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MG MGF Technical - Head stuck on steel dowels

Hi,

I'm changing the head gasket for the second time and I can't shift the head. It's stuck firmly on the steel dowels. Does anyone know how to shift it. Has anyone heard of this problem before?
Ken Waring

has the gasket actually failed?
Leigh Reid

Yes, coolant in the oil. No oil in coolant and compressions are fine all at around 155 ish. Changed the original gasket and plastic dowels for MLS and steel dowels after failure coolant to oil and oil to coolant, compression fine and no overheating. Head cgecked out OK. The head was tight on the dowels, dowels inserted to 11mm proud, but pulled down fine with the head bolts. Either I damaged the gasket somehow or the bubbling on the shim is the culprit. Anyway I won't know til I get it off.
Ken Waring

Hi Leigh,

A tap with a rubber mallet on the sides of the head might be enough to break the friction between the dowels and head.

When the head is off it's worth checking the liner heights. From memory between 2-4 thou projection is about right. Any lower and you're doomed to another failure.

Also check the head for flatness before re-fitting, you may not need to skim the head. If you do decide to do a skim, a bit of advice which I got from Dave Andrews is to peen the area of the firing ring. The surface of the original head is hardened skimming can expose small cavities in the casting and can lead to another failure. Peening is where you use a blunt punch to dent the area of the firing ring prior to skimming to remove the hidden porosity in the casting.

I even made a video which you might find useful http://www.youtube.com/watch?v=_G6RlW2HQtg

Good luck.

Tim
T Woolcott

Thanks Tim. The head came off easily the next day. Amazing what a night's sleep can do. :-)
The head is fine, only one place borderline 2thou. Three liners are good but one is high at the front and low at the back but not below the block. So I've risked it by using the seat it and let it sweat for a day method. Then slacken and re-tighten. Worked on the Nissan with a very similar MLS gasket. I tested the torque on the head bolts out of interest and came out at 44 lb/ft +/- 2/3 lb/ft except for one bolt which was 49 lb/ft next to the dodgy liner. Probably meaningless but I've got nothing to lose because if it goes again then it's a scraper. :-(

Ken
Ken Waring

Hi Ken,

Good to hear it came off in the end. May be with the bolt tension removed the interference fit with the dowels released a bit.

If the tensions on the bolts varied it might be worth changing them too. If they've past their elastic point when re-tightened they won't apply the right tension. You can check the bolts by measuring them but I don't have details of their original lengths.

The fun bit is putting it back together again. I seem to remember that the most frustrating part was getting the lower bolt of the inlet manifold back on. You need bendy arms!

Good luck

Tim
T Woolcott

> seat it and let it sweat

ok, google failed me, what's that then?
Leigh Reid

Yep, changed the bolts, not the same quality as the originals. Successfully completed the first 100 miles so far so good.
Interesting, no bolts on the inlet manifold all replaced with studs, piece of cake. Still need bendy arms because being a tad lazy I left the fuel rail attached to the manifold. Saves a lot of time.

I vacuum tested then vacuum filled the coolant. Then pressure tested. This can let you gestimate the air left in the system, air compresses but the coolant doesn't.

Just live with the fear for a few weeks now.

Ken Waring

Leigh, tighten the head down let it sit like that for day. Then slacken off and repeat the whole procedure. This is the recommended Nissan method used on the SR20DE, similar engine with a very similar MLS gasket. I chose to do this because having fitted an MLS gasket the head had a leak, coolant to oil only, with no obvious failure point. Led me to believe the problem was insufficient compression of the gasket around the waterways and oil ways somewhere. Anyway the engine is singing sweetly now. When they go like this you can almost forgive them anything. ALMOST, this engine is in the last chance saloon if it goes again then sadly it's goodbye.
Ken Waring

This thread was discussed between 09/07/2013 and 22/07/2013

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