Fork Oil

Whatever viscosity suits the wear in the internal damping parts and your riding style. Could be 20w to 40w, I use 5w but have completely different internals based on CBR600RR Showa inserts.

'70 Commando with lightly modified dampers ( I forget the name). I tried 30 weight and the forks were VERY stiff. 20 weight is a lot better but 10W was too light.

Mk3 with Covernant modification I found 20wgt made the ride too rigid gone to 15wgt and is a lot better, I am using Maxima fork oils.

Mk 111 I use 20 Weight fork oil , but 160 c.c. Each leg. Progressive suspension springs . I'm happy with that and I tour with full camping equipment on the rear too .

ELLIS said:

What weight fork oil should I use in a MK3 Commando. I believe the capacity should now be 180cc according to Andover Norton.

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Trial and error.

And whilst trialing and comparing, ensure you use the same brand as the weight ratings between brands vary wildly.

in my 74 Mk2, i've been using Maxima 57901 20WT Standard Hydraulic Fork Oil - no issues.

10 wt recommended for Lansdowne conversion.

Marty Smith & his fellow Americans use A.T.F. & ' tuned ' with motor oil for desired viscosity , centuries ago .
We used A T F .

BUT , now theres Power steering Fluid , which was the same thing . But has seal / rubber THINGS & suchlike .
So might be good . Dashing & daring , you could try Synthetic Power Steering Fluid . It'd keep the moisture
out better , perhaps .

I rang up Castrol & said Id put Synthetic P S F with Mineral P S F , and now there was smoke & flames coming out of it .
This got his attention .
He assured me it was ' no problem ' Mixing Syn. & mineral , there . After I said that might not actually be the case .

Would it be correct saying for a 73 Commando Roadster the correct amount of oil per fork is 180cc considering 15W is being used?

ELLIS said:

What weight fork oil should I use in a MK3 Commando. I believe the capacity should now be 180cc according to Andover Norton.

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It's actually a bit of a pointless question since there's seemingly no standard for measuring the viscosity of fork oils - its a bit like motor oil vs gearbox oils, the numbers mean very different things.
Somewhere in the net, there's a largish list compiled by one of our friends across the pond, listing a huge sober of different makes of fork oil, the claimed viscosity and the measured viscosity. There was no correlation between brands, but a reasonable fit within each brand.

In other words, brand X 15wt (hate that term!!) could well have the same measured viscosity as brand Z's 30wt or brand Y's 5 wt.

The only solution seems to be to pick something that you like the look (and price) of and try various grades to find one that works for you.

On a Norton though, that's a real PIA due to the slow speed of filling the forks.

I've put a Landsdowne conversion on mine, and am currently running Putoline 10 - purely because its reasonably priced, widely available at a chain of shops here in a range of viscosities.