Smoke from engine when driving before fully warm

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Kevin
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Smoke from engine when driving before fully warm

Post by Kevin »

My Traveller has a 1275 midget engine that was rebuilt under 10,000 miles ago.
This problem occurred occasionally in the last couple of years when on warm up normally after 1 to 2 miles a smell can be detected a bit like oil heating up and then shortly afterwards when accelerating a puff of smoke (sometimes quite large) comes from the exhaust it seems to only happen with temperatures at this time of year (and a couple of times in the spring) as its been fine all through the summer and has just started to do it again although not every time.
When this originally started I thought it may have been down to the fact that the bypass hose was blanked off during the rebuild of the engine so earlier this year I had a new bypass tube fitted and a new water pump with the correct outlet and fitted a new piece of heater pipe for the bypass hose as its like the original although I have since found it available in silicon.
Anyway the car runs absolutely fine apart from the puff of smoke and the reason for going back to a bypass hose was that I thought that maybe the front of the head was warming up quicker than the rest causing possibly a pinched valve but obviously not in my case, any suggestions as nobody at my local branch seems to have had this issue before and I don't know what to try next especially when it seems to be air temperature related.
Cheers

Kevin
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Re: Smoke from engine when driving before fully warm

Post by MarkyB »

Is it blue smoke?
It sounds like valve guide wear, over night oil runs down onto the valve head then burns off when you start the engine.

Does something similar happen if the engine is left to tick over for a long time?

"Once you break something you will see how it was put together"
Kevin
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Re: Smoke from engine when driving before fully warm

Post by Kevin »

I would say it's grey blue, it doesn't do it on start up only after driving 1 - 2 miles and it only does it once no matter how long the journey and it's never done it in traffic, when rebuilt the head had new guides and valves, that's why I am puzzled.
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Kevin
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Re: Smoke from engine when driving before fully warm

Post by IslipMinor »

shortly afterwards when accelerating a puff of smoke (sometimes quite large)
Kevin,

I used to get this very regularly on our 1380 when running without the bypass hose, as is well documented!! Reinstated it and nothing for years now.

There is a humungous thread on the MG Enthusiasts' BBS:

http://www2.mg-cars.org.uk/cgi-bin/gen5 ... subject=97

The thread is 'Engine Breather and HUUGGGGEEEEE blue clouds' and a more recent one 'Engine Breather OIL SUCKING Yet another engine'.

Unfortunately neither come to any definite conclusion, despite lots of discussion and not a little abuse.

There are 2 common themes on these postings:

One is that the blue smoke is accompanied by excessive oil consumption, which was not the case with my engine.

The second is a belief that the timing chain cover is filling up when the oil is cold(er) and getting sucked up the crankcase ventilation tube connected to either the PCV valve or carburettor vent connection.

Maybe try disconnecting the hose from the timing cover and seeing if it still produces the smoke?
Richard


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Re: Smoke from engine when driving before fully warm

Post by Kevin »

Hi Richard what can I say you hit the nail on the head I just popped out to have a look at my breather pipe to the carb and there was a trace of oil on the end so it looks like I have found the problem and just now need the cure, looking at the MG link you gave there seems to be 2 different breather caps and as I have the one with the smaller gauze that may be the problem that its the wrong size of rocker cap, I will have to have a play around and see what is available. Like your engine its not wear that's causing the problem.
Cheers

Kevin
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Re: Smoke from engine when driving before fully warm

Post by bmcecosse »

And certainly not a pinched valve ! :roll: My advice is to fit a rocker cover with breather pipe - and T it to the pipe from the timing case - this will reduce the excessive suction from the timing case - which could well be causing the plug of smoke you report.
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Re: Smoke from engine when driving before fully warm

Post by Kevin »

Well it looks like its oil mist being drawn up into the carb though the breather pipe that is the problem when the engine is warming up with cooler temperatures.
I have had a look through the MG posts and it appears that it is down to crankcase pressure and there is mention of vacuum issues ( not that I have a clue about that ) but it seems there is a lot of variations and it appears them problem is made worse when there is more air going into the engine than coming out which puts the oil mist under extra pressure causing it to rise up the breather pipe into the carb. Twice yesterday and going to work today when the car was warming up and when I got the smell of oil I made sure I only accelerated gently until the smell had gone and there was no smoke so it only occurs under acceleration.
Interesting suggestion Roy however could that not increase the air entering the engine which may make it even worse and won't that also affect the carb mixture as well.
I have checked my breather pipe and that seems sound with no soft area's to cause issues, however when I looked at my plastic filler cap it has 2 vents in it 180 degrees from each other on the sides but underneath the top rim each one is approx 1/8" x 1/4" which is more than the plain chrome ones as they just have a central hole.
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Kevin
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Re: Smoke from engine when driving before fully warm

Post by bmcecosse »

If there are 'pressure' problems - then that is blow-bye on the piston rings, or possibly valve guides if they are badly worn ...... The suggestion of adding a breather cover was simply to reduce the 'draw' on the timing case pot - where the suggestion was that a slug of oil was being sucked up from the can... If the suction is split between two points - there is much less chance of that - but yes - overall it's still going to draw the fume (but hopefully not a slug of oil) into the inlet manifold - where it will be burned! Think of it as 'upper cylinder lub' perhaps ? If you don't take the oil fume away - then pressure in the crankcase will just blow oil out of every orifice - particularly the rear labyrinth where it will gently work it's way round onto the clutch.... Not a great idea...
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Re: Smoke from engine when driving before fully warm

Post by Kevin »

Kevin wrote:My Traveller has a 1275 midget engine that was rebuilt under 10,000 miles ago.
To add to my original post oil pressure is 60lbs when hot and running and 30lbs on tickover when set up on a rolling road it was producing 60+bhp so no engine wear issues.
After following Richards link this does appear to sometimes be a problem with 1275cc engines that have been rebuilt that doesn't happen when hot and running not as you have suggested with constant crankcase pressure also it wasn't a problem when they were new with the rocker cover without an input breather so the issue must lie elsewhere.
Cheers

Kevin
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Re: Smoke from engine when driving before fully warm

Post by bmcecosse »

The oil pressure is 'ok' although not brilliant....however irrelevant to this problem. A Compression check may be worth doing if you can beg/borrow/steal a gauge ? To check for crankcase pressure - with hot engine (after a run) - remove the oil filler cap and rev up - is there a plume of smoke/fume ? I agree though - the 1275 A / A+ engines need all the breathing they can get! Am I right in thinking you have the PC valve on the inlet manifold - to take away fume? Maybe the diaphragm is past it's best??
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