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Midget and Sprite Technical
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Thread: One off oil burn (valves?)
Posted 09 August 2017 at 14:50:53 UK time
Graeme Williams, Kent, United Kingdom

Each time I take the frog out I get a one-off blue smoke incident. It happens after about a mile and usually if I have stopped at a roundabout or traffic lights. As I pull away - lots of smoke. I wont happen again until next time I'm out. Even a long downhill run on trailing throttle doesn't produce oil smoke.

(I mention that because in 1966 when I was a college in Leeds if I ran down that very long hill to the north of Leeds Bradford airport in my Frog -different car- I would get clouds of blue smoke at the bottom).

My thoughts are oil seepage passed the valves while the car is standing and that this works its way down the stem for a few minutes after start up.
Worn valve guides are I guess a possibility but what puzzles me are the seals on the valve stem. What are these intended to do as I can't see from the sketchy pics I have what there purpose is? Would one of those failing cause these symptoms?
It's a 1275 btw.

Posted 09 August 2017 at 15:10:46 UK time
Dave O'Neill 2, West Midlands, United Kingdom

Sounds like oil sucking to me.

I'm sure there's a thread in the archive about this!

[runs for cover]

Posted 09 August 2017 at 16:00:10 UK time
M J Pearson, Kent, United Kingdom, mikepearson03@yahoo.com


If you have the "o"ring type valve stem seals get rid of them, I dont think anyone knows how they are supposed to work. Get some of the later type which cover the guide and have like an oil seal around the stem. You can change the seals without taking off the head, there are a few methods of stopping the valves from dropping. I used a bent aluminium rod through the plug holes. Stopped all my smoking problems. Have since changed the head for a metro one.


Posted 09 August 2017 at 16:06:05 UK time
P Bentley, Surrey, United Kingdom

I am with Mike, for the cost in and time, I would change the seals if only to rule them out at this stage.
In the meantime stay away from that hill in Leeds as well, sounds a PITA !

Posted 09 August 2017 at 16:11:53 UK time
Graeme Williams, Kent, United Kingdom

DAve O'Neill: troublemaker! Been there, had that, but not on this engine. Had given it a thought though!!! I did wonder whether the FWBs had anything to do with it, or even if I had the wrong torque on the rear hub nuts.

Posted 10 August 2017 at 03:15:03 UK time
1 Paper, Missouri, USA

Yepp... there are some old ghost in this room, enter the arcives at your own risk ... take a sandwhich with you,

If you find an old muslim hating spirit wondering about... the secret word is "lead infused fuel balls"

Some people use rope inside the cly head to keep the valves from droppjng ....if it is the quilds that are worn, then pop the head off and deal with it then


Posted 10 August 2017 at 08:29:12 UK time
Bob Beaumont, Greater London, United Kingdom

Sounds like oil suck. Pages in the archives!. Interestingly I recently fitted twin HS4's to my 1275 frog. They have the air bleed connectors in a different place to the HS2's. It meant I had to run a new pipe and Y piece back to the timing chain cover. I had some clear plastic tubing so used that instead of the rubber variety. Its fascinating to watch the oil being drawn up the pipe when the engine starts up. It almost reaches the Y piece. The pipe is not full with oil and its doesn't reach the carbs.
In the past I did experience oil sucking and solved it by replacing the rocker box cap and the pipework to the carbs. Our old friend Lawrence (who experimented and found an engineering solution)was a bit incredulous that it would work but the problem for me anyway was solved.

Posted 10 August 2017 at 09:56:36 UK time
Graeme Williams, Kent, United Kingdom

Bob: not oil suck, at least I don't think so. I had that issue with my original MkIV and so know all about it. I was very much involved right at the outset on that issue and still very much convinced that it can and does happen on certain engines. Because I have a single large su it has the connection point on the carb which I suspect is more gentle than the MKIV connection onto the manifold, even with a psv.
Saying all that, I think I will have a closer look at the connection pipework to see if it is oily!

