is anyone else shocked at how the air intake plenum (see pic of "air intake plenum' on a late model MK2 below) was/is designed to connect to the carbs?

the two outside (rearmost and foremost) ears of the four ears on the carbs connect to the plenum's outside ears with bolts as one might expect, but the two inside ears are something else entirely. they are merely locating pins! what's up with that?

when looking closely at what might have forced engineers into making this poor compromise, i've decided it was the necessity of a mounting bracket for the AED and how it, in turn, made accessing a proper bolt on the inside ears nearly impossible. i can see no other explanation.

if i previously had any reservations WRT replacing the behemoth that was the standard air cleaner on my Mk2, with a couple of pancake elements (and replaced the two pins with two bolts and nuts), they have now been dashed, and my conscience cleared. ha

 

If you don't want a fire remember to fit drain tubes to plenum drains.

 

Polished:

 

yes, good idea. mine has been replaced, of course, with the pancake cleaners. currently in the trunk with its air cleaner companion.

 

Pancake cleaners = stone catchers = rubbish.

 

"stone catcher"...a humorous sobriquet, no doubt. but IMO undeserved. they can contain, like mine, the same type of open celled foam as any other foam filled air cleaner out there. shape, pancake or otherwise, is of little importance IMO.

no comment on the locating pins in the air intake manifold? one has to wonder why the engineering team deemed a gasket necessary between it and the intake of the carbs if one side was to be, essentially, left loose.

 

There is not a decent pancake filter foam on the market. Our Oilco has tested them all. Even the oiled variety. I'm talking filtration standards like Donalson & Mann + Hummel. Pancake filters are stone catchers.

 

No comment on the locating pins in the air intake plenum chamber. Cummins made a movie in the '50's called "The Hourglass". It is as valid today as it was then. It takes one heaped teaspoon of dirt/silica to ruin an engine. Top air filtration is critical to long engine life. All pancake filters are rubbish unless you are racing & rebuilding the engine frequently to spec. Then you can run open trumpets.

 

"The Lady doth protest too much, methinks." --Queen Gertrude--

 

Wear Debris from a running in motor plus Silica. Nice combination for wearing out an engine prematurely. You may burst into flames if you wish but professionals will listen.

It's your car. Bugger it up if you wish.

 

Watch Cummins "The Hourglass" ~ I'm sure it's on YouTube somewhere.

 

Are you talking about just foam, or the one with the paper element as well ?

 

Huey
Glyn is totally correct about pancake filters being stone catchers.
If you live in an inner-city environment, you might be OK, but any country driving will involve dirt and dust.
The plenum chambers are a pain to fit but having a decent air filter is an absolute necessity.
I had my Mk2 plenum off yesterday while chasing a fuel leak in the flex hose I have feeding the carbies from underneath.
To reattach the plenum, I jam it in the correct position on the locating pegs with foam rubber between the plenum and the body. I then use a magnet to attach to one flat of the head of the bolt and insert it in place.
Then I (contorted) finger tighten followed by 1/2 AF ring to tighten. (I am looking for an extremely thin walled 1/2 inch ratchet ring spanner to do this job).
cheers

 

i didn't re-attach mine, and don't plan on it...anyway with respect to the provenance of the locating pins...

i'm imagining some sort of automatic choke being demanded by the advertising department at Jaguar sometime in the early 60's, and when the AED was thrown out there as a candidate they, the advertising dept, jumped on it. trouble was it had to be, for some reason, mounted right where those two inside bolts, that never were, needed to be to secure the air intake manifold to the carb inlets. the engineers, in my mind, must have fought tooth and nail to prevent it from being mounted there, but lost the battle... they must have been livid!

after all, who designs two flanges with a gasket in between and then clamps them together on ONE side only? who does that? it's ridiculous! smh. at least now, with the pancakes, i have them clamped together with a bolt and nut on BOTH sides.

BTW, heard tell that one of the drawbacks of foam filled air cleaners on dirt bikes is that they must be cleaned more often than other materials due to, get this..., they are more efficient at catching dirt and debris.

 

The pins are intended as locating pins to help attach the plenum and to ensure the carbs are spaced correctly and thus square to the head. It's a way of ensuring there are no vacuum leaks if one side of the carb-to-head nuts is tightened more than the other, and that the throttle linkage doesn't bind.

The carb to plenum joint has no fluid pressure, all the gasket needs to do is keep the dirt out. Both the plenum and carb flange are rigid enough to ensure that the clamping force needed to maintain a dust seal across the entirety of the gasket face can be attained by a single bolt on each side. I've pulled a number apart over the years and I have never seen any evidence of insufficient clamping force- -the gasket is always well in contact with each surface and no signs of dust incursion across the face.

The spacing function of the pins is just as important as the clamping function of the bolts. Bolts are poor locating devices, thus the combination of pins and bolts - they each do a function.

 

i agree that an air leak between the air filter and the entrance to the carbs is of lessor importance than elsewhere in the induction system. no question.

 

That SU AED enrichment device was around a long time before MK2s.
It was definitely fitted to MK7s in 1952.

 

XK140's as well.

 

If it has a "paper" media element as well you should be fine.

 

Jaguar used the SU starting carburettor when they were still SS in the 1930s. Much as we may criticise it, it's quite a neat device and must have been a wonder of technology pre-WWII.