I'll stop it smoking if it kills me

[Itsme]

Hi Thumpeteers.

I hope you are in a thinking mood as I am having another crack at stopping the Mighty Midget smoking so much. Up to now honing the barrel and checking the rings, fitting a PCV valve to the engine breather and being reserved with the right hand have all had some affect, but sadly nothing has stopped it smoking and using oil. It does smoke in very particular circumstances however.

Oddly since I changed the exhaust for a new one, Chinese copy of the standard unit, it has developed a very strange habit. It doesn't smoke immediately on start up from cold, but after a couple of hundred yards it smokes so much it should be wearing a nicotine patch, then after about half a mile it stops smoking and doesn't do it again whilst warm. Stop for a cuppa however and the sequence repeats but the smoke clears up quicker.

Today I noticed that there was oil leaking down the front of the motor so I took the exhaust off and there was oil on the pipes under the engine. The exhaust ports are both black, dry and sooty and when I shone a torch in the exhaust valve stems are similarly black and sooty, but dry.

I took the rocker cover off and re-torqued the head bolts, three spot on one loose. If I look between the head and barrel there is some evidence of oil staining, but it is impossible to see where it originates. The plug is a perfect light brown with no trace of oil residue burnt or otherwise.

This is most perplexing as it makes the first half mile of my day very embarrassing as I ride along with my own blue trail following me. I don't want to start pulling things apart and replacing things until I have some understanding as to what might be the cause as parts for GNs are either very expensive OEM or cheap crap Chinese. I will pay for OEM if I have a reasonable idea that it will make a difference, but I do want to avoid Chinese as other than the exhaust which seems reasonable quality everything else I have tried from China has ended up in the bin very quickly.

I am at your mercy Thumpeteers.

Spartacian the hazy. 

[iansoady]

The loose head bolt and oil in the head / barrel area would make me suspect blown head gasket but it does sound a bit odd.

[mthee]

Intermittent  smoking might be a sticking PCV valve which will be the easiest thing to remove and check first. Also, this might have caused/exacerbated the external leak. To help source the external leak, I'd  degrease the engine to within an inch of it's  life. Good luck.

[Itsme]

Thank you both for good suggestions. I too thought the head gasket would be a good suspect, but I didn't think of the PCV sticking I must admit.

What does strike me is that this may simply be a design fault which gets worse as the mileage climbs. The Mighty Midget now has 46,000 miles on the clock so everything is getting a bit loose. My mate who was an engineer and has been riding bikes for the last 50 years thinks the scavenge side of the oiling system may be unable to cope. There certainly is a lot of oil sloshing around in the rocker box so maybe he has a point.

I can't understand the perfect light brown colour of the plug though. Whenever I have had an 'oil burner' the plug tends to show oily residue and a black colour.

I am getting a bit frustrated with it now as that first half mile and knowing that if I use the full performance of the motor (okay that's a relative term) that I will be needing to put a fair bit of oil in in a very short distance is ruining an otherwise nice bike.

It's funny really as if asked I would say I love old bikes, but the reality of constantly having to think about what's wrong rather than just enjoying the ride is getting on my nerves. I'm sure it is only temporary and when (and if) I solve this issue I will be in love with the MM again, but for now I am grateful to my friend Jill for the use of her not very exciting, but dependable little Lexmoto. Did I really say that??!!

Spartacian the fed up.

[Moto63]

for now I am grateful to my friend Jill for the use of her not very exciting, but dependable little Lexmoto.

Spartacian the TURN COAT
[/quote)
🤪😉

[Itsme]

Lol Guilty as charged M'lud.

Spartacian the seeker of a quiet life

[iansoady]

How does the oil from the cam / rocker area return to the crankcase? If it is via drillings in the head / barrel then it will need to pass through the head gasket which I would expect / hope would have a reinforcing ring / O ring arrangement to stop leakage. If oil was exiting here it wouldn't affect plug colour. The intermittent nature of the leak may be due to expansion of various parts closing slight gaps.

[johnr]

first of all, the cylinder head bolts that live inside the head will need to have copper washers under them to stop oil leaking out of the enclosed internal part of the head and 'out' down the studs, giving the impression of a duff head gasket. this will only leak whilst the engine is running and oil is circulating.

[johnr]

have you checked the valve stem oil seals? the engine oil runs down the valve if the seal is duff and into the exhaust port when the engine is stopped, when you start it up, the oil burns off in the first half mile of the journey, then its stopped from running down the exhaust by the internal pressure of the exhaust. if the crankcases are being presurised by a blocked breather thiss will be worse as itll be forced down the valve guides.

[Itsme]

Hi John

The bolts do have copper washers under them, I remember putting them back when I re-fitted the head. I changed the valve stem seals about 2000 miles ago, BUT there is no guarantee I did a good job or that the seals were good quality.

Thanks for the thoughts though.

Ian

[Steve Lake]

hi spartician the frustrated..
maybe you have resolved the problem by now, but just in case you haven't, and having the 'perfect plug condition' in mind, it would seem the oil that is being burned is entering the exhaust flow after ignition, i.e. exhaust valve stem seals etc, to enter the exhaust stream the oil must be under some pressure (to overcome the pressure of the exhaust gasses) or you have a (very) faulty valve stem or seal. are there any oil galleries in the head (on the pressure side, not the scavenge side) that may have found a way into the exhaust. as the smoking decreases once the engine is hot rather indicates that a gap is closing up  once hot.
hope you get to the bottom of it ( as my mate said to me when i told him i was off to the hospital to get my piles sorted out )
pip pip

[mthee]

With mates like that, who needs an enema?!

[Moto63]

With mates like that, who needs an enema?!

🧥🚪🚕😉

[iansoady]

Youtube used to tell me "You have no friends". Sadly they seem to have changed their messages even though they were quite correct......