Intake Manifold Cap Screws

From the factory, Commandos had unique double knurled small hex cap screw, with a split ring washer.

In the past, I've had one vibrate loose and fall off, ending my ride.
What ,if any, aftermanrket improvements are people running to prevent this from happening?

Currently, I'm running a safety wire hole drilled version of the factory cap screw.

I've looked for other ways, but I think this is the best and only solution in this application.

It doesn't look like anyone offers a small head 12pt fastener which is (or can be) drilled for safety wire.

In 48 + years of owning my Norton I only had one carb manifold come lose, but at the time didn't know what was happening when the bike started to run on one cylinder it was night and 50 miles from home, I just turned that carb fuel off and ran the 50 miles home on one cylinder, next morning first place I looked and the 2 screws were lose, easy fix, that was about 30+ years ago and hasn't done it since but most people don't replace the spring washers and keep using the old ones but they do lose their spring that keeps them tight.
But every oil changes it's always wise to go over the bike to make sure everything is tight, no need to safety wire them if you use good spring washers and replace every few time the carbs have been removed, it's all about maintenance, both my screws were still in the manifolds they just came lose, I am still running the original allen head bolts/screws.

Ashley

Loctite every time.

elefantrider said:

From the factory, Commandos had unique double knurled small hex cap screw, with a split ring washer.

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They're not unique, they are 5/16" Whitworth thread so they have smaller heads that take a 7/32" Allen key (below right) unlike UNC which takes a 1/4 inch key (below left).

I know they are Whit. I meant they are unique in that they are the only double knurled cap screws on the bike. New replacements are not double knurled.

UNC does also work in this application (a little looser) but the larger hex does make it a little more difficult to access with the key.

I perfer safety wire rather than loctite here, for ease of disassembly.

elefantrider said:

I meant they are unique in that they are the only double knurled cap screws on the bike.

Click to expand...

They weren't the only double knurled cap heads on mine, just a manufacturer's eccentricity I'd guess.

Surprized nobody offers an ARP 12 pt kit for this.

Well if using UNC threads that are a bit loser then no wonder you have troubles with them coming lose, so why going to UNC over the WW threads, I never use Loctite on my manifold bolts and still using the original bolts from new.

elefantrider said:

Surprized nobody offers an ARP 12 pt kit for this.

Click to expand...

Why when the original allen head bolts work, just replace the spring washers when needed.

The bolt I lost was in fact an original one. Just pointing out that UNC is close enough that it will work.

I picked up some sample NordLock washers at a trade show, and saw a convincing demo on a vibration machine.
On their demo machine, the spring washers didn't really do much to prevent loosening with heavy vibration.

I use what I have, I have built up a big collection of new spring washers for my shed when working in the maintenance section of the Tec College I worked at for 31 years, have never really had a problem with lose bolts and nuts and my motor is hard mounted in the frame, in all the 49 years with my Norton and 44+ years in the Featherbed frame I have only had the 2 manifold bolts come lose on one carb, lost the nut off my left rear muffler mount and top gear box mounting nut and once 2 rear engine bolts come lose from the engine plate and crank case, not bad for coming up to 49 years of ownership, forgot lost my original horn on the Bruce HWY the mounting bracket was still there but no horn, was mounted behind at the rear of the bottom GB/engine plate about 20 years ago lol.
Great when you own your Norton from new you remember things like that, I still run all my original engine bolts but the frame engine plate mounts I run high tinsel bolts with fine threads and spring washers and nuts and spacers between the frame mounts and plates so they don't bend the frame mounting points from overtightening the bolts, have never had them come lose at all.

Ashley

To rat on myself, when I first bought my combat these fasteners were fixed with locktite. to remove the locktite, i used a brass brush that had somehow gotten wax on it. It took me about two thousand miles to figure out that I had waxed the threads. I got pretty good at tightening the screws on a hot engine. Later I realized what I had done and scrubbed the wax off of them and they have never loosened since. Sometime the pain you suffer is self inflicted.