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MG MGF Technical - Serious Head Damage. Calling for speciallist

Hi,

some interesting pics of a damaged VVC cylinder head from a German newbee. He's sounds like an experianced mecjanic or student and he's just working at the engine repair. He asked at our German Forum for the measures to grind the head.

OK, we told him all we know and sent him the required _documents_ about engine overhaul.
Managed to post some pics from him.

Here we go.
I think it's strange that the up to 0.3mm deap marks from the gasket pressure ring are uneven. Strong at the outlet valves and less or nothing at the inlet valves.
He had measures to the height difference between liners and block and found at
Cylinder 1to3 = 0,05 mm
Cylinder 4 = 0,02 mm
instead of the usual 0.1mm at each.
I think this means the liners have dropped into the block ?
Why?

http://www.mgfcar.de/hgf/ch_100_1401.jpg
http://www.mgfcar.de/hgf/ch_100_1402.jpg
http://www.mgfcar.de/hgf/ch_100_1403.jpg

Over to comments, recomendations.

Regards
Dieter
PS if of interest, the German thread is:
http://www.roadstervision.info/mgboard/showtopic.php?threadid=4095
(copy@paste should work)
Dieter K.

Hi Dieter,
interesting pictures... My 10 cent on the following scenario: Looking at the waterways on both inlet and exthaust side there is something not right.
Has the exthaust side upper coolant channels seen any water at all?
Airlock, or just gas leakage from the cylinders blowing away the coolant? Look at the shiny alu and not a trace of sediments .
Compare to the inlet side with traces of at least something sedimented in the waterchannels.
If so the outlet (exthaust) side has got much more heat during the time the engine has been running = soft alu at that side and hence deep marks from the fire-rings in the head-gasket.
At least a possible solution to the damage...

BR, Carl.
Carl Blom

This is not uncommon. The inlet side of the head is constantly cooled by the incoming charge.

The impressions left by the fire rings do look quite severe. I would be checking the hardness and flatness of the head .
A Richards

I think the mean question should not be why it was happened.
The question is how to get the engine back alive.
Is it enough grinding the head, perhaps replace the liners or anything else or is this the typical sign of a death of an engine?

Greeting
Torsten

Torsten Ohms

Torsten,

To understand how to get the engine back alive, one first needs to understand why the problem has ocurred.

So, you must first determine how hard the head is and how flat it is, then check the build manual to see if enough of the surface can be removed.

The liners do sound low at the measurements quoted about and should really be re-seated to somewhere between 4-6thou proud of the block deck.

I seriously doubt that the engine is toast.
A Richards

Yes, understanding what problem had occured.. One step after the other.
A German MGR speciallist said at our Forum already:
"Forget the engine, cause the liner seats may have dropped and the liners are sitting cambered in the damaged bore ..."

Measuring hardness.
OK, to get results about aluminium softening due to overheating.

However, you mentioned how many of the surface could be removed.
The manual says 0.2mm only. Do you think all the 0.3mm marks could be grind off if the total head height remains still inside the stated height of 118,95 to 119,05 mm (@new head) ??

> liners ... re-seated to somewhere between 4-6 thou proud of the block deck

Re-seating, OK, I understand, ... but how ?
Please explain, there's IMO no way to put in shims or anything like that ??
. How can that be done ?
(I know there should get any special seal stuff to the middle step?)

Does he need new liners as well ?
May the old have got mis-aligned ?

Regards
Dieter
PS. I'm in touch with Torsten at the other Forum, though.
Dieter K.

Hi,

just an update about what happend in the last days.

RE: Re-seating
*one* reliable? engine block repair would be to re-align the liners. Remove the liners and aluminum should be weld to the existing liner seat. Then mill the seat from new. This process is said to having been suggsted to MGR by any engine auverhaul company, but wasn't found economic by MGR.

However, the unlucky owner found the risk for an engine repair to high. He's looking for a second hand VVC engine now.

So if anyone could supply a second hand VVC engine to the Stuttgart area ;)
Drop me a line.

Another bunch of _nice_ images to follow if the thread is still alive on this weekend.
Dieter K.

