Smoking Engine - Any thoughts?

[3potjohn]

Does anyone know what is the effect of a breather that is not working as it should? How much oil is in the motor? I am clutching at straws a bit to come up with the solution, other than oil getting in via guides or rings.
My T160 smoked like hell and that WAS the guides.One of my old beemers smokes after its been on the sidestand but they all do that.

[moriniboy23]

Engine and both rocker-cover breathers are checked or blown through and clear, but yes, a blocked breather would give me the symptoms

[EVguru]

Morinis always seem to smoke from the rear cylinder, just like most of the exhaust apparently comes from the rear cylinder. Try removing and/or blocking your balance pipe just to be sure.

You may have treated your rings too gently. Ring tension is only a few pounds static, combustion pressure pushes the ring against the bore. A full throttle acceleration from low rpm in a highish gear develops nice high pressure to seat rings. Localised heat build-up is the enemy, so coast the engine at light throttle for a couple of minutes afterwards.

[moriniboy23]

Ive had them for 30 years and Morinis dont routinely smoke like this..... Cars back off to escape the swirling cloud of oilsmoke I leave in my wake. Ive only seen primitive prewar 2-strokes on the Banbury Run produce anything akin to my engine

I have been running the rings in with extreme prejudice on occasion, up some steep hills and down on a shut throttle and 50 miles on, it's not getting any better, and only on the rear cylinder not both. I've now got the engine out for a fourth time, measured the rings gaps on the engineer-checked bores (fine). The pistons and barrels are both stamped B. Ollie at North Leicester warned me about the tiny bevel on the oil control ring, not shown or mentioned in the Manual and by a fluke, Id assembled it correctly according to Ollie, with the bevelled edge upwards, so it's not that either. All the smoke is coming out of one silencer, so ive even tried swapping the silencers over to see if somehow oil has got in. It hasnt. I really dont think the balance pipe is making any difference. ollie is stumped, my bike mechanic mate is stumped and so is the engine remanufacturer who has done some work on the top end, measuring the bores, valve-guide to valve stem clearance and recutting valveseats. His only suggestion is that somehow the rear rockerbox is getting WAY too much oil that it cant disperse and is being forced down the valve guides and burnt.

['It must be a .....']

Hi, I've been following the thread and the most obvious solutions have already been tried.

Still clutching at straw suggestions:

Are you using a 501/500 (catch tank) or 350 breather system (labyrinth/s in the pipes)? You could try running it to atmosphere on clear through breather pipes just to test if it is a breather/pressure problem. Some Camel/Coguaro 501s use a labyrinth type breathers but having never owned a 350 I don't know if they are the same.

Later 501 cylinder castings can be porous, evident by oil around the push rod tunnel area and usually worse on the rear cylinder which suggests more oil is around, but whether this is from above or due to crank throw I don't know and is probably not a pressure issue?

Hope you get it sorted soon, Ian

PS Using 501 rocker covers?

[morini_tom]

PS Using 501 rocker covers?

Now there's something I've never thought about before. (And apologies for partially hijacking the thread.

My 501 dart has black rocker box covers. I've certainly never painted any and when I built the last engine up I transferred the black ones across from my old 501, on the grounds that the chromed ones in a dart were thermally not great. I cannot remember what colour covers came with my 1st 501 but given that I've never seen a kokusan 501 without chrome covers, I wonder if in the mists of time I fitted the dart rockerbox covers without thinking about it...

The crows feet will be in the wrong place... And what about the size if the breather compared to a 350 one?

This could explain the amount of carbon build up on the combustion chamber of both my 501 engines. I expected it of the first, very worn engine but not the second, which is less than 4000km since new. Neither of those engines visibly smoked though. Also the top ends always looked well oiled and I would have thought I'd have seen signs of rocker wear if the crows feet were mis-positioned


Simon- where in the country are you? I know it would mean another head swap but if you wanted to borrow my good spare (siamese seated, uncracked) head to see if that cures the smoking issue then you're welcome.

Tom

[moriniboy23]

Hi , I am using a plain tube to vent the crankcase after using a baffled one that actually wasnt blocked either.

