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Cylinder Head Gasket Oil Leaks


Nigel Clark

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13 hours ago, Nick Jones said:

Why wouldn’t a smear of sealant help with a low pressure joint face? It does.......

Presuming you have bigger breathers John? Marcus is right on the money about that. These engines sweat when worked hard unless they are very fresh or they have big breathers.

Nick

Because a gasket should seal a flat face, which is as rough as is the finish it is machined to, but not to seal faces are being held apart by the bulged face at the stud holes.    I don't think Nigel has  said what type of gasket he uses - the Payen type of course has a heat sensitive sealant built into its surface, so that any other is superfluous.

Breathers? The rocker cover of course, and I have a breather on the fuel pump hole in the block.    Both are connected and go to a catch tank on the bulkhead, so that the hose from the block breather slopes upwards.     Oil vapour condenses there and runs back into the block, while water vapour doesn't condense until the gases cool further - sort of distillation! - and are vented at the top.     The catch tank stays dry!

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Re breathers, the little 1/2" breather on the rocker bx is barely adequate for normal driving, but the PCV valve certainly helps if all is functioning. Say a race TR5 (I think it was a bitza, but 2.5pi engine in a TR4 may be a better description) and they had used a 1 1/4" breather to catch tank, it was huge! On my Ford engine I have 2 breathers, block (often blanked off, which is nuts) and cam cover. I have these 2 going into a catch tank, and that breathing into the airbox to provide a little vacuum especially at high rpm. Originally I had 2 catch tanks, the block one about level with the breather with teh hose looping up only a couple of inches. That could get half full in a single 20 minute session, but lots of 7000rpm stuff happening, which is when theengine starts to breathe. New setup has that breather going up about 24" now, and virtually nothing collects in the catch tank. 

But breathers are often ignored, and yet are incredibly important for an oil tight (ish) engine.

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If the closed circuit breather system is not used and the rocker cover is the only means of releasing  pressure in the crankcase then oil leaks will occur as there is not crankcase breather.

The original open breathing had a rocker cover and crankcase breather. This is because both temperature differences and the dynamics in the engine cause different pressures in different parts of the engine. Hence the use of two breather. The close circuit system is designed to create a very small vacuum which will over come these differences.

Dave   

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37 minutes ago, dave.vitesse said:

If the closed circuit breather system is not used and the rocker cover is the only means of releasing  pressure in the crankcase then oil leaks will occur as there is not crankcase breather.

The original open breathing had a rocker cover and crankcase breather. This is because both temperature differences and the dynamics in the engine cause different pressures in different parts of the engine. Hence the use of two breather. The close circuit system is designed to create a very small vacuum which will over come these differences.

Dave   

On the TR6, the original breather is merely a pipe from the rocker cover to the air plenum, there's no crankcase breather that I'm aware of. There's a flame arrestor fitted in the breather pipe, probably because of fears that malfunctioning over-rich PI could cause petrol to find it's way down the bores and into the sump, thence out through the breather. That could make for an almighty bang in the plenum if the engine were to spit back through the throttles!

Nigel

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1 hour ago, Nigel Clark said:

On the TR6, the original breather is merely a pipe from the rocker cover to the air plenum, there's no crankcase breather that I'm aware of. There's a flame arrestor fitted in the breather pipe, probably because of fears that malfunctioning over-rich PI could cause petrol to find it's way down the bores and into the sump, thence out through the breather. That could make for an almighty bang in the plenum if the engine were to spit back through the throttles!

Nigel

The pipe from the rocker cover to the air plenum is the close circuit system and hence does not require a sump breather. It when than pipe is disconnected, and allowed to vent into the air the small vacuum is lost and pressure can build up within parts of the engine. This can result in oil leaks and what was called a sweaty engine!

Dave  

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1 hour ago, JohnD said:

My breather system is passive, no assist from the intake, and it's not 'sweaty'!

Sorry John the intakes does assist by set-up the small vacuum within the engine.

A sweaty engine is an old term whereby it sweats oil.

Dave

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The air plenum (or the filter housing as on 13/60 Heralds) gives practically no depression at all, certainly not enough to make a gnat's difference to crankcase pressure. All it does is draw the gasses that do vent into the engine. John is right on this.

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47 minutes ago, dave.vitesse said:

Sorry John the intakes does assist by set-up the small vacuum within the engine.

A sweaty engine is an old term whereby it sweats oil.

Dave

Both misunderstand.  The OE system was connected to the intake, I know that.    MY breather sysem is not connected to the intake in any way.    It's very much non-standard.  And it doesn't sweat, leak, or even deposit oil in the catch tank.

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Thanks John,

It's the OE system I was making ref to, not your own. The proof the OE system does have intake assistance is if you take the oil filler cap off the engine will stop as it's then drawing air in through the oil filler hole. Hence the small vacuum in the crankcase and rocker cover. Generally without this vacuum oil leaks can happen.

On a track car, Triumph, I have seen where an electric fuel pump has been used, the un-used  mechanical pump hole in the block has been re-used to take a sump breather pipe. The rocker cover pipe then vents out into a catcher. Retofit I guess.

Dave

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2 hours ago, dave.vitesse said:

The proof the OE system does have intake assistance is if you take the oil filler cap off the engine will stop as it's then drawing air in through the oil filler hole.

On a Mk1 Vitesse, maybe. Perhaps on a Mk3 GT6. Not on a 13/60 with the breather to the air filter. I never tried it on my PI.

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11 hours ago, dave.vitesse said:

The proof the OE system does have intake assistance is if you take the oil filler cap off the engine will stop as it's then drawing air in through the oil filler hole.

