How To Shorten Motorcycle Forks – BMW R80 Build

In this video I will show you how to lower your motorcycle forks. It makes a huge difference to the overall line of the bike and will separate your build from all the others.

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⏰ TIME STAMPS

I hope you’re having a great day. – WRENCH ON!
JOSHUA

The forks are gone on the BMW and I just got the call that we are ready to make the spaces to shorten them I’m quickly going to grab these two because maybe we’ll have time to adjust those as well so while I’m driving to my friend’s Workshop let’s use the time for some

Context the BMWs had for their time relatively long front suspension travel which made for great riding Comfort but at the same time it makes the bike sit oddly high in the front so we’re going to drop it and there are multiple ways how you can actually lower your classic

Motorcycle Forks you could either machine the actual Fork tube or you can go the easier and cheaper route that’s what we’re going to do and make or buy a pair of spaces and from what I’ve seen that works for most conventional motorcycle Forks so I’m going to show

You how to do it but first we need to get the forks off the bike we start by taking the handle bus off the bike next it’s onto the brake cipus and I noticed again that on an old bike like this the blow torch is your best friend

And if you’re looking for a good one I can definitely recommend you this one which is the power blow torch from rothenberger with MPP gas the tip doesn’t get hot it works upside down without spitting Flames I’m very happy that I have this one because I had to

Use it on almost every single screw to get the forks out anyways back to the Brakes now that the nut is off you can take a M8 bolt and screw it into the rod that holds the caliper in place and pull it out towards the bottom with that out you can then take the caliper off the next step is to unscrew

The Top Nut while the forks are still on the bike on the AirHeads this nut is relatively flat which is why a regular wrench or socket is prone to slip off because they have these chamfered edges for that reason BMW provides a special tool in the original tool kit but you

Don’t need that if you have it great but if you don’t have it you can take a regular 36 mm socket and just grind these champ fit edges off until it’s really flat that way you get a good drip and the nuts should come off Next you can take the fork stabilizer and the front fender off before unscrewing the axle nut and taking the front wheel out with an 8 mm hex socket and in my case fire you can unscrew the two bolts in the triple Clamp and now we get to the part that I struggled with the most the for tubes had so tied in the bike that I had to use the blowtorch to heat up around the triple clamps so I could pull them out bit by bit that’s actually not the right way to

Do it I found a little trick in Brooks Airhead garages videos if you have a BMW you probably know that channel very well and if you don’t you definitely have to check it out all by BMW all you have to do to make your life a 100 times easier

Is to take a large blade screwdriver and gently tap it into the slot on the Trier clamp once you have the fork out of the Trier clamp you can take the spring out Mark the top side and drain all the oil by pumping the forks a few

Times next you want to carefully clamp one of the Fork Sliders into a visce and it’s best to use some plastic vice grips like these or towel to protect the fork now we start with the fun part because now it’s time to take the fork apart we

Start by loosening the small nut on the bottom first and after that the big one and it’s it’s best to use the adjusted socket for this one again because it’s also very flat the ones on this bike needed some persuasion like all the other nuts and bolts but at some point they came

Loose quite forcefully with a normous socket I might have damaged this one but nothing happened now we take off the small nut and the washer that sits underneath before we actually take off the big one inside the big nut there is a rubber damper which often gets very

Hot and yeah braks for the next step put something underneath the fork that can absorb the rest of the oil that’s still in it because we’re now going to P the piston and the fork tube out of the fork slider on top of the Piston there’s another small washer that you don’t want

To lose on this bike it was so stuck that I didn’t have to worry about that just keep that in mind because you now want to gently shake the fork tube with one hand underneath it until you can grab the piston and pull it out and with the Piston out you now have

The forks as far disassembled as we need them to be so let’s see what nck is doing Sorry to interrupt but by the way MO is a word that you definitely have to learn that’s how we say hi up here in Northern Germany and that that is nickel if you have watched some of my other videos you might already know him because he’s helped me countless times with the forks

Already this assembled we made a quick plan and took some measurements because I’m going to use his lace to make the spaces but if you don’t have access to a lace don’t worry I’m going to tell you in a second what you could use instead

And how you have to measure to get the right dimensions for your spaces but first let’s make the spaces for the BMW so I can better show you and it’s also the first part that I’ve ever machined so it’s quite Exciting All right that’s the spaces done and we even had time time to adjust the aluminum pubes that I’m going to use to make some Fork sleeves for the BMW but that’s for a future video now let’s take a look at how the fork Parts actually work together so we get a better

