ENGINE SEIZURES

[TTM]

I can't magine myself taking the head off and replacing all the many usual small bits while reusing the same headgasket. How does one make sure it will seal as well as if it were new, because it's made of metal doesn't mean it hasn't gone out of shape because of clamping efforts.
It just doesn't make sense to me, at least on dated engine designs such as 944s.
A headgasket is a "fuse" that may show a weakness in the ECU settings if it blows up. I know steel headgaskets are favoured in some heavily modified engines, but at this stage engine life is often measured in hours instead of thousands of miles.

 

[jasonp]

hiya all, how much are the cometec head gaskets? or a good alternative? regards jason

 

[333pg333]

I've used Cometic H/gs for some time now. Yes they can leak, but I think this could be down to surface condition and highboost. The highboost can induce headlift. It doesn't have to be much but you get the coolant overheating/pressurising and going into the secondary expansion tank we run. The benefit of the Cometic is that you can just lower the boost and drive home. This has saved me a few very long and expensive tows from a track many miles away. Headlift is the domain of guys running 22+psi. We have also pulled out the original headstuds and put in new ARP ones. I also found out that ARP have different grade studs...after we put mine in. So I don't know what grade they are but they've held on so far over many trackdays without a leaking headgasket. I'm also not running nearly as high boost on the track just in case but have hit 30psi on the street.

To clarify, we have had to replace the Cometics a few times so they are not indestructible. They perish around the sealing rings due to what we believe must be the headlift.

Back to Barry's thread. It will be very interesting and informative as usual to see what he finds. Some might find this thread interesting too. Many might have read about this Swedish fellow's build but it's always good to re cap. He covers off some of his heating issues and remedies for them.
http://forums.rennlist.com/rennforums/944-turbo-and-turbo-s-forum/349341-corleones-new-engine-is-running.html

 

[paulf968]

Patrick. thx for the rennlist link, I had heard about this guy in Sweden 'Corleone' as he has quite a reputation amongst you turbo power hunters! I don't normally visit that forum so knew nothing of him -- just look what date that thread started!!.

Baz, the insight into head gasket issues is very helpful. I guess most well looked after cars will have had a new gasket at some time. The problem comes with an untouched high mileage car which you might believe is bullet proof. One day there might be a problem, then again it might not suffer. All part of the ownership experience ie balancing cost v benefit !!

Baz, which turbo are you thinking of using in your Mk 2 engine?

 

[bmnelsc]

This is very good info but a little scarey also. Are there any symptoms to look for or is there a method to check if there is some blockage without lifting the head?

My '91 S2 has about 50k miles (near as I can tell) and used about half a litre of oil on a spirited round trip of near 1800 miles across the mountains between Edmonton, Alberta and Vancouver, British Columbia. Great fun - I'd like to do this trip a few more times (familiarity = faster).

On a few occasions, at higher altitudes, the temp guage climbed up well above its normal operating range although still out of the red. Ambient temperatures were warm - around 85F and up and the AC was in use. I have noticed that - from cold - it will heat up to about half the guage and then cool down. I'm suspecting this is due to the thermostat positioning as previously described. I've had a rad flush last year and new belts, seals and water pump two years ago. So if there is a way to monitor for this condition I would be most appreciative as I'd rather not do a preventative head gasket if it could wait until belts, etc are required again in a couple of years.

Thank you all - I'd really hate to blow it up....

 

[bazhart]

The Cometic gasket will last without rotting so no issues there but do check out the coolant relief holes are similar and if the head is a bit warped (or the block) they may leak.

Those with really old cars and no reference of a HG replacement - need to get it done otherwise the coolant will simply miss the rear end of the engine that will overheat = goodbye engine!

Baz

 

[Diver944]

ORIGINAL: bazhart

Those with really old cars and no reference of a HG replacement - need to get it done otherwise the coolant will simply miss the rear end of the engine that will overheat = goodbye engine!

Bummer [&o]

The S2 is now at 202k miles with no history of a headgasket change, and it just had new belts last week (which would have been a good time to combine both)

 

[Super_Marv]

ORIGINAL: Diver944

ORIGINAL: bazhart

Those with really old cars and no reference of a HG replacement - need to get it done otherwise the coolant will simply miss the rear end of the engine that will overheat = goodbye engine!

Bumm
The S2 is now at 202k miles with no history of a headgasket change, and it just had new belts last week (which would have been a good time to combine both)

Ditto.

