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MG MGA - Blown Engine
|Driving 100 miles to the shore this weekend, I was about 50 mles in and oil preasure started to drop to 30 lb. I thought maybe the because it was 95 degrees this day, and I was pushing it at 70 MPH, that it was thinning out the oil. Soon the dreaded knocing and loss of power. When I pulled over there was a lot of oil dripping out both from the cotter pin and between the engine and rear plate. I let it cool and started again and stil bad grinding noise. I suspect the rear crank bearing. Any suggestions?|
Sorry to hear about that. I am not an expert, but as soon as I read the line about a large amount of oil coming out the cotter pin hole I was thinking broken crankshaft Sadly it seems to happen a lot. I wonder if every one fails eventually, and you never know when your time will come...
On return from Silverstone I had the exact same problem, I am sorry to shock you but if you have a look at the image you will see the horror that is my crank. Anyone in the metalergy bus. may be able to explain. My engine is with Oselli engineering here in the U.K and so far no further problems have been found with the rest of the engine parts,(so far). Maybe it is a feature of the 3 bearing engine that the rear of the crank is vulnerable, however for the crank to go in the place that mine has, seems to me to point to a materials problem.
1957 1500 standard spec.
trying to upload photo but at 1.08meg I am told the image is to large, tried to compress into a zip file but still to big, help!
|OMG - my engine is the original untouched 1600 with 80,000 km on it - does that mean mine is going to go any minute? the oil pressure is 70 cold and 40 at tickover but drops to 60 when hot at 3000rpm but about 25 at tickover.|
GM Adams - have you got access to Photoshop to reduce your photo file size?
|Is your image file a BMP file or a JPG file? Open it with Microsoft Paint and save it as a JPG file if it is a BMP file, also save it again even if it is already a JPG file. Then check the size.|
|If it is my crankshaft that is broken should I assume the block is shot and I need a new engine?|
|Several years ago while I was driving along rather gingerly I got a very noticeable vibration from the engine and pulled over and checked for tight spark plugs etc. The engine started fine but vibrated severly upon acceleration(I hate calling toll trucks) so I made it home in 3rd. gear going about 20 mph. My 1500 engine just had the crank ground and other things done by a VERY well known MG expert about 2500 miles before this happened. I pulled the engine and took it to a local machine shop and as he was taking it apart he said everything looks good until he tried to pry the crank out. There's your problem, flex in the crank which meant it was cracked. He examined it and said that whoever did the work didn't know what they were doing because-(I'm not sure I got the terminology right)- the journals where the connecting rods attach to were ground at a right angle instead of leaving a radius for extra strength. I figure the MG place that orginally did the work must have farmed this job out or had someone new do the work because it cost me a lot of money twice. I replaced this engine with a 1622 and have great driveability since.|
|O.K. saved the image as a JPG and it should now show the crack, I have turned the broken end of the crank the wrong way round and placed it in the block. Interesting to note the crystal like form to the metal at the left bottom, while the rest shows more of a shear. N Wessely writes "Journals were ground at a right angle instead of leaving a radius for extra strength". The picture clearly shows sharp edges. I have plus 30 pistons in this engine and now I think the journals may have been re-ground at the same time by the p.o.
|Any sharp right angle simply creates a stress raising point. The radius takes this factor out. Ensure future machinist is aware (they ought to be already).|
|There are comments about cracked crankshafts and the importance of correct journal radii in Malcolm Green's MGA Restoration Guide - the section on 'Inspection & Machining' He states that the 1600 crankshaft is more crack prone but doesn't give a reason. Maybe the extra engine power and therefore extra stres. Mike|
|G.M., -- I have one that looks exactly like your pictue, but at the other end between #1 main and #1 rod journals. See here: http://mgaguru.com/abused/ab1.htm|
I no longer have the part, but I do have the 4x6 glossy picture from 1989. I think the inside radius was okay on mine, but it broke anyway about 19,000 miles after a regrind (around 169,000 miles total).
30 to 50 years and hundreds of thousands of miles makes for lots of stress cycling on the crankshaft. It does about 400 million rotations for every 100,000 miles. I think that gives my car about 1.5 billion rotations of the crankshaft, but it's the 3rd engine and 5th crankshaft by now. I can't swear that any of them have gone more than 170,00 miles.
|The crank in my first MGA broke just like the one in Barney's picture. It was a snowy November night in 1975 and it broke as I drove through Glenwood canyon heading back to Denver. I spent the next 150 miles on the end of a rope behind a Ford pick up truck. All I had was a sleeping bag to stay warm as we went over Vail Pass through the Eisehower tunnel and down into Denver.|
|R J Brown|
Look on the bright side- You wouldn't have been any warmer if the car was running ;-)
The car was a coupe. Heater worked great! Year round :-(
To keep the windshield clear I had to open the vent window to blow on it. cold night.
|R J Brown|
|WMR Bill, Pennsylvania, USA |
If it is my crankshaft that is broken should I assume the block is shot and I need a new engine?
From my experience, no. I heard a loud clatter many years ago when I lifted off the throttle at about 70 mph. The noise went away when I accelerated and the oil pressure was good, so I assumed something was adrift in the clutch. After several removal and replacements of the engine to check the clutch and transmission, I pulled the pan and found a broken crank. Under power, it caught itself like a ratchet. I drove it 10 or more miles that way. Anyway, there was no damage to the rest of the engine. I put a used crank in and continued driving it.
|k v morton|
|My dad broke the crankshaft in my '59 sometime around 1965. He had the block align honed, the bores sleeved back to standard, and installed a reground crank. That engine was still running in 1991 after a lot of use. The blocks are pretty tough.|
|The 1500/1600 crankshaft is weak. I've broken them in half racing.|
The 1622 crank is much better and the 3 main MGB stronger yet.
This thread was discussed between 05/07/2008 and 10/07/2008
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