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MG MGA - Mechanical tach / 5 main engine

In another thread, someone mentioned drilling a Metropolitan 1500 block for a mechanical tach drive. That got me wondering if it would be possible for a machine shop to drill an early 5 main (18GB) block for a mecahnical tach drive. Of course, it'd mean replacing the camshaft with one from a 3 main and sourcing the actual tach drive bits...but would it be do-able?
Andy Bounsall

With all the extra possible problem areas in a mechanical tachometer, together with the drain on horsepower, the electrical tachometer is the answer to your prayers.
The factory couldn't wait to get rid of the mechanical system. At last no wearing parts outside of the instrument itself, no oscillating reading etc. etc.
Of course with Concours it is a different matter, but you have a non standard engine anyway.

Mick Anderson

When weighing the pros and cons of a 3 main 1800 vs a 5 main, the argument in favour of the 3 main is normally that you can retain your existing mechanical tach. Proponents of the 5 main claim a stronger bottom end and smoother running engine. Just wondering...if this is possible, you could end up with the best (or worst?) of both worlds.
Andy Bounsall

The 3 main blacoks without tach do have a flat in that location, making conversion quite easy.

The 5 main blocks don't have a handy flat and trying to come up with one, welding to cast iron and then machining, is far more fuss and money than simply fitting a 1965-68 large facre tach that looks right and fits the hole in the MGA dash.

I like mechanical tachs (we use them on many of the old race cars) but it isn't worth trying to convert a 5 main.

If you are mad keen to have a mechanical tach and don't care about original appearance, a TR-6 tach can be adapted, with mechanical tach drive incorporated (I've done that before)
Bill Spohn

I have an 1800 18v engine with a Jeagar tack that is electric. I had the mods done at MoMA in New Mexico. I also had the machine shop adapt an dummy tack drive on the engine. Unless you look real close, the tack has two extra small screws to match up to the back of the tack. It looks original and reads perfect. Even the engine looks to be an 1600 engine.It can be done and it cost about $200-250 for everything to make it look right.

This thread was discussed on 13/08/2008

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This thread is from the archive. The Live MG MGA BBS is active now.