Head Gasket Failure. Possible Causes.

[Tim Falce]

Following on from my small fire yesterday I removed the head to find the gasket has gone on No.6 cylinder (front of engine). As can be seen from the pictures there is quite a large piece missing.

I've never seen one go like this before and it would account for the masses of white smoke when it went.
Is this a usual type of failure and what may have caused it? I have had problems with the car running hot for the last couple of races so it could have been going for a while. There is also a couple of small stones sitting on top of the piston but no marks to the piston, bore or head so they may have fallen in as I removed the head or yesterday while I was checking things at Silverstone.
Engine is a 4.2 Jaguar XK lump.

[phoenix]

Originally Posted by falcemob

Following on from my small fire yesterday I removed the head to find the gasket has gone on No.6 cylinder (front of engine). As can be seen from the pictures there is quite a large piece missing.

I've never seen one go like this before and it would account for the masses of white smoke when it went.
Is this a usual type of failure and what may have caused it? I have had problems with the car running hot for the last couple of races so it could have been going for a while. There is also a couple of small stones sitting on top of the piston but no marks to the piston, bore or head so they may have fallen in as I removed the head or yesterday while I was checking things at Silverstone.
Engine is a 4.2 Jaguar XK lump.

Looks like it has burnt through to me. Also looks like a possible leak near the exhaust valve at around the 7 o'clock position close to the waterway? I imagine the process could have been:

running too hot - > head distortion -> leak at head/block interface -> escaping exhaust gasses close to 1000 degrees C -> burnt gasket.

Could we see a pic of the piston with the piston at TDC?

[Tim Falce]

I've also noticed that it's gone on No.1 and 2, it's got hot and the gasket is burnt with the rings not looking too good. I'll do some more pics as soon as my camera is recharged.

[Tim Falce]

Here's the piston at TDC and the rear two cylinders on the gasket.

[thebear]

Aside from assembly/torque/re-torque errors I would have the head and block into a shop that can verify if the mating surfaces are truly flat. If overheating was evident you were probably leaking combution into the water jacket as shown in your pix.

"Back in the days" when I was racing I used to put a smear of heavy weight motor oil (any) on my finger and run it around the top of the cylinder bores just prior to installing the head. This woud result in furious smoke upon inital startup but also provided a known carbon seal at the gasket interface.

. .

[Al Weyman]

Yes definitely check that block surface carefully as well as the head, you are luckier than I was with my head gasket blow which has lunched the block and head beyond economic repair. Looking at the size of the head chamber plus pop up pistons I would say you are running a hell of a lot of compression, maybe this has caused detonation resulting in the head gasket failure. It may be worth checking your C/R calcs again and maybe you need to come down on the C/R a bit as fuel aint what it used to be I would have thought even with a radical cam much over 11:1 on legal pump fuel is pushing it a bit especially if running a bit of ignition advance and using conventional gaskets! I am not convinced that it was'nt a combination of these factors that caused my failure.

[GORDON STREETER]

Tim, it looks like detonation to me but not necessarily all the time.
I seem to remember that there was a problem at Spa with some dodgy fuel at the last meeting you did there ?
If you have detonation at any time it normally starts by burning the head gasket as its the thinnest part and gets hottest first. From then on its a downward spiral as it doesn't take much to blow it through at its weakest point.
The problem is you can't hear detonation with a crash helmet on and the only way I have got over it is to use the same fuel all the time, even if it means carrying it miles to a meeting. If I have to buy any from an unknown source I use a fair bit of octane boost. I know it may not produce the maximum power but at least its safe.

[Al Weyman]

BTW as I am lead to believe pop ups will always tend to promote detonation more than flat tops and probably required to get the C/R high enough with the Hemi chambers (no squish area). One of the down sides of a hemi chamber I guess.

[phoenix]

Originally Posted by GORDON STREETER

Tim, it looks like detonation to me but not necessarily all the time.
I seem to remember that there was a problem at Spa with some dodgy fuel at the last meeting you did there ?
If you have detonation at any time it normally starts by burning the head gasket as its the thinnest part and gets hottest first. From then on its a downward spiral as it doesn't take much to blow it through at its weakest point.
The problem is you can't hear detonation with a crash helmet on and the only way I have got over it is to use the same fuel all the time, even if it means carrying it miles to a meeting. If I have to buy any from an unknown source I use a fair bit of octane boost. I know it may not produce the maximum power but at least its safe.

Now you say it, I can see some minor indents on the piston close the the spot. Must admit I have only ever seem the result of major detonation - which is a bit more obvious, even to the untrained eye!

[GORDON STREETER]

Its always a chicken and an egg situation in cases like this as to what starts it as you did say it has been running hot lately and obviously this is one of the problems that cause gasket failure as well.
As I said it looks like detonation to me and if you havent altered anything on the car or engine over the years then there's your answer. Have a think back as presumably its always been reliable in the past.

