2Smoke Posted May 7, 2013 Report Share Posted May 7, 2013 I've got an NC30 in the garage that has a bit of a smoke habit, once warmed up it smokes like buggery with oily deposits in the exhaust. The smoke increases with throttle, and only happens once its warmed up. I'm thinking crankcase pressure is forcing it past the rings, while the engine is running there is hellish pressure coming out of the oil dipstick cap! I've been looking for the crankcase breather, can only spy the one on the top of the rear cylinder cam cover, which seems clear (has a vacuum while running, is this right?) Is there another breather on the engine somewhere? Or could it be something else? It's definetely using engine oil, and I've not seen a motor burning oil like this one does! Cheers! Paul Link to comment Share on other sites More sharing options...
CMSMJ1 Posted May 7, 2013 Report Share Posted May 7, 2013 Only that top one as far as I know - lots of pressure at dipstick is probably normal - might be someone on there started their bike without the cap...and it peed and gushed nicely. Smoking that bad is going to be scabby rings innit. Has it been sat? The top breather will dump a load of shit out of it if you hold some kitchen paper in front of it when running. It makes a mess of your air filter if you let it.. Link to comment Share on other sites More sharing options...
2Smoke Posted May 7, 2013 Author Report Share Posted May 7, 2013 Nah it's been in daily use for ages. Just started smoking last monday, seems strange for it to happen so suddenly! Link to comment Share on other sites More sharing options...
speedy sie Posted May 7, 2013 Report Share Posted May 7, 2013 valve guide seal,there is some oil adative you can get to swell the seals up?. Link to comment Share on other sites More sharing options...
BudgetBoy Posted May 7, 2013 Report Share Posted May 7, 2013 What sie said,, but don't use additive (IMO),, replace them all.Additive is not a cure just a temp fix. Link to comment Share on other sites More sharing options...
Superdunc Posted May 7, 2013 Report Share Posted May 7, 2013 Valve stem oil seals normally make themselves known on closed throttle, not when you open the throttle. Leakdown or compression test required me thinks. Link to comment Share on other sites More sharing options...
BudgetBoy Posted May 7, 2013 Report Share Posted May 7, 2013 Valve stem oil seals normally make themselves known on closed throttle, not when you open the throttle. Leakdown or compression test required me thinks. leakdown would be the better opinion as you can pinpoint the problem better. Dunc:- Im really interested why regarding the stem seals.. I was always led to believe the oil gets thinner as it gets hotter (well duh lol ) but the oil seeps past the hard seals down the valve and into the combustion area and out the exhaust.The more you open the gas the more oil is pumped to the top of the engine and thus more oil can go down the valves. It could also be rings granted but surely the bike would idle iffy and not run correctly through the rev range. Im am genuinley interested though mate.Everydays a school day and all that.. Link to comment Share on other sites More sharing options...
Superdunc Posted May 7, 2013 Report Share Posted May 7, 2013 I've always been taugh, and it my experiencet that oil smoke from the exhaust on over run, i.e. closed throttle. This is because the cylinder still tries to pull air in on the inlet stroke, but as the throttle is closed it causes a partial vacumm which draws oil past the knackered seals. Hope that makes sense. Link to comment Share on other sites More sharing options...
lorenzo Posted May 7, 2013 Report Share Posted May 7, 2013 As dunc said, vacuum is highest on a closed throttle, so what tends to happen is that oil is sucked past the seals on change downs and idle etc, then when you open it back up, it clears its throat a bit and spurts out a bit of a cloud as you initially get going again. Link to comment Share on other sites More sharing options...
2Smoke Posted May 8, 2013 Author Report Share Posted May 8, 2013 Engine rebuild time then I think, just strange how it was fine then started smoking! I'll go through a few things this afternoon and see how it looks. May have to knock up an adaptor for my compression tester as the NC uses tiiiiny little plugs! Cheers all! Link to comment Share on other sites More sharing options...
2Smoke Posted May 8, 2013 Author Report Share Posted May 8, 2013 Pretty much zero compression on the rear right cylinder. Oops. Link to comment Share on other sites More sharing options...
CMSMJ1 Posted May 8, 2013 Report Share Posted May 8, 2013 That'll do it... Link to comment Share on other sites More sharing options...
2Smoke Posted May 16, 2013 Author Report Share Posted May 16, 2013 *strokes chin* hmmmmm.... Link to comment Share on other sites More sharing options...
srad34 Posted May 16, 2013 Report Share Posted May 16, 2013 Jebus, thats not meant to be there now is it? Link to comment Share on other sites More sharing options...
Beanerno1 Posted May 16, 2013 Report Share Posted May 16, 2013 Holy piston batman!... Is there a matching bent valve in the head? Link to comment Share on other sites More sharing options...
CMSMJ1 Posted May 16, 2013 Report Share Posted May 16, 2013 That'll do it... Link to comment Share on other sites More sharing options...
BudgetBoy Posted May 16, 2013 Report Share Posted May 16, 2013 JB weld then EDIT:- i have to put "joke" incase folk thing im being serious Link to comment Share on other sites More sharing options...
2Smoke Posted May 16, 2013 Author Report Share Posted May 16, 2013 Valves are good.. Although the exhaust valves on both cylinders look as if they've been running a bit hot. Maybe due to the virtually non-existent end can (some chinese carbon thing, horrible loud) and stock jetting? Link to comment Share on other sites More sharing options...
Hendo Posted May 16, 2013 Report Share Posted May 16, 2013 I love stuff like this. What do you think has happened to it? I thought these little NC's are supposed to be bulletproof...? Link to comment Share on other sites More sharing options...
Beanerno1 Posted May 16, 2013 Report Share Posted May 16, 2013 I love stuff like this. What do you think has happened to it? Moyder!... Moyder most foul! It was the gudgeon pin with the conrod in the engine block.. Link to comment Share on other sites More sharing options...
drunkn munky Posted May 16, 2013 Report Share Posted May 16, 2013 I got boxes of spare pistons and various engine parts should you need any let me know Link to comment Share on other sites More sharing options...
2Smoke Posted May 16, 2013 Author Report Share Posted May 16, 2013 I think I'll be needing a piston mate! Will re-ring the lot too, think the lads dad wants it right! Let me know how much please.. Link to comment Share on other sites More sharing options...
drunkn munky Posted May 16, 2013 Report Share Posted May 16, 2013 Just postage mate Link to comment Share on other sites More sharing options...
2Smoke Posted May 16, 2013 Author Report Share Posted May 16, 2013 Thanks! will PM you my address... Link to comment Share on other sites More sharing options...
Beanerno1 Posted May 16, 2013 Report Share Posted May 16, 2013 Give me a shout if you manage to find rings for a decent price, best I could find was around £40 per piston! Link to comment Share on other sites More sharing options...
Superdunc Posted May 16, 2013 Report Share Posted May 16, 2013 *strokes chin* hmmmmm.... Valve guide oils seals? Link to comment Share on other sites More sharing options...
2Smoke Posted May 16, 2013 Author Report Share Posted May 16, 2013 Valve guide oils seals? Just changed them, and rebuilt it and tried it. Still the same... Link to comment Share on other sites More sharing options...
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