Fork Oil Grade

Other fork oil threads have been a bit derailed by the volume/quantity discussion of Imperial/British/American/metric units

This thread is started for the fork oil grade only.....I live in hope !

I see on the Castrol web site that 10w30 is no longer available and my very old bottle of it is nearly empty.

Castrol is now available in 10W, 15W and 20W specifications.

I have refurbished my forks with many new parts such that they are as new.

My use is country roads, dual carriageways and no motorways at a pace commensurate with my age, police patrols
horses, cyclists, HGVs, the usual riff-raff and speed cameras.

I am tempted to fill with 15W Castrol fork oil

What do you think?

I've used similar before..... now they contain trans oil..... Anything except dry for me.

There is no standardized 'grade' for fork oils. 10w oils from a variety of manufacturers don't have to adhere to a set.standard.

All you need to know about fork oil viscosity.

I used Silkolene 20 grade last 'refresh' simply because I had it on the shelf. I know refilling can be a pain, but given the small quantities involved why not just try what you propose and see?? Doubt you could damage anything..

As suggested, there will be no damage so try whatever you want and see how it works. I've used ATF in mine for 15 years but that's with the Fauth fork mod. Probably too light for OEM forks.

In the old days, I used SAE 20. It's no longer available around here and I weigh more so I use SAE 30 today. Both non-detergent, not synthetic.

I read somewhere on here 20/50 was an option - so, if it’s good enough for the engine, that‘s what I’ve used.

I could never use any thing thicker than 10Wt folk oil, But that depends on the wear in the internal parts , With a new parts in ,I used 7.5 wt Motul folk oil and I'm quite happy, when the weather warms they will even get better , I hate stiff suspension.

After I renewed my Roadholders, I visited my local motorcycle specialty shop and asked what they had in fork oil. When I was told the price was about $30 per quart, I put in 20W40 motor oil.

Slick

Works for me:

https://www.walmart.com/ip/MAXIMA-F...tevdbd3ziEckjB2EiAhoC5qQQAvD_BwE&gclsrc=aw.ds

p400 said:

View attachment 79175

Click to expand...

Generally, I like to do what the manual says but if you study the forks column, you'll see that just about anything is acceptable. ATF, 10W30 and 20W50 are not equivalent. Forks I've taken apart that had ATF often were a mix of homogenized ATF and water (white goo). When I've used multi-grade oil I find more black sludge in the bottom. I seldom see either with plain SAE 20 or 30.

I used this:

I always liked this (20 wt.) in other bikes. In the Norton is was VERY stiff in cold weather. When I changed to 20-50 engine oil (as directed by bill), it was MUCH improved.

Perhaps this chart will clarify things (or confuse things further)


FWIW I am using Bel-Ray Fork Oil 15wt in my forks with Landsdowne Dampers. I tried 3 other weights
of the same oil until I decided 15 wt worked best for me. Be aware that since there is no standardized
set of values for fork oil, one brand's 15 wt may be the same as another brands 7.5 wt or 20 wt.
Oils marketed as for forks generally have anti-foaming additives (not that I am able to evaluate how
oils without this actually perform). YMMV

lazyeye6 said:

Perhaps this chart will clarify things (or confuse things further)

Fork oil weights

FWIW I am using Bel-Ray Fork Oil 15wt in my forks with Landsdowne Dampers. I tried 3 other weights
of the same oil until I decided 15 wt worked best for me. Be aware that since there is no standardized
set of values for fork oil, one brand's 15 wt may be the same as another brands 7.5 wt or 20 wt.
Oils marketed as for forks generally have anti-foaming additives (not that I am able to evaluate how
oils without this actually perform). YMMV

Click to expand...

Wow! That's a lot of fork oils! I never knew there were so many!

This is what Norton recommended in their specs for the Commando PR, Castrol CR130, an SAE 30 motor oil, or approved equivalents. Somewhere I have a letter from them where they suggest either 20 or 30, depending on circuit roughness. I used SAE 20 motor oil in my PR for most tracks, and it seemed to work well. I did sometimes use SAE 30 for bumpier tracks, and for really high speed tracks like Daytona. That was with stock front forks with no mods. I also tried 20 and 30 weight fork oils, and they also worked well. I really didn't see that much difference in using the different oils, but maybe I was just not that discriminating about suspension feel back then. The one thing I did notice is that the damping felt much stiffer at the beginning of a race, but improved rapidly as the fork oil heated up. At the end of a challenging race, the sliders were uncomfortably hot to the touch.



Ken

I prefer 30wt in my forks.

I use 20 W. fork oil. I'm overdue for a change .

Thank you for your replies. I was hoping to get the fork oil grade and a comment on its performance.

I've seen the Perter Verdone table, the table from the manual and the Spec for the PR previously. And
realise that the various fork oil specs do not entirely correlate.

And I realise I will not cause any damage by the use of the "wrong" oil.

And of course I do not want to over think this !

In summary using Peter Verdone's table for cSt at 40C as a sort of arbitrary comparison:
Castrol 10W = 15.00
Castrol 15W = 46.50
Castrol 20W = 68.00

Estuary Boy - Silkolene 20W = 67.70, but no comment on stiff/soft
JBruney - Trans oil = no PV table data, no comment on stiff/soft
MexicoMike - ATF = no PV table data, with comment probably too light for OEM forks
Marshg246 - 20SAE then 30 SAE = no PV table data & no comment (ATF water & Engine oil black sludge issues)
Landspeedracer - 20/50 engine oil = no PV table data, finds it good?
Carl H - Motul 10w or 7.5W no specific data, but PV data for Motul Comfort Medium 5 - 10 = 35.30
Texas slick - 20/40 engine oil, no PV table data
Mylar - Maxima 15 = 46.00 "works for me"
Concours - Kal-Gard 20W or 30W no PV table data, but too stiff for Norton & 20/50 engine oil much better
Lazyeye6 - Bell Ray 15W = 53.00, tried 3 others settled on Bell Ray 15W for Lansdowne
Lcrken - Castrol CR130 30SAE or 20SAE for PR depending on race track
Ilf8ed - Redline 30 heavy = 66.80 ? Prefers 30W in his forks

It also depends a bit on the ambient temperature........

It is a bit of a pain to change fork oil so I think I'll go with my original thinking of Castrol 15W due to new forks
and increased pot holes and uneven road surfaces causing more bumps for the forks to deal with.

Have road surfaces got worse or is it due to me now being old and notice the jarring more than I did 40 years ago !

If I find 15W too stiff or soft I can drain as much as possible, measure the outflow and add an appropriate
amount of 10W or 20W.

I've already over thought this too much !

Front Forks and it's damping are a personal thing.
All I can suggest to you is if you can still get then Kenny Roberts fork oil. You have to mix equal amounts to get say 15 grade etc .
I no lomger use motor oil inside mine, because as it has been stated elsewhere, you get a dark/black stuff left at the bottom when you drain/clean it.