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MG MGF Technical - HGF - It did happen!

Sometime last year i wrote about the sudden overheating of our 95 MGF 1.8i. Replacing the expansion tank cap cured the water blowing out and the car ran well until a couple of weeks back. The missus noted excess white smoke when cold, and lumpy running. Sometimes it wouldnt start at all. When hot the car would run fine.

It got worse though to the stage the heater went cold due to loss of water. Coolant colour was fine but the oil was now emulsified.

I whipped the head off this weekend and apart from the cambelt juming teeth when i tried to unto the bottom pulley (is this a known problem?) it was straightforward.

The head upon inspection was fine, the HG had been replaced with newer type and metal dowels, its pretty much flat aswell, no way you could get a feeler gauge under a metal rule.

Checked the block and liners, these also appear fine, no gaps and the liners are level with the block face, it was all very clean...

So the question is, what caused my HGF failure before i put it all back together?

Was it simply a case of its first overheating last year caused the start of the problem which with continual use started to get worse? I hope it is this one but i would expect signs of warpage on the head, but there are none!

Is there anything else i should look for?

Gareth
Gareth Kidman

You mention that the liners are level with the block.This might be the problem,the liners should be above the block level by something like 0,125mm. At work ,so doesnt have the correct figures at the moment. Someone else will probably fill in the liner limits.

BR, Carl.
Carl

>>Someone else will probably fill in the liner limits.

Dave Andrews posted this on one of the other current HGF threads.
Dave Livingstone

Yes, here it is:

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&mode=thread&subject=69&source=T&thread=200602110717289578

Dave Andrews, MK, DVAndrews@aol.com
The correct liner height is 4-5 thou (0.1mm to 0.125mm). Uneven liners can cause two types of failure, leaching of combustion gases into the coolant with resulting pressurization of the coolant, (this can also occur when liners are overall too low) and break away of the elastomer seal round the bolt holes/at the edge of the head between the cylinders where the liner heights differ.

Dave Livingstone

If you can't tell the liners are proud of the block then you prolly can't tell the head is flat either, you should get a machine shop to put their straight edge against it.

Cambelt jumping teeth, I guess this means you tried to lock the cambelt by locking the cams instead of locking the crankshaft?

time to change the tensioner (a good idea anyway) and waterpump then(not designed to take that kind of side load).

Will Munns

Thanks for the replies.

Nothing wrong with my own straight edge, i will check properly once the block has been properly cleaned.

So they should protrude 4-5 thou above the block face? What if they are level?

Failure of gasket was definatly break away of the elastomer seal round the bolt holes.

What is the best way to lock the crank?

Gareth
Gareth Kidman

Sorry to hear the bad news Gareth.

Like Carl et al I was struck by the observation that the liner heights were level with the deck of the engine block. As posted, they should be 0.100 to 0.125mm proud.

If they are so low, you may need to visit a machine shop as Will suggests to get the block 'decked'.

Or perhaps have a chat with Dave Andrews and get some advice (he's based in Milton Keynes). Mike Satur could be worth a call too - he's up in Rotherham...
Rob Bell

>>Like Carl et al I was struck by the observation that the liner heights were level with the deck of the engine block. As posted, they should be 0.100 to 0.125mm proud.

<<<

As we all know access isnt exactly great to the block and its hard to visually tell if the liners are in fact 4-5 thou proud, they definatly do protrude above the level of the block as a quick 'rock' test with my trusty steel rule reveals. Not exactly scientific but i have run out of daylight and i dont have my feeler gauge.

Gareth
Gareth Kidman

You could be in luck then Gareth. Fingers crossed that when you come back to check in daylight, the liners will be within spec.

Regarding the head, specialists often recommend that the head is hardness tested. This is very relevant here, with the history of over heating: this can lead to the alloy loosing its quench and going soft.
That said, if there are no evidence of any rings around the combustion chamber, then again, you may have been lucky and got away with it.

Thereafter, replacing the head gasket is reasonably straightforward - but clearing all that mayo isn't a particularly enjoyable task.
Rob Bell

"The missus noted excess white smoke when cold, and lumpy running. Sometimes it wouldnt start at all. When hot the car would run fine.

It got worse though to the stage the heater went cold due to loss of water,

Is there anything else i should look for?"

Pressure test the head to check for cracks.Look for signs of 'steam' cleaning in the ports/head/pistons. check for coolant leakage across the inlet manifold.
mike

As mike advises double check the inlet manifold gasket Gareth.

Particularly prone to failure on early F's

When it starts going it leaks into inlet tract causes dampness that manifests itself as steam and misfires on starting.
It happened on #4 cylinder on our ex '95 F.

If not noticed in time the water level will drop till you overheat and HGF blows :-(

jt (Happy St Davids Day)

John Thomas

Manifold gasket inspected when it was taken off and looked fine, its being replaced anyway so can rule it out.

Is it worthwhile taking out the ball bearing valve?

Gareth
Gareth Kidman

There are two of these - the so-called jiggle valves. Worth removing? I wouldn't be so sure. If they are working fine, I'd keep them in - but it would be interesting to hear Mike's opinion on this.
Rob Bell

This thread was discussed between 27/02/2006 and 02/03/2006

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