29 replies to this topic

[slpj24]

Hi, I have joined this forum to see if anyone has experienced this.

I believe this is one for Dan, or for anyone here who has experienced this.

I run a 1275 A series engine in an Austin Healey Sprite. Engine is circa 1968. Although inline and not transverse it's not so different. The crankcase breather system differs in that it only has one breather cannister, at the front, on the timing cover. Otherwise it connects to the twin SUs via a Y piece the same way as on a classic Mini. The other difference of course, is that mine doesn't share the engine oil with the g/box . I hope you wont mind if I post here, as our engines are the same.

The engine spec.
1275 +30 19320 pistons. 1300GT head. Standard Cam. Twin HS2, KandN air filters. Long centre branch exhaust manifold. Plastic mesh vented oil filler cap. 20/50 mineral oil. Oil pressure on cold start 80+, hot 40/50+. Circa 20000 miles on engine since last rebuild. One of many in it's life.

Breather system.
Pipe from the timing cover breather cannister, via a Y piece to the individual connections on the carbs. Plastic wire mesh filled oil filler cap, on the otherwise sealed rocker cover.

Engine condition
No excess blowby, the compression is good. No oil being forced out of the front crankcase oil seal, or the oil scroll on the rear, or from the sump gaskets.

Here's what happens.
After starting the engine, --- from dead cold or almost dead cold, on cold days, mostly in the winter or early spring, after driving about 2-3 miles, or in other words just as the engine is warming through, when on the over run, and the vacuum is high, a column of liquid oil is sucked under vacuum from the timing cover, and into the engine.

This results in a thick cloud of blue smoke as the engine tries to burn off the oil injected into the combustion chambers.

If the revs are allowed to die down to tickover, or of course the engine switched off, the oil sucking stops. If the engine is allowed to rest no more than a few mins or even less, when driving on again, the sucking of oil is not repeated, until the next start from dead or near to dead cold.

I emphasise a column of liquid oil. Not oil mist or vapour, and not a few drops. The entire breather pipe is filled with an unbroken column of liquid oil. So much so that it drips from the exhaust tail pipe if allowed to continue doing this.

I have fitted a clear plastic pipe to the breather cannister and observed this happening, on numerous occasions.

Note: This does not happen on warm or hot days, when the only difference is that the oil is warmer, and hence thinner. It doesn't happen, when starting from hot.

For this to be possible the timing cover has to fill with oil to the level of the internal entrance to the breather cannister. As it only does this when cold, and then ceases once warm, it is clear the oil level in the timing cover must reduce as the engine warms through.

I understand that oil is injected into the timing cover, under reduced pressure, via the front camshaft journal/bearing, through the small hole in the camshaft locating endplate, which is mounted to the front of the engine front plate. My conclusion is that too much oil is being delivered, whilst at the same time, it can't drain back into the sump fast enough.

Stripping the engine revealed, that the 2 drain holes in the front main cap were clear, as was the large hole in the engine plate, more or less adjacent to the camshaft hole.

If the drains are clear, and the large hole that could act as an over flow, does not prevent this, then the oil must be entering the timing cover faster than either the drains or "overflow" can remove it.

When the oil thins sufficiently, and presumably the oil pressure is therefore also reduced, the 2 drain holes catch up, and the oil delivery slows, allowing the oil level to subside below the level of the breather cannister entrance, and the oil ceases to be drawn by vacuum suction into the induction system.

There is no mistake about what is happening, and I am fairly certain -- ish--, why. It is my thinking that too much oil is continuosly escaping past/under the camshaft endplate, and not only passing through the oil feed hole that it should pass through, once per revolution of the camshaft.

As there were far more A series engines installed in Minis, than were ever installed in Sprites and Midgets, I'm hoping that someone here will have heard of this, and know the "exact" cause, and hence solution. Naturally I have asked in the Spridget world, and in fact I've been aware of this problem for over 25 years. I have yet to find someone else who also has experience of it, until very recently, and this has prompted me to seek others in order to gain a better understanding. So far I seem to be the only one with answers to this, and I just can't believe that after 50 plus or more years of the A series engine, I'm the only one who has heard of this.

