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200tdi head gasket confusion


Adam001
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Hey,

I have a discovery 200tdi engine that begun overheating but was otherwise running ok, so ran without the thermostat for a bit. (pump, thermostat and rad fine)

I am trying to get my head around the head gaskets. The gasket on the engine now is a no hole gasket, apparently the thickest one but neither the haynes or paddocks seem to know anything about them. I do not know who fitted this gasket either.

I have read the haynes about selection and it says to use piston protrusion to gauge whether you use a 1,2 or 3 hole gasket...so I intend to do it on that using feelers or dti, but what about if the head has been skimmed in the past, do I need to take that into account, to maintain compression?

Regards

Adam

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Done a little more reading, and it seems skimming the head make no/neglible difference and can be ignored. This true?

dont see how having manufactured holes in a gasket helps with overheating....

I'd be looking at coolant, thermostat, rad, water pump, watch for leaks of oil and water underneath, change your oil and keep a close eye on it, keep an eye on the water level too. If either is going down you might have a cracked block but you'd know about it because either you'd have mayonnaise on your oil filler cap or dipstick, or you'd be pissing oil out of somewhere. Check the water and the oil, is my advice.

If you're worried about the head and gaskets, change 'em.

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That is true. It's been a while for me but aren't 200 Tdi heads flat? so skimming has no real effect on compression? just valve clearance. I seem to recall but combustion & valve cutouts in the pistons. I wonder if I've still got the pics of taking it apart?

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Yeah I'm not to sure as not seen the inside of one, I just assumed that removing material would make the compressed volume smaller and raise the compression, but perhaps it is neglible as the intake volume is also changed by the same neglible amount?

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I cant find any pics of the head, but the pics of the pistons are in this old topic I did years ago. http://forums.lr4x4.com/index.php?showtopic=11960&st=0

Removing combustion space will affect compression but I doubt a skim would do enough to cause problems. I've faint memories of a mate building a quick TDi back then & he used the thinnest gasket to get the slightly higher compression, along with other mods it flew & never blew up.

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Theoretically, you would always use the same head gasket thickness as the factory item unless -

(a) You have replaced one or more pistons.

(b) You have had the deck skimmed (top of the engine block)

It doesn't matter so much that you have the no-hole gasket - the difference between one and the other is only .10mm, so nothing will go bang and you won't notice any difference in performance.

However - standard head gasket will almost certainly have been 2 - or - 3 hole gasket, so the head has been off before.

Skimming the head will make no difference to the required gasket thickness, as the combustion happens within the piston crown - rather than in the space between the piston crown and head (known as the squish band). If you want to get it right, then you would have to measure piston protrusion, find the highest one, then select the right thickness gasket, then check valve stand down (how far below the surface of the head the valves sit), to ensure factory - standard clearances.

A few golden rules with the TDi engines -

Never use a thinner gasket than the one you took off unless you have done the required checks.

Always check valve stand down if the head has been skimmed

Always check piston protrusion if any/all of them have been replaced/deck has been skimmed.

Don't assume that by putting the thickest head gasket (no-hole), is an alternative to checking piston protrusion/valves stand down (the crank/cam/tappet timing dictates that)

Les.

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Hey, I reassembled the block/head yesterday.

I measured the piston protrusion and I found that a 2 hole gasket would have been fine, but to play it safe I put a 3 hole gasket on there. seemed no reason why a no-hole gasket was used, or to put one back on again.

I didn't check valve stand down, it didn't occur to me, shame as there seems to be no reference to it on this site other than what you just mentioned. I have turn it over by hand to do all the tappets and all seems fine in that respect.

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