Why do cylinder head gaskets fail?

[spinmaster]

I have been told that there is usually a reason why head gaskets fail on K Series engines and it's quite unusual.

My car has a VHPD engine, which hasn't overheated (although it was raced two years ago) and has been running perfectly.

This seems to be a relatively common problem. Has anybody just had it go for no reason, without any underlying more serious problem?

 

Thanks

[Peter Carmichael]

The compression rings on the gaskets never fail. The silicone beading sometimes fails, but the new design fixes this. There are various mechanisms by which the mating surfaces on the head can be compromised - uneven liner protrusion, too little liner protrusion, too much liner protrusion, cavitation erosion, airlocks, wrong coolant...

[spinmaster]

Hi Peter,

 

Looking at the posts I thought it was a common problem. It certainly is in Elise's and MGF's.

 

Is that because of cooling problems with these cars?

[AMMO]

Gaskets fail when engines are incorrectly designed? The way the K series liners are located is a bit of a joke. I heard a story (from a very reputable source) that head gasket failures on the K series was costing Rover £8,500.00 a week in warranty claims.

 

Luck of the draw if it pops or not.

 

AMMO

[Jason Plato]

I think there are issues with the rear engined cars with thermal shock from the large quantity of cold water that is in the pipes that go all the way to the front of the car ( radiator ) . the thermostat opens and in rushes all the cold water into a hot engine ???

 

Dave

[AMMO]

Nope

 

I had a friend who now works at Lotus Engineering that worked for a firm called Scott Griffin (I think, may be mistaken, it was a few years ago). His job was to get Cosworth Sierra engines on a dyno at full chat at maximum temperature and dump 200 gallons of freezing cold water through the water jackets. This was to see if the head gaskets would pop. They didn't. The problem with the K Series is simply bad design. If it was designed properly it would not fail in normal circumstances, which it does.

 

You can defend this engine until the cows come home. The bottom line is that the bore is too small. the stroke is too long. the valves are too small, the rods are too short (in the 1800) the ports are too small and it pops head gaskets.

 

Apart from this it is quite light and dinky. Other positiveaspects are...........................erm..................hmmmmmmm......................ehhhhhh. Dunno can't think of any at the moment.

 

I still like 'em more than a Crossflow though!

 

AMMO

[spinmaster]

Hi AMMO

 

So you are a big K Series fan then!!??

 

It is bloody frustrating though. I think I going to have to learn to replace it myself or get a throw away engine like a Fireblade!

[Gridgway]

I understand that the location of the head with the dowels is also prone to failure.

Graham

[Peter Carmichael]

Neither Ammo's post or any of the others contradict my assertion that the compression ring does not fail. Ammo is correct in that the gasket design itself is not at fault, but factors affecting the location and integirty of the facing surfaces, which I suppose comes to much the same thing.

 

Whether it is common or not depends on much more than the engine design. The installation design is obviously not all it could be also.

 

In caterhams, the *crap* radiator fan switch which always fails is responsible for many overheating events and subsequent failures - they should wtop fitting thi and sort out a proper solution. Failure of the pressure cap can also give similar symptoms to a head gasket failure.

 

I have had an ordinary Supersport engine fail on account of the incorrect coolant choice and a likely overheating event when the radiator crcked while lapping the Nurburgring. Given perfect cooling at all times I doubt there would be many reported head gasket problems at all...

 

... which all means that if you take care you can have a lifetime of reliable service.

[AMMO]

As Peter says there is nothing wrong with the head gasket. I was at AER (the people responsible for the X-Power engines) when they took delivery of the first K-Series for conversion to Super 1600. Once dismantled it was quite apparent that the head gasket was not working properly as the fire rings in the gasket were free to rotate. This obviously meant that there were insufficient clamping forces. The only problem with the K-series is the shoulder in the block where the liner sits. It is too small to do it's job properly. If you add to this the possibility of SAS (soft as ****) grade metal in the block and head, inconsistencies in machining and heat treatment you open yourself up to a load of problems. Once the head is torqued down and the engine is run a combination of the pressure and heat will make the shoulder collapse.