Posted 10 August 2017 at 11:49:55 UK time
Graeme Williams, Kent, United Kingdom

Bob: interestingly this problem has only been noticable since fitting a new camshaft and triangular plate. Remember a lot of Lawrence's theories around that area?

Posted 10 August 2017 at 11:53:38 UK time
GuyW, UK

It may be that oil, when cold, is accumulating on the top of the head sufficient to submerge the tops of the guides at which point it then sucks oil down the guides as you pull away from your roundabout. The oil will still feed through the rocker shaft and rockers fairly fast even when cold as it is under pressure, but of course the drain down the pushrod holes is just by gravity so when the oil is still cold and viscous this is slower than when once warmed up.

Replacing valve stem oil seals may help, or it may be that the rocker gear is a bit worn and oil is coming through a bit faster than it should.

Posted 10 August 2017 at 11:56:29 UK time
GuyW, UK

In line with that suggestion of mine - a new cam shaft / plate may be closer fitting and restricting the oil flow out at that point, leaving a higher pressure in the oil gallery behind that is the feed direct to the rocker shaft. So it could speed up the oil delivery of the cold oil to the top of the head.

Posted 10 August 2017 at 12:01:52 UK time
Bob Beaumont, Greater London, United Kingdom

Here we go!! I fitted a new camshaft and plate but no oil suck problem!

Posted 10 August 2017 at 12:32:02 UK time
GuyW, UK

Bob, I wasn't saying a new camplate and cam would cause the problem directly. But maybe coupled with other variables like the degree of wear in rocker gear temperature,oil viscosity, condition of oil pump etc etc. it could all add up. Clearly it didn't in your case.

Anyway I am not describing Lawrence's "oil suck" problem. That was well established to be a different feature completely from what I just described regarding oil on the head.

Posted 10 August 2017 at 12:43:39 UK time
Bob Beaumont, Greater London, United Kingdom

Guy I was being a bit cheeky! I guess the answer will lie if there is oil in the pipe from the timing cover and in the carb. If not then the answer may well be as you suggest....

Posted 10 August 2017 at 12:53:13 UK time
GuyW, UK

OK, sorry Bob.

Posted 10 August 2017 at 12:57:33 UK time
Graeme Williams, Kent, United Kingdom

For the record: New rocker gear. The original camshaft had excessive end float (about 25 thou) and this was reduced to about 7 thou (hope I recall these numbers correctly). Like the idea of Guy's about flooding the head.

Posted 10 August 2017 at 13:25:57 UK time
William Revit, Tasmania

Just out of interest----------
Did you replace the timing chain when you did the cam
If yes, was it a double row and was the old one single or double

Posted 10 August 2017 at 13:43:44 UK time
Graeme Williams, Kent, United Kingdom

Yes, but not the sprockets. It was (and is) double row without tensioner. We had to file the sprocket boss to get the endfloat on the cam correct despite renewing the end plate.

Posted 10 August 2017 at 13:50:41 UK time
Graeme Williams, Kent, United Kingdom

On the valve front, there are suggestions that the seals can be replaced with head in situ. I realise you need to stop the valves falling into the cylinder but how do you compress the springs because presumable the conventional compression tool can't be used?

Posted 10 August 2017 at 14:06:48 UK time
Dave O'Neill 2, West Midlands, United Kingdom

You would need to fabricate a tool to do the job. Fine if you enjoy fabrication, or if you're planning to use it again and again.

If you're just going to do it once, it's probably easier and quicker to take the head off.

Posted 10 August 2017 at 15:08:30 UK time
GuyW, UK

There is a tool sold on eBay that hooks under the rocker shaft in some fashion. I have done it several times using 2 large flat bladed screwdrivers. It's not difficult, but just watch your fingers!

Posted 10 August 2017 at 16:26:37 UK time
Graeme Williams, Kent, United Kingdom

But you would have to remove the rocker shaft beforehand!

As I have a very expensive Cometic gasket which I can reuse 5 times I can afford the luxury of removing the head, bunging it in the back of the car and driving to a man who I know would love to flex his valve spring compressor.

