Work continues on the new/spare engine. I finally found the courage to try that welding trick to remove a bearing race from a blind hole. Bugger me, it works.
I shouldn’t have been so surprised. I’ve warped enough steel with weld to know that weld shrinks as it cools. Welding so close to a large, complicated, precision aluminium casting is a bit fraught though.
The fancy(?) airbox I built works well now, but is a tiny bit big- it sometimes touches the wiring loom, and you can hear it vibrating through the firewall. It’s almost like I built it to suit a car without an inch of Dynamat on the firewall. Weird.
It’s also a bit rectangular. I’m sure I can make something better. But first we design it with CAD:
I have discovered the joy of using a former. Spending half hour making something you were only going to throw away seems like a waste of time, but it makes shaping the sheet metal amazingly easy, and very accurate.
No, I’m not showing what the welds looked like before linishing them back. Pulse welding might keep the sheet metal from warping, but it’s not pretty.
Test fit box, add an air inlet, and then paint:
So pretty. I even treated it to a new air hose, since the old one was a bit crap. Rubber end seals made out of a bit of old gumboot for Kiwi authenticity.
The new air filter is from a Nissan Tiida or Cube, a 1.6litre engine that makes 112hp, so it should flow enough air.
We’re reconsidering the engine in the Mini- it’s great, but it doesn’t suit the way we actually use the car.
The current engine was built to be fairly powerful to suit a fun car, something to thrash about, maybe the odd track day or autocross. Unfortunately we seem to have installed it in something with leather seats, wilton carpet, and immaculate bodywork. It’s way too shiny for the mud, and too expensive for a close encounter with the tyre wall. Blasting down the motorway is fun for about half an hour, and then 3900rpm becomes tiring despite inches of Dynamat under the carpet.
So we’ve bought a new engine. I plan to fit a 2.9:1 diff (cruising at 3200rpm instead of 3800rpm might be nice), a more sensibly weighted flywheel for smoothness, and a cam that will make lots of lovely torque rather than outright power. We’ll see how it goes- we can always put the old engine back if it’s not right.
Or put the old engine into something a bit less precious.
As part of driving a Mini with a solid mounted subframe, sporty cam, and lightweight flywheel, I’ve naturally become interested in the art of vehicle refinement, and specifically the isolation of engine noise and harmonics from the passenger compartment.
It turns out to be an exceedingly complex science when done properly, and effective solutions tend to be extremely specific, but there are a few broad principles to start with. Like this one concerning rubber mounts on vibrating components: the brackets supporting the rubber mount should be as rigid as possible, and the rubber as soft as possible.
So, the exact opposite of standard 1960’s Mini exhaust mounts then. Right. Where’s my welder. Let’s start with the rear mount:
Those rubber cotton reel mounts are rock solid. Modern exhaust mounts are little more than a couple of rubber straps, designed to stretch and move. So that’s what I’ll use, and make up a couple of brackets to bolt it to the existing mount holes. (Minis from around 1990 used this style of hanger, but with welded-on brackets.)
Interestingly, the exhaust gets about 8mm longer when it’s hot. I’m going to need to align this mount carefully so it doesn’t hit anything.
And now the middle mount. Same deal:
That’s the standard mount in the front- just a big block of solid rubber. It really doesn’t move much.
And there we go! All fixed. The loud booming from the rear cabin has completely gone, and the exhaust is free to expand and move about a bit without stressing the mountings. We’ll see how long it lasts…
We went on a long trip with a couple of friends from the Mini Car Club of Auckland. They called it the “Off the Beaten Track” journey, because we avoided as many main highways as possible, and mostly drove on small back roads.
Fast, tight, windy back roads, including a few that are used on the Targa NZ rally. You’ll note that Alan and Shelagh’s Mini is a bit lighter than usual, but we managed to keep up just fine.
We put over 1000km on the Mini in 4 days, and nothing broke or fell off, though the tyres had a good workout.
