Idler Gear Bearing Issues
These seem to come mostly from 3 main causes;-
Poor Quality Bearings
There were some counterfeit bearings getting around for a while, these were not to the same specification as the originals, having shorter needle rollers and few of them, their load carrying capacity was markedly reduced as a result, These chewed out rather quickly, often with rather dire results.
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Post #6 in this thread has some of the counterfeit bearings;-
https://www.theminif...ild-essentials/
Heating of the Casings to remove the Bearings
Heating the casings distorts them. While they may appear to still retain their shape after heating, the bearing tunnels often twist resulting in a loss of alignment to it's opposing bearing. This can be observed as typically one side of the idler gear shaft will have 2 heavy wear bands, though it can show up on both ends of the shaft.
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The distortion will occur on either the Gearbox or the Flywheel Housing casings. As well as this banding, it will show up on the Thrust Faces machined in to the casings.
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Never heat the housings. The factory recommended explicitly against it and warn it will distort them. The distort occurs because the castings have irregular thicknesses, irregular shape and heating with the likes of a butane torch will never heat evenly. The Factory do however suggest warming them in hot water. From all the housings and gearbox cases I've had for repair from doing this, it's not a case of if the housing distorts, but it will.
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Only ever use the correct tooling for removal of these bearings. I've also seen some people hydraulic them out with grease, this usually works, but I've also seen cases where the bearings have been stubborn and the end result being a nicely punched hole placed neatly though the housing. With great care, using a very small grinding stone, they can have 2 slots ground in them and let them fall out, but great care is needed not to go through the bearings and damage the case. The ground material and that from the grinding stone needs to be cleaned away very carefully. I would not recommend this method if either bearings that you'll be using are still in the case as there's a risk some of the grinding dust will lodge in the bearing or behind it. It's harder to clean away thank many realise.
Housing Misalignment
I've found the late Gearbox Cases and Flywheel Housings, from roughly around 86-ish on, to have poor alignment. There is a whisper that these are matched and shouldn't be mixed, but that's not at all correct. The Factory did state;-
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There are 2 alignment Dowles fitted to the Gearbox case on to which the Flywheel Housing should retain precision alignment on to. Certainly on the earlier casings this alignment most of the time was very good, within tolerances to ensure good bearing and shaft life.
On the casings where there is misalignment, it usually shows up on the Machined Thrust Faces and on the Shafts of Idler Gear, in a similar way to when the housings are heated, but on both sides. Usually you'll see opposing wear on the casings thrust faces.
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This misalignment results in short bearing life, damage to the Idler Gear Shafts and rapid wear of the Casings Thrust Facings.
