Engine Failure - Thoughts?

[mogdobz]

Well my engine packed up today! It was fine this morning. Started without complaint later in the day but after I pulled away it quickly developed a knocking noise - this rapidly deepened and power dropped away. Within fifteen seconds and about the same number of feet traveled I knew it wasn't getting anywhere. I pulled over and parked. The engine was running very unsteadily at any choke setting - a bit like it was running too lean. The visceral juddering grumble and knocking suggest something fatally mechanical, but I'm no expert. Any thoughts on what it could be?

[mowogg]

Possible head gasket. Can you check the compression? If you don't have a guage can you see how easy it is to turn over on the handle?

[oliver90owner]

Are you sure it’s not gearbox (or even clutch) related? Maybe your whining gearbox has finally said “enough is enough”?

If a head gasket, every second stroke on the starting handle likely has no compression - the most often head gasket failure is between numbers two and three. If the gasket is proven to have failed, the cylinder head may need skimming.

[myoldjalopy]

I would expect more of a clattering noise were it the head gasket. An actual knocking could well be a broken crankshaft - its happened to me in the past - engine developed a knocking noise which increasingly got worse and it soon became obvious I was not going to be able to drive home.

[mogdobz]

Thanks for your thoughts, all. Tremendously helpful.

I doubt it's transmission related. The gearbox is a bit crotchety but I don't think it would reach into the motor and strangle itself - more likely a dying gearbox would do some big buzzing clanking grinding noises? Unless anyone knows any stories to the contrary!

I'll look around for mayonnaise in the radiator and lack of compression first. Then if it doesn't seem to be the head gasket I will investigate the innards.

I hear that draining and straining oil can be useful for identifying bits of metal indicative of catastrophic failure - can anyone say if this is or isn't a good idea? Particularly since I can't warm the oil up?

[mogdobz]

I would expect more of a clattering noise were it the head gasket. An actual knocking could well be a broken crankshaft - its happened to me in the past - engine developed a knocking noise which increasingly got worse and it soon became obvious I was not going to be able to drive home.

It did seem fizzy whizzy clattery, but I only forced it twenty yards down the road to park before taking it out of its misery and calling the AA. My main priority was turning the thing off

What sort of symptoms does a broken crankshaft generally produce?

[myoldjalopy]

From my own experience, a broken crankshaft was a loud knocking that progressively got louder, together with a loss of power. Your 'fizzy wizzy clattery' might well be head gasket - its hard to tell at a distance simply from a description of the noise. But a failed head gasket will not always result in mayonnaise in the cooling system, if the breach is between two cylinders. I had a head gasket failure between cylinders 1 and 2 once and the result was a clattering noise, rather than a knock, but no mayonnaise. So a compression test is a better way to go, initially.

[mogdobz]

From my own experience, a broken crankshaft was a loud knocking that progressively got louder, together with a loss of power. Your 'fizzy wizzy clattery' might well be head gasket - its hard to tell at a distance simply from a description of the noise. But a failed head gasket will not always result in mayonnaise in the cooling system, if the breach is between two cylinders. I had a head gasket failure between cylinders 1 and 2 once and the result was a clattering noise, rather than a knock, but no mayonnaise. So a compression test is a better way to go, initially.

Thanks very much for your advice. I checked today and there's no compression on the second stroke. No mayo in the radiator, though.

I suppose head gasket is now the leading theory!

[myoldjalopy]

Yes, it won't take long to remove the head and take a look.