Has anyone here experienced this before, or heard of it? If so your input would be greatly appreciated.

Thanks.

[Ethel]

Some ideas to try,

Disconnect the hose to the carbs & feed it in to a catch tank, don't forget to block the connection on the carb side. This will eliminate the suction & tell you if it was possibly too much.

Remove the oil filler cap, it could be holding low pressure in the rocker cover that's interfering with oil drain down. Worn inlet valve guides could be communicating manifold vacuum upwards.

Inspect the rocker gear, it's the top end of the pressure oil feed & it drains back via the, cam follower gallery & timing chain cover - it may just be passing more oil than can drain down.

Pretty sure the oil feed goes up to the rockers via that cam bearing, so if it is peeing out from the bearing there wouldn't be much left to go to the rockers, or perhaps a blockage in the rocker oilway is causing back pressure. Head gasket, the wrong (undrilled) rocker pedestal....?

[slpj24]

Hi thanks for replying so late at night. Another midnight oil burner then :).

I take it then this is a new one. I was hoping someone would say, yeah I know all about this, happens a lot, lol.

Well anyway, there is only one breather hose on the Spridget. If you disconnect it, there is no possible suction path up the timing cover cannister, and then yes the oil suck would stop.

Removing the oil filler cap doesn't help, tried that many times. I wasn't aware that the cam followers drained to the timing cover. Do you have a schematic that shows that?

Yup oil is fed by a vertical shaft to the head from the front cam bearing. Sadly no, the shaft is completely clear, and the rocker shaft free to disperse oil. No back pressure.

[ANON]

as ethel said just run a catch tank. as long as the engine is good then you'll be fine just leaving it in place.

i've had this happen a couple of times over the years, perfect condition engine, fresh build and it just sucks oil through. pop a catch tank on and bob's your uncle.

[Dan]

I think the point is that it shouldn't happen so what is wrong? Fitting a catch tank would stop the smoking, but might not fix the fault and if it's to do with internal pressure as much as manifold vacuum then by the sounds of it the sump would empty fairly quickly if the system was left open. It would be bodgery.

It's very nice of you to suggest I might be able to help with this and I'll try certainly but I'll point out I'm not a professional or an engineer. Having said that, my mind immediately went in the same direction as your own and I started thinking about the timing chest oil drain. I think the larger hole is not going to come into this, it's not an overflow but part of the breathing system and from memory by the time oil reached that level the breather can's port would be completely submerged already. And I think it's unlkely the chest is actually completely filling up anyway, that would be around half a pint of oil I'd imagine and would really test the crank seal. It would put a lot of load on the engine for the timing gear to be running in that much oil, you would notice that. It would not take much of an increase in the oil level at the bottom of the chest for the amount being flung about inside there to increase massively. It would then build up on the wire wool in the cannister until there was a complete blockage of the breather. So as you say there is either too much oil getting in or not enough getting out, but maybe not to the extent you have imagined. I was thinking the problem might be to do with excess cam and main bearing clearance allowing too much oil in but the more I think about it the more it seems that it's the drain causing the problem. I don't know that more oil would be getting in to the chest when the oil is heavy, yes there is more pressure but that's precisely because there is less flow through the bearings and ports of the engine. You say this is a rare thing but something that has been happening a while. Does it only happen to specific odd engines? You have checked the drains are clear, but have you compard them to the drains in another bearing cap? Are they perhaps undersized or not cleanly bored? I think your problem is going to end up being something that simple. Whatever you find, I'd be interested to know.

Usually, non-Mini problems don't get put in this section but we let A series specific stuff hang around here.

[slpj24]

edit, Dan posted as i posted. thanks Dan, I'll read your post now. :)

Hi Anon, thanks very much for your comment.

