Extra thick head gasket for Mondeo Ecoboost?

[kerplunk]

Mignon said:

If as you say the head is not too warped at the top and is now flat at the bottom then I suggest you give the valves a quick lap to check their seating and slap it back on.

Aargh I was half hoping you would say that and half hoping you wouldn't.

When it's done and back on the road I want to feel confident the engine is sound and isn't going to sting me again a few thousand miles down the road and putting a bent cylinder head on a new short block seems (to me) like begging to be seriously disappointed. You wouldn't be the first to tell me I'm worrying about it too much though. Before I did the oven thing some friends told me to just torque the exhaust camshaft down and if it still spins freely then don't worry about it. Which I did and it does (spin freely).

Is that a good measure of 'not too warped at the top'?

[Mignon]

kerplunk said:

Aargh I was half hoping you would say that and half hoping you wouldn't.

When it's done and back on the road I want to feel confident the engine is sound and isn't going to sting me again a few thousand miles down the road and putting a bent cylinder head on a new short block seems (to me) like begging to be seriously disappointed. You wouldn't be the first to tell me I'm worrying about it too much though. Before I did the oven thing some friends told me to just torque the exhaust camshaft down and if it still spins freely then don't worry about it. Which I did and it does (spin freely).

Is that a good measure of 'not too warped at the top'?

Yes, it sounds ok.

[kerplunk]

Mignon said:

kerplunk said:

Aargh I was half hoping you would say that and half hoping you wouldn't.

When it's done and back on the road I want to feel confident the engine is sound and isn't going to sting me again a few thousand miles down the road and putting a bent cylinder head on a new short block seems (to me) like begging to be seriously disappointed. You wouldn't be the first to tell me I'm worrying about it too much though. Before I did the oven thing some friends told me to just torque the exhaust camshaft down and if it still spins freely then don't worry about it. Which I did and it does (spin freely).

Is that a good measure of 'not too warped at the top'?

Yes, it sounds ok.

hmm in which case calculating compromise gasket thicknesses might be back on the agenda, when you've got a minute - plenty to do, no rush

[kerplunk]

Penelope Stopit said:

kerplunk said:

The result of the 2nd attempt is the same as the first attempt - no perceptable change. For the record the head was in the oven for 3 hours and for 2 of those hours the temperature was maintained at 209-215C (it took the best part of an hour to reach 200).

I think that's probably the end of me trying to get something out of the old engine and I'm now in a waiting game for a 2nd-hand engine.

Is this lack of success down to skimming before cooking or are there other possible reasons?
There is no way I'm running up a big electric bill in cooking heads

I dunno, whilst the skim was 'large' in some terms, against the whole mass of the cylinder head it's tiny and difficuilt to see how that would make a significant difference.

[Mignon]

kerplunk said:

hmm in which case calculating compromise gasket thicknesses might be back on the agenda, when you've got a minute - plenty to do, no rush

A number of things need to be considered. First of these is to restore the compression ratio. Most combustion chambers, except for hemi heads like the CVH, do not have an area the same as the bore. They have squish areas so 1 mm skimmed off the head does not equal the same volume as a gasket 1 mm thicker. On average the chamber area is about 85% of the bore area and also gaskets tend to be a couple of mm bigger than the bore to allow for oversizes so generally 1 mm off the head = 0.8 mm on the gasket thickness. You can measure your combustion chambers and work out how much of the bore area they represent.

You say 28 thou or 0.7 mm was skimmed off in total. Most of that will have been on the end cylinders. Not much will have been taken off the centre two. The average taken off each end cylinder will be about 3/4 of the max skim at the very ends of the head so let's say 0.5 mm. Multiply that by 0.8 and we get about 0.4 mm. So a 0.4 mm thicker gasket should just about restore the CR of the end cylinders and lower the CR of the centre two somewhat.

If you knock off a bit more to split the difference then a 0.3 mm thicker gasket will raise the CR of the end cylinders a bit from standard and still reduce the CR of the centre two but not by so much. I might be tempted to go for this as a compromise.

Next consideration is piston to valve clearance but this is normally at least 3 mm on petrol engines and 1 mm to 2 mm on diesel ones. You aren't going to get contact but while the head is stripped you can measure it. Bring a piston to TDC. Lay the head on the block on the old gasket with a valve in one exhaust and one inlet guide. Nip it down with a couple of bolts. Move the valves up and down to see how far they have to travel to hit the piston. You can put an elastic band or a clothes peg on the valves to stop them dropping out while you fit the head.

