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MG Midget and Sprite Technical - Pinking cleared - I think...

Chaps


Many thanks to one and all. Slightly weak mix appeared to be the root cause of the pinking. Turnned (HIF44) mix screw in about 3/4 turn...et voila, cooler engine and now no pinking.

Guy ...as you have a similar set up, curious to understand how your crankshaft vent/breather is set up. On fitting the HIF44 a couple of months back, I routed the breather to the carb port, but of late, the car has been losing oil/dripping it into the drive, much to the annoyance of the C in C. I am thus thinking the vacuum is inadequate, so have re-installed the vac valve on the inlet manifold, and plumbed it back in there - in the hope of it reducing the backpressure on the crankcase seal, and thus eliminating the leak. It did the trick last time!

Regards

Mark
Mark O

Ohh - can of worms question!

As specifically you ask about mine, my tale is this:
I started with a standard '71 set up of front chaincase via cannister to the "Y" branch feeding into twin SUs bodies.
(Connection direct to the intake manifold would provide too much suction without the control of a PCV)

When I changed to HIF44 I kept the same system, but connected direct to the single HIF body as mine has a breather pipe connection. Not all HIF44 have this.

At first it continued to be reasonably oil tight and smoke free, but as the mileage has increased it first began leaking a little oil (not much) and blowing blue smoke. To limit the blue smoke I added a catch tank into the sealed oil breather system. This consists of an air tight tin, with a long inlet pipe from the chaincase, a wire filter and then a short extractor pipe that still connects to the HIF44 body.

The oil catch tank certainly reduced the blue smoke for a while and did not upset the crankcase pressure reduction system as it is still a sealed system. But the blue smoke has worsened again with rising mileage. It's an engine wear problem which I need to tackle soon as it is getting increasingly embarrassing!




Guy W

And just to help open the can of worms, here's where to make the connection on the HIF44.

Pipe




Lawrence Slater

And my setup from the breather pipe on the timing cover.


Lawrence Slater

Except Lawrence, the connections on my HIF44 are in different positions to that diagram! In fact, I think yours are too!
Guy W

Sorry Lawrence. That sounds aggressively contradictory! It wasn't meant that way. I think the diagram is somehow all back to front though, compared to mine. Addition of a mirror would sort that out though. More or less.
Guy W

Chaps

Yes - Until yesterday my set up with HIF 44 was similar to Lawrence's, but I don't think the differential pressure is adequate at the carb - thus I have moved the take off back to the inlet manifold and re-used the vac valve - from owners club - the funnel shaped thingy. Too early to say if it has cured the problem, but with the twin SU set up previous to the HIF 44 it seemed to work fine. Time will tell.

Not a great fan of catch tanks. They seem to be more prevention rather than cure and another possible souce of an air leak, thus a lower DP, thus another source of problems.
Mark O

I agree, the catch tank I made was in order to put off the evil day when I need to strip this engine down again. I wouldn't otherwise use one. But it is a sealed system, not one that breathes freely to air as in my opinion that they simply defeat the active crankcase pressure reduction system.

I haven't tried connecting to the manifold. Although it may give more suction it is in effect at the wrong time. i.e. manifold depression is at its greatest when the engine pistons are sucking most (high revs) AND the availability of air is suddenly cut off by the butterfly closing. i.e. on the over-run. The systems like the late Y branch/twin SUs and the HIF44 connection draw their suction from upstream of the carb butterfly which provides a more constant depression. And one which is at its greatest at full throttle when piston blow by and therefore crank case pressure is also at its greatest.

That's all theory though. Its what works for you and your engine that matters most and there is certainly more than one workable solution depending on your priorities and the amount of engine wear
Guy W

Guy

I'll suck it and see - literally!

Deffo leaking oil previously - and looked like crankcase seal area.

My thinking is that DP is increased at the manifold thus reducing pressure on the seal. Whilst I appreciate that engine suction pressure will not be as great at low revs, crankcase pressure will not be as great either, thus adequate DP/vacuum in the crankcase will be maintained.

As an aside - is there an easy way of cleaning out the filter/wire wool mess lurking in its cylindrical housing near the timing cover?
Mark O

Mark,
Certainly worth a try.
On WOT the manifold depression is not at its greatest because it is pulling in air freely through the carbs, but that is exactly when piston blow by is likely to be at a maximum, and therefore crankcase pressure build up at its highest. But the DP at the manifold is at its highest when the butterfly is closed i.e. on a fast over-run, not on full throttle.

