Detonation and blown cylinder head gasket (Fiat TIPO-SOHC)

[unomas]

Hi Guy !

My name is Martin, and I think you will not remember me, but I was posting a few doubts regarding the preparation of my 1372cc SOHC-TIPO Fiat Uno Turbo head cylinder.

If you don`t remember it, it was the thread : viewtopic.php?f=13&t=631

I need from your experience, like in the past, to solve one problem that actually I`m facing.-

I used the car with the cylinder head modified, and after a thousands of kilometers I blown the head cylinder gasket.

It was working fine, until I disconnected the knock sensor (don´t ask me why I did that, because I`m still asking me too).
While the sensor was plugged and while I blow 0.9bar of pressure, everything worked well. One day I tried to test it on a highway to the limits... It seems the limit was really short because I was able to run it until near 1.2bar and 7000RPMs. Just for a few seconds....

After that I got this :




Another 2 views (close up) :






As you can see these are the 3rd and 4th cylinder. It seems the gasket was blown, instead of melted.

In the 1st and 2nd cylinder this problem is not presented :




I`m wondering if you can help me to determine (based on your experience) if the problem was due detonation, or it could be a problem with the CR and the works that I did over those 2 chambers.
I know is difficult to help me, just with photos, but I`m worried about the possibility that I did something wrong, because the problems were presented only in the two chambers that I worked.

Now I`m facing another related problem. If the problem was due the high CR, or the high pressure blowed by the turbo, I can go down with a specialy designed MLS cylinder head gasket. But, as you know, the MLS requires a more flatness surface than the common. And that, now that I have th engine mounted, is really hard to do.

I hope you can help me , as you did it in the past, with your wisdom.-

Let me know if you need something else, or another view of the photos (I have millions).
Martin
Argentina.

PD : Sorry , again , for my english.-

[trickymex]

Looking at the head there does not seem to be much sign of detonation, have you any pics of the pistons??

I would guess that either the head or block are not 100% flat or the head was not torqued down properly or a combination of the two, simply because there is little sign of det

Does anyone else care to confirm or disagree with my view here??

Ricky

[unomas]

Looking at the head there does not seem to be much sign of detonation, have you any pics of the pistons??

I would guess that either the head or block are not 100% flat or the head was not torqued down properly or a combination of the two, simply because there is little sign of det

Does anyone else care to confirm or disagree with my view here??

Ricky

Thanks Ricky for your point of view.-

I think the flatness was very well done in the two surfaces (block and head). But following your thoughts I can tell you the gasket was, almost impossible to remove from the head. And it was really, really, easy to remove it from the block side.
I think, and I repeat you, following your thoughts, may be the quality of the flatness was not the optimal as I thought.

Here is a picture of the pistons :



Sorry for the "out of focus" picture, but is the only that I have until I take another.

Thanks for your comments.
Martin

PD : Please let me know how you can detect the detonation signs throw a picture.

[Rich Ellingham]

It looks like there is some evidence of detonation on the fire rings, maybe the picture isn't quite clear, but the tell tale sign of detonation is a crimping of the fire ring like its been done with a pair of pliers. GC will give his view. Is part of No1 piston missing or is it just the photo?

[unomas]

It looks like there is some evidence of detonation on the fire rings, maybe the picture isn't quite clear, but the tell tale sign of detonation is a crimping of the fire ring like its been done with a pair of pliers. GC will give his view.

Nice!!.. thank you Rich for your comments. Are rely useful to develop a better preparation in my chambers.-
Just to give you more information about the head gasket that your are seeing : is a 2.4mm cylinder head gasket, TARANTO brand (one of the most important brands from here). It is not the regular width (1.6mm).

In the beginning of the preparation I was afraid to use this cylinder head gasket, due this large width, I thought this could be a problem in the future , because you have a more weak surface (the piston ring of the head gasket) supporting high temperature, instead of the cast iron from the cylinder head. (I really hope you can understand what I meaning with this).
If you have 31cm3 in the combustion chamber, you will need near to 2,7mm width of head gasket to decompress 8:1.
And I think you can get the same decompressed relation if you are able to get 36cm3 from each combustion chamber.
In the past, my previous consult was exactly this, I asked to GC, how responded awesome, how to extract cm3 of the combustion chamber.

Is part of No1 piston missing or is it just the photo?

No Rich, there is no pieces of piston broken in any of 4. It is just a few drops of cooling water.

May be you can find more information in these pictures :

*- Once I removed the rest of the gasket :



*- this is another angle of the combustion chamber (3rd and 4th) :



I hope I was clear. If not, please let me know and I will try to repeat the questions using another words.
Martin

[tmvolumex]

One thing that you need to do for sure is to run additive in the cooling system in your engine. From the pictures, there is a tremendous amount of rust in the cooling passages, and it appears that you run water only. The right additive (eg: antifreeze or water-wetter) - in the right proportion - in the coolant can not only raise the boiling point of the fluid in the cooling system but it will prevent nucleate boiling ( see: http://en.wikipedia.org/wiki/Nucleate_boiling ) and corrosion.






Good post Tom - edited by GC

[Guy Croft]

It's been detonating for a long time - the severe erosion (pitting) of the squish band shows this - and the gasket has finally given up. You need to take all the pistons out and inspect them. Well done readers who saw the signs.

It's a good job the gasket blew otherwise the pressure would have punched thru the pistons. Causes have been considered many times on this forum, too high CR, engine too hot, intake air too hot, fuel octane too low, wrong plugs, too lean, over advanced etc etc.

Search by 'detonation' and have a thorough read.

GC

[unomas]

Thanks a lot guys.

I will keep in mind all the recomendations you gave me.

thank you.
Martin