Well, almost. My 17 yr old 968 has done nearly 100k with no history of the headgasket being changed and I had the belts changed earlier in the year [&:]

 

[scam75]

Common theme here! My 20 year old turbo would appear to be on it's original HG at 106k miles and the belts were done only 400 miles ago.[&:]

Stuart

 

[Lowtimer]

Up to you, but going by your sig line I would definitely want a new head gasket before chipping it.

 

[sawood12]

Baz - is there no way of getting a boroscope in there to look for signs of blockage? If I understand you correctly the risk here is if the material between the sealing rings breaks down and happens to block the coolant passages, suggesting that it is not necessarily a certainty. Clearly with so many high mileage cars kicking around which have probably not had HG changes the occurrence of this failure mode is rare. Is there a safe-life (either time or mileage based) after which if the problem hasn't occurred it probably wont?

 

[scam75]

ORIGINAL: Lowtimer

Up to you, but going by your sig line I would definitely want a new head gasket before chipping it.

Indeed! To make matters worse we had the cambox off too when the belts got done.

So, Baz. Do you reckon this is purely an age thing or does mileage come into it? We have a cross section of cars here with anything between 100k and 200k still on original HG's.

And as Sawood is asking, is there anything can be done as a "health" check rather than removing the head?

Stuart

 

[bazhart]

It is really important to understand the issue here. The std or cometic head gasket forms a barrier between the block and the head and apart from a few insignificant bleed holes it only allows the coolant to travel back down the block then up at the rear into the head and then forward to the outlet.

When they perish/corrode the fist signs are that in between the coolant casting chanells where there could be a passage between the block and the head (but usually obscured by the gasket) the gasket material thins and then becomes porous and then creates a short citcuit leak path so the coolant no longer needs to travel back down the block and foward accross to the front of the head but can just travel to cylinder one or two - then up into the head and then forward and out, leaving the rear cylinders to overheat and thero syphone forard slowly mixing with the flowing coolant and out.

Cometic gaskets will not have this rot problem but due to stress relieving of castings (since they were machined and going through thousands of heat cycles) many block tops are slighlty distorted and some leak coolant out due to the cometic being less compliant.

You need to remove the cylinder studs to re-skim the block and this is not easy nor always successful as the threads get stretched and often need re-tapping a larger size and studs replaced to do the job effectively - so for all normal applications the std gasket is just fine.

2.7's, S2's and 968's will suffer most (because they have one (not two) coolant inlets, a smaller block coolant volume and height) and especially in the case of the S2 tighter shorter pistons std (less taper and clearance).

In my experience - 10 to 12 years is the safe maximum for this head gasket - not so much to the point that it no longer seals the compression - but to an age at which it will start short circuiting the coolant and run the risk of local overheating. Age is the main cause as the coolant remains in contact with the gasket when you are not using the car.

Most 2.5 8 valve 944's are so torquey that they are not being driven so hard as to get too hot these days (and run very cool anyway in the cylinder area) and probably not enough for a problem to occur - but most S2's are still driven fairly quickly and could easily suffer and the consequence is probably the death of the car as fixing the damage is very expensive and far more than having a head gasket replaced.

Those of you that know your gasket has probably never been changed - and seem to be trying to find ways to avoid the cost - don't be so tight - they are generally very reliable and affordable cars but this is a serious issue that I have only recently realised (while looking into other turbo cooling issues) and IMHO explains most of the damage I have seen previously and is a must check and must do if not sure issue. I cannot think of any way to easily check out the condition of the gasket inside except looking in with a camera through the coolant outlet hole with the casting removed.

Have not yet decided on a turbo for the mk2 engine - just about to adjust the C/R for 1.8 bar (over atmospheric 2.8 as some people rate it) and still contemplating between twin staged turbos, supercharged and turbocharged linked or one big turbo. I'll get the basic engine finished first then weigh up space etc before going in a direction to finish it off.

In many ways it is a project too far because we are not only involved in sponsorship or support in both the Porsche Championship next season and the Boxster series (building engines etc at the moment) and developing more cost effective solutions for the 997 3.6 and 3.8 engine cylinder scoring issues (including testing some new specially manufactured slightly oversized pistons) and different cooling flow rates in two seperate test 996 cars - but also thinking about what car it would be best to develop this next season to enter the Porsche Championship with in 2012.

