The starter motor has to fit both the bellhousing and the ring gear on the flywheel. There are a couple of options here with different starter motors from different cars. The original Midget one won’t fit as it is too big, and the Rover one rotates in the wrong direction. The options seem to be a Frontline starter motor kit (expensive), a Ford sierra starter motor or a Caterham starter motor. (Edit in 2014 – the Sierra one has been known to not last very long) All the motors need a spacer to make the starter cog engage with the flywheel ring at the right point, if this spacer is too small then the starter cog hits the flywheel all the time, if it’s too big, the cog wont engage properly and there is a possibility of ether the cog or the ring gear stripping. The starter I used is a Caterham one, as it made sense to try and match the bellhousing and starter. I managed to buy a ‘faulty’ one form eBay for £35, turns out it isn’t faulty at all. The Caterham starters are expensive from Caterham direct, however, and the cheapest solution is to use a correctly spaced Ford sierra starter (Edit – if you don’t mind doing bump starts later on).
I bought the spacer with the bellhousing direct from Caterham, which meant everything lined up. However, the starter motor needs some modification to get it to fit. On the block, the area with the engine number on it needs to be ground away, as does a little off the lower flat bit as well. Some people grind the ribs away as well; the Ford starter motor is bigger and needs more taking off here, whereas the Caterham one can fit without changing the ribs.
The Caterham starter is very compact, although quite a lot needed to be ground off the engine number plate. To get the whole thing to fit, the spacer was thinned out a bit on its inner end so that it fitted behind the rib between the engine and the flywheel. The starter motor mounting plate was also modified so that the whole thing could be put on and off without having to take the bellhousing off every time; this also meant that the bolts line up much better and the whole thing is easier to put on.
The bit with the pink dot on it used to be round, I chose this method rather than the grinding away of the engine ribs. The starter motor fits very close to the engine, I can get a sheet of paper in between but that’s it. It is also very close to where the exhaust manifold will go, so some kid of heat shield arrangement is needed.
The following shows how off-round the mounting plate is:
When you’re putting it together put the bellhousing and starter together without the gearbox and make sure that the cog on the starter is fully engaging with the ring gear. If it’s driving on the angled bit at all eventually it’ll push the ring gear off the flywheel, and then it won’t start, and you have to take it ALL apart again…
Turned out that pushing the ring gear off also bent and cracked the engagement mechanism on the starter motor, meaning it wouldn’t slide in and out of the starter motor housing properly. That’s a new starter motor needed then; I’ll keep the knackered one for spares.
Re-spacing the starter motor (so it doesn’t operate on the lead-in section) and fitting some small angled brackets on some of the clutch retaining bolts to keep the flywheel on, and it’s been fine ever since.