Hitchcocks Forum

I'm just in the process of fitting a set of second hand B5 fork legs to my 612 bullet.

Just been going online to see how much fork oil they need (seemed prudent to change it before fitting them) and it seems others have already run into the same issue I just had ie. the top caps are in EPIC tight. These ones have certainly never been out. It seems many owners are actually just emptying and filling them from the bottom.

Here's how I did it:

First off, the top cap is a reverse thread, clockwise to unscrew. It has a recessed 12mm hex. The chromed slot-headed top-caps in the end of them are purely decorative (well, they also prevent water trapping) and are conventionally threaded.

The hard bit of this job is holding the fork leg tightly enough to unscrew them without damaging the fork, this is where people are falling down, I've seen multiple threads on the subject all over the internet. My top tip is to clamp it in the bottom yoke. I'm fortunate in that I had a spare one. I clamped this in a vice and clamped the fork in the yoke. In any case, first time doing this job, you're probably going to need to set aside half a day and get the forks out of the bike and onto the bench. You might want to remove the bottom yoke (or buy a cheap indian one to use as a clamp).

I then had to apply a lot of penetrating oil to the cap then a lot of heat to the outside with my burner torch. It still took a great deal of force to undo! The ideal would be a burp-gun with a 12mm impact bit, I'd expect that to waltz it out. As it was, I used a big allen key with a bit of pipe and whacked it a few times with a hammer to shock it into moving.

It'll be reassembled with plenty of anti-seize compound on the threads/plug and it should only really need to be nipped up, there is no way it can unscrew when the fork is fitted ont he bike. I expect it to simply unscrew next time.

For future fork oil changes, I think the procedure will be to unscrew the fork from the casquette and slide it down so it's sat just above the bottom yoke. Clamp the yoke again and it should be simple enough to unscrew and remove the top plug with a long hex bit.

I also think it would be possible to do the initial removal like this IF you have a burp gun and a long reach kex-key. Otherwise you'll need it off the bike so you can get some heat and leverage on it.

I can't see a dealer doing this. I'd be prepared to bet if your 500EFI has only ever been dealer serviced, the fork oil has never been changed.

The thread formed on the fork stanchion that screws into the casquette is not a left hand thread, it's just that you are undoing it from the bottom (so to speak) so it is clockwise to undo.
They can be a bugger to get undone though.
The later type are a LOT easier.

PeteF wrote: ↑

Sat Aug 29, 2020 1:18 pm

The thread formed on the fork stanchion that screws into the casquette is not a left hand thread, it's just that you are undoing it from the bottom (so to speak) so it is clockwise to undo.
They can be a bugger to get undone though.
The later type are a LOT easier.

No. You are talking about a different screw thread altogether.

For clarity, it is this type of fork:


The fork has a male and a female thread on the top of the stanchion. A large plug cap with an o-ring screws into the top of the stanchion, the spring and spacers can be removed from the top of the fork once this cap is removed in the same way as you would on a Japanese bike. They are fitted rediculously tightly from the factory and people struggle to remove them. This is a REVERSE thread, tightens anticlockwise.

The male thread which you are referring to that screws into the casquette is a standard thread. Even later ones don't have this thread, they clamp in but they still have a top cap.

I stand corrected, not come across that type.

Yes, the so-called in-line forks are fitted to later models of C5 (I think they are fitted to all B5 models). My 2015 has the in-line forks. It is MUCH easier to change the fork oil on this later type. Basically just remove the mudguard, caliper and wheel, loosen the hex cap screws at the top of one fork leg. Loosen the top and bottom yoke nuts and slide one fork leg out. Drain the oil into a measuring jug, noting how much oil came out after pumping the forks up and down. Browse suitable forum for fork oil weight and quantity. Realise there is neither consistency in how much oil comes out of each fork leg (between owners, the same amount came out of each leg on mine), nor a definitive amount of oil that should be used to refill each leg. Haynes specifies a figure that is way higher than what came out of my fork legs, other sources state different amounts, so I adopted a middle stance, not wishing to overfill. So, anyway, put x ccs of oil in the fork leg, refit it to the bike and then repeat with the other fork leg. I have learned over the years on various bikes to do one fork leg at a time; that way it’s a lot easier to establish how a fork leg should be refitted. BTW the early models of C5 had the offset forks but several owners complained of a significant “high” speed weave. It wasn’t present on all bikes (probably rider weight variances etc) but RE switched to in-line forks and this solved the issue. The B5 Bullet never had a problem, probably because the riding position is different and it had bigger wheels.

Interesting about the high speed weave. My C5 has "straight" forks (2019) but does have a slight weave over 70mph. I always put it down to the screen and it doesn't bother me as I very rarely go that fast anyway and it'sin no way excessive. Perhaps they didn't fix it after all.

No, assuming correct tyre pressures etc I feel it’s probably the screen. Mine does the same; it didn’t without the screen. It’s not a scary weave, but I don’t often venture to those giddy heights on my C5 either....

Incidentally, I put ATF in my forks and got a lot nicer action. i understand it's about SAE 7.

Most weaves are due to something at the back-end. Front end issues usually result in cornering instability, tracking along linear defects or judder/vibration under power or braking. An under-inflated or over-sized rear tyre or a top-box are favourites.

I've been putting multigrade fork oil in most of my bikes these days. 5w-15 from Halfords. I started because the forks on my sports tourer were losing damping due to overheating of the oil after long, complex roads.

As far as I know ATF is 42 but it is great for forks on what we are riding about on.

And a standard multigrade is fine too and so is a straight 30 and so is ------ Ive tried all sorts of stuff and it never made any difference.