Tuesday 3 November 2015

Gearbox Rebuild and Assembly Completed

It is time to celebrate, so have opened a bottle of Penfolds Bin 389 to keep me company as I write this blog post. I would have ordered pizza however with the World Health Organisation declaring that bacon, salami and ham causes cancer a few glasses of red will have to suffice.

The rebuild and assembly of the gearbox is now complete. This has taken a bit longer than expected with a few hiccups along the way, some parts were difficult to obtain and many special tools were required for either assembly or dis-assembly. Many thanksto Garry Simkin for assisting me with the rebuild and Crawford Hall for all the special tools and some fine engineering machining work along the way. Hall and Hall (Dean) were also helpful in providing a number of rare parts.

So this box now has a new ring and pinion, new bearings, new seals, new pinion bearing carrier, new oil pump, new selector forks, and an array of new gears and dog rings. All the internals have been crack tested and the setup tolerances are absolutely spot on. So, a photographic dissertation of work over the past few weeks:

The above photos are representative of the assembly of the Limited Slip Diff (LSD) and mounting of the Ring gear. The brand new ring gear did need a bit of work to be suitable for use. 
It was a loose fit over the housing and the bolt holes were slightly oversize. 
This would have caused problems as the ring gear would have undoubtedly ended up off centre when bolted up, even by a few thou, which would have resulted in the ring and pinion going alternatively tight then loose as they rotated, resulting in severe stresses. It would also have made accurate setup immensely difficult.
To fix it, Crawford enlarged (machined out) the centre hole of the ring gear and press fitted a thin internal collar so that the Pinion then became a tight hand press fit on the housing. He also fitted four hardened pins (which can be spotted in the photo above) so that these take the shear load and not the bolts withing the oversize holes.

The next step was the assembly of the Input shaft bearing and seal holder, then slip in the Input shaft (top photo in the above set - the splines go into the clutch, mounted on the back of the engine). 
The Input shaft fits into (with a spline) the lower Layshaft. 
The gearbox oil pump drive gears were then fitted and tightened with our neat special tool.

Yes, the gearbox oil pump even works. 
Hand turning the layshaft resulted in a copious volume of oil being pumped. The quantity that would spray onto the ring and pinion gears (as well as the bearings via oil galleries) when the engine was buzzing at 11,000 RPM would be interesting to observe. 

The Pinion gear along with the LSD is then fitted into the gearbox with the ring gear teeth engaging onto the Pinion gear 

The above photo shows the Left Hand side cover plate fitted over the ring gear. 
Now it truth there was a bit more to it than simply bolting this on. 
A critical part of setting up a Ring and Pinion is ensuring the height of the Pinion gear is set correctly, as illustrated in a prior post. 
But then you need to set the 'backlash' and 'crush'. The backlash is the amount of movement or gap between the teeth of the Pinon and the gears in the Ring gear. The crush is the amount of preload on the tapered bearings on either side of the ringear. The crush is necessary to compensate for expansion of the magnesium gearbox case as it gets hot, to ensure the tapered bearings never become loose. 
The backlash ensures that the pinon and ring gear teeth are not jammed together (which also distorts the crush measurement). 
This is all done with adjustment of spacers on either side of the LSD, under the tapered bearing inner races. So it actually needed a couple of assemblies, measurement and then bearing / spacer removals (and new spacer manufacture by Crawford) and reassembly until we were totally happy with the setup tolerances.

The next step involved fitting and setting up the three new selector forks (sourced from Hall and Hall, lucky these were available) - refer top photo.
To do this accurately we had Crawford make a special jig that located the selector shafts in the exact location that they would be when the rear of the gearbox case is fitted. 
We were then able to mount the selector shafts (with all detent balls and springs) and the dog rings that the selector forks move on the Pinion shaft and then tighten up the securing nuts on each selector fork. The jig also then allowed us to check the working of the gear change when we had fitted all the gears later on to ensure that there were correct clearances and the dog rings engaged correctly. 
This work was fiddly and took a solid day of fine tuning and adjustment before we were totally happy with the alignment. Much easier to do with the gearbox on a bench than at the track!

Next step (series of photos above) was to then assemble all the gears, dog rings, spacers and bearings plus selector forks in the correct sequence on the pinion shaft (top shaft) and the layshaft (bottom shaft). 

There were a number of other minor repair jobs completed on the Gearbox as well as the major actions mentioned above. A number included thread repair, and example being the gear change selector mounting on the top rear of the gearbox, which must be undone and removed for each gear change. The steel fitting has been undone and tightened a few times on this box and perhaps over tightened a few times and the thread in the magnesium fitting was shot, so this was bored out and replaced with a steel insert. Other items requiring work included the new oil pump body that I acquired, which did not fit the original steel rotors and needed internal machining to work. Plus other items such as new studs etc etc.  

After tightening nuts, removing the selector shaft jig the back case of the gearbox was bolted on.

The Universal Joints / drive shafts were then fitted on both sides - Garry being the obliging hand model in the photo above demonstrating greasing up the UV joint roller bearing cups.

All done all finished (photos above).

The two photos above are the 'before' photos for comparison. 
Looks almost the same - where has all the money gone?