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MG MGB Technical - '71 to '73 MGB

In 2001 I bought a 1971 mgb roadster that had not run since 1987. By 2006 I had it running, and by 2009 it had a Pennsylvania inspection sticker on it. However, I was told it would not pass inspection again because of the rust conditions of the car, particluarly in the rocker panels and floor. Big bucks to fix. But lo and behold, I ran across a 1973 MGB body, without engine and transmission, but with most of the rust repaired, especially the really expensive areas. So I bought it with the idea of stripping my '71 and transferring the parts to the '73 body. The '73 still needed some welding, but that's minor.

Well the drive train is in, the front and back suspensions, brakes and steering, and most of the dash have been put back together. I am close to the point where I at least want to turn the engine over. I've had some wiring problems trying to interpret two different wiring diagrams, but I think I've done OK so far.

My question is this: Can anyone think of any major problems I may have missed in this transfer? I would appreciate any thoughts or suggestions that might lead to a successful transplant from a '71 to a '73. Then all I will have to decide is which grille to put on. I have all three. Thanks! Curt
C Pieper

A couple of things depend on whether you are using the 71 dash and instruments in the 73 body or using the 73 items, and whether you are using the 71 or the 73 harness.

On the 71 the coil ignition feed went via the (RVI) tach pickup and that is what triggers the tach. On a 73 the coil feed comes direct from the fusebox and the (RVC) tach has a trigger wire from the coil -ve.

The 71 had an electric oil pressure gauge whereas the 73 had a mechanical.

The 73 has an anti-runon valve but the 71 didn't. That uses a tee in the oil pressure line with an oil pressure switch, plus a special ignition switch plus associated wiring and fuse. But using a 71 engine you shouldn't need it anyway.

If your 71 had an 18V engine with HIF carbs same as in 1973 then the control cables should be very similar if not the same. But if the 71 had HSs then the cable runs and linkages are different.

There are other differences between the two cars, but that should all be in the body wiring, not the engine.
PaulH Solihull

This thread was discussed on 19/10/2011

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