Tolerance
Matt spent some considerable time explaining to me the difference between tolerances. As I understand it, clearance fit is where the hole is larger (a wheel axle), transition fit where the hole is the same size (like a gear) and interference fit where the hole is smaller
(like a bearing in a car hub). Engineers, feel free to write in and correct me…
I really enjoy TIG welding after MIG welding since I was a boy, but I’m not very good – yet. You really need to be at it regularly to train the muscle memory of feeding the rod and knowing what the material is doing before you blow holes in it – so James offered! TIG is so much more precise than stick or MIG welding and I love watching the professionals.
Once James had loaded up the rocker arms, it was my turn to give them a radiused finish similar to the original. Top end done!
BOTTOM END
I decided after getting a little low last month to start again. I started making a bracket to hold the dial gauge to the crank cases, so I could measure the end float. I also needed the internet on my phone, as my measurement tools and my brain work in metric, yet all my Norton manuals and tips from my learned friends are in Imperial.
Hutch told me to buy the Zeus chart book, which helps with this and other fascinating engineering issues, so for less than a tenner, I’ve ordered one. It’s perfect for the workshop; the pages are laminated!
Anyway, I bolted the crankshaft into the cases, cleaned all the nuts, bolts and studs up and torqued everything all up. Original Norton nuts and bolts are really sharp and accurate, in case you’ve never noticed.
Anyway, the end float was found to be 1.4mm, or 0.05in. The Norton manuals I have all agreed
that an ES2 should be 0.127mm, or 0.005in. So I had 10 times too much crank float.
Then, I measured all the crank shims I had, laying them out. By my calculations I needed to lose 1.27mm which split evenly across the two sides, was 0.635mm. I think. So I stripped the cases, removed the crankshaft which came out with the roller bearing inners attached, added the shims, which I could almost exactly split evenly for each side and did everything up again.
The readings I got made no sense – I had added more than 1mm of shims, yet still had 1.2mm of end float. Bad words were said, beard was scratched and then I realised – I had placed the shims on the outside of the roller bearings and not in between the bearings and the crank flywheels! I couldn’t see how it would make that much difference, but I knew it was wrong. So take apart the cases, again, remove the crank, again, take the shims and prize the bearing off, then shims on, bearing on and put back together. Again.
I couldn’t believe the dial gauge when I saw it – 0.129mm clearance; as close to perfect as I could get! It had only taken me eight times to get it right.
Now to check the con rod was central… luckily, that was fine, so the cases were taken apart one last time to check, seal and finally assemble. I used Wellseal, which is horribly sticky and far too runny at first; Nev told me to squeeze some out into something and let it solidify a little, then spread it on both sides after half an hour or so. This I duly did after making sure the mating surfaces of the cases were nice and clean and then bolted it all up, hopefully for the last time.
PISTON BROKE…
The sense of achievement gave me a spurt of enthusiasm. The gudgeon pin was a tight fit in the piston, so I heated it up and the pin just slid in. We’re on a roll, I thought, moments before the gudgeon pin circlips fired themselves across the workshop. Hands and knees filthy, I eventually found it and popped it in.
With the wind behind me and long-awaited thoughts of riding my ES2 streaming back, the next job was to fit the new piston rings for my 0.30in
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