It’s not a car, it’s a hobby. It’s not a car, it’s a hobby. It’s not….

The last time we had the head off we noticed that one of the brass blanking plugs was moving, and would need to be fixed soon. And then a few days ago we heard a bit of a rattle from the drop gears- so it seemed like the perfect time to pull the engine and check it out.


There have been one or two unpleasant surprises. Like the oil leaking past the primary gear and onto the clutch:



We know it’s getting past the primary gear because the main seal is spotless:


Turns out the brand new primary gear we bought from Minispares has 0.006″ clearance on the front bush when it should be 0.004″ to match the rear bush. I guess it explains the drop gear rattle. It looks like the odd clearances caused the gear to tilt while running, overheating the front edge of the bush as well as allowing oil past. It’s the one on the right:


Fortunately we have a spare primary gear which has good clearances all round, so that’ll be going in after polishing the crank bearing surfaces.

While we were in there, I decided to check the cam and followers. I’d come across a few articles* and forum posts lamenting the quality of cam followers produced since c.2011, and since we bought our followers in 2012 I wanted to check that all was well.

All was not well. This is what a cam lobe and follower should look like:



Note the lobe wear on one side, and the circular wear on the follower. This indicates that the lobe is touching the convex radius on the follower face correctly, and that the follower is rotating properly. Only half of our cam lobes looked like this- and this one was the best.

Here’s what the other four looked like:



Cam wear in the centre of the lobe indicates a flat faced follower, and the back and forth scuff marks on the follower face clearly show that it isn’t rotating much.

Since we’ve only done 500km I’m really, *really* hoping that the cam can be salvaged by fitting new followers, otherwise we’ll need to buy a new $400 cam as well as the $100 followers.


Oh, and the head plug that’s moving? Fairly common, it turns out, and the repair is straightforward. Here’s the plug, it should be flush with the head surface but this one’s started to move back into the head about 0.2mm. Since it intersects the fire ring of the head gasket it needs to be fixed.


Simply tap the plug, and extract it using a stack of washers:



Then tap the hole to 3/8NPT, install a solid pipe plug with a bit of retaining compound for luck, and machine it flat again. Which I’ll do once I find my 3/8NPT tap.


*The best articles are at and

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