[Al Weyman]

Did you put a thinner gasket on last time you built it Tim, somehow I seem to remember some discussion on this a while back or was I dreaming as that can make a difference and it may have been marginal, ask Zef he stuck two on one on top of the other) at Lydden to bring down the compression after blowing a gasket in qually and it was fine for the race infact he won the class!

[Tim Falce]

This is an engine I bought over the winter, yes I know I said I would never buy an engine someone else had built but it was there and it was a reasonable price on the face of it and I didn't have time to do one myself.

At Spa some people did report having problems with fuel but I did practice on Tesco's 99 and filled up in the paddock for the race and the getting hot problem was the same on both tanks, slightly better in the race.
I have been running a lot of advance, up to 36 degrees and have had discussions on this and some people recommend only up to 29-30 degrees on these engines and some up to 40. I'll now go the low side and see what happens.

I'm wondering if maybe the gasket has been going for a while as the engine would run fine for around 10 minutes and then the temp would creep up and it would pump a litre or two of water out.
I did a sniff test which was OK and it would hold 20psi of pressure when I pressure tested it but both of these were when the engine had only been ticking over long enough to get it up to temp so maybe it could have been giving way after slightly longer, it would also account for dumping a bit of oil in the catch tank as well.

The problem with the engine is that it is very trick and was built for a well known (in Jaguar circles) German Racer and could have been standing around for a good few years without use apart from being turned regularly. I have also noticed some off centre pinch marks around some of the sealing rings which makes me think it may have not gone on square.
One other thing is that on a rolling road earlier in the year I was told it is running on the rich side across the rev range.

[GORDON STREETER]

Just a quick thought I can't really see from the pictures, but is the gasket smaller than the bore or head chamber diameter ? as that will cause the problem even if its only a small amount hanging inside. Has it been rebored ? because if it was marginal on CR before it might push it over the top. Running rich would actually make it run cooler so thats OK.
Get a proper car Tim. not one of these namby pamby lookalikes

[Tim Falce]

Engine has been rebored +60 afaik but the gasket diameter is 10 thou larger than the bore. Looking at the pinch marks I am going along the lines of it not being fitted properly.
What's the best way of checking the deck for flatness as I only have some steel rules, not anything that I know is engineered perfectly straight.

[GORDON STREETER]

The quickest way to check to see if a surface is flat is to push a decent surfacing block across with a fine's emery or production paper on it, you will easily see if there are any imperfections. But I don't think that's your original problem.
As for not fitting properly as it has studs I would think that was difficult ?

[Al Weyman]

Just buy one of those steel set square things you can slide up and down from B & Q or somewhere should do the trick. Does the 10 thou from the bore seem a tad close as it allows little tolerance for core shift or gasket production accuracy, I know on the Chevy engine the gasket is 4.125" for a 4" bore which would be 4.040" max as you would'nt want to bore one more than 40 thou and race it so that would give you a generous 32.5 thou from gasket to bore, just a thought.

[Tim Falce]

Thought I'd check the bearings, what's caused this? The gold shadow is not copper showing through, It's the reflection of my florescent lamps. The white bits look more like a deposit rather than the white metal flaking.

[Al Weyman]

Detonation pounding the bearings? I had the same. Check that compression.

[Al Weyman]

See here http://www.nb-cofrisa.com/docs/web_fallos_ing.PDF Scroll down and look at the picture showing the symptom of overloading, looks just like yours. It may go like a rocket with that engine but maybe it needs rocket fuel to power it!

[davyboy]

I had a similar headgasket failure to yours Tim on a Modsports Midget. When it let go the escaping charge set fire to some of the bodywork on the car - scary stuff. Prior to the failure the temperature would just continue rising, it wouldn't stabilize. I had a ridiculously high compression ratio and put the failure down to detonation. I think there's a very high chance that you've had something similar going on there.

[GORDON STREETER]

Tim I do know where there's a quick well proven Anglia that could be for sale

[GORDON STREETER]

But I don't know if you could handle the power

[Tim Falce]

Thanks for all the help, sooooo, am I looking at a complete rebuild, the crank looks good, or just a new gasket and bearings? Oh that is near enough a complete rebuild isn't it.

[Al Weyman]

In view of the fact you have bought the engine and are not 100% sure if the spec I would cc the head, and do the same with the block with piston at TDC to determine what compression I had (you will also need to measure the compressed gasket thickness and add that to the equation and if after a bit of research it was deemed too high with the fuel/cam combo I would take the opportunity to have the pistons machined down a tad to lower the compression, fit new bearings and rings, determine if a head skim and maybe a block deck is required and put it back together and try the timing at 36 degrees all in and see if you can listen for any pinking if its evident back off the timing till it goes away, what else can you do?

[Tim Falce]

Originally Posted by falcemob

Thought I'd check the bearings, what's caused this? The gold shadow is not copper showing through, It's the reflection of my florescent lamps. The white bits look more like a deposit rather than the white metal flaking.

On second inspection it is the top layer of metal that is flaking off.