If you have plenty of valve to piston clearance then a gasket about half as much thicker as what was skimmed off the head should do you.

[Penelope Stopit]

kerplunk said:

Penelope Stopit said:

kerplunk said:

The result of the 2nd attempt is the same as the first attempt - no perceptable change. For the record the head was in the oven for 3 hours and for 2 of those hours the temperature was maintained at 209-215C (it took the best part of an hour to reach 200).

I think that's probably the end of me trying to get something out of the old engine and I'm now in a waiting game for a 2nd-hand engine.

Is this lack of success down to skimming before cooking or are there other possible reasons?
There is no way I'm running up a big electric bill in cooking heads

I dunno, whilst the skim was 'large' in some terms, against the whole mass of the cylinder head it's tiny and difficuilt to see how that would make a significant difference.

Ok thanks for your input, it's looking like a no goer for me but on the other hand I could if needed try it the once using your method of checking the true temperature

[PeterBurgess]

A word of caution with regard to heating up heads, usually it takes some sort of impact, but we have seen valve seats move when the heads are very hot, this shows up as a line twixt seat and head in the chamber and/or in the valve throat. These are usually ok to tap back into place but may not be good idea to recut seats or run it if the insert is not 'home'.

[Penelope Stopit]

PeterBurgess said:

A word of caution with regard to heating up heads, usually it takes some sort of impact, but we have seen valve seats move when the heads are very hot, this shows up as a line twixt seat and head in the chamber and/or in the valve throat. These are usually ok to tap back into place but may not be good idea to recut seats or run it if the insert is not 'home'.

Mine's a Peugeot XUD Diesel that I haven't removed yet and know nothing about how it's built, I did ask earlier in this topic if there was anything to take note of. This is all very interesting to me

[kerplunk]

Mignon said:

kerplunk said:

hmm in which case calculating compromise gasket thicknesses might be back on the agenda, when you've got a minute - plenty to do, no rush

A number of things need to be considered. First of these is to restore the compression ratio. Most combustion chambers, except for hemi heads like the CVH, do not have an area the same as the bore. They have squish areas so 1 mm skimmed off the head does not equal the same volume as a gasket 1 mm thicker. On average the chamber area is about 85% of the bore area and also gaskets tend to be a couple of mm bigger than the bore to allow for oversizes so generally 1 mm off the head = 0.8 mm on the gasket thickness. You can measure your combustion chambers and work out how much of the bore area they represent.

You say 28 thou or 0.7 mm was skimmed off in total. Most of that will have been on the end cylinders. Not much will have been taken off the centre two. The average taken off each end cylinder will be about 3/4 of the max skim at the very ends of the head so let's say 0.5 mm. Multiply that by 0.8 and we get about 0.4 mm. So a 0.4 mm thicker gasket should just about restore the CR of the end cylinders and lower the CR of the centre two somewhat.

If you knock off a bit more to split the difference then a 0.3 mm thicker gasket will raise the CR of the end cylinders a bit from standard and still reduce the CR of the centre two but not by so much. I might be tempted to go for this as a compromise.

Next consideration is piston to valve clearance but this is normally at least 3 mm on petrol engines and 1 mm to 2 mm on diesel ones. You aren't going to get contact but while the head is stripped you can measure it. Bring a piston to TDC. Lay the head on the block on the old gasket with a valve in one exhaust and one inlet guide. Nip it down with a couple of bolts. Move the valves up and down to see how far they have to travel to hit the piston. You can put an elastic band or a clothes peg on the valves to stop them dropping out while you fit the head.

If you have plenty of valve to piston clearance then a gasket about half as much thicker as what was skimmed off the head should do you.

Many thanks for that detailed reply - fantastic.

[kerplunk]

PeterBurgess said:

A word of caution with regard to heating up heads, usually it takes some sort of impact, but we have seen valve seats move when the heads are very hot, this shows up as a line twixt seat and head in the chamber and/or in the valve throat. These are usually ok to tap back into place but may not be good idea to recut seats or run it if the insert is not 'home'.

I'll look out for that - cheers

[Mignon]

kerplunk said:

Many thanks for that detailed reply - fantastic.

You are very welcome.

[kerplunk]

Well thanks for everything but it's all moot now. Yesterday a 2nd-hand engine appeared on ebay - first time I've seen one since the meltdown in August - so I've pounced on it. Hopefully it's a good 'un, or I'll be be back! vroom vroom

[Mignon]

Good luck with it.