Spark plug cap won't fit

[ChrisCurvyS]

Attempted to change the front plug today to cure a long-standing problem with my curvy not firing on the front cylinder after being left out in the rain or not ridden for a while.
Thing is, once I'd taken the plug cap off, it didn't seem to want to go back on again fully, both on the existing old plug and on the new one after I replaced it. I felt it click onto the plug as I pushed down but it was still a good centimetre or two from slotting fully into the socket, and I tried applying a fair amount of force. Any ideas?
There's a thread on sv rider about exactly the same thing but it ends without any resolution. Additional info - the bike always ran perfect once warmed up, even in torrential rain.
I tried starting it with the cap in place to see if it was connecting and nothing happened - just a dimming of the dash lights in time with pressing the starter button, though that might be down to me breaking the lead while wrestling the cap (I also drained the rad).
Never changed the plugs myself before but I suspect the cap may be non-standard - there's no triangle marker as per the manual and it doesn't widen at the plug end as the ones I've seen in pics do.
Excuse the essay - any Yorkshire or Sid squid expertise would be greatly appreciated!

[Sid Squid]

Remove the plug and check that it fits the cap. The majority of plugs have a small thread on the end, sometimes they are supplied with an adaptor for the older style connector, this is screwed to the small thread. Make sure your plug and cap are compatible.

[ChrisCurvyS]

Many thanks Sid. Just checked using the cap and the other new NGK CRE8 plug I've got for the rear cylinder, and the plug has no adaptor on it - just the usual 1cm or so long thread.

It fits into the cap with a nice click but I'm increasingly thinking the cap isn't SV650-specific and maybe is too long. Like I say, it's got no arrow to indicate the exhaust side and it looks like it's been cut to fit at the bottom.

If it's been sticking out like that all along, it would explain the misfire after being left out in rain wouldn't it?

[Sid Squid]

Got a picture? Sounds like the cap is too wide to fit down the tunnel, although I can't think of a cap that large a diameter such that it wouldn't fit. An ill fitting cap would certainly not guarantee good ignition - I can only imagine it would get worse if it were wet.

[ChrisCurvyS]

I'll get a pic tonight Sid. I don't think it's too wide though as it's clicking into the plug as it should - instead I think it's too long, from the top to the socket the plug fits into.

I suspect a well-meaning mechanic friend who did some work on the bike a while back has replaced the HT lead and cap together (I vaguely remember him saying something about the former). He probably used a cap he had lying round the workshop, not noticing that it was sticking out a little bit behind the radiator.

IIRC there was a long dry spell after he did this but the problems with the rain and dampness started soon afterwards.

Oddly, when the bike's been left in the shed and not used for a while, (rather than left in the rain) it will actually start on both cylinders but start misfiring on the front after a few minutes. Could it be that moisture is accumulating in the bottom of the plug well because of the loose cap, then when the heat starts to come through it's evaporating up into the bottom of the cap and causing it to short?

Or is that complete tosh from the mind of someone who got a D in physics GCSE?

[Bibio]

is there a drain hole on the curvy cylinders? if so it might be worth checking its clear.

also i think the OEM plug cap has a flange on it that covers the plug hole when the cap is fully on, this stops the water getting in and it's well documented to put a little silicone or RRG round the flange to make a better seal.

[ChrisCurvyS]

Thanks Bibio - yeah I was planning to do the silicone thing for extra piece of mind once I get a cap that fits properly. I want to try it without any first though to make sure it is the ill-fitting cap that's the central problem.

I'm now pretty sure it is - spoken to my pal and he confirmed he fitted a replacement cap with the HT lead, and didn't realise it was protruding. He was apologetic but it was a freebie and done with good intentions, so I'm not complaining.

I checked the drain hole (right side of the bike isn't it?) and it was clear - thanks for the suggestion though.

Just need to get myself the proper fitting cap - hoping to get one from the yellow curvy being broken in the 'for sale' section. Looking at about £35 all in from Robinson's Foundry otherwise.

[Bibio]

just get a whole coil assembly from the bay or anyone on here selling one. mind you for £35 you know its new and the right one.

[ChrisCurvyS]

I know - it's just the inner stinge resenting spending that much on bits of rubber!

Seen two clean-looking complete coil kits on fleabay for £30 inc delivery from a breakers. Tempted as then I'll have a spare.

[Bibio]

it's not a bit of rubber it's a vital part of the bike.