Posted 10 August 2017 at 17:12:11 UK time
GuyW, UK

Personally although l have replaced seals several times now without removing the head, l actually prefer to do so even if it does mean using a new head gasket.

Posted 10 August 2017 at 17:24:23 UK time
Dave O'Neill 2, West Midlands, United Kingdom

There is a really nifty valve spring compressor available for the Ford CVH engine. You just remove the rocker from its stud and fit the tool in its place.

If only the A-series was a s simple.


Posted 10 August 2017 at 17:40:30 UK time
1 Paper, Missouri, USA


Thats the anwer ix go with, i to have the cometic...love it

BoB... i see a problem in your set up

You said the oil gets sucked up almost into the carbs, but night quite in a clear tube from the timing chain cover to the carbs Y piece

Thats not good, on the timming cover there is a canister and inside that canister is a metal gauze the way the system is supposed to work, the engine heats up, the tube is sucking air from the crank case into the carbs creating a Negitive vacume inside the crank case that vacume (if the engine is seealed properly) is what controls blowby and keeps the oil inside the engine instead of pissing out al over the ground

The purpose of that metal gause inside the canister is to collect the heated oil mist and let it cool down and allow the cooled oil to convert back to a liquid state and drain back into the engine cranl case

The onlg thing that should be flowimg thur the pipe from carb to timing cover is air pressure not oil, or very minor amounts

What is probably happenkng is one of 3 things,

1. Worn out engine and needs new rings, scroll seal eye brow cober files back to flat and new gasket and seal up air leaks around sump gasket, dip stick tube, and front crank shaft oil seal any place air can be sucked in that will neutralize the negative pressure inside the crank case... you can also in lue of a re ring if not to bad yet is to add in a catch tank between the carb and timing cover

2. Replace the metal gause, its ither missing or has corroded and packed up and the oil is by passing the guase and getting caught in the vacume from the carb

3. Is the tube from the timing cover going to the carb. Is it connected before or after the butterfly if its connected after the butter fly its pulling (port???) Vacume which around 9to12 psi( bars im not sure) which is way to much vacume if its conected before the butterfly its ???? And only around 1to 3 psi and rhe correct amount

As to the gause inside the canister it is just a soapless stainless steel commercial pot scrubber ...its like long sheards of stainless steel loosely bound but just a wad of that if its packed up or missing

Hope that helps


Posted 10 August 2017 at 18:04:24 UK time
Alan Anstead, Kent, United Kingdom

Bring it over. I have the seals already on the shelf.

Posted 12 August 2017 at 15:36:44 UK time
Graeme Williams, Kent, United Kingdom

"not oil suck, at least I don't think so"

This morning I fitted an oil separation chamber in the hose between the timing cover and the carb. Based on just the one run so far but no oil burn off.

Posted 13 August 2017 at 03:42:07 UK time
William Revit, Tasmania

Lawrence would love this then
I've continued thinking about his oil sucking problem on and off

How's this for a theory
With the excessive cam endfloat the oil can escape easily and drain back to the pan but with the clearance now back to minimum the waste oil from the front camshaft bearing, especially when cold has to force it's way past the plate and might cause the oil to froth in the timing cover, overfilling it and causing oil to go up the breather and maybe the new timing chain links could possibly have larger end plates to help stirr it all up in there
It will be more than interesting to see if the oil seperator actually the job


Posted 13 August 2017 at 06:45:10 UK time
M Wood, Strathclyde, United Kingdom

Might be worth reviving the following thread - the follow up to the long thread mentioned above: http://www.mg-cars.net/mg-midget-sprite-technical-bbs/engine-breather-oil-sucking-yet-another-engine-2014091416212710294.htm

Just an idea...


Posted 13 August 2017 at 08:06:23 UK time
GuyW, UK

Worth reading if you have half a lifetime to spare, but l strongly suspect this is not oil sucking in the true Lawrencian sence. It may have similarities, but l doubt this is drawing oil up from the chain case as a continuous surge in the way that Lawrence's car did.

