Lancia TC head gasket failure

[idv]

Hi
I have just removed the head off my 2L Lancia, because of a blown head gasket between number 2 and 3 cylinders, to find the head gasket had creeped into the cylinders on all the gaps between 1-2, 2-3 and 3-4. There is 1mm or more of the gasket protruding into the bore. The bits in 2-3 had detonated and burnt the gasket through.
The gasket was only replaced 6 months ago and would be lucky to have 1500 Km on it.

Is there a known reason for this? :?:

I have checked the obvious. Head is flat. Bolts were not loose. Block is flat. The torque wrench was cheked before I assembled the engine.
I think the head gasket was a thick one because the head has been shaved into the inlet valve seat.

I'll try to get a photo of the gasket on the weekend.
Thanks.

[Guy Croft]

Hi,

That's bad luck. You've done your best with the rebuild.

From your description, detonation is a possible cause, for one of the following reasons:

1. Overheating engine (especially at the back of the block)
2. Fuel octane too low/compression ratio too high
3. Intake air temperature too high.
4. Ignition timing over-advanced
5. Over lean carb jetting.

I don't know your engine spec (modified or standard) but certainly the TC engines with a single carburettor are especially prone to detonation, from cause 3, combined with the rather poor mixture distribution at the rear end of the head. Hot engine and hot intake air amount to the same thing really, taking the cylinder into the danger zone for detonation, all it needs then is weak mixture to set it off. Truth is though, it can be a mix of all these things. 1 & 4 are closely linked, and 2-5 can cause 1 etc.

Well-calibrated fuel injected units and those with twin carbs that are kept cool enough (engine/air temp) rarely suffer from this problem, but with 9/10 TC heads that come off single carb engines I see pitting (from light to very severe) in the rear combustion chamber and most of them have blown the gasket at one time or another.

If it proves to be detonation - publish one or two photos of the engine in-situ so I can see the layout, and give me the engine spec, unless it is a standard unit (in that case I know it). Also comment on running temperature, ignition timing settings etc. That way I can guide you on what to do to prevent it happening again.

GC

(revised by GC after Andy's post on gasket shifting below)

[sumplug]

Can this also occur if the head gasket moved as the head was being put on? If the corners are not held then the gasket could move back.

Andy.

[Guy Croft]

Sorry, yes, good point Andy.

Assume the head gasket dowels were in place and it was fitted correctly (bearing in mind what Andy says)?

Perhaps photos would be a good idea after all.

GC

[idv]

Hi, Sorry to take so long to get organised.
The setup is a single carb with port matching to a couple of mm, standard exhaust manifold, again port matched.
The head has been ported behind the valve seats and the mouth of the ports opened out to match the gasket. Standard valves with 1608 cams, the distributor drive was needed and I could not source suitable cams at the time. This motor was originally built 10 years ago.

The pistons are high compression. I wanted standard 1800 pistons but I think they are 1800 9.8 cr pistons. I have 195 - 200 psi at 600rpm with the carburettor fully open, no spark plugs. The pistons are only 84.35 mm.
I am now running electronic ignition with individual coils on each plug.(this has increased the low rpm tourque while controlling detonation.)
This setup would detonate around 3000-4000 rpm if the engine was hot or the timing was advanced with the distributor

[Testament]

A couple of photos from my 124CC motor which did a similar thing a couple of weeks back. Blew cylinder four to the small coolant passage between 3&4 on the intake side.
I think this engine has had detonation problems in the past as there is evidence of a weld repair on no.4 combustion chamber. I don't recall any particular occurance of detonation that caused it to blow on this occasion, but rather it got a bit hot, 100-110deg. C once or twice and warped the head a little.

The pitting in the head can be cleaned up (sorry no pictures atm.) but is this piston too far gone to re-use? This is just a road car, and I will be replacing the single carb with 124BC 40IDF's.

[Guy Croft]

Some classic pictures there, well done for publishing them; yes the piston is relatively untouched - personally I'd want to take the piston out and polish it to get rid of loose debris, check the ring lands and for bore damage caused by any scuffing from metal lost from the top of the piston.

GC

[Marc]

After many years I have come to the conclusion that these engines blow head gaskets in that area because the heater valve needs a built in bypass.Flow from the water pump is cut-off when the heat is off and causes an increase in head temp in that area.I have confirmed this with a laser temp guage gun,12 to 20 degress hotter when the heater valve is closed at the head !
Its a common problem.Fatigued head bolts,poor quality head gaskets are also suspect,but the problem is flow of water.Try looping out your heater core until you find away to add a bypass valve.Chrysler makes one that will work on our engines in terms of design,I have not tried it.I loop mine out for the summer and put it back to normal in cold months and always leave it on.You should also install a full flow high performance thermostat that fails in the open position.If these cars were built today a different heater core valve design would have been used.The problem gets worse if you increase cylinder head temps by increasing HP.

[Guy Croft]

That's a good bit of investigation and good tip too, well done Marc.

I loop the outlet in the back of the head back to the pump on race units where there's no heater.


GC

[Marc]

Thanks Guy,
I really think there would be a recall had they continued to produce the cars today.I cannot tell you how many heads I have seen with blown head gaskets around cylinder no 3 on 8v's.I used to think they went to an external thermostat for serviceabilty issues,I now think it was a quick fix for a bigger problem.

[Guy Croft]

Yes, quite possibly, though of course the problem in those days was by no means confined to the TC Fiat engines. Just in case you don't know already, F/L changed the coolant outlet and stat location to the back of the head on later generation engines, ie: the 8v TC and 16v with reversed port layout.

Quite possibly the use of software modelling on coolant flow and heat transfer brought on the change of layout.

GC

[Uros Piperski]

Can someone post some photos, please? I'm not sure I understand where the bypass valve should be connected. Is this typical only for early heads? I understand the late heads don't have the problem. What about a 1979 132 2ltr engine?

[Guy Croft]

Uros, hi.

Please refer to photo - we were talking about the pipe at the right-hand end of the head that is the heater feed. When the heater valve is closed it flows no coolant.

GC

[Uros Piperski]

Thanks, I get it now.

[idv]

Hi I just wanted to reply to give some feedback on what I found after replacing the head gasket.

Going through the list on what Guy suggested as possible reasons for failure:

Overheating - No, engine was never getting to half temp as I haven't used it in anger yet.

Octane/Compression ratio - Borderline, however I have run this settup for some years without problems.

Inlet air temp - No all temps were cool.

Ignition timing advanced - This is relatively conservatively set because of the compression ratio, Max 32 deg.

Over lean carb jetting - Well, I had this checked a couple of years ago. But it couldn't hurt rechecking.

The primary barrel was running lean and the accelerator pump not working correctly! The second barrel was ok. So driving around gently was actually doing more damage than full throttle. Any acceleration using only the primary barrel went straight to lean and stayed there, openning up the second barrel brought the mixture back to an "acceptable" level.

The carburettor was stripped and put into an ultrasonic cleaner. New gasket kit fitted and put back into service. The mixtures were checked again and now found to be acceptable.

The engine is a lot more responsive now. It's amazing how you don't notice the drop off in performance.

Thanks for the advice.