Mini Car Club of Auckland organised a dyno day, so we went along to see how our engine compared.
It didn’t do too badly at all.
It ran nice and smoothly and ended up making 64hp at the wheels, which was pretty good. Most of the other 1275s were making around 50hp, though there was a highly tuned Cooper S and an 8-port 1430 that showed around 80hp.
The modified air box appeared to work, with the fuel mixture remaining stable at high revs.
It’s summer. It’s hot. Mk1 sliding windows are adorable, but they don’t let much air in.
Cheap junk from China to the rescue! It’s ugly, but it works. The fans are only held in place by magnets, so they’ll be easy to remove when it cools down a bit.
The other thing I’ve had to tweak is the wiper arms. They’re blinding if the sun is at just the wrong angle, so I’ve added a piece of grey adhesive vinyl to the offending face. Unlike the fans, it’s surprisingly discreet.
With the engine finally running without tearing itself apart, we took the Mini to Hitech Motorsport in Drury to have it tuned on the dyno.
I was under the impression that they had a stock of SU carburettor needles and would be able to finalise the tuning, but I was wrong.
They identified an airflow restriction in the airbox at high load and got the ignition timing dialled in, but didn’t change the needles. “It’s a bit lean at the top end,” they said, “try fitting some AF needles and bring it back.”
Maybe I’m out of touch with the cost of dyno tuning, but I imagined I would get a bit more for my $800. If you want something done right, do it yourself. So we bought an Innovate Motorsports Wideband Air/Fuel Ratio gauge, cable tied it to the dashboard and fitted the sensor into the exhaust, and began to figure out the ideal needles for this engine.
But first, the airbox restriction: easily solved by cutting a big hole in the top of my airbox. It still has cold air forced into the area from the intake duct, but it’s free to take as much air from the engine bay as it needs. The lean condition at top revs disappeared instantly.
Update from June 2016: Eventually we’ve ended up with AF needles (as recommended by the lads at Hitech), but modified to enrich the idle. Now we’re reliably showing a 13.5:1 mixture at idle, 14.5:1 mixture at a very light cruise, and 11 to 12:1 under acceleration. I thoroughly recommend getting a wideband air/fuel ratio gauge- it makes tuning amazingly easy.
The last time we saw the rear brakes they were freshly installed and looked like this:
The rear brakes were one of the first things I finished, before we figured out that cast iron needs to be zinc plated, and that some newer cast iron parts are quite weak, especially when it comes to threads. In the excitement of final assembly I couldn’t be bothered going back and bringing the cylinders up to the same standard as all the rest, hence the brakes now look like this:
Gross. The bleed nipple hole isn’t deep enough and only engages 3 or 4 threads, and so they’ve partially stripped, allowing brake fluid to weep out. The cast iron brake cylinders have rusted. This is clearly unacceptable. Out with the Helicoils, zinc plating bath, and black paint!
No, *Engine mounts*.
The Mini turned out a bit louder than we expected, despite the tons of Dynamat and plush carpet. Very frustrate.
A few changes improved it a bit (sealing the exhaust slip joints with maniseal, removing the lower engine stabiliser, lowering the idle speed) but the engine vibration was always present- with a particularly obnoxious resonant boom at 1100 and 3000rpm.
At a Mini club meeting Simon from Minibitz pointed out a couple of cars that were buzzing the same way, and he had a theory- recent genuine Rover engine mounts were of poor quality, and the rubber was too hard. Cars with new engine mounts (like ours did) had this problem, while cars with old mounts didn’t.
Turns out he was right, and the folks at Minispares have started making decent quality engine mounts to the correct specifications.
I fitted a pair of the new mounts yesterday. The difference is miraculous. It’s still a noisy little box from the 1960s, but it’s no longer deafening. The steering wheel doesn’t vibrate, all the dashboard rattles have disappeared, and we can drive at 80kph (3000rpm in 4th) without our heads imploding.