Cylinder spigot damage

The likelihood is that the liner will continue to crack, from the lowest point of the triangle, downwards, below the top of the barrel. If any pieces break out.....

What has happened to the missing piece?  I would machine the spigot off below the broken out section, or have new liners fitted. What overbore is it?

The only other option I can think of is to round out the bottom of the broken out section with a Dremel or whatever, to remove the point from which a crack could form. However, the likelihood is that, if the spigot has broken once, it is past its sell-buy, and will break again. I certainly would not rebuild the engine as it is.

Ian C

Hi Tony,

The gaskets for spigoted barrels don't have flame rings in them, at least, they never used to.(The spigot does the job) so if a portion of the spigot is missing, then it is almost guaranteed that the head gasket will blow at this point. You could try dressing the edges to minimise further cracks and use a copper head gasket (in itself a 'marmite' part on the great/avoid scale) but I would always be worried about more bits of spigot breaking off and wrecking the top end.

As I see it, you have 3 choices:

a/ weld/braze and machine the area back to correct profile. This will almost certainly mean a rebore is required and have read many times that rebores over +.040" are no good for spigots, but that maybe only on the 650's, (but 600 bore size is the same.)

b/ machine the spigots off and use a gasket for a non spigoted head. Insert rings MAY be available to fill in the gap in the head, but in practice they aren't necessary, the flame ring will still seal, or

c/ get the barrel sleeved with a liner that has the spigot on it.

For what its worth, my 650 has spigotless barrels and a head for a spigoted cylinder and the gaskets with a flame ring work fine on it, hence my quote that the filler rings aren't really required. (Its another thing to go wrong!) so I would go for b/ - it will also be the cheapest one

My experience? Gaskets without flame rings and no spigots will fail very quickly, and as for copper, I never got one to seal both gas and oil properly.

Hope that this helps,

George.

I doubt if anyone will be brave enough to just recommend you put it back as it is, for fear of the blame if it goes horribly wrong. But have you any idea how it happened? If it was bashed on the workbench, maybe the best thing is the "do minimum" option and grind it into a shallow dipping curve. If the rest is OK, why should the rest of it be any more likely to spontaneously drop off than the spigots on any other Norton 99?

There's been discussion about those filler strips before. The first I remember was someone asking why his cylinder contained a chewed up metal worm...the ring had escaped.

The spigots can scarcely alter the compression ratio anyway, so is there any point in filling the gaps?

Hi David (and Tony!)

What you said about the filler rings I agree with you -they aren't a 'can't run without it' item, and can fail spectacularly.

However the spigots primary job is as a flame ring for the gasket, not a head locator. If there is a hole in it (as Tony described), then the gasket will have to face up to around 140-150bar (~1500psi) pressure (more if it 'pinks') and flame temperatures of over 800°C. My own experience is that gaskets without flame rings wont do this for more than a few minutes of gentle riding, let alone large throttle openings. The copper ones may well cope ok, as long as you don't mind chasing oil leaks.

Like you,  it would be good to know the cause of the damage. If it is because it is bored over +.040", I'm sure it is game over and the spigot should be removed (though I am happy to be corrected on this for 99's).

But, it is Tony's bike and only he can choose what he feels is best for him. 

Regards, George.