Vintage Road Racing Association

My Oil Filter cover is held on by three 5mm studs and the nuts are 5mm threads and take an 8mm wrench.

For the past few years, they have been silicone’d but I was told that if I showed up at Shannonville like that I would be sent home.

The problem is that it’s pretty much impossible, at least for me, to drill a hole for wire in a 5mm nut with a 1/16 or 3/64 drill. There is not much meat, and it typically ends up going through the thread and once its screwed onto the stud you can’t get the wire through.

If I stay closer to the outside of the nut it simply leaves an open hole on the outside which defeats the purpose

Is there such a thing as an acorn nut with a 5mm thread but with a head for a 10mm socket, or would I have to have that custom made. I was thinking about buying 6mm nuts, screwing in a 6mm bolt, sawing it off and tapping it for 5mm

I’ve spoken to the usual suspects like Grainger and they don’t carry anything like that.

The other alternative is to split the cases and have them machined for 6mm studs on a mill, which I really dont want to do.

Brian, curious, which bike?

Hey Brian,
Some possible solutions.
12mm nut with the center welded shut, redrilled and tapped for a M5 thread then drilled across the corners for lockwire. A short tube extension welded to the M5 nut bringing the end past the protruding stud then drilled straight across. Lastly install the M5 nuts then drill across the protruding stud and lockwire like its a castellated nut. All 3 would be acceptable. I'm sure you can come up with something that will work.

Remove two of the studs and replace them with M5 capscrews that are easy to wire

Why not just remove the studs and use M5 bolts? Cap Heads are easily drilled.

I really don't like using bolts with very fine threads in cast Aluminum and screwing them in and out all the time as they are probably only good for a couple of dozen insertions, even if the torque limits are respected.

I ended up just turning a M6 nut with 6mm threads, into a M6 nut with 5mm threads and drilling them. I'm still going to have to use silicone on the ends as they are supposed to be Acorn nuts but at least they will be wired. Next time the motor is apart I'll have the housing drilled and tapped for 6mm threads and use 6mm studs.

I did have enough space to get the drill in and drill through the stud. I wanted to do that with my brake adpater plates on the GPZ but Michael was worried about weaking the bolt and recommended against doing it. For that I ended up just welding the nuts to the bolts as they will never have to come off again.

Another idea - hexagonal bar of the largest diameter that will fit the space available, drilled and tapped internally to your 5mm thread. Longer than the stud so that you could either drill the lockwire hole across the full diameter, flat to flat, or across the points.
https://www.metalsupermarkets.com/shapes/hexagon-bar/