Missing Miners !!

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

Post Reply
gjb02
Posts: 287
Joined: 20 Jul 2002, 20:37
Location: United Kingdom
My Cars:

Missing Miners !!

Post by gjb02 »

Is anyone missing any miners? Or pot-holers? No, shame I just found a group in the corrossive pitting in my cylinder head!!![:(!]
My question is, how much can be skimmed off a head?? The main part of corrosion is adjacent to the No.3 cylinder at the edge of the water gallery, and is quite deep pitting. I don't work in thou so I'd have to say it's close to 0.3mm - 0.7mm deep, and is the reason for my misfire and coolant pressurisation. Can this amount be skimmed off a head, without effecting the compression ratio too much? My local engine centre decided to take the weekend off starting this lunchtime!!! A very bad coincidence as I have only just got the head off, to take around. So no answers there.
Please help forum members!!
Yet another reason to keep your coolant changed regularly! The previous owner must have believed water was sufficient. Probably the worst head I have seen in some time![V]
User avatar
AndersDK
Posts: 6060
Joined: 21 Feb 2003, 04:56
Location: Denmark
My Cars:
x 1

Post by AndersDK »

Gareth -
I can't make the decision for you - but from own experience a pitting up to 0.7mm is really pushing the limit for what's possible to grind off.
From memory I believe that the PSA XUD (diesel) engines have a HG thickness range of approx 1.5 - 2.2mm.
My guess is it's pretty much the same for the XU (petrol) engines - which means you MAY just barely save your CH by a standard machining process. Even if the machining should exeed the limits by some 0.05 - 0.15mm - as this would be fairly within the spread of good working conditions - all tolerances considered.
Cross my fingers for you untill exact figures are thrown on the table here - as a machined CH plus new HG & bolts in no way is a catastrophic expense. Compared to a new CH that is.
gjb02
Posts: 287
Joined: 20 Jul 2002, 20:37
Location: United Kingdom
My Cars:

Post by gjb02 »

Am I right in thinking that, valve clearance aside, if the head is skimmed and a standard gasket is used, the compression ratio would increase?? Would this in turn put more pressure on the head gasket, bearings, etc. But would it not also increase performance?
I suppose my main worry is the valve clearance issue.
Haynes says the max difference in head height (132.00mm+/-0.15mm to 131.85mm min) is 0.30mm. If the skimming exceeds that, are the valves going to hit the pistons??
The new gasket is 1.45mm as was the old. I don't know if there is a thicker gasket for the 16v. Do I really need it??
Any ideas??
oilyspanner
Posts: 1246
Joined: 26 Oct 2003, 16:08
Location: United Kingdom
My Cars:

Post by oilyspanner »

Compression will not change as the head is flat, you may find yourself looking for some very thin shims though.
Stewart
jeremy
Posts: 3959
Joined: 20 Oct 2002, 16:00
Location: Hampshire, UK
My Cars:
x 2

Post by jeremy »

A good engine reconditioner will probably be able to build up the eroded areas of the head by welding and then re-surface the head. I think this is a very common job as eroded waterways etc are very common on alloy heads.
jeremy
gjb02
Posts: 287
Joined: 20 Jul 2002, 20:37
Location: United Kingdom
My Cars:

Post by gjb02 »

Thanks Jeremy, I had an idea that wassomething that could be done. Do you have any idea of the costs involved in this welding process??
User avatar
AndersDK
Posts: 6060
Joined: 21 Feb 2003, 04:56
Location: Denmark
My Cars:
x 1

Post by AndersDK »

Gareth -
In principle this alu-alloy welding is just a filling process - using a special electrode - or wire - utilising a standard arc welder.
It's in no way a costly process - only the time involved getting the tool ready - and cleaning out the pitting from the head - would be the expense added to the milling/machining process.
My guess approx 1 extra labour hour.
So at least Gareth - you may sleep well with peace in mind untill monday morning where you have a chance to talk to your local engine centre.
And thanks from me also to you Jeremy - for remembering this rather simple & common repair method [8D]
- it's written behind my ears now [;)]
jeremy
Posts: 3959
Joined: 20 Oct 2002, 16:00
Location: Hampshire, UK
My Cars:
x 2

Post by jeremy »

Anders
It used to be common practice to pre-heat the head before welding but I don't know if that is still considered necessary using modern TIG welding. I should imagine the most difficult part of filling a gasket face is to ensure there is no erosion or undercutting at the edge of the new metal. I recall a garage proprietor showing me a Porsche head he had welded after it was damaged by theives who hit something and smashed the radiator and continued driving. He didn't have the correct oven and I seem to recall used a domestic oven and I think used gas to do the welding.
Jeremy
Post Reply