My Spitfire does that - stall - or at least run very rough, when the cap is taken off - which has always had me baffled when its suggested that the tappets are adjusted with the engine running - I don't think mine will! But I digress!

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9 hours ago, NonMember said:

On a Mk1 Vitesse, maybe. Perhaps on a Mk3 GT6. Not on a 13/60 with the breather to the air filter. I never tried it on my PI.

I agree as the 13/60's breather pipe is feed into the air filter it will doesn't have any effect on the carbs if the oil filler cap is removed. Good point.

All those cars with breather pipes either into the manifold, using a Smiths valve, or to the carbs will be effected.

Either way the principle is the same. I have been digging around trying to find the reference book it's in.

Dave

 

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Many years ago I went to look at a local member's engine, as it was making a very odd noise. It had an alloy rocker cover, and the noise was whistling through the tiny hole in the cap. Like a pressure cooker relief but in reverse.

There was so much vacuum in the engine you could not remove the filler cap if the engine was running, and the whistling became a wail on the over-run. 

He went back and queried this with the Triumph specialist he purchased it from, and was told that was normal as it was ne of his old race engines. The engine was certainly not standard. But that might much vacuum? It was like the intake system was routed through the crankcase.

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1 hour ago, Anglefire said:

My Spitfire does that - stall - or at least run very rough, when the cap is taken off - which has always had me baffled when its suggested that the tappets are adjusted with the engine running - I don't think mine will! But I digress!

My Mk1 Vitesse does this, though I raise the idle quite a bit before starting it, and will run, though roughly. Ok for checking which tappet/s are noisy with an old feeler.

Edited by daverclasper
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That test and result - take off the cap from the rocker cover, and the engine stops - shows that the crankcase ventilation control valve, this one

TR4A Emission Control Positive Crankcase Ventilation Valve

is faulty.     

The valve is intended to limit the aspiration of crank gases into the inlet when the throttles are closed, and inlet vacuum is maximal.  But if it's not working then an excess will be drawn in.    Open the cap, and thr faaulty valve will allow even more gas in, making the mixture weak and killing the ignition.

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The TR6 breather from the rocker goes to the air plenum. The breather is therefore between the air filter and throttle butterflies. Unless the air filter is blocked, there won't be much vacuum in the air plenum, certainly far less than the 13-14" Hg manifold vacuum my car shows at idle. Removing the oil filler cap doesn't make this TR6 engine stall.

Nigel

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1 hour ago, Nigel Clark said:

Removing the oil filler cap doesn't make this TR6 engine stall.

Yes, the system as you describe is equivalent to the 13/60 Herald system - feed to just behind the air filter with no noticeable vacuum.

The system John showed - used on Mk1 Vitesse and Mk3 Spitfire among others - is a "positive crankcase ventilation" system using the manifold vacuum but with a regulator. It ought, as John says, to be somewhat tolerant of cap removal because the regulator minimises the air flow thus achieved. My Vitesse certainly doesn't stall completely if I remove the cap.

Late Spitfires like Mark's feed the rocker cover breather into the carbs, where the tapping goes into the constant depression chamber. Again, this is inteded to limit the vacuum applied in the crankcase. With these, though, removing the cap feeds in air to the critical place in the carb and completely messes up your fuelling. I'm not surprised Mark found it stalled. If you want to run without the rocker cover (for tappet checks) on such an engine, you need to put a plug in the breather hose.

The "local member's engine" that scrapman mentioned probably had a faulty PCV, as John described.

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Sorry chaps the small vacuum principle was taught to students and I don't see any reason to doubt this. Remember the closed circuit system took time to evolve, but in all these systems the vacuum  principle is fundamental.

A faulty PCV valve will give more immediate problems before you even took the filler cap off.

Dave  

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Well, Dave, I've got thirty years of engine control design experience for both road cars and race cars. I also do work for a vacuum science specialist (former rocket scientist) who would laugh at our use of the term "vacuum" here.

The crankcase breather system on the 13/60 and PI is "closed" but not "positive". They don't use vacuum. More modern cars often have a split breather system, with a big vent before the throttle (atmospheric to all intents) and a very small one after the throttle. The objective is to encourage some flow, to help extract the blow-by gasses, not to achieve a "vacuum".

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Where the breather pipe is on the air (air cleaner) side of the carb a vacuum is created by the air being drawn into the intake (by the engine) passing over the breather tube. This creates a sucking effect. The draw back is there is no limiting in place, hence further development took place. Remember it's a very small vacuum. As with a lot of this, things are not all they may seem when you first look at this system. I totally understand why it's not obvious, because it isn't. Some of our past design engineers were very clever people.

Dave  

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I would dearly love to use a PCV on my spitfire, but with ITB's it is impossible. Unless Rob has some pointers for me? Same will apply to the PI engine setup.

So for now the vacuum (read "anything less than atmospheric pressure) in the plenium is as good as it gets. Also means no oily smells as happens when vented to atmosphere.

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8 hours ago, daverclasper said:

My Mk1 Vitesse does this, though I raise the idle quite a bit before starting it, and will run, though roughly. Ok for checking which tappet/s are noisy with an old feeler.

Bit of miss info here from I. When the filler cap is removed it doesn't stall, though a difference in running. It's when the cover is removed, I have to increase idle to keep it running

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13 minutes ago, daverclasper said:

Bit of miss info here from I. When the filler cap is removed it doesn't stall, though a difference in running. It's when the cover is removed, I have to increase idle to keep it running

It can depend on many factors why in some systems and cars the engine stalls with the filler cap removed and others not. But one thing is clear it will weaken the mixture as extra air is being sucked into the manifold or carb(s) and that will change the running of the engine.

Dave 

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