Head Gasket Gone Help

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AndersDK
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Post by AndersDK »

James [;)]
For a starter -
The diesel engine has a compression ratio in the vicinity of 1:30
- whereas the petrol engine has this ratio in the vicinity of 1:10 (round figures).
This means you do not in practical terms have a combustion chamber in a diesel. The piston TDC position simply is right next to the (closed) valves surface - just barely not hitting them.
The valves are located similar as in a petrol head - but their surface is just under the level of the head's gasket surface - i.e. it looks like the valve heads are just barely countersunk in the head.
The swirl chamber is in fact a narrow bore - similar to the bore for the sparkplugs in a petrol - but only a few mm in dia. Instead of the spark plug you have the injector at the end of this bore - i.e. higher up on the head - and exactly under the injector the bore is much wider. This makes the injected fuel swirl in the widened bore - to better mix with the compressed air - and it's right here the combustion starts.
Another bore next to this contains the coldstart glowplug - tip of which just barely peep in to combustion chamber. The glowplugs are simple heating elements - getting white hot glowing - to aid the compressed air reach the needed temperature for diesel combustion - when the head (engine) is cold.
This is exactly the main difference between diesel & petrol combustion : the diesel engine compresses the air taken in so much - that the compressed air instantly heats up - to such an extent that the sprayed in diesel mist ignites.
Did you know that the suction side on a diesel engine is directly connected to free air (or the turbo pressure output) ?
Simply a large hole out the free air !
In real life you have of course the usual ducting with air filter etc. - and the turbo & intercooler if fitted.
But no accelerator throttle flap !
If you ever comes to own a diesel car - then during service & engine test - you should not try block off the suction with your hand [:o)]
- chances are the situation gets "off hand" [:D]
acrowot
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Post by acrowot »

If you are going to have the head skimmed or indeed just change the head gasket, I would suggest a new cambelt (they are very cheap), re-adjusting an old cambelt is not advisable.
James.UK
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Post by James.UK »

Hmmm all velly intelesting..Thank you Anders for the explanation. Oh and my ZX auto *IS* a diesel. Fortunately I have not had reason to touch the motor yet apart from servicing and maintenance.. If it aint broke-- [^]
Dunno why they don't use sidevalves on diesels and avoid the risk of engine damage when a belt breaks though.. Maybe I'm prejudiced in favour of the old slow revving "run for ever" diesel marine engines of days long gone.. [:D]
Intake side is interesting, I assume a turbo is just to boost up the air intake i.e. increase airflow and compression? and the cooler is needed because compressed air gets hot, and hot air expands and would defeat the purpose? When the warmer weather comes I will take a good look at the intake side of my ZX though. Just to make sure its as free flowing as it can be.
As a young apprentice I once took a load off the head of my old MK 3 jag to improve compression, it worked great for a while, but after about 5,000 miles the cast iron pistons broke up when doing erm a fair ole speed!! [;)] and a con rod took a short cut out through the side of the crankcase... whoops... [:I] But that's the sort of thing that can happen if you don't think things through thoroughly before you start tuning up engines. [:o)]
Meanwhile I'm off to the library to get some info on diesel engines... [:I] Thanks again to you all for the info ... [:)]
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AndersDK
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Post by AndersDK »

james -
About the turbo issue :
It's purpose is in fact to increase the flow rate of intake air - to get as much as possible amount of air into the engine.
The more air you can get in - the more fuel can be combusted correctly - and the engine returns better performance.
The reason why you have the intercooler is that cold air retracts in volume - thus even more air can be pressed into the engine.
As the increased air taken in also means a lot more strain on the engine parts - turbo engine variants are special build with more sturdy parts - to last as long as a standard engine.
From previous experience you know what that means to engine reliability [;)]
Many "soft hat" car owners (like me [^]) are interested in engine tuning as well as sports drivers - simply because of the potiential engine torque increase - which gives an incredible increase in daily driving comfort.
JohnM52
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Post by JohnM52 »

Hi
East of Scotland Engineering at Sighthill are very good for skimming work (don't be put off by the shed appearance). Piston and Components at Clermiston will supply anything else you need as well as buying from GSF of course.
This keeps you all in one area of town
JohnM
Phil Probets
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Post by Phil Probets »

[quote]<i>Originally posted by James.UK</i>


Maybe I'm prejudiced in favour of the old slow revving "run for ever" diesel marine engines of days long gone.. [:D]
I have now installed two XUD7TE engines in my boat. Original HP is 90, with a charged air cooler using raw water this increases to about 120/130 HP. These are very reliable engines and I complely re-built them before the installation. I've lots of details if anyone else ever wants to attempt the same thing.
louis1
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Post by louis1 »

i would not get the head skimmed because i did and 20.000 miles it went again, if the head is warped it is probably fu**ed, you would be better getting a new head.
good luck louis
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