Iron Head - Barrel Gap

[simon.holyfield]

Guys,

Having reground my cylinder head joint face, I find the gap to the barrel face is about 0.020". Given that this has not been resleeved and has been running like that for donkeys years, is it acceptable?

[Simon.Gardiner]

I'd say leave it as it is - contact with the outer level when tightened is apparently to stop heads distorting and I don't think Ariel heads do.
Also, the head runs hotter than the barrel and less of a heat path into the barrel should mean a cooler barrel...
(Info from Phil Irving, 'Tuning for Speed' )

SG

[simon.holyfield]

I'd say leave it as it is - contact with the outer level when tightened is apparently to stop heads distorting and I don't think Ariel heads do.
Also, the head runs hotter than the barrel and less of a heat path into the barrel should mean a cooler barrel...
(Info from Phil Irving, 'Tuning for Speed' )

SG

If Slide Rule said it, it's good enough for me. What page in his book?

[Simon.Gardiner]

Carefully read the short section 'Cylinder Head Joints' in the chapter 'Top Half Reassembly'.
(I'm using the 6th edition but I don't think this bit is substantially different to earlier editions.)
You might need to apply a bit of reverse-logic in places. For example, the advice about how a broad joint can assist the head cooling by facilitating a flow of heat from under the exhaust seat area into the barrel....
I don't think you've got an issue with the exhaust valve or seat, you might be more interested in not having the barrel assist with cylinder head cooling (or at any rate, not any more than it has been for the last donkey's years! )

SG

[nevhunter]

In my experience the double lapped head/barrel Joint on the cast iron OHV Ariels is the best in the game. Next best thing for reliability to having it one piece (as the 1916 Harley 8 valve racers had). and many Bugatti's. Nev

[charles.bulloch]

I am a bit surprised at the advice on lapping in the head to the barrel. On my 38 VH engine there is a gap of very roughly half a millimeter between the head and barrel on the outside surface so there is no point in putting grinding paste anywhere else than on the spigot. Is this normal?

[Roger Gwynn]

It is normal to have a gap where there should be one, it is only necessary to use coarse paste to create a gap lost by lapping in the joint. I suspect that several hours of lapping would be required unless there was very little gap in the first place.