Engine noise, loads of black smoke, down on power.

[John Mason]

My son took me out in my Ruby on Saturday as the weather was nice. The car started easily as it usually does and the engine purred just fine. Within two miles it developed a noise which increased and decreased with engine speed. It sounded like something fouling the prop shaft. We obviously stopped and found nothing.  The engine then refused to start and only started when kind passers by assisted in a push start when the car was at a fast speed. It ran rough with billowing black smoke from the exhaust. It was at this point that I realised something was seriously amiss within the engine. 
We limped back to its new home my sons house.  We will need to strip it down to see the extent of th damage but I suspect there will be some bore scoring.  My block is already bored to +60 oversize. As the car is not a competition car and not driven harshly what do forum members think about reboring to +80 oversize if required.

John Mason.

[Mike Costigan]

Black smoke suggests an over-rich mixture; bore wear would show up with blue smoke. Before you start stripping the engine down, check the carburettor and fuel lines.

[Alan]

Some blocks bore to +80 some don’t it’s a matter of luck really and no way to tell until you try. I’d go for putting a liner in the damaged bore.

[AustinWood]

I agree that it's most likely a fueling problem.

[John Mason]

Thanks for the replies. The black smoke I described could be blue as my eyesight problems get worse I see colours slightly different. Before I gfurther I will do a wet and dry compression test before pulling it apart.

John Mason.

[jpsmit]

the colour of your plugs will quickly help you determine if the mixture os too rich - soot = rich

[Bob Culver]

If it is anything to do with oil and rings and pistons, to be that obvious should be immediately apparent using the compression tester protruding from the radiator shell.

[John Mason]

An update. Together with my son we have commenced a strip down and removed the sump {oil pan for USA forum members.) together with the gauze filter. The oil looks good and has only done around 500 miles but will be replaced. There were no metal bit or parts of pistons or rings. Something I was expecting. We then removed the head and found number 3 piston crown black with burnt oil. More than the other three but not excessive. But obviously burning some oil. An examination of the bores found them ok with no score marks much to my relief. The head gasket had however blown between number 2 and 3 bores thus resulting in loss of power as it would only have been running on 1 and 4. This obviously the cause of the problem and is in the process of being replaced. What I can’t understand is what caused the noise which altered depending on engine speed. I know in my own mind it must have been gasses passing between the two effected bores as the pistons moved up and down but it was so loud.
When the gasket is fitted I will report again but I think it will put things right. As to number three piston that can stay until things get a lot worse. I want to use my car this summer
I have always just used a smear of grease on both sides of a head gasket when fitting. What do others use. I ask because my last gasket has not seemed to last that long.

John Mason.

[David Stepney]

It would be worth checking to make sure that the head is reasonably flat. Put a straight edge along it and see if you can get a thin feeler gauge anywhere along the length. Anything more that about 2 thou and I would get the head skimmed. Given that the gasket has blown between Nos: 2na d3, I would pay particular attention to the head between those cylinders. And yes, a blown gasket between the two middle cylinders is noisy, as when one is on the firing stroke, the other is on the inlet stroke and the mixture in the cylinder that is trying to charge itself will burn and tend to blow back into the inlet manifold.