24th March 2020

Shim grinding sat down

So first day of COVID-19 lockdown so no excuse not to go to the garage. I’d got the shims from OCT so it ought to be a simple job…

Shim grinding

The only shim with a very tight (zero?) clearance is the primary side outer exhaust. OCT supplied the required .260 shim but having installed it there was still a long way to get the correct gap.

I started off being just like a proper engineer with a wet stone and rubbed away. It was taking ages and eventually I gave in and headed for the electric grinding wheel that lurks in the back of the garage. In my mind I remembered someone advising against the use of the wheel. I can only think this warning is because it must be easy to take too much of the shim – but also if, like me, you hold the shim against the side of the grinding wheel it’s dead easy for it to catch and end up in your eye (wearing googles are we…)! So I came up with a method that worked well – turn on the wheel turn it off and as it slows down put the shim again the side of the grinding wheel while rotating it between thumb and index finger. This took the shim down at a leisurely pace with an even grind. The shim also didn’t get hot which might be the case if you held it against the wheel too long. I took regular measurements, hand finished it on the wet stone and offered it up several times before I got acceptable clearance.

I’ve gone for consistency across the exhausts at an Imperial measure of 12 thou’ that’s wide of the recommended 10 thou but aside from the closed valve it was working alright loose. The other issue is the non availability of big shims to reduce the gap.

Cylinder head without cam bucket and showing damage

Worn cam buckets + a deep score on the centre bearing journal

Cylinder head showing OR cam

Cam in place prior to tightening – note you can just make out ‘OR’ stamped on cam

So with the shims complete it just remains to torque the exhaust cam down. Gert Schnogl told me it’s 3.5 kgs applied in increments of 1.5, 2.5 and 3.5 kgs. He also sent me a PDF of the Atlas workshop manual – email this site if you want a copy.

Next steps are the inlet side, clean the carb, inspect the rear suspension for seizure and then shove the motor back in the hole connect it all up and fingers crossed…

Something good may come out of this damned pandemic!

Nick 🙂

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