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MG Midget and Sprite Technical - air/fuel ratio & exhaust manifold

I would like to install a air/fuel ratio gauge into my 78 midget. The cat-converter is connected directly to the exhaust manifold and I was told that the oxygen sensor for the gauge needs to connect to the exhaust system somewhere before the cat-converter. So my question is, how do I do that? As you can see in the picture, there is a really big bolt screwed into a hole in the exhaust manifold. I don't know what that's for or why it's there but it gives me access before the cat-converter. The hole is about 22MM in diameter.

Also one other question - there appears to be a small crack in the manifold, should it be replaced all together because of this? Thanks for any replies.

D



DLW

D:

The crack doesn't look too bad yet, maybe brasable/weldable?

Use your bolted access port for your sensor.

The pic posted below is from my spares pile, the manifold is from an unknown car, came in a pile with my donor Midget, but the carb looks like a Spitfire setup. Note the 2 port positions: the one with the X (not drilled/threaded) is in the same position as yours with the bolt. The one with the arrow is the EGR valve port on the Spitfire, FYI the OD on the pipe measures dead-on .75" , but this port is not drilled/threaded on your manifold.

Didn't the 1500 go in the Marina as well as the Mig and Spit? Looks like a one part, many applications deal. What I want to know is this: Is that a Factory Installed Bolt? Wouldn't surprise me. Anybody know where the EGR valve was on the Marina?

North American 1500 Midgets have the EGR valve on top of the in-out manifolds: Was it the same for the Home Market cars?

R


Richard 1979 1500

My 79's stock/original exhaust manifold looks exactly like this picture.
Rik
Rik Hogan

DLW, the crack doesn't look that bad, perhaps it can be welded up. Mine was broken completely and it was welded up and is still on the car. That was back in 1989!
Clive Reddin

D -

The big bolt in your manifold is plugging the fitting for a pipe that used to come from the air injection pump. As for Richard's picture, it shows an earlier manifold that had the EGR valve mounted down low. Later ones placed the EGR at the top, sticking straight up, and your manifold will have that configuration.

Having said all that, you can most likely mount an O2 sensor where that bolt is with no problems whatsoever.

But I need to address that crack... a few years ago, the front branch of my manifold broke off right about where that crack is starting on yours. Just so you know.

-:G:-
Gryf Ketcherside

Thanks everyone for the great feedback. I'm going to look into welding the crack. I'll ask my welding instructor about how to go about doing that and I'll do more research on a weldable fitting for an O2 sensor to go into that hole. It would be nice if it would just fit and I wouldn't have to do any welding. Currently I'm looking at the Cyberdyne CYB-8941 and the Auto Meter ATM-2244 O2 sensors and the Auto Meter seems like it will work the best, I just need to find out if it's made of titanium so that it will be compatable with the Cyberdyne Air/Fuel gauge I've already decided on.
DLW

This thread was discussed between 16/11/2008 and 17/11/2008

MG Midget and Sprite Technical index

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