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Gearbox Adaptor Plate, Part 2 – Dave's Garage Zetec RWD Mk1 Escort Ep 8

Dave's Garage UK Zetec RWD Mk1 Escort – Episode 8 title card: gearbox adaptor plate, part 2

Part 1 ended with a thin-steel template that lined up on both the ST170 Zetec and the first-generation (NA) Mazda MX-5 gearbox. In the eighth video of the Zetec RWD playlist, Dave’s Garage UK uses it to make the real adaptor plate and gets the gearbox bolted to the engine for the first time. He admits it’s harder than he expected, and that he’s surprised how much work goes into a part you can buy relatively cheaply.

Video: Dave's Garage on YouTube · watch “Ford Escort MK1 Restoration. Gearbox Adaptor Plate Part 2. MX5 NA to Zetec ST170” on YouTube

What happens in Episode 8

Starter motor position (1:04). Before cutting any thick steel he settles where the starter goes. One mounting hole on the template is drilled and used as a pivot, the other is slotted, and the starter is moved in until it engages the ring gear properly. He checks it with a battery wired up as in his earlier engine tests. Once it engages and disengages cleanly, nuts are welded on at that position as drill guides, with extra metal left around the starter area on the final plate.

Drilling the plate (2:37). The final plate is 6 mm steel. The template is clamped down and every hole drilled through, and a bolt goes into each hole as it’s done so nothing shifts.

The centre hole (4:47). The big centre hole is cut first, while the plate still has plenty of material to hold. He finds the centre from the original card template, drills a 6 mm hole there, and makes a simple circle-cutting arm for the plasma cutter: a strip of steel with a pivot bolt at one end and an 8 mm hole at the other to fit the torch tip, with penny washers as a loose bearing. A 3 mm pilot hole gives the plasma somewhere to start, because piercing the metal with the plasma wears out the tips.

Final shape (6:58). With the template bolted back on as a guide, he plasma-cuts the outline, adds reliefs for the crank sensor and starter, and leaves extra metal round the starter. A flap disc tidies the edges, and a test fit shows every bolt hole is where it should be.

Countersinking (9:17). The engine bolts are countersunk from one face and the gearbox bolts from the other, so the plate can sit flush on both. A proper countersink cutter that size was surprisingly expensive, so he takes a 22 mm drill bit and regrinds its point to the 90 degrees the countersunk screws need, using a home-made jig to hold the grinder at 45 degrees. After a better cutting relief and a resharpen, it cuts clean, flush countersinks.

Bolting up (13:35). The MX-5 box is light and easy to offer up. One countersink ended up on a locating dowel, which may now have to come off. Most holes line up; one is close enough to open out with a drill and one is too far off to use. The gearbox is now attached to the engine on two bolts.

Still to sort

  • Clutch. An MX-5 clutch plate is far too small for the Zetec flywheel’s friction face, so he’s waiting on a different clutch to see whether its splines suit the MX-5 input shaft.
  • Starter clearance. The bellhousing needs relieving with a die grinder for the starter.
  • Sump and bolts. He plans to fit the sump to see which lower bolt positions are usable.
  • Gear lever. The MX-5 shifter sits on a remote selector rod, so he’s wondering about shortening it to bring the lever about 6 inches forward and clear of the handbrake.

Lessons for your own Mk1

  • Fix the starter before cutting metal. A pivot hole and a slot let you find the right engagement before the position is set.
  • Cut the hardest hole first. The centre hole is easiest while the plate is still large.
  • Plasma needs a pilot. Start from a small drilled hole to save the torch tips.

Mk1 context

This plate decides where the gearbox, and so the gear lever, sits in the Mk1’s tunnel, which is why the lever position comes up already. The clutch question is next in the playlist.

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