Sunday, March 15, 2015

Gearbox Rebuild - Part 3 - Gears In

<This post is part of the 'Winter Project 2014/15 - (Gearbox Refurb)' project>

With the mainshaft built up in the previous post, it's now time to mount it in the gearbox. Already in place, detailed in this post are the selectors, the reverse gear and the oil strainer. Just like in the previous post, I'll be using a step by step guide, two in fact, this one posted by Mini Mania to help me get the gears in and also this video for bolting it all up afterwards. I also found this article from The Mini Forum an incredibly helpful read.

No matter how much research is out there, there's nothing like experience so here we go...


Looking at the bearings originally removed from the box, the first motion bearing was in very good condition and able to be reused. The main centre double bearing though would need replacing as it was suffering from a shredded ball, rather it than me! As I didn't want to buy a cheapo copy replacement set, I thought I was going to have to shell out the going rate of about £50 (ish) for a genuine set of  'RHP' bearings.

Shopping around however, I found that Guessworks were selling second hand genuine 'RHP' items for £12. With such a huge saving to be had by getting the second hand set, I couldn't resist and bought them. When they arrived I was glad I did as they were in excellent condition and looked like new.

'New' - second hand
bearings from Guessworks.

As the 'new' bearing doesn't come with the outer retaining ring, the one from the old bearing needed to be swapped used.

'New', well second hand bearing
with old ring.

Mainshaft Install
Lowering the mainshaft into the gearbox is fairly straight forward, it goes in long end of the shaft first and then lays flat as the syncho hubs sit in their respective selector forks.

Mainshaft in.

Next thing to go on is the first motion shaft with its internal roller bearing, also as this shaft hosts the 4th gear, it needs the 4th gear baulk ring.

First Motion Shaft goes on here.

Next the bearings need to be installed. I focused on the first motion shaft end first, but to ensure the mainshaft was central and straight, I also loosely fitted the main centre double bearing at the other end. Using a drift, the first motion bearings were tapped into the case, once all the way in, the large circlip locked them in place.

Main centre double bearing fitted loosely...
first Motion bearing tapped
in, ready for the circlip...
Once the circlip in on,
this side was complete.

Turning the gearbox around tp the main centre double bearing, ot too was driven into place and once fully 'home', a quick spin of the mainshaft confirmed that nothing was restricting it.

Main centre double bearing.

Inserting the laygear was a little hindered by the fact I had already bolted the top of the oil strainer in and bent over the locking tabs. Luckily though there was just enough space (with a wiggle) to squeeze the laygear through the gap. I'll have to remember to leave the oil strainer bolts until after the laygear next time.

Very quickly I realised that the right hand thrust washer needed to go in first! So removing the laygear, the thrust washer was put in place and the laygear was once more wiggled through the tight gap. The other thrust washer drops in from above as the laygear shaft is fed through.

I decided to reuse the old thrust washers as they were in pretty good condition and gave an end float of 5 thou. Reading through the article on The Mini Forum, the end float tolerances are between 2 thou and 6 thou so 5 thou is fine.

Laygear in.
3rd Motion End
With the layshaft in place, the locking plate can be inserted between the notched in the laygear shaft and the reverse gear shaft. Then the shim can be placed under the locking plate.

Locking plate

Then the shim behind
the locking plate.

Now the 3rd motion bearing retainer can be bolted into place over the shim. In the picture below, I haven't bent the locking tabs over as I needed to check with the feeler gauges that there are no gaps between the retainer and the housing.

Then the 3rd motion bearing retainer.

If there was a gap, it would need to be re-shimmed until it was gone, but thankfully it was tight as a drum so the lock tabs were bent over and the final big nut put in place along with it's locking washer. Torquing the nut up to the required 200(ish) Nm (150 ft lb) proved to be very difficult. The only was I could do it was to turn the gearbox upside down and stand on it while pulling on the torque wrench. It was a bit of a heave, but eventually the torque wrench 'clicked'. Once that was done, the locking washer was bent into place. (To do this, the gearbox was locking in exactly the same was as in this post.)

3rd motion shaft done.

1st Motion End
Turning the gearbox round again to the 1st motion shaft end, there are a few parts that need to go on, the first being the locking washer and the nut. The nut is a rather unusually sized 1 1/8 inch and a deep socket is essential to get it torqued up to the required 200Nm (150 lb ft).

1st motion nut

Once the lock tab is knocked over, the next thing to go on is a roller bearing carrier. as it's an interference fit with the shaft, it needs to be driven into place with a wooden mallet.

Roller bearing carrier.

The last thing to do is to place the cage over the carrier and pop the rollers in the gaps.


And that's it all done for now, the gears are in!

Working on the gearbox was a very enjoyable couple of hours and nowhere near as difficult as I first thought it was going to be. I'm pretty pleased with myself that with fairly mediocre mechanical skills and a cheap set of tools, I have actually managed to get the gearbox back together. It just goes to show what can be done if you put your mind to it. Whether it works or not is still to be proven, but I'm quietly confident.

For further research on how the gearbox works, I found this article on The Mini Forum an interesting and in-depth read.

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