Are inlet sealing rings essential?

[Oldmogman]

Does anyone know whether the metal sealing rings between a 1275 inlet manifold and head are essential for smooth running?

I'm in the process of re-gasketing the inlet manifold (Metro, water heated) and carb on my 1275 Minor to ensure there are no air leaks (the car is jerky at low speed, but pulls like a train once the throttle is opened), and noticed there are no rings fitted, even though the inlet manifold and head are machined to accept them.

Are these rings essential for an air-tight seal, or are they more about smooth gas flow or gasket location?

In short, should I try to track down some rings, or re-assemble the manifold as-was?

And if rings are essential, does anyone know where I could get some from?

Thanks all!

[Alec]

Hello OMM,

no I don't think they are essential, but they helped align the manifold to the head.

Alec

[chrisryder]

i cant imagine they're that important. from what i've read in the vizard book, a long time ago the 'art' of lining up the inlet manifold with the ports was laboured over intensively thinking that it would make or break an engine. but according to dyno tests the lining up isn't critical. i think the locating rings were employed with a view to getting perfect alignment.

they wont make a differece to gasket sealing, i can imagine with them not fitted you may get some fuel puddling in the dip. so i think the worst you'll find is that when you remove the manifold again in the future you'll get a dribble of fuel down the side of the head.

[bmcecosse]

Obviously without the rings - as Alec says, the manifold may not align well. You will also have a nasty 'step' where the rings are missing. Easy enough to make if you find a tube the correct diameter, or even by rolling up a strip of steel...... Of course on a modified head the rings are eliminated - and the head and manifold are ground out to maximise area and minimse resistance to air flow. Best to leave the manifold UNHEATED - and use an AAA needle in the carb if it is an HIF 38, or a BDL if an HIF44.

[Oldmogman]

Thanks guys - sounds like there's nothing to lose and maybe even something to gain by fitting rings.

Bmcecosse - I'm intrigued about your suggestion of leaving the manifold unheated. Presumably this increases the density of the incoming charge? But would this be in the summer only? (I'm assuming the heating is there to stop the carb icing up?).

So would leaving the manifold unheated be simply a matter of turning off the heater tap, or would I need to by-pass the manifold completely? Or perhaps there's a way of plumbing in a separate on/off valve for the inlet manifold, so I can still use the heater (very useful for helping to keep the engine cool in traffic jams!).

Cheers

[bmcecosse]

There is no hope of the heated manifold stopping any carb icing - it's downstream of the carb! Twin carb manifolds have no heating.....why do folks think the single carb manifold needs heating? I suppose it's just possible that in winter - it may help fuel economy slightly - but i wouldn't bank on it.