 

I have experience of this from re-linering air cooled motorcycle engines. Once the liner is shrunk in, even putting pressure on the liner with a 30 ton press doesn't have the same effect as running the engine. The liner will 99% of the time settle and the engine has to be dismantled and re-machined. This is also what Scholar Engines found. They supply the engines for an Exige one make series. They weld up the block, re-machine and assemble the engine. Once run on the dyno the engine is dismantled, re-machined and re-assembled. I correctly predicted that the liner would sink 0.003" from my experience with bikes. If you think that the DFV relies on a copper berryllium ring which sits 1thou proud of the block for the head to seal you must realise that something that moves by 3 thou is not really acceptable.

 

 

AMMO

[Rob Walker]

I have found that K liner protrusion varies enormously from engine to engine. I have seen liners sitting below the top of the block and protruding .004" on the same engine. When I built my latest engine I had the block skimmed to give an even liner protrusion of .006" and fitted the Mike Satur Gasket together with steel head dowels and bespoke Liners. Touch wood alls still sound and the engine is pushing out a reliable 230Bhp.

[AMMO]

Rob

 

Sounds like the proper way to go. With 0.006" protrusion even if it collapses 0.003" you should still be OK. Keeping my fingers crossed for you.

 

AMMO

[Rob Walker]

Ammo,

 

The fire rings on the gasket are not designed to clamp to the flat section of the gasket when the head is torqued down. If you examine a new gasket there are compression stops of .050" at each and and the fire rings are .070". When you torque the head the head will only compress the fire rings until the stops are reached. This allows the block to expand longtitudally keeping the fire rings clamped between the head gasket face and the liners which again are designed to move. " too much IMO " my bespoke liners are a tighter fit into the block and thicker walled to reduce movement. It has been my experience that the poor location of the stock liners causes the fire rings to fret into the head gasket face up to .025" and metal be transfered from the head gasket face onto the fire ring. The Satur Gasket and steel dowels seems to have cured this. Dave Jackson has just striped his K and reported no head gasket face damage. However the gasket had failed on the rubber oil seal around the oil feed up through the head dowel. The latest Satur gasket has been redesigned to cure this problem.

[Peter Carmichael]

As has the latest rover gasket.

[AMMO]

The other thing I noticed was that the liner fit on the engine I saw was very loose. Maybe some of the fretting problems you talk about are from this. I have never encountered a head gasket with a fire ring that was supposed to move. Sounds like a daft idea.

 

Is the Satur gasket the same?

 

AMMO

[Rob Walker]

Ammo,

 

I don`t know I haven`t had to replace mine yet. Dave Jackson will know, hello Dave ar you there?

[Jason Plato]

Just as a corretion - there was no visible damage to the gasket or seal's around the oil feed or oilways , but the syptoms suggested that that was the most likley point of failier . the new satur gasket fitted had a change of design around this area to allow a pressure release .

Only road miles will tell if the new gasket has cured the problem ..............

 

The car ran in "suspect" condition at curborough , so it certainly wasnt affecting performance 😬

 

dave

[Jason Plato]

The fire rings on the satur gasket can rotate if pinched between thumb and finger - but there was not lateral movement .

 

Dave

[AMMO]

Just checked with a friend who builds K-series. The fire ring on a new gasket should be only just free to rotate. The one I saw was very sloppy after it had come out of an engine. He uses the stock head gaskets and has had no competition engines fail so far. Mind you they only do about 200 miles between re-builds.

 

He said a lot of attention must be paid to torquing the head. He prefers to use a spring type torque wrench rather than a click type one to pre-load the head bolts to 25 Nm. He reckons a friend of his built one with a click type wrench and it failed almost straight away. He seems to think that if the head bolts have a lot of lube on the under head and thread a click type wrench may actually overtighten them as the bolts seem to turn a lot more that with the spring lever type.

 

The blocks are machined to take tighter fitting liners with a wider locating shoulder.

 

It would be nice if Rover would start building them with the mods already incorporated at some point. Save Rover some warranty money and make life easier for the K-series tuners.

 

AMMO

[Jason Plato]

Ammo - how you described the firing rings is how mine felt - both old and the new gasket .

 

Maybe the method of setting the torque is the reason so relativley few reputable modified or home built engines gaskets fail vs standard rover built engines , due to maybe careless torqueing of the bolts ?

I think that my possible failier could be due to oil pressure and high revs around the now modified oil feed .

 

just a thought .

 

dave