Last time we looked at my Austin 1800 ute project, I’d got the 1999 Honda Integra donor car home… and was wondering if the Honda’s engine would fit in the Austin engine bay!
The short answer to that question is: no, it won’t.
The longer answer is: yes, with enough work, it probably will.
Dimensions
The big problem with fitting a different engine to the Austin (and this must also apply to the original Mini and Morris 1100) is that the engine bay is so small, especially in width. The engine bay in these cars could be small because the brilliance of the Issigonis design in placing the gearbox in the engine’s sump resulted in a really compact driveline – even in today’s terms.
To be specific, the Austin 1800’s 1.8 litre engine and 4-speed manual gearbox have a combined length (ie width, when installed transversely in the car) of just 700mm. In contrast, the Honda Integra’s 1.8 litre engine and 5-speed manual gearbox have a combined length of about 870mm.
In the Honda, the length of the engine/gearbox is in part catered for by the use of chassis rails arranged so that the right-hand one passes over the top of the gearbox extension – in this car, the gearbox actually extends past the inner edge of the chassis rail towards the wheel well.
But in the Austin, such an approach can’t be used – the original small chassis rails are at the wrong height.
So, including a little more space to provide minimal clearance, the Honda engine/gearbox needs a distance of about 900mm between the chassis rails – the Austin has available only 850mm. Therefore, 25mm of extra space needs to be found each side.
And it gets more complicated.
The length of the Austin engine bay (when the powerplant is installed transversely, this becomes the width of the engine/trans) is quite tight. Leaving room for a thin front-mounted radiator, this dimension varies between 570 to 650mm, depending on the height at which you make the measurement. The variation in this measurement is because of the transverse tubular hump (arrowed) located in the Austin’s firewall: this is where the front suspension displacers (combined spring/damper units) mount.
I hoped that the Honda’s engine could be positioned so that the intake manifold was located above this hump and the gearbox extension for the driveshafts was located below this hump. However, while that was perhaps possible, the Honda’s alternator would need to be moved, as it would otherwise foul the firewall hump.
The only dimension that initially looked sweet was height – the Honda engine is much shorter than the original Austin powerplant (which has the gearbox mounted under the engine, remember). But even that confidence was soon dispelled when I made more careful measurements – it appeared that the sump of the Honda engine may hang dangerously low!
Making it happen
To cater for the extra length of the Honda engine/trans, the inner guards and chassis rails of the Austin needed to be heavily modified. But before we get into the required changes, what did the standard metalwork look like?
Here is the view into the engine bay, looking towards the left-hand side (left-hand side as viewed from the driver’s seat). You can again see the hump running transversely across the firewall for the suspension units – but why has the inner guard got a big grille in it? That’s because in the original design, the radiator was mounted at one end of the engine against the inner guard – and the air flowed out of the radiator into the wheel well.
Here is the view of the right-hand side inner guard. This one doesn’t have a grille in it but has various indents to cater for the battery, which was originally mounted on this side of the engine bay. The surface rust has come from spills of brake fluid and (probably) battery acid over the decades, so removing the paint.
But it’s inside the wheel well where things get (even more!) interesting. Shown here is the left-hand side wheel well. Starting at the right and moving towards the left, you can see the:
· End of the steering rack
· Tube that contains the suspension displacers (yep, the tube goes right across the car and so you can see out the other side)
· Rectangular opening for the driveshaft
· Small chassis rail and the radiator grille above
· Front-mounted opening for one of the cabin cold-air ventilation ducts
Given that the original radiator grille would need to be filled, and that the chassis rails would need to be altered in shape to cater for the longer engine/trans, the next step was to (gulp!) grab a 100mm angle grinder and 1mm cutting discs and cut out the inner guards and chassis rails.
The Honda engine/gearbox could then be lowered into the Austin. Prior to this occurring, the power steering pump and air conditioning compressor were removed (they won’t be needed) and the alternator removed (it will be needed, but its revised location can be determined later).
Now started a juggling process that took many, many hours. The Honda engine could be positioned in different locations transversely and fore/aft, but furthermore, it could also be tilted forwards or backwards. Changing each of these aspects also changed:
· How the driveshafts lined-up with the Austin body driveshaft holes
· Clearance between the crankshaft pulley and the LHS chassis rail location
· Clearance between the gearbox extension housing and the RHS chassis rail location
· Clearance from the rearwards gearbox extension (containing the driveshaft outputs) to the firewall
· Clearance from the gearbox speed sensor to the firewall
· Clearance between the intake manifold and the firewall, and between the intake manifold and the firewall hump
· Clearance between the gearchange mechanism and the steering rack
After trialling many different iterations, I could see that the engine simply wouldn’t fit. The next step was to…
Cut off the outermost crankshaft drive belt pulley and then….
…remove the gearbox speed sensor. This will need to be remote-mounted and driven by a flexible cable – the body of the sensor is too large and fouls the firewall.
These changes made fitting at least possible!
By mounting a wheel and tyre positioned at full lock and suspension bump, clearances could be assessed to the powerplant, suspension radius rod and tyre, and….
…. differently shaped chassis rails could then be trialled.
Making new chassis rails
The new chassis rails were formed from 3mm thick steel sheet. The shape in side elevation was made in a cardboard template and then the steel sheet was cut with a 1mm cutting disc in an angle grinder.
The required bends in the plan-form shape were made with a hand bender, using a gentle radius former. When these bends were correct, further cardboard templates were made for the required shape of the top and bottom flanges; these were then cut out as two single pieces and welded in place.
The forward part of the new chassis rail fits within the original chassis rail.
Despite looking finished, this chassis rail was actually unable to be used. Why? Well, with the engine positioned to suit this chassis rail design, the sump hung too low at its forward edge – so the engine had to be rotated to being more upright, which also required moving it forward a little… and so making this chassis rail the wrong shape!
Aaagh….
When the maximum clearance in most directions is just 10mm, things aren’t quite as straightforward as they might first appear…
That’s enough for this issue – next time we’ll look at the final iterations of the new chassis rails, and also something else that proved much harder to make than the chassis rails – the new structural inner guards, formed from 2mm steel sheet and containing recesses for the fusebox, airbox and radiator overflow container…
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