light grey line up the bore where I am assuming the nip up occurred.</p><p>I intend over the Winter to investigate this by stripping the top end down. I have a lot of experience but Vincent are new to me. I am thinking the oil ring it probably tight in that place on the piston, hence oil getting up the bore.</p><p>Has anyone had a similar problem I am asking or any advice from people more knowledgeable than myself please.</p></blockquote><p></p>
[QUOTE="Tony Wilkinson, post: 111901, member: 4387"] I bought my 1950 Comet a few months ago from a Dealer. After some running problems I fitted an electronic ignition as the mag was weak. I then had the engine nip up on me on a long straight. I was doing about 60mph, whipped the clutch in sharpish for a few seconds, let out and it started and ran ok since. Now although the bike has loads of compression and runs really well, it smokes when hot, mainly on down gear changes. I got with it a load of receipts for new parts bought a couple of years ago, including a new exhaust valve and lower valve guide. I only assumed these had been fitted by the previous owner. Cutting a long story short, I managed to get hold of the last owner who informed me he had indeed fitted the new valve and guide but had not investigated further as the piston looked new. I bought a little endoscope thingy off ebay to look down the plug hole. The bore looks recently rebored and piston does look new and has no carbon on it. However I can see a faint light grey line up the bore where I am assuming the nip up occurred. I intend over the Winter to investigate this by stripping the top end down. I have a lot of experience but Vincent are new to me. I am thinking the oil ring it probably tight in that place on the piston, hence oil getting up the bore. Has anyone had a similar problem I am asking or any advice from people more knowledgeable than myself please. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Nip up Comet
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