Mk3, LH Switch Cluster Screws? (2012)

My LH switch cluster screws pn 06-2488 are stripped out, Phillips type. I managed to get a couple out and was going to replace them with socket head cap screws. But the manual shows them as being #10 UNF, and they aren't. They look to be #8, not fine but very fine. Has anyone else noticed this discrepancy and can you give me the proper size? I'm thinking about drilling them out, tapping to 10-32 and using SHCS if I can't find replacements.
JD75

Can't say I know the size, but Rocky Point Cycle lists them for ten bucks (covers both left & right side for the MK3 - look under the Norton section then go to Stainless - Front End.

...that is a good link above, thanks L.A.B.
Here is what I found on an early s/n MKIII, I'm not the original owner so anything may have happened since birth but the rest of the machine is unmolested so odd as it is the fastener threads are mixed on this one.

MC threads are #10-32


Switch housing halves are M4 and #10-32 how bizzare.


All the Best.

AntrimMan said:

Switch housing halves are M4 and #10-32 how bizzare.

Click to expand...

10-32 and M5 coarse are very similar in both diameter and pitch so it's anybody's guess.

My RH cluster has 10-32s, the LH looks like 8-40 if there is such a thing, could be M4 like someone said. This is an original bike. Oh well, it's a 75 Norton, looks like there are several variations.
I'll make it work.
JD75

Corrected see comments below
Just adding this in, as I spent time looking over the various possibilities. I purchased my bolts from Bolt Depot.
4 - Socket cap, Stainless steel 18-8, #8-36 x 7/8 for the switch assembly on the clutch assembly. #8-36 x 1 - should be as stated above - 4mm x 0.7.
4 - Socket cap, Stainless Steel 18-8, #10-32 x 1 3/4 for the Master cylinder to the throttle housing.
There are 3 remaining that join the Throttle housing together.
1 - Socket cap, Stainless Steel 18-8, #10-32 x 1 1/4
1 - Socket cap, Stainless Steel 18-8, #10-32 x 1
1 - Socket cap, Stainless Steel 18-8, #8-36 x 1 - should be as stated above - 4mm x 0.7.

The M4 and M5 metric are very close, and I was able to screw the above screws into my Bolt Depot thread checking tool "#21136 Internally threaded screw gauges, US and Metric" into the 4mm x 0.7mm thread and the 5mm x 0.8mm thread. The dimensions are nearly identical. I do not think Norton would have used any metric, but they seem to somewhat fit, but slightly loose. The tool is plastic, so it had some give that metal threads do not have.

winsur4 said:

I do not think Norton would have used any metric,

Click to expand...

The switch clusters were manufactured by Lucas and therefore presumably supplied as complete assemblies including clamping screws (but not master cylinder screws). UK manufacturing was also beginning to 'go metric' by this time and Lucas was certainly using metric threads (for instance, the Lucas T160 starter motor assembly has some metric threads).

winsur4 said:

4 - Socket cap, Stainless steel 18-8, #8-32 x 7/8 for the switch assembly on the clutch assembly.

There are 3 remaining that join the Throttle housing together.
1 - Socket cap, Stainless Steel 18-8, #10-32 x 1 1/4
1 - Socket cap, Stainless Steel 18-8, #10-32 x 1
1 - Socket cap, Stainless Steel 18-8, #8-32 x 1

Click to expand...

I assume you mean #8-36?


I pulled a RH cluster out of the spares box.

The two larger possibly original Posidriv screws certainly measure up as 0.8mm pitch, not 32 tpi (Edit: although it is close. The major diameter is more than #10 = 4.826mm) and are a good fit in the casting.
M4 x 0.7mm is just over 36 tpi so #8-36 will probably screw in, however, #8-32 does not as it is too coarse.