I'm very interested that you say you have had this happen too. Especially in that you have had it on new builds

I prefer to run a sealed breather system, rather then go the catch tank route. I am more interested in it getting to the exact nub of the problem, the root cause, rather than masking it. I want to fully understand the exact nature of the fault, and rectify it, rather than modify the system to compensate for it. After all, when the engines were new, this didn't happen.

But, once x number of thousands of miles have been covered, irrespective of re-building the engine, as you too have experienced, this problem can occur. Thus there must be an identifiable and therefore rectifiable cause. That is what, with the huge collective experience of people such as yourself, I am hoping to find.

I've read the excellent and clearly explained descriptions by Dan of how the breather system works on the mini setup. And no doubt there are others here that must have that degree of knowledge. It is that knowledge, that if I may, I would like to tap into. Unfortunately the BMC technical department no longer exists, and any text on this subject must be long lost.

But my instinct is that some long term owner of a mini has had this before, or has such an in-depth knowledge of the A series, that they know exactly why and hoe this happens, and which (worn) engine part, is the major or sole cause

May I ask Dan, if you are reading this, could you tell me one thing that I haven't been able to find in your excellent explanations.

Referring to the canister on the timing cover, or old side tappet cover, the mesh filled "oil separator" as it is sometimes called. What is it's precise purpose, and how does it achieve this?
Some say the wire mesh inside the canister, is there to catch hard particles in the oil, so they are not drawn into the induction/engine.
Some say the mesh is for oil droplets to form against, and hence drain back to the engine. And that it is placed in close proximity to the cooling fan, to aid this "condensing" action.
Some say it is better to remove the mesh completely. Others say it is essential to the correct operation of the breather system.

Does anyone have the concise, and official explanation of exactly what it is and how it functions? Or indeed know where I can read it?

Also. Does anyone know or have access or a pointer to, the exact description, of the oil delivery system to the timing chain cover? I know that it is fed through the small hole in the camshaft end plate. But I would like if possible to see an accurate description of how this works, and the amounts of oil concerned etc.

I do hope you will not think this to be a waste of your time. I also hope you will not think me dismissive of your suggestions to rectify this problem.

I know what the problem is, I've spent enough time finding out that much. But I need more input from others such as Anon, who have also experienced it, in order to identify with certainty the exact cause, and therefore the solution, that allows the breather system to be re-instated, as designed, and released to retail when the cars were in production.

I also need to hear from others who have a thorough knowledge of the engine lubrication and breather system to design level if possible, even if they have never heard of or experienced this odd problem.

Thanks very much.

Edited by slpj24, 27 February 2012 - 11:41 AM.

[Ethel]

I was suggesting a catch tank only to help with diagnosis. Now I've woken up I reckon I was wrong about the tappet chest drain down though.

I doubt you'll find that sort of precise information. There are so many variables, the clearances on all the engine bearings, oil viscosity, rpm, pump capacity, relief valve operating pressure....

You could make an approximation from the size of the hole in the cam retainer plate and the oil pressure, but even that will be subject to the amount of cam end float.

As far as I'm aware the can is an oil separator & just collects fine oil particles so they can form bigger ones capable draining back against the air flow. I don't think there's any purpose in its location, other than convenience. There'll also be water vapour in there that you'd prefer not to condense.

[Dan]

I thought so, Anon seemed to be suddesting it a permanant modification.

The mesh is there to condense the oil out of the vapour, and it does so simply be having a lot of surface area really. It's proximity to the cooling system is irrelevant (Mini has the same cannister at the back of the engine on the clutch housing). It also acts as a flame trap but I think that's sort of a bonus feature more than by design, looking at the history of the breather system. The history of the systems will help you understand how they work, look at the website of Somerford Mini Specialists for exploded diagrams of all the variations of the system used in Mini over the years.

Intersting that you say this never happened on new car. Would anyone have thought anything of it in the '60s? When the car only had to pass a visual smoke test and smokey cars were the norm in the cold? If it happens to one car in a few thousand, would they have thought anything of it?