Posted 13 August 2017 at 08:51:43 UK time
Richard Wale, Oxfordshire, United Kingdom


I had a similar problem on our 1380 about 10 years ago on a newly rebuilt engine. About a mile from start up, a plume of white smoke out of the exhaust, and a misfire, which would re-occur occasionally under load.

At the time I had had a 12G940 head made up by a very well-known local supplier, converted to unleaded with bronze guides and also removed the bypass hose from the pump to the head at the same time - YES I know about only changing one thing at a time!

Anyway, that was the beginning of a 3-4 year saga that was finally resolved by tracing the misfire to a 'nipping' No. 1 exhaust valve, changing the valves guides to Peter Burgess's 'guaranteed not to nip' bronze valve guides (and they don't!) and reinstating the bypass hose to get a good water flow around the front of the head during the warm-up phase.

Make sure that there are no valve stem seals on the exhaust valves (required on the inlets), open up the exhaust valve tappet clearance to 0.003" more than the normal setting for the exhausts (I remember your advice Peter). See what the effect is. One change at a time!

If still smoking, retard the static ignition at least 5 and see what the effect is.


P.S. Although all the above worked very well, I found out later that the 'well-known' supplier had completely mis-measured the combustion chamber volumes, and they were 18.5cc instead of around 21cc - the calculated 10.5:1 CR was more like 11.5:1, so fitted a 'Cometic' head gasket to correct the CR. Finally that head cracked, and Peter B made up a nice new one for us - no smoking problems at all.

Posted 13 August 2017 at 12:02:44 UK time
Nigel Atkins, Northampton, UK

you've done a Prop sence. :)

Soon Prop will have us all converted to his way.

Posted 13 August 2017 at 18:27:11 UK time
GuyW, UK

So l have, Nigel. How senseless of me. Too much reliance on spell checker, which l think has reverted to an American English dictionary. Apologies!

Posted 13 August 2017 at 18:58:50 UK time
Nigel Atkins, Northampton, UK

No need to apologise Prop has me now checking his spelling is wrong! and my spellchecker here doesn't like the s in apologise.

Posted 13 August 2017 at 21:42:54 UK time
Growler, South, New Zealand

Did someone say "seance"?

I've had the same issue, it was Prop's suggestion #2- clogged mesh in the breather canister catching oil, not allowing it to drain back properly, and getting ingested when the engine was first started. Once everything had warmed up the problem went away.

It went away for good when I changed the canister.


Posted 13 August 2017 at 23:39:24 UK time
Graeme Williams, Kent, United Kingdom

No burn today!
Rather than repeat that message every time I wait for three clean runs next time.
I think Bill's thoughts on oil suck when it's cold and therefore higher viscosity makes sense. We'll see!

Posted 14 August 2017 at 04:56:54 UK time
1 Paper, Missouri, USA

My rhought with this and with lawerance was to simply let the engine warm up a few minutes before driving, that will let rhe oil warm up and circulate much easier

Yeah...spell check haha i wish it worked on the bbs, not my more better accomplishments


Posted 14 August 2017 at 07:01:58 UK time
GuyW, UK

Another contributing factor for oil pooling on top of the head is if the burst of smoke follows on from braking for the roundabout or junction. Especially if it's at the bottom of a hill.

Posted 17 August 2017 at 18:17:48 UK time
Graeme Williams, Kent, United Kingdom

Solved the problem.

I have fitted a collecting chamber between the timing cover and the carb so that any oil can collect at the bottom of the chamber.

I ran without the car connection - no oil. So it isn't high sump pressure forcing oil out.
Connected the carb and there is now oil in the pot. Suck up by the induction vacuum when the cold oil builds up in the timing cover and reaches the vent pipe. THe chamber is preventing it reaching the engine and so the blue smoke has stopped.

Pics show the chamber installation and the oil in the bottom. So the winner is :
Bob Beaumont

I have had so many discussions where people say this cannot happen. I've experienced it on an earlier engine (to a much greater extent) and now on this one.


Posted 17 August 2017 at 18:19:10 UK time
Graeme Williams, Kent, United Kingdom

Missed a picture.


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