IT's only gone and done it!

Allanxantia · Post by **Allanxantia** » 10 Jul 2006, 14:26

Just when I thought I had a bargain, the Head gasket has gone. Its getting hotter all the time and pressurising the header tank. I am doing it at the weekend but have a couple of questions.

The head has not given up yet it still runs, will I need to skim it. Its just that I will then need to get that done during the week and will take the job into next week.

Also the metal gasket I need, which thickness should I order?

Stewart(oily) · Post by **Stewart(oily)** » 10 Jul 2006, 14:29

Its better to get the head skimmed, normally I go for the thicker "repair" type of gasket, have fun.
Stewart

mbunting · Post by **mbunting** » 10 Jul 2006, 15:15

Couldn't help chuckling at this.

My "bargain" 405 might have a blown head gasket - I'm running with the therm out to stop it overheating and loosing water, and to top that, the power steering has now developed a 1L a day leak.

Can't afford to fix either at the moment, because I spent money on something else because the car was ok...

Gammy leg · Post by **Gammy leg** » 10 Jul 2006, 16:30

Best time to check the head is when it's off the block. Only then can you say whether it needs a skim or not. I have re- fitted heads that have exceeded the manufacturers tolerances in the past without any trouble but the decision must be yours.
Skim jobs don't cost that much so it may be wise to be safe than sorry.

Gammy

f00lzz · Post by **f00lzz** » 10 Jul 2006, 20:07

Just as important..... get it pressure tested and then skimmed. If the head has gone because of overheating or overheated since it went it is almost certainly in need of skimming. Get a 'decent' gasket either from Citroen or a specialist head refurbisher such as Motorcast on 01939 236000, they can also pressure test/skim/supply head bolts/all gaskets etc and work is immaculate.... I have used them several times now and can only say they are the best around. (If you decide to use them.... give them the old gasket with the head, they will determine the correct gasket thickness for you).

Post by **Peter.N.** » 10 Jul 2006, 21:24

If the head is cracked you will probably see evidence of water at the top of one or more pistons when you remove the head, if there is none its probably just the gasket, if its done around 150k this is par for the course, but dont let it boil or it probably will crack. As advised dont even think of doing the job without having the head machined.

Citroen do a 'repair' gasket for the XM which is laminated steel, like a set of feeler gauges, it looks as though it ought to last forever. I fitted one to My XM about 25k ago and have only topped the water up once in the last year.

fastandfurryous · Post by **fastandfurryous** » 11 Jul 2006, 11:11

f00lzz wrote:give them the old gasket with the head, they will determine the correct gasket thickness for you

This won't be accurate.

The way to determine which thickness of gasket is needed is by piston protrusion.

You measure the amount that the pistons protrude from the top of the block at TDC, and this measurement then relates to the gasket thickness (number of notches, and there are 2 different systems for this)

Make sure you get it right too, as a too thin gasket will mean pistons hitting valves. Too thick and the compression will be poor, resulting in bad starting and poor efficiency.

f00lzz · Post by **f00lzz** » 11 Jul 2006, 16:49

I think that they use the old gasket plus the knowledge of how much they skim from the head to determine the required thickness of the new gasket. Obviously if you havent got the old gasket then the method using piston protrusion should be used

Allanxantia · Post by **Allanxantia** » 11 Jul 2006, 19:28

The issue is time. I don't have time to take the head off till Saturday and then won't be able to get it machined until some point next week and re-assemble next weekend. Pain. Was hoping to get it all this weekend. Unless anyone knows a 24hr machine shop in Glasgow!

fastandfurryous · Post by **fastandfurryous** » 11 Jul 2006, 20:28

f00lzz wrote:I think that they use the old gasket plus the knowledge of how much they skim from the head to determine the required thickness of the new gasket. Obviously if you havent got the old gasket then the method using piston protrusion should be used

I have a feeling that should be vice-versa. The piston protrusion method is much better to use, will be more accurate, and actually measures the critical dimensions. The "look at the old gasket" method should be a backup if you have no method of measuring protrusion.

after all... you wouldn't want to go to all the trouble of doing the work, and then find that when you crank over the engine after refitting the head that the pistons touch the valves.

f00lzz · Post by **f00lzz** » 11 Jul 2006, 22:08

Yep you may be right... but I bet that shipping the block as well as the head to the machine shop will put the project beyond most peoples (running an old Xantias) pocket. The idea of 'examining' the old gasket is to determine which type/thickness/notches etc.... armed with that info. a relatively simple calculation gives you the new gasket type/thickness/notches req'd.

fastandfurryous · Post by **fastandfurryous** » 11 Jul 2006, 22:15

f00lzz wrote:Yep you may be right... but I bet that shipping the block as well as the head to the machine shop

Why on earth would you need to ship the block to the machine shop?!

You siimply measure the piston protrusion! Either accurately with a DTI, or (very slightly) less accurately with a straightedge and feeler gauges. Given that you should clean the block surface anyway, and it's a good idea to clean the piston crowns, it's a 5 minute job while you're already there.

Post by **Peter.N.** » 11 Jul 2006, 22:16

Citroen only do one thickness of gasket for the 2.1td! They call it a 'repair' gasket.

f00lzz · Post by **f00lzz** » 11 Jul 2006, 23:20

fastandfurryous wrote:
f00lzz wrote:Yep you may be right... but I bet that shipping the block as well as the head to the machine shop
Why on earth would you need to ship the block to the machine shop?!

You siimply measure the piston protrusion! Either accurately with a DTI, or (very slightly) less accurately with a straightedge and feeler gauges. Given that you should clean the block surface anyway, and it's a good idea to clean the piston crowns, it's a 5 minute job while you're already there.

Kowalski · Post by **Kowalski** » 11 Jul 2006, 23:32

Will the piston protrusion change between the engine being made and you taking it's head off? If it has changed, you've got some fairly bad wear somewhere on your bearings. If it doesn't, all you need do is count the notches in the old gasket and get a new one with the same number of notches. A lot of people won't have the correct equipment to measure piston protrusion and its a lot easier to quote notches and causes less confusion.