Although that point has made me think again about worn parts. Does your block run cam bearings? I can see a situation where a worn cam bore in a plain block (or a worn bearing) or excess cam endfloat might allow more oil to collect behind the retainer and maybe get through around the cam itself. Although again I would think thicker oil would stop that rather than encourage it. I wish I had an engine in bits here to check over as I'm having trouble going through this in my head!

[slpj24]

Dan, thanks for your post. You echo my thoughts exactly about the drag that excess oil would cause in the timing cover.

Let me add a little more. I have quite a bit of detail so far not said, as I didn't want to obscure the issue.

I'll come directly to my findings.
The camshaft endplate, has a small hole in it. It's only function seems to be to deliver a measure amount of oil to the timing cover. The open groove at the front of the front journal on the camshaft, is aligned exctly with that hole, once in every revolution of the camshaft. Oil under some degree of pressure is emitted.

The cam endplate, is only part of the equation. It is bolted to the front face of the engine plate with three bolts. Two of it's functions are to set and control camshaft end float, and to stop the camshaft coming out of the block face.

The front face of the engine plate, has a very smooth flat surface. The camshaft plate sits up against this surface. Imagine that there was a large gap under the camplate, between the engine plate and the camplate, through which oil could escape. In other words, it would not need to await the revolution of the camshaft, it would seep, under pressure, continuously into the timing cover.

I have photogrphic evidence that supports this theory.

I have concluded, that not only is the camshaft endplate (on my engine at least), distorted, but so too is the front face of the engine plate recessed, at precisely the sections between the 3 bolts, that form the triangle shaped fixing points of the cam plate. Or to put that another way, the cam plate is only tight against the engine plate at the bolt locations. There is as much as a 4 thou gap in between in the remainder of where the two surfaces should sit tightly together.

So, in addition to the the designed amount of oil feed, an extra unintended amount is being delivered. I haven't done the maths to compare the amount of oil delivered once per revolution, with the continuous extra unintended amount delivered through the gap. However, I reason that logic dictates this to be the reason the timing cover fills to excess, and thus a sudden increase in vacuum in the breather system, takes the oil in a column into the induction.

I know this does not sound feasable, and I am yet to fully convince anybody. But if you review my evidence, there is no other possible explanation. If this is the case, I further reason that --( as I now have confirmation of other engines displaying the same symptoms --) the same evidence could be found in other well used A series engines.

by the way, I agree, the "overflow" hole is in the exaxt position you describe. I've measured it, both in zize and height. Even as the timing cover fills to the level described, the hole must be unable to cope with the level of oil and allow it all to escape.

Also, the 2 small drains at the bottom in the main cap are completely clear and unobstructed.

I believe that under the correct conditions (cold ambient and engine temperature),with a worn A series engine, the oil is which is being delivered too quickly, and is still too thick to drain quickly enough, behaves as describes. As the engine warms, even if the oil delivery remains the same, the drain can cope with it. But maybe the oil level remains elevated, albeit below the critical level of the canister entrance.

What do you think. I have to go out now, I look back in later.
Glad you allow non mini content, with A series connections :)

[Ethel]

The cam retainer is a thrust bearing on both sides, the hole lubricates the chain pulley to retainer face. There'll be some bias from driving the dizzy via helical gears.

I think pressure differential will be a large part of the issue. The port through the mains cap isn't that big so having more pressure in the sump than the timing cover could stop or reverse the flow. The big hole Dan mentioned should communicate between the 2 chambers and equalise the pressure but maybe it can't keep up with the manifold vacuum? Twin carb Minis had a limiter valve directly on the manifold rather than the usual carb connection.

[dklawson]

There is a lot to read in this thread and I apologize that I cannot take the needed time this a.m. to review all that has been said in response to the problem.

My purpose in posting is only to suggest one other site where you may want to raise your question.
http://www.britishca.../18/1/Spridgets
The British Car Forum in the U.S. is a multi-marque board with free membership. There are a lot of Sprite/Midget owners there who may have seen this problem before and could offer first-hand advice.

