The 'Commando' fork on my Slimline Commando was leaking on one side, so Yves and I took it apart last week. Except changing the oil, I had neither done anything nor opened this fork since I bought the bike 5 years ago.
We were in for a surprise, two surprises actually.
The first one, quite obvious, was that the left stanchion was shorter than the right one by about 4cm. The rest of the fork appeared identical on both sides, including the springs. On my bike, the disc is mounted forward on the left, with an AP Racing calliper. I have never heard of anyone mounting different sizes stanchion in the same fork.
After consultation with several friends and 'Norton wise men' including Norman White and Andy Savage, we decided to replace the shorter left stanchion by a longer (ie. Commando) one (600mm).
At that point, what had been right in front of our eyes all the time struck us, those are NOT Commando forks: the pistons are shorter and made of alloy, they have a different shape, and four holes instead of two...those are MANX forks.
Twice 150ml of SAE20 fork oil later, on the road, the bike felt precise and very smooth on the Belgian potholes. Flying Carpet grade, in fact.
There is a real difference 'before' and 'after', I don't think the stanchions lengths was much the issue, rather probably the oil was too thin before and the bushes were past their prime.
The only small negative point, but it could be subjective, is that I think the fork twists slightly to the right upon braking, which it didn't do before. However, after 50 odd miles, this feeling had mostly gone away. So perhaps the yokes simply had to settle in with the new stanchion...