Understanding of how the spaces work all right so those are all of the main parts of the front fork there are small parts in here but we don’t have to disassemble that for this job so what’s important to understand is where the Piston sits because that’s the part that connects

The fork tube and the fork slider right here at the bottom there are like big washes basically the for piston slides in from the top all the way through here the Piston then slides right in here and is connected firmly at the bottom with this nut so this whole assembly doesn’t

Move this all stays together on top of the piston on this side sits the spring and the bottom of the fork tube sits right here so these walls that I talked about sit on this side of the Piston which means these parts can’t move apart like that but with this assembly the

Fork tube and the fork slider can actually move in opposite directions and when the fork gets compressed what happens is that for one the spring gets compressed to the Top Nut on the fork tube but also the oil that is in the fork has to flow through all of these

Little holes right here and that makes the fork respond differently to hard impacts compared to soft ones and then on the top side the spring is held inside the fork tube with this nut so this is the main assembly of the fork so now let’s see where the spacer goes what

We do is we place this spacer right here before the Piston would sit right here and sit against the ring now it sits higher up because we have the spacer in between and the spacer is actually the contact point to these Rings the fork tube can’t go all the way back out

Because it’s blocked by the spacer and that makes that your fork sit as much lower as your spacer is high how you get your measurements for your spacer is you take the piston and the inner diameter is determined by the bottom Rod so make sure to get a good measurement of that

To be on the safe side I would measure in different locations as you can see this one at the bottom is 15.1 18 but at the top it’s 15.37 so the inner diameter of your spacer has to be a little bigger than that so it can actually Glide along

This rod and what you also want to keep in mind that you never want to block all of these oil holdes at once the best would be if you never block those because it actually is a vital part of your forks some Fork types have a spring

That sits on here on the Piston if you have that put your spacer in between this part and the spring that way you always have the spring over the holes and the oil can flow freely on the BMW I don’t have that spring but since the

Spacer isn’t too big we don’t cover too many holes at once and it only really matters when the suspension goes very far in so I’m not too concerned about that but just keep that in mind for the outer diameter you want to be a little smaller than this ring right here and on

The BMW that is 25 mm so we went with 15.6 on the inside and then 24.8 on the outside also since I don’t have a spring the amount that the forks will sit lower is exactly the amount of the spaces so 30 mm obviously it’s great to have very

Precisely machined spaces with the right dimensions but if you don’t have access to a lathe and you still want to drop your forks you can actually look for some stainless Ste tubing has very similar Dimensions to what you need just make sure that the walls aren’t too thin

And that the spaces don’t rub anywhere now let’s put everything temporarily back together and put it on the bike I’ve actually got a complete rebuild kit that I’m going to use when I do the final assembly of the bike but for now I just need one of those and also I’m

Going to use some Progressive Fork Springs on the final assembly which have a much tighter spring at the top and then a wider spring at the bottom to put everything back together we start by sliding the space up over the piston and then the Piston goes into the fork tube

Here you can use the fork Springs to push the Piston a little further in because with the spacer now it’s not too easy to actually get it aligned with the hole on the other side you just have to wiggle around a little bit until it actually pops through the hole so with

That you can pull this out and push the whole thing into the fork slider now it’s time for the new skateboard roll that sits inside this nut which you can then push in and screw that into the fork slider next up we have to secure

The Piston to the nut so we put on the washer first and then put this little nut on I’m going to tighten everything just by hand because I’m going to rebuild it anyways but if you’re going to do this properly then please check your manual at this point

Because you need to know the torque specifications and you would also have to add some oil at this point keep in mind that you should probably reduce the amount of oil that you’re putting in what I think I’m going to do is calculate the volume of the spacer that

I put in and reduce that that amount of oil if you know a better method for how I can determine the right amount of oil that I have to put in please let me know Down Below in the comments but we move on and put the springing make sure that you put the

Right side up this one is marked at the top but most often they’re also a little bit narrower at the top not by much so if you’re in doubt just measure the top and the bottom and you should know which one goes up with the spring install we

Have now everything back together and we can put it back on the bike depending on how big your space is and how much the spring now sticks out you might have to cut your spring to actually get the nut back onto the fork tube but I think with

This it should be fine once it’s back in the bike so I’m going to try first and then go from There this actually works quite nicely I’m holding the nut down with my thumb and then twisting it with the palm of my Hand and that is how you can lower your front FKS the relatively easy way it might be hard to tell on camera but definitely makes a big difference to the overall line of the bike I might have been a little bit conservative with the spacer height next time I would probably

Go for 40 mm or so I hope this video helps you to lower your own Forks good luck with that and if you want to watch another video check out this one right here as always thank you very much for watching and I see you in the next one