[ANON]

can't remember exactly what i've had it happen on but definitely a series, ford pinto, couple of ford x-flow and i think a hilman imp engine?

all were fresh builds, non standard if that makes any difference, not always smoking straight away though.
went through different checks, basic compression test, leakdown test and oil pressure tests at factory take offs and other places where possible.
always showed up fine and after lots of head scratching and talking to people who had been involved in engine work for years we just put it down to the engine actually sucking the oil/vapours through rather than excessive crank case pressure.

when we fitted catch tanks there was a minimum build up of oil that in turn confirmed the lack of excessive pressure.

hope that helps.

[slpj24]

Back just in time to make my own dinner. :)

I'll have a read through and digest the recent posts, and reply a little later

Meanwhile thanks for the responses.

[slpj24]

Well, that was a long dinner.

Thanks for those last replies. Yup, I'm already on another bbs http://www2.mgcars.org.uk. It includes a lot of guys from the US. But so far no post from them. I think they are watching us as we discuss it.

Dan, the 1275 Spridget engines, run pressed bearings in the block. I think only the very earliest ran directly in the casting.


Anyway. Some developments. But first a question that has direct relevence to the subject that follows.

Does anyone have the torque setting for the camshaft locating plate? It's not in Haynes for Spridgets, and not in the BMC factory book for either Spridgets or Minis. They are 7/16th bolts, so until now I've been doing them along the lines of the timing cover for the same size.

But, and here's the killer. My camplate is distorted, and it's overly compressed at the bolt locations. When the camplate is installed, the bolts must flatten the white metal to a degree anyway, and in use over time that increases slightly with the heating cooling of the engine. We've found this to be the case when engines that have not been rebuilt, have then been stripped, and show this camplate deformation at the bolt locations.

Because I have re-used the camplate on my engine, this has had the effect of pulling down the camplate at the bolt locations, as it is so thin, and raising the strectches in between. This has resulted in a gap between the camplate face and the engine plate face. This is what I concluded is the reason for the excess oil getting into the timing cover, perhaps assisted by a worn front cam bearing, and high oil pressure. But the prime cause is the distorted cam plate.

But what I hadn't thought of, was that re-using a camplate would cause this excess oil to happen. I fiigured as long as the end float measured ok, and the thrust surface(s) was ok, then no reason not to use it again, as many times as I rebuilt the engine. Lazy and tight, but I didn't seeing it causing a problem

Now though it seems that not only should you not re-use a cam plate, but you shouldn't over tighten it either.

Of course this doesn't affect you if you don't have a connected breather, and or maybe, higher oil pressure and or +ve sump pressure, etc etc. But for my engine and at least 3 others this could be the cause.

One other effect it has had on my engine, is to cause the recession of the surface of the engine plate that I described in my earlier posts.

So how tight should the cam plate bolts be? Even with star washers, if intalled too loose, they will undo over time.

So, does anyone have any torque figure for the cam plate bolts? I'm amazed they aren't quoted by BMC.

Edited by slpj24, 28 February 2012 - 10:19 PM.

[Dan]

Rover quotes the cam plate screws as 8 lbft. I have a couple of used Mini front plates and cam plates kicking about, I'll have a close look at some and see how flat they are. This will be of great interest because if the act of reinstalling a previously distorted cam plate is capable of deforming the front plate, it might be a big contributor to one of the Minis traditional major oil leaks. If the plate is deforming there, it won't press on the gasket properly. It is quite common for oil to leak from behind the front plate and this is generally assumed to be down to the half moon seal, maybe that's not always the case. Something I've never really given much thought to is where the oil slot in the cam end gets its oil from. It doesn't intersect the groove in the journal, so is it just collecting the oil from the bearing space or does it pick up from somewhere in particular? Are all the drillings into the bearing in the same plane? I can't remember and as I say I don't have an engine here.