I could not get the 8-36 screws from Bolt Depot to fit, so I assumed they must have been 8-32. Now that I started to put my clusters back together I cannot get the 8-32 to fit either. The threads are too coarse and the shaft diameter is too big. I went back and measured each of the original screw sizes. The 8-36 threads do appear to be correct, but the "factory" Norton screws are .150 in diameter as measured by my calipers. The official 8-36 screws from Bolt Depot did not work as they are slightly too big in diameter, measuring at .160 which is slightly smaller than the official size (.164) according to all the charts I have found so far! This sent me back to looking at the 4mm screw, but it is supposed to be measured at .157, which would still be too big. If I can find an 8-36 bottom end tap, I might try to enlarge the screw hole. Perhaps a "small" M4x0.7 screw will fit after all. On my previous MKIII I drilled the smaller screw holes out and I think tapped them to a M5x0.8, as the treads were stripped.


I took out my 50 year old Craftsman 4mm x 0.7 die, and cut all my 8-36 down. Remarkably all the threads lined up, with not a single thread crossed. All 5 fit perfectly. It now takes all kinds of wrenches to work on a MKIII. The metal removed during the cutting looked like a fine spring,

Just fitted new Sparks switches to my Mk3 and the screws are M5x08. Hope this helps.

ELLIS

winsur4 said:

The 8-36 threads do appear to be correct, but the "factory" Norton screws are .150 in diameter as measured by my calipers. The official 8-36 screws from Bolt Depot did not work as they are slightly too big in diameter, measuring at .160 which is slightly smaller than the official size (.164) according to all the charts I have found so far! This sent me back to looking at the 4mm screw, but it is supposed to be measured at .157, which would still be too big.

Click to expand...

I think M4 major diameter can be less than 0.157"

https://www.engineersedge.com/hardware/metric-external-thread-sizes1.htm
"Major Diameter Max-Min.
M4 x 0.7, 3.978- 3.838mm (0.1566"-0.1511").


I removed three remaining (one lost) rusty-headed screws from a spare LH cluster which measured 0.152-0.153" and approximately 36 TPI, definitely not 32 TPI.
I measured a selection of various new stainless M4s which were 0.151" - 0.153" and an identical thread pitch to those removed from the switch cluster. I also measured #8 -32 as 0.160" therefore the original screws seem to be M4 than #8.

ELLIS said:

Just fitted new Sparks switches to my Mk3 and the screws are M5x08. Hope this helps.

Click to expand...

The original Mk3 Lucas switch clusters. however, have five (M4?) and two (M5?) clamping screws (plus the four master cylinder screws).
https://andover-norton.co.uk/en/shop-details/17074/switch-cluster-screw-set-850mk3-only-17-pieces-

winsur4 said:

Corrected see comments below
Just adding this in, as I spent time looking over the various possibilities. I purchased my bolts from Bolt Depot.
4 - Socket cap, Stainless steel 18-8, #8-36 x 7/8 for the switch assembly on the clutch assembly. #8-36 x 1 - should be as stated above - 4mm x 0.7.
4 - Socket cap, Stainless Steel 18-8, #10-32 x 1 3/4 for the Master cylinder to the throttle housing.
There are 3 remaining that join the Throttle housing together.
1 - Socket cap, Stainless Steel 18-8, #10-32 x 1 1/4
1 - Socket cap, Stainless Steel 18-8, #10-32 x 1
1 - Socket cap, Stainless Steel 18-8, #8-36 x 1 - should be as stated above - 4mm x 0.7.

The M4 and M5 metric are very close, and I was able to screw the above screws into my Bolt Depot thread checking tool "#21136 Internally threaded screw gauges, US and Metric" into the 4mm x 0.7mm thread and the 5mm x 0.8mm thread. The dimensions are nearly identical. I do not think Norton would have used any metric, but they seem to somewhat fit, but slightly loose. The tool is plastic, so it had some give that metal threads do not have.

Click to expand...

I think the above explanation that the Lockheed master cylinder used metric, so the above metric socket cap screws are the ones to use.