I am using chrome 501 rocker covers but Ive taken both breathers apart and can blow through them.

Ian, even if the barrels are porous, surely the nikasil lining will act as a barrier. I dont understand which bit can be porous and cause a combustion chamber of excess oil to burn

Tom, I am along the road from your old university in Bath - I offered you tools and a cuppa while you were there, I distinctly remember! Im currently using a second set of (guides-checked and seats professionally recut) 501 heads after the first smokey run, so Id put money on it not being 2 faulty heads in a row, but thanks for the offer.

Im looking at a top-end-dismantled engine with something approaching despair, and short of trying a spare 501 barrel and piston, or swapping current piston front and rear and resigning myself to a smoky front cylinder instead and engine out for a fifth time with a better idea of where the problem lies, I really dont know what to do next

[EVguru]

There's no way the top end should be over oiling if your main breather doesn't have the labyrinths fitted.

With 170,000Km on it's 656cc engine, my Honda Beat smokes. It's usually under acceleration from low rpm (high manifold vacuum), or especially if it's been standing. That's what I'd expect from valve guide/seal wear. It's a 12 valve SOHC and there's a lot of oil up there.

Good compression, but burning lots of oil under load suggests that the bore finish is screwed up. The FZR1000Exup derived engine in my GTS1000 consumes oil. It's commonly reported that these engines either use almost no oil, or do so steadily and it's down to bore finish.

[moriniboy23]

Maybe it's time to dig out the spare barrel & piston and get it checked/deglazed... It was smoking before I had it glazebusted (with paste not stones), so I dont believe it's my engineer who's ruined it. They measured the bore and declared it unworn and it does LOOK fine

Ive got the Nikasil outfit near me that all the racers use, so all is not lost with this barrel if it IS at fault.

['It must be a .....']

Hi, I only mentioned the porous cylinders as for some reason the rear one usually weeps more oil from the push rod tunnel than the front: I agree with your thoughts that the nikasil acts as a barrier.

Is it usual practice to deglaze nikasil bores when replacing rings?

Take care, Ian

[EVguru]

Ive got the Nikasil outfit near me that all the racers use, so all is not lost with this barrel if it IS at fault.

Well talking to them might be a good idea. I'm told the best way of recreating a new bedding in surface in Nikasil bores is an Aluminium Oxide brush hone of around 240 grit.

[moriniboy23]

The engineers I used, either already knew or took advice, and used a paste and kept well clear of stones. They said it did need deglazing though

[morini_tom]

Simon- yes, I remember- that must have been what, 10 years ago? Worrying how time flies on!!

To follow up on my post this morning, I've just been and looked at my rocker boxes and I can't see any difference between the black ones (which I assume are dart 350) and the chrome ones (which I know are excalibur 501), so wrong rocker boxes probably a red herring unless someone knows better?

[George 350]

Ok, here is a thought for you.
My non Morini bike is an old Norton and as such peruse the NOC website message board from time to time.
Recently there was a big discussion about the new 961and heavy oil consumption/smoking from the exhaust - the guy suffered 1 litre per 1000km oil consumption! After pages of discussion, the cure was the piston clearance, ie there was too much skirt to bore clearance. Only a tiiiiiny bit, but enough. New pistons were the answer.
You have 'deglazed' your bores, so you have increased their diameter. You are running used pistons which will be slightly smaller than original. If you now have too much clearance, then there could be too much oil for the rings to cope with, especially as the original bore finish is now gone and is 'rougher' than the original, therefore holding more oil in the tiny pores. The 'fix' for you may be to go to the next size up piston?

From my own experience in the motor industry, 'Nikasil' and other similar bore plating systems are incredibly tough and normally don't need attention until absolutely stellar mileages.

George.

[moriniboy23]

no the rockercovers are internally identical to match the ditto heads.

the bike smoked pre and post deglazing but i take your point. i wonder why the v experienced engineers havent considered/mentioned the piston? they dont look very scuffed or anything but im willing to try my other barrel and piston. im off on holiday tomorrow so im going to get it checked while im away