Head/barrel joint question.

[TonyBaxter]

Evening all.
I have been lapping in my 350 iron head to barrel joint. I was quite happy with the result, but then taking a second look, realised that the liner is a thou or two lower than the actual barrel spigot. The spigot has an even look with the head face, but I'm wondering if the liner should really be level with the spigot, which would greatly increase the surface area of the mating face.
Thoughts please. Many thanks, Tony.

[Simon.Gardiner]

Tony
I've been taught that the way to do these is to finish with coarse paste on the outer face and fine on the top of the spigot, so that when the head is seated there's a few thou gap on the outer face.
Then when the head is tightened down seal is essentially on the very outer edge of the spigot, not right the way across it.
(There are probably a few topics in the Forum where this is discussed is some detail.)

SG

[Roger Gwynn]

Either the liner was not fitted correctly in the first place or it has moved. It is usually held in place by an interference fit but if it is not tight enough it could drop down, however it looks like your cylinder has seen some use so if there was to be a problem it is likely to have happened by now. I would prefer to see the full width of the spigot acting as a joint, although it may well seal as it is. The coarse paste is only necessary if the 2 surfaces start to touch in order to increase the clearance.

[nevhunter]

If it's not touching on the outer area just get a good surface on the inner one. IF you're after the best get both surfaces involved but lap the outer a bit longer with oil only on the inner so the inner gets more pressure on it's surface.This arrangement is very satisfactory and needs no gasket. or retensioning. Nev

[TonyBaxter]

If it's not touching on the outer area just get a good surface on the inner one. IF you're after the best get both surfaces involved but lap the outer a bit longer with oil only on the inner so the inner gets more pressure on it's surface.This arrangement is very satisfactory and needs no gasket. or retensioning. Nev

Nev, if you mean by the outer, the area outside of the spigot where the head bolts through, then there is a big gap. I would have to reduce the height of the spigot by quite a bit. My main worry is that as the liner is a tiny amount lower than the spigot, I need to grind the spigot down until I can lap the liner too.
I could just try it and see if it will seal as it is, but I guess it will build up a layer of coke at the top of the liner/head joint. The previous arrangement with the home made 'gasket' of, I think, aluminium, had caused a large ring of coke to form at the top edge of the barrel.

[TonyBaxter]

Either the liner was not fitted correctly in the first place or it has moved. It is usually held in place by an interference fit but if it is not tight enough it could drop down, however it looks like your cylinder has seen some use so if there was to be a problem it is likely to have happened by now. I would prefer to see the full width of the spigot acting as a joint, although it may well seal as it is. The coarse paste is only necessary if the 2 surfaces start to touch in order to increase the clearance.

The liner appears to be only a couple of thou low tbh, I could try some more lapping.

[TonyBaxter]

Tony
I've been taught that the way to do these is to finish with coarse paste on the outer face and fine on the top of the spigot, so that when the head is seated there's a few thou gap on the outer face.
Then when the head is tightened down seal is essentially on the very outer edge of the spigot, not right the way across it.
(There are probably a few topics in the Forum where this is discussed is some detail.)

SG

Yes, I had read previous topics, it's a bit like reading 'oil' threads!

[nevhunter]

Going back to Roger's thread the possibility of the sleeve moving would worry me. IF sleeves do move they soon cause a lot of damage as the rings pop out the top as soon as the sleeve moves down a bit. If the sleeve is too thick in the wall it also weakens the cylinder above the base flange and the 350's are a bit weak there to start with so I prefer to not sleeve them or use a thin sleeve. Nev

[ian williams]

i would have thought there would be a step in the bottom of the bore that the liner goes up to and then its pressed in so that there is a slight amount proud of the top of the cylinder, then it can be machined flush or left a couple of thou proud for when the head goes on and is pulled down .

i love the perkins liners, you can tap them down with a bit of wood . .