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MG MGA - Cause of death

http://www.rawlinsbrothers.org/mga/images/seizure.jpg

Well, I guess this finally explains why it quit running all sudden like. Luckily, that was my "spare" engine. Pending straightness and lack of cracks, it is going to donate its cylinder head to the original engine.
Del Rawlins

Looks like typical damage caused by pre-detonation. This is caused by having your timing too far advanced, or a mixture that is too weak. Having said that it also looks like the piston has hit the head too, so I am guessing a con rod has let go too.

You may well find that other parts of the engine are still OK - Cam, crank, small bits, so don't just junk the whole thing.
dominic clancy

I didn't notice any signs of contact on the head, but I'll look it over more closely when I am out in the shop again. No matter, because it has to be taken apart and cleaned anyway, then I am going to check for cracks, most likely using dye penetrant. I should be able to get a couple of expired cans from work that we can no longer use on aircraft.

The engine was one which my dad received in trade many years ago, with unknown history. It was swapped in (1992) so I could keep driving the car while the original was overhauled, to be held aside for eventual restoration. Got mostly done with the original engine but never got back to it or the restoration until now. The oil pressure with the spare was never great and the seizure in '99 came as no huge shock. At that point, I was only driving it a few times each year anyway.

I'll be happy if just the block and main bearing caps are salvageable. The crank already has one strike against it, in that the threads for the pulley bolt are horribly cross threaded, which I discovered when I attempted to install the correct bolt for the starter handle. Rather than mess up the new bolt, I just threaded the existing one back in. Even if a con rod didn't break, I'd never be able to trust them again after a sudden stoppage. I won't know for a few years since I'm not going to do anything else with this engine (other than remove it) until after the car is finished, using the original engine.
Del Rawlins

You were right, it looks like it did hit the head after all, since the layer of carbon was slightly disturbed. I didn't notice it before, but the #1 and #4 pistons are at different heights, so the con rod has definitely let go inside. Therefore all bets are off as to salvageability of the block, but it will be a few months at least before I get the rest of the engine removed. Another thing I found last night that I thought was interesting, was there was no thermostat installed.
Del Rawlins

Del,
Even if a rod failed doesn't mean the block is not useable. Unless it punched a hole in the block or severly scored the cylinder wall, chances are excellent that it is OK. These engines are pretty tough.

Good luck,
GTF
G T Foster

B-series engines are remarkably durable.
I once had a customer tow in an MGB that had stopped running. "The oil light came on so I kept driving to find a gas station". She didn't make it.
It had 0 compression in one cylinder and when the head was pulled all that was visible was a con rod with a wrist pin through it. When the pan was removed there was a pile of mangled aluminum and rings inside.
The owner was a student and had very little money so we gave everything a good cleaning and honed the cylinder which was marked but not scored. We took a used piston that was found underneath a workbench, put on new rings, changed the oil and sent her on her way. Compression and oil pressure were acceptable and she got at least a couple of years of use out of the engine.

Rich
R.J. McKie

If the height difference between the pistons is only small, it could just be a big end problem. If there is no hole in the block, the block is probably OK.
dominic clancy

>when the head was pulled all that was visible was a con rod with a
>wrist pin through it. When the pan was removed there was a pile of
>mangled aluminum and rings inside.

Damn. Well, I'm not going to count on anything until I pull the engine and the pan off, which won't be for a while yet. I didn't see any external signs of damage on the sides of the block, so I am still holding out hope. I may even be able to use a new set of +.020" pistons in it that I have had sitting in a box for the last 14 years, since it turns out the bores are standard size. But this engine is a low priority, since the original is on a stand and is what will be going back into the car when the time comes.
Del Rawlins

This thread was discussed between 27/09/2006 and 30/09/2006

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