Wire wool filter - either change for fresh "pan scrubber" (wire NOT plastic!) or just thorough washing in petrol paraffin etc, The wire isn't actually a filter as the gaps are far too big for that. But it is a condensation system to precipitate (wrong word!) the oil back into liquid form. The wire wool being cooled by contact with the cannister wall which itself is in the air stream from the rad. Not terribly efficient but probably has some effect. And the wire wool is probably also there to reduce the occasions of oil surge that we all know Lawrence is the world's expert on! ;-)
Guy W

Guy

Manifold depression - My thinking was in considering the effect of Mr Bernoulli at high revs i.e. the high flow of the mixture gases under the manifold inlet port effectively lowering static head and thus sucking in anything from the crankcase....akin to how the carb proper works...The DP so created would hopefully be greater than that within the body of the carb - which is throttled by the butterfly. I guess whilst all this is very interesting and a noble pursuit of fluid dynamics - the only true measure is the wrath of the C in C when next the car is parked on the drive.

Wire wool mess - yes thanks - info much appreciated. How do you extract it from the canister? I have a feeling it is coated in gunk and causing a partial blockage - which does not help our first issue above...


Mark O

****Many thanks to one and all. Slightly weak mix appeared to be the root cause of the pinking. Turnned (HIF44) mix screw in about 3/4 turn...et voila, cooler engine and now no pinking.*****

Congratulations... im glad you solved this...

BUT im not sure I understand how leaning out an engine by 3/4 of a turn on the carb thats already running lean can have possitive effects.


Adjust
IN = lean
OUT = richen

Prop
Prop and the Blackhole Midget

Prop

Blo*dy glad you you don't fiddle with my car!
Clockwise (IN) on HIF44 enriches the mixture

Cheers

Mark
Mark O

Mark, if you can blow easily down the breather pipe, and thus through the wire mesh inside the timing cover breather, then I wouldn't bother to try and remove it, as it's likely not blocked at all. I cleaned mine (timing cover off) in a petrol bath.

Also, when you connected the breather pipe to the HIF, you did connect to the right pipe I take it? There are 2. One for the fuel breather and one for the crankcase breather.





Lawrence Slater

Guy, not aggressive at all. Your right I should have said that pic I posted earlier was illustrative, depending on which version of the HIF you have, and which side in a twin setup.

Here's a nice pic of a twin setup showing the connections more like that depicted in the earlier pic; But still not exactly the same.

There seems to be quite a few variants of the HIF SU series carb's. Mine isn't exactly like those either. I'll get a better pic of mine later.


Lawrence Slater

"Aggersively" dis-agreeing with lawerance

On the crank case oil seperator, the gause can be bad, or wornout and yet still be able to blow all the way thur the hose and out the timing chain cover

The purpose of the gause inside the oil seporator can it that the gause is really just a pots and pan scouring pad, the gause is shreaded metal strands that are loosely bonded and extremely pourious, so the oil mist is sucked jn and then traped in the. Mesh of the gause, it then cools, solidifys and drains back into the timing cover

So if the mesh becomes clogged, corroded, or rusty..then the oil mist will not get trapped in the mesh and will continue up the hose and into the carbs....thus fail

This is another reason why driving this cars often is so essential...if they seat for along time the risidue oil will just tarnish into a big rust blub like a cat fur ball caught in the cats throat

Mark 0,

...you got me!! congrats...I really hope that a simple lean condition was the issue, it feels good driving out of the valley of dispear, doesnt it.

Prop
Prop and the Blackhole Midget

I don't agree with that prop. As much as anything else, -- condenstation catcher/former, it's my view that the "wire wool" in the timing cover is there to catch any hard bits that would otherwise end up in the engine. I also can't see at all how it could wear out, or rust unless the engine sat idle in a damp environment for a very long time. As long as you can easily blow or suck through it, it should be fine.

Oil drip from the sump rear scroll, is something that many, if not most A series engined Spridgets suffer from, - some more than others. It's mostly caused by crankcase pressure, which isn't overcome by the vacuum from the manifold or carb connection. Getting the right amount of vacuum, seems to have been a bit hit and miss with BMC, given all the variations they tried. And too much vacuum can cause other problems, such as oil sucked into the engine -- the other long subject that Guy alluded to lol. Also as Guy says, as the engine(rings) wear out, blowby increases, and the vacuum isn't enough to overcome the crankcase pressure. Mine drips a bit now too. The only way to cure it permanently seem to be a proper oil seal instead of the scroll on the rear of the crank. http://www.spridgetmania.com/part/RIC777/Oil-Seal-Crank-Kit---1275

I've never fancied paying the price, and I'm not sure of how reliable long term they are anyway. Does anyone have any long term experience?

Lawrence Slater

The original incarnations of the A series were very low power (28bhp) low revving and simple engines, for which the crankshaft scroll seal was a perfectly adequate solution. They were expected to do only moderate mileages in a lifetime of motoring along England's green and leafy lanes..

