Air filter help

swooshdave · Jul 22, 2019

gortnipper said:
I did the same. Easy. Mount the bracket on the inside of.the battery tray and it supports the lock more than just one bolt would.

I’ll try to get a better picture tonight. I’m not going to take the back plate off. That’s the bolt that fell into my crankcase and I think it’s cursed.

gortnipper · Jul 22, 2019

This is kind of a crappy picture before my restoration, but you get the idea.

I have had to flip it to the other side now, using the ham can threaded mounting bosses at the bottom front of the battery tray, since I now have a 2:1 high pipe on the left which blocked access to the key.

NickZ · Jul 22, 2019

Looks pretty straightforward. Thanks guys. I think I will use the threaded mounting bosses on the battery tray as well since I won't be using them for a back plate.

swooshdave · Jul 22, 2019

NickZ said:
Looks pretty straightforward. Thanks guys. I think I will use the threaded mounting bosses on the battery tray as well since I won't be using them for a back plate.

Post pics when you’re done!

gortnipper · Jul 22, 2019

NickZ said:
Looks pretty straightforward. Thanks guys. I think I will use the threaded mounting bosses on the battery tray as well since I won't be using them for a back plate.

If you do that, and run it on the primary side, you will need to be careful with not having additional keys on your ring. See how close it is when I mounted it above that using central hole above the level of the base of the battery tray. The threaded holes are about an inch below that.

NickZ · Jul 23, 2019

swooshdave said:
Post pics when you’re done!

Will do. Probably be a couple weeks before I get to that.

NickZ · Jul 23, 2019

gortnipper said:
If you do that, and run it on the primary side, you will need to be careful with not having additional keys on your ring. See how close it is when I mounted it above that using central hole above the level of the base of the battery tray. The threaded holes are about an inch below that.

I see that from your photo. I may try to get a little fancy and have the bracket bend so the switch is oriented as standard, although my wire harness length here is a limiting factor.

ILLF8ED · Jul 23, 2019

K&N makes a stock size filter that fits into the Norton ham can stock unit for all ‘68 to ‘74 Commandos pre MkIIa. Unless this is the one that allows grit in, wondering why anyone would not use this. It has larger surface area than the small cone type filters and everything fits like ignition switch bracket.

NickZ · Jul 23, 2019

illf8ed said:
K&N makes a stock size filter that fits into the Norton ham can stock unit for all ‘68 to ‘74 Commandos pre MkIIa. Unless this is the one that allows grit in, wondering why anyone would not use this. It has larger surface area than the small cone type filters and everything fits like ignition switch bracket.

Do you know the part number?
I probably can't use it because the Amal Mk2's on this bike are very different from the concentric Amal Mk1, but I'd like to check it out.

swooshdave · Jul 23, 2019

I doubt the stock Airbox will work.

NickZ · Sep 5, 2019

swooshdave said:
Post pics when you’re done!

After a lot of digging, the solution I went with is to use 2 K&N RC-1250 filters, but they needed to be modified by having some of the width cut off. I bought these from Old Brits and Fred was kind enough to modify them for me. I covered the cuts with some material from a particle mask because there were some open areas in the cut portion. With the mod, everything just fits. I went with the simple approach with the ignition switch. You can see it in the 2nd picture. I had to drop the wire harness for the switch between the 2 filters. There is just enough room for the battery retaining bar and there was an indentation in the oil tank right where there needed to be one.

Fast Eddie · Sep 6, 2019

A bit too late for you Nicksz, but for future ref, oval filters are available that negate the need for such mods.

NickZ · Sep 6, 2019

Fast Eddie said:
A bit too late for you Nicksz, but for future ref, oval filters are available that negate the need for such mods.

Wow, I thought I looked everywhere for oval, round, single, dual and could find nothing with the correct dimensions. For future reference, do you have a part number?

acadian · Sep 6, 2019

Still don't understand why people insist on using those filters, it's like a sandblaster for your cylinder walls. Stick with stock or oiled foam if aftermarket is what you're after

Fast Eddie · Sep 7, 2019

NickZ said:
Wow, I thought I looked everywhere for oval, round, single, dual and could find nothing with the correct dimensions. For future reference, do you have a part number?

It’s a while since I searched for them, they used to have a full catalogue on line where you could search through, with patience. I can’t seem to find that now.

First thing I’d do is check the ID of the filter where it mounts to the carb spigot and then as Matt at cNw if the tapered K&Ns he suppliers for his FCR kits fit.

Failing that, have you tried this search function: https://www.knfilters.co.uk/search/universal/oval-tapered-universal-air-filter/

Onder · Sep 7, 2019

People go to the KN type filters because they are a lot easier to deal with. But Im less worried about airflow than filtering ability which is why
I still use the stock setup. Other bikes, such as the Trident, are tough to source original filters so you dont have much choice.

jsnorton · Sep 7, 2019

I have a 73 850 that I have been using K&N air filter since 1978. Just keep them maintained and they work great. I also turned the ignition switch to the left side pointing out.