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MG MGA - Autopsy Results
|I finally removed the seized engine from my '59 1500 and tore it down. This is the engine that seized in '99, which my dad got in trade from somebody, which was kind of a question mark when we installed it in '92. The disassembly was both interesting, and enlightening. I went into it with several possible theories on what had happened. All of them turned out to be true to one extent or another, with the exception of the crankshaft not being broken, along with some things that I wasn't expecting. |
I got the sump off, and it was literally full of metal, including most of #4 piston, a wrist pin, part of #4 con rod, and miscellaneous bits. Only the top 3/4" or so of #4 piston was still in the bore. Besides the top, only a few pieces of the piston were bigger than 1" across. The block has a chunk of #4 cylinder missing at the bottom where it was impacted by the rod, along with a crack running down one side of the cylinder, which must have been the source of the coolant I found when I drained the sump. I'm pretty sure the head was good because I had it magnafluxed and it is now on the rebuilt original engine.
I'm not sure exactly where the failure started, but in addition to the broken piston, #4 rod was broken at the wrist pin, and the rod bearing was also seized on the crankshaft. A stray piece of metal jammed itself in to the gears at the distributor drive, and broke teeth on those gears. The distributor drive had to be pounded out of its hole with a punch. Several of the other rod bearings showed signs of failure, and none of the bearings looked healthy. Somebody cross threaded a coarse thread bolt into the crankshaft in place of the dog nut for the starter handle, so that is probably not worth messing with either. The compression rings on #3 piston were broken, so it was on its way out as well. The camshaft was seized in its bearings, and had to be beaten out. Lots of impact marks on the camshaft where the rod was flailing around.
Basically, the engine had lots of problems, any of which would have eventually been fatal. I knew it had issues soon after we put it in, so the moral of the story is don't keep pushing an engine that is on its way out, if you want to be able to salvage it later on. The first picture is the damaged #4 cylinder in the block:
|The second picture is the remains of the piston that were large enough to pick out of the sludge in the bottom of the sump, plus the wrist pin (also in the sump) and the top of the piston that remained in the bore:|
|The camshaft. If you look closely, you can see the chipped drive gear.|
|The busted connecting rod.
|I had a similar failure a few years ago, where a con rod failed and went through the side of the block. The engine still ran, albeit a little unevenly! I still have the piston somewhere (or at least the remains of it)|
I hope you're keeping the broken bits. I still have the piston crown and the short end of the crankshaft from my two engine failures. They are great fun to show people. Mine were both rebuildable, though.
|k v morton|
|I'm definitely keeping the piston and rod, but I'll most likely toss the camshaft. I dunno what I am going to do with the block, since it is a little bit large for a conversation piece. Maybe I can use it for the base of an equipment pedestal or something.|
|Del.. It's hard to determine froma photo but would it not be possible to install a sleeve?|
|Maybe, which is why I can't quite bring myself to throw it outside into the snow. Whether it is worth any heroic measures to save it is another matter, since 1500 blocks aren't exactly rare, particularly on my premises. I have a total of 3, counting this one, and only one car to put them in.|
|Del - From experience (not pleasant), I would guess that the gudgeon (or wrist) pin pinch bolt broke. This could be either the result of over reving the engine or an over torqued pinch bolt. I was told that this usually happened on #1 or #4 piston. Cheers - Dave|
|This is what I found when I tore mine down back in '70. I was able to drive it about 10 miles home; it only knocked when I backed off on the gas pedal.|
|k v morton|
I had a similar experience the same year with a Mk II - Crank shaft broken clean in half, but still cranked for 10 miles with a lot of rattling !
This thread was discussed between 04/03/2010 and 20/03/2010
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