2nd Trial Fitting

Some say restoration is a noble art. Others know better – it's mostly swearing, compromise, and learning the limits of what you can jam into a Triumph engine bay. 

Click on the photos to enlarge.

First I had to evict the father-in-law's Jag from his garage, nextdoor to mine, and wheel the tub on its old chassis into it to make room in my garage.

Then my replacement chassis was bright from the top car park and rolled into place.

Then the Mazda MX-5 engine was lowered into place on a clean, bare chassis, unencumbered by a tub, assisted by No.2 Son. 

Since the tub has never been on this replacement chassis, there’s freedom to trial fit the engine without constraints. It makes it easy to assess mount positions, pulley clearance, sump height, and everything else the body would otherwise obstruct.

Chassis Geometry: The Mounting Problem

The stock MX-5 engine mounts might have done the job if the driver-side chassis rail hadn’t come with a rebate – a well-meant feature for the original GT6 engine that throws off the level. As a result, the engine sits at a slight cant, like a wonky picture frame, with the alternator fouling the turret.

Fix: Plate over the rebate. Then take two extra angled brackets (MX-5 style), rotate them 90°, notch them and then weld them into the inner corners of the chassis rails. This allows the standard rubber isolators to sit squarely and correctly.

Crank Pulley and Rack Clearance:

The stock crank pulley, with its dual grooves, flirts too aggressively with the steering rack. The answer is clear: a single-groove pulley (as I've deleted the PAS pump pulley, which runs on the outer groove), preferably lightened and aluminium. VMS Racing in the USA makes one, but it's dual groove but they don't ship to the UK.

Solution: Either have a standard pulley professionally machined down to just the back pulley and have it balanced, or get a friend in the US to forward the VMS part and have that machined to a single groove. The latter would be better, as it saves crank weight and hence reduces rotational  resistance.

Sump Clearance:

The sump is currently sitting on the crossmember, but the fabricated / modified mounts on the chassis rails should give a centimetre of two of clearance.

Alternator Clearance:

Still an issue, but due mainly to the slight tilt of the engine toward the driver side, occasioned by the rebate in way of the driver side engine mount. Will be solved by the mount mod and, if there's still not enough clearance, slight shaving on the suspension turret by a centimetre.

The Coil Pack Scuttle Issue:

I mentioned this on the 1st trial fit post, but the BP4W's coil packs sit too tall for the Triumph's recessed scuttle. A video exists showing a fabricator cutting into this area, but it leaves the 'how to tidy it all up' bit to the imagination.

Fix: Cut a precise rebate into the scuttle and weld in an L-shaped flange reinforcement, 6cm in from the edge, across the full recessed span. The top of the L faces upwards to restore rigidity.

Transmission Tunnel: 

Not Carbon, Not GRP. Aluminium is the smart choice. Heat-resistant, workable, and light, it beats GRP or carbon fibre in this context. A GRP or plastic tunnel might still serve as a plug for templating the ally version.

The Supporting Cast

• Inlet manifold bracket: Originally fouled the turret. That’s no longer an issue.
• Scuttle brace: Will be added post-rebate, possibly full-width, to reinforce the mod.
• Clay or cardboard mockups: May be used to shape the new inboard  engine mounting bracket before committing to metal.
• Steering shaft & rack: Forgot to bloody well check, but it's simple enough to swap the chassis over and refit the engine to see if there's enough clearance; however, from the photos I took it looks reasonably clear.

Conclusion

This is not a story of clean bolt-ons. It’s about wrestling two sets of engineering logic into uneasy alignment. The new chassis offers opportunity and headache in equal measure. With clever mount fabrication, pulley slimming, and scuttle reinforcement, the BP4W is beginning to look like it belongs. Photos document the war wounds. The triumph, if it comes, will be well earned.

I'm nearly in a position to get the tub on a rotisserie - I just need to weld a couple of braces across the door apertures to prevent the tub twisting when it's off the chassis. If I weld the underneath with even the slightest twist in the shape, it will never come out and rest square on the replacement chassis. Door shuts would be all over the place. 

My main problem is that I don't understand modern engines with all the fluff that goes around them - they're nothing like the simple engines I took apart in my 30s. All the electronics are quite confusing and require some deep research, added to which, the Haynes Manual is next useless for the engine I have, falling between two main variants. ChatGPT does help though - I take a photo of a part and ask ChatGPT what it is, hoping to get a sensible answer, which is not always the case.

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