As the engine design was progressively modified with bigger capacity, more power and higher outputs the potential for increased blow by, higher crankcase pressures and increased rear scroll leakage also progressively followed suit. And the designers produced a series of methods of initially relieving crankcase pressure, and then finally of actively extracting excess pressure. Each design suited to the characteristics of the particular level of engine development.

I don't agree that it was "a bit hit and miss with BMC, given all the variations they tried". The various methods they used were each appropriate at the time to the level of engine development. They represent an evolution of methods prompted by the increasing problem as power etc was increased.
Guy W

Not sure I agree with all that Guy. As you say the scroll started life on a low power engine, and was good enough. But then, rather than design a proper oil seal onto the back of the crank as the engine power was increased over the years, they just bolted on vacuum extraction, and that was partly because of environmental concerns -- emmisions control -- including oil pipes discharging to the ground under the car as on Ford pre-crossflow engines for example, which just had a pipe down the side of the engine. It was more of a constant under-funded fiddling, than properly designed evolution I reckon. Typical of the British car and Bike industry, hanging on to old designs for various reasons, whilst the rest of the world -- Japan -- old sold and out designed us.

Even with a standard 1275, with a new scroll cap (when you could still get them) I've had a little oil drip from the rear of the crank.

Anyway here's another pic of my carb showing all the pipe connections.


Lawrence Slater

Same facts, different interpretation, that's all.
No way of knowing now. But I do think that one shouldn't apply hindsight to the decisions taken at the time. I doubt very much that when the A series was putting out a whopping 28bhp, they ever imagined that within 20 years they would be churning out over 100bhp! I think active crankcase extraction probably became relevant at around the 65bhp mark, and maybe that is about the time they should have been looking at doing a proper rear crank seal. Prior to that it didn't really matter.

But as you say, lack of investment and probably a failure to understand how fast the changes would come in from the competition. From then on, they were always playing catch up!

And of course, by then they were putting all their innovation expertise into transverse engines - where they were well ahead of the field - and the old in-line A series was already doomed!
Guy W

Chaps

Interesting stuff - and I too have thought about simply blowing the thing through with the compressor -but worry a little about blowing bits of metal back into the crankcase. Removing the timing cover in order to clean it with petrol/solvent seems OTT, but must admit I cannot see another way of cleaning it satisfactorily.

Interesting about the seal. It strikes me though that the root cause of failure is blow by - worn rings/liners or something similar presumably - but as my engine is allegedly re-conditioned, perhaps some form of induced crankcase gas extraction is required by design.
Mark O

Mark,
Unless you have other reasons to remove the chaincase - like a worn / leaking front oil seal - then I would just leave it well alone. It will get washed through with oil or oil vapour when the engine is running and as the oil is filtered then any unlikely bits there will get filtered out anyway.

Regarding crankcase extraction. On the 1275 it is needed anyway - it isn't just a "fix" for worn engines! In fact, its on worn engines that the system struggles to match the increasing amount of blow by.
Guy W

Guy

Re extraction, yes I agree - it does seem that way. I think mine is even slighly higher compression than stock - which I guess will not help matters. As aforesaid, I have replaced the vac valve o nthe manifold - which worked with the SU set up beforehand. Whether the retrofitted HIF affects it adversely or not remains to be seen...I'll keep a wary eye on the driveway!
Mark O

Mark I agree with Guy, I wouldn't go to the bother of removing the timing cover unless the mesh is blocked, and as I said, if you can easily blow through it, via the breather pipe it can't be.

Another thing to check is that the oil filler cap mesh isn't blocked, and that the air intake holes in the cap are clear. Air is drawn IN via the oil filler cap, via the vacuum from carb/manifold conection. It's then sucked down through the block via the push rod holes, and out via a hole in the front of the block, into the timing cover and into the engine. Thus hopefully relieving the crankcase pressure.

If that oil filler cap is blocked, eventually you'll get resistance to air/fumes trying to be drawn into the timing cover. The other thing you can check, is to remove the dip stick and see if you have +ve pressure there.

And after all that, your drip may turn out to be leaky cork or rubber, sump to block seals, at the rear of the sump.

As an aside.
Did I read somewhere that someone had fitted a drip tray under their engine?
Lawrence Slater

Yup here it is. About half way down in this thread.
http://www.british-cars.net/mg-midget-sprite-technical-bbs/2-turbo-exhaust-2012011110511517187.htm

It belongs to Robert (Bob) Midget Turbo






Lawrence Slater

This thread was discussed between 22/07/2013 and 24/07/2013

MG Midget and Sprite Technical index

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