Whilst I’ve been rebuilding my Mini’s engine over the past week and a half, something which I was worried about and which has puzzled me for a long time is how to set the "end float". I’ve found there’s little help on the internet or in books of how to set this, or what importance it is, or even what it is – hence me attempting to write this. So here goes…

The end float is the amount of travel allowed between the gearbox casing, transfer casing and the idler gear. The idler gear is the middle gear out of the three transfer (drop gears), the bottom being the input gear, and the top being the primary gear which attaches to the crank.

The idler gear end float can be adjusted by simply replacing the idler gear shims which are available in different sizes, or can be very carefully sanded down using fine sand paper and a glass pane (for flatness) if too big. The shims fit by simply just placing them on the end of the idler gear itself, and there is no special way round they fit.

So there’s the basics, now how to set it up…

First of all I did this without attaching the gearbox to the block since its a lot easier and thankfully I had Ian helping me who told me it would be best to do it like this (he’s someone who’s done it before!). We cleaned up the transfer case housing taking extra care to clean the gasket surface as well as cleaning up the gearbox gasket surface that it mates to. We then trial fitted the transfer case onto the end of the gearbox (with no gasket or any other gears attached apart from the input gear) and we eventually got this to fit smoothly and easily by carefully modifying and sanding down the pins which attached to the gearbox and through the transfer case.

Once that was done, we trail fitted the idler gear on the gearbox and then into the transfer case roller bearing, and again mated it back up to the gearbox making sure it didn’t require much effect to push it on. After it was a good fit with little effort to push on, we fitted the gasket and used a small amount of new engine oil to stick it to the surface. I also used a cable tie to attach the top half of the gasket so it didn’t get in our way and so that it wasn’t bent very much.

Then the fun can begin. We cleaned up two shims that I had lying around and fitted them to the idler gear. We pushed the idler gear into its bearing in the gearbox then pushed the transfer case over the top until it was tight up against it. Next we grabbed the correct bolts which hold the casing on and torqued up the bolts to the correct torque level as per the Haynes manual.

Once that was done, we could then begin measuring the "end float". This is done, at first, by simply sliding a feeler gauge down, in between the gearbox-side shim and the idler gear itself. The feel of the feeler gauge should as tight as what it should be when setting the tappets – a firm feel but one which can still be moved around. Below is a photo of Ian with the feeler gauge measuring the gap.

At first this felt too slack and therefore one of the shims was too big. Off comes the casing again and we measured both shims, and then measured the other shims we had. By doing a little math of how much more gap we needed, the sizes of the current shims and the shims we had to play with, we could work out a combination which would work. Luckily I had another shim which made up the size first time which was a little thicker than the first one we tried, and this worked perfectly.

Again to check this, the transfer case had to go back on, including gasket, and torqued up again to the correct setting. Once that was done the feeler gauge went back in and hey-presto, the gap "felt" right.

To double-double-check this, Ian brought a DTI gauge with him. A DTI gauge (or Dial Test Indicator) is a device which can measure the distance between one point and another with huge accuracy. A vernier gauge is also great for doing this, but there is no way of physically getting one into the gearbox to measure the distance.

After 5 minutes of setting up, to make sure the DTI gauge was in the gearbox well and did not move, we could then begin measuring the end float using this method. We set the "end measuring pointer" (not sure what you call it) to point onto the idler gear itself. Ian then pulled back on the idler gear using his fingers through the hole in the transfer case where the primary gear sits and we took a reading from the gauge. And then, same again but Ian then pushed forward on the idler gear to see how much movement there was. We then took another reading and compared the two. It was perfect, so good news.

Below is a photo of how we mounted the DTI gauge in the gearbox.

Once we were certain that the distance was correct, the job’s done – its as simple as that. The shims are not attached to anything, they just "float" there (probably hence the name?) although you might find them difficult to remove on occasion since the oil sticks them to the idler gear quite well.

The next job on assembling the engine came down to removing the transfer case (again), and retaining the idler gear inside its ball-race in the transfer case until later – making sure the shims didn’t fall out or at least get mixed up! We then lowered the block onto the gearbox with all its new gaskets and so forth, then re-attached the transfer case. So long as the correctly sized shims which we’d previously worked out as described are fitted the same way around, then the end-float is set. In theory!

Finally, for your reference, here’s a little bit of blurb on the size of the end float gaps, as per the Keith Calver article on Mini Mania

The official manual end-float size is Between 0.003" and 0.006" (3 and 6 thou or 0.076mm and 0.152mm)

However, in the article written by Keith, he recommends that 6 thou is too big in any situation. He also states that for non-performance street cars (ie, standard Mini’s) he uses no more than 3 thou. Finally, he says for performance weekend-racers 4 thou is good and possibly a touch more if using straight cut drop gears (as was I). Perfect!