In many ways a 996 would be the most difficult but best to demonstrate all our engineering expertise - but they are not yet eligible (despite being cheap enough and suitable) - so we should have got more involved in the 944/968 engine ware a few years ago and this last 4 cylinder project is really just to finsih something we have started - to learn more about stand alone systems we will employ and see what we can achieve - rather than a serious commercial project - for which it is just too late.

Baz

 

[barks944]

Baz, what do you think of the rotrex centrifugal supercharger? They are used on the Konigsegg, supposed to be very low friction and can spin at turbo speeds.

Is this a good approximation of the coolant path on the 944: http://picasaweb.google.com/lh/photo/RtuRsjy_uyoDNskP81Q8L6MbsNT45TfpLlOThgxHMAQ?feat=email

 

[bazhart]

Barks the picture would be right if the coolant entered at the lower left hand end of the block - then correctly passes backwards and up into the head and forward where it then needs to be seen coming out of the top.


Baz

 

[sawood12]

Might be worth checking out the Lindsay Racing guys to see how far they got with working with Cometic on a 944 Turbo specific Cometic gasket. Like I said before, they seemed to think the main reason for leakage issues with them was because of the use of a 928 gasket. If they've developed a 944T specific gasket they may have solved the leaking problem in almost all cases.

 

[ChrisW]

I would never have thought about replacing ahead gasket on an engine , --- but a related question.

If the antifreeze content is increased on race cars stored in trailer over the winter (I wonder why that might be required [][] ?), could this also justify head gasket replacement for the following season ?

I was told that this might be an issue ...

 

[George Elliott]

Chris,

I dont think Anti freeze will harm a stored engine in any way, one point to note is that excessive antifreeze may reduce the protection from freezing.......only heard that recently.

What I was going to say regarding the head gasket subject; - it may not appear as a replacement part for any scheduled servicing (as the timing belt does for example), but the original fit part as manufactured by Victor Reinz does corrode and the waterways therefore become seriously compromised.
I have seen this on a 951, 110k mile approx, hot day, 1.2bar VDO measured Boost, lots of beans in 3rd gear overtake, 4 seconds later.....hiccup in power delivery.......pfffffffff, condensation from exhaust with 30degC ambient, coolant tank pressure.......rear-most cylinder gasket had popped when I got the head off. (I did not overheat the engine)

If I consider the theories being made here, I am 100% certain they are correct, - the gaskets the bean counters permitted on the production line were never intended to last 20 years. (they contain mild steel !!!!! mine was basically rotten)
My Cometic Gasket has behaved perfectly since - it is obviously superior for general use up to perhaps 330bhp, - the real big power tuners will use bronze o-ringed heads perhaps. I did not need to skim the head on mine as it was not cooked and the faces were perfect.

Baz, I appreciate the thought and effort you have made to share your findings publicly, I always wondered why these engines are known to fail nearest the bulkhead.
The steam vent upgrade is also a nice idea, even as a precaution - it also offers a tiny but perhaps significant coolant flow path out of the back of the engine (can the head casting profile vent air without it?)

Porsche's accountants have created a challenge for your specialist automotive-engineering business.
I think Porsche still plan to offer marginal engineering design quality in their regular (non GT) sports car products, and perhaps also in the GT's of the future as DFI is adopted and the old GT1 engine family is phased out

Good luck with the 997 scoring issues, there are a lot of folk depending on a result.

George

 

[bazhart]

I still think the standard gasket is probably best as it allows some distortion of the block to still be sealed - but I agree that for higher boost turbos you need something extra to stop it sliding sideways under pressure.

We had some Wills rings made for our stage 2 3 litre turbo and decided to fit them to the original 3 litre turbo (road tested by P & 911 W) just in case the buyer wants to up the boost (don't forget it was left standard despite the massive increase in performance).

I am not at work where the records are today but I think it made 350 lbs ft and 300 bhp - with all the performance coming in the mid range. Raising the boost would lift the bhp a lot and a bigger turbo would increase it again - but then you would lose the lovely non-lag flexibility it presently has.

Building the 3 litre 16 valve variocam engine now - so looking forward to firing that one up soon.

Baz

 

[Alexw]

I've been waiting to see a 16v turbo on here for a while, been puzzled why its not done often as I'd have thought 16v = more air flow? And a variocam too, awesome, keep us updated!