Is it an early or late VVC? does it have the remote thermostat and the oil cooler or not?
cheers
Pete C

Hi,

Well, in my admitted ignorance...

I'm trying to get my head (!) around how the head has fire ring depressions on one side only. You can't push one side of the liner into the head on its own, the entire liner has to go into the head, doesn't it? Any depression must go around the full circumference.

Or does the head expand, and warp, so that there is a larger gap on the inlet side and the exhaust side gets hammered.

Alternatively some misalignment with the head and block, so that the liners are more proud on the exhaust side? The head surface machined at an angle? It's difficult to conceive that anything could be this bad.

I dunno, just trying to find a crazy theory to fit the evidence.

Regards, Kes.
Kes

It is the hot gases passing between the gasket fire ring and the head that "carve" the aluminium.
Pete C

Hi,

Pete, nothing has been said about gases passing the fire ring. If they did (and hence straight into the water jacket) there would be other effects, such as loss of coolant, subsequent HG failure, etc.

I have assumed (with no real reason) that the depression is caused by the liner hammering or fretting into the head material. I would have thought that blow-by would show as quite marked erosion in particular places, not graduating around an arc on all the liners, as the photos show. But I could be mistaken.

By the way in my previous post I meant 'The block surface machined at an angle', not the head. The head would pull down square - within reason! This theory needs the liners to be slightly more proud on the exhaust side than on the inlet side.

Regards, Kes.
Kes

Hi,

the engine is late MY2000 _with_ steel dowels.
No evidence for unever proud.

And the owner found traces of mayo.
http://www.mgfcar.de/hgf/mayo_100_1809.jpg

However, I think the hammering or fretting theory might be reasonable.

I'm still thinking about stress due to uneven supplied heat to the block and head.

It's all on the hot engine side, is it ?
How about this disaster sequence within a few couple of minutes:
Coolant loss *whyever* and no coolant present --> uneven and huge heat to the exaust side --> stretch bolts get longer due to expansion from heat --> clamp force to gasket gets low or lost --> (head aluminum looses hardness)? --> liners or gasket ring starts hammering at the gap ..... --> at any time the driver woke up, pulled over and stopped.

Another bulk of images.
http://www.mgfcar.de/hgf/kolben1.JPG
http://www.mgfcar.de/hgf/kolben2.jpg
http://www.mgfcar.de/hgf/kolbenbank.jpg
http://www.mgfcar.de/hgf/kurbelwelle.jpg

Spot on a liner from below
http://www.mgfcar.de/hgf/liner_von_unten1.jpg
Liner condition looks fine. (Notice steel dowel)
http://www.mgfcar.de/hgf/laufbuchse_innen.jpg

http://www.mgfcar.de/hgf/vvc2.jpg

Regards
Dieter


Dieter K.

more like:
Coolant loss *whyever* and no coolant present --> uneven and huge heat to the exaust side --> aluminium block get longer due to expansion from heat --> clamp force between gasket and liners gets low or lost --> (head aluminum looses hardness)? --> liners or gasket ring starts hammering at the gap ..... --> at any time the driver woke up, pulled over and stopped
Pete C

Hi,

<-- stretch bolts get longer due to expansion from heat -->

The alloy cylinder and head will expand at approx twice the rate of the steel stretch bolts...

<-- clamp force between gasket and liners gets low or lost -->

The clamping force on the exhaust side would thus be greater than on the inlet, and 'the gap' less...

Maybe the inlet side 'lifts' a little under this proposal, or the exhaust side is pulled down even harder on the liners.

I once calculated that the difference in expansion rate between the block/head and the stretch bolts was equivalent to tightening the bolts at least 90 deg every time the engine was warmed up, and then releasing them when it cooled. With a cooler inlet side the difference would not be equal across the head. Even without the disaster sequence outlined above this could cause fretting on the exhaust side.

Dieter, you didn't say why the engine was dismantled in the first place.

Pete, shouldn't everyone in NJ be in bed?

Regards, Kes.
Kes

Kes,
the block is aluminium, liners and bolts are steel/cast iron
block raises, bolts stretch and liner doesn't keep up...

oh, I'm at work, BTW.
Pete C

This thread was discussed between 15/01/2005 and 20/01/2005

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