Cosworth BOA - Rev Counter

Cosworth BOA - Rev Counter

This is going to be very vehicle specific but apart from being for a six cylinder engine the signal feed to the rev counter was totally unsuitable for my Cortinas old Rev counter. Therefore I made a hybrid by fitting the Granada donors rev counters internals into the Cortinas instrument cluster.

Mobirise

Granada Rev Counter

The donor rev counter is removed from its cluster. The needle, needle park pin and dial face are removed.

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Cortina Rev Counter

The Cortinas rev counter is also removed from its cluster and dismantled to its major components - Housing, Mechanism, Face.

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Granada Rev Counter

The Granada rev counter is secured by three plastic pillars and securing screws. It has a small circuit board that protrudes to the side.

The Cortina rev counter housing needs additional holes to be made and enlarged as required to accommodate the Granadas mechanism.

Granada mechanism offered into position and rotated to find best fit with consideration given to central alignment of dial, location of mounting legs and any obstruction to the protruding circuit board.

Large central hole drilled to clear three pins on the back of the Granada mechanism.

Hole elongated as required to ensure clearance. Holes also drilled for mounting pillar screws. The pillars must be kept clear of the illumination bulbs in the housing. It is only possible to use two of the three mounting pillars, the third having to be cut off flush.

Window cut into side to clear protruding circuit board.

Window cut into side to clear protruding circuit board.

Circuit board protruding through the window.

The Granada mechanism isn't as deep as the Cortina mechanism so the pillars are spaced out with a stack of alloy washers to push the dial face out far enough.

The original Cortina dial face is mounted in place on the Granada mechanism with double sided tape (use a decent brand).

The excess plastic is trimmed away.

The spindle of the new mechanism is slimmer than the original so the Cortina needle is a loose fit. The Granada needle has a small metal sleeve in its pivot so this needs to be withdrawn and insert into the Cortina needle. The hole will need opening up slightly for this. Sadly I have lost the photos.

A new stop pin is added by drilling a very small hole in the required position and fixing a piece of stiff wire into it.

The new hybrid instrument is refitted to the Cortina cluster ready for the next stage.

The original flexible circuit board from the Cortina rev counter needs adapting to work with the modified instrument.

Sections have had to be carefully cut away to clear the back of the new mechanism. The three pins protruding from the back of the new mechanism are the electrical connections.

The corresponding connections from the Granada instruments circuitry are removed and attached via thin flexible wire (car speaker wire) to the relevant parts of the Cortinas circuitry.

Wires are also added to transfer power to the illumination circuit as some of the had to be cut away.

All back together.

Looks completely original.

Mobirise

The contents of this website are purely a reflection of my own experiences and knowledge gained whilst working on my various projects. Anything you do based on what you have read here is done so entirely at your own risk.
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