Swapping your old forks with a set of modern, better-performing upside-down forks sounds like a complex task, and it is. Thankfully there are some great aftermarket products available to simplify the job. In this edition of our Workshop Series, the crew at Cognito Moto walk us through the fork conversion process by demonstrating the fitment of a Suzuki GSXR front end to a seventies Honda CB750 using their own specialized parts.
But first, why even perform a fork conversion in the first place? There are a few reasons you may decide you want to change your motorcycle’s forks. Firstly, and most obviously, you may want to improve your motorcycle’s handling. While the conventional forks on your retro bike may have been the latest whizz-bang tech in 1970, they certainly won’t perform as well as the forks referred to in this feature. Secondly, your old forks may be in need of a serious overhaul. Rather than buying new stanchions (or re-chroming the old ones), seals, springs, and internals it may only cost a bit more to install a modern alternative. Lastly, you might want to beef things up. If you want your old bike to have a tougher, more bullish stance modern USD forks are a sure fire way to achieve that.
So with all that in mind I will now pass you over to Cognito Moto frontman Devin Henriques who will run you through the basics of how to perform a motorcycle fork conversion.
“Today, we’re going to be walking through how to do a fork swap on a ’79 CB750 using parts from our Cognito Moto catalog. For this fork swap, we’re going to be adapting a set of 2011 Suzuki GSX-R 600 forks to our Honda. The procedure will be the same whether it’s a GSX-R, modern Yamaha or Honda fork. This walkthrough assumes you have a basic knowledge of motorcycle maintenance and how forks work. If not it’s always a good idea to ask a professional for assistance or to perform the task for you.
Removal of the original forks
If you have a workshop manual for your motorcycle it will walk you through the process of removing your motorcycles old front end. We’ll assume you have already removed the handlebars, switchgear, headlight, and gauges and disconnected any wiring and cables that are attached to the forks. You will now want to place the bike on a stand or jack and safely secured so it can’t topple over during this process. Now follow the steps in your manual to remove the forks. Once everything has been loosened lift the front end of the bike using your jack and slide the old fork down and off the bike. On this bike, we also removed the exhaust so we could sit the bike on a jack.
Installing the Cognito Moto steering stem
With the old forks off you need to remove the original stem from your GSXR forks and press in your Cognito Moto CB750 conversion stem. Depending on the bike, and depending on the fork, there’s a number of different stems that we offer along with conversion bearings. The conversion stem, in this case, is roughly about a half an inch longer than the stock stem. If we installed the forks as is the bearing would be sitting on the threads, and there would be no way to tighten it up. This is why we have developed these custom conversion stems.
Start by dismantling the GSXR forks so you have the lower clamp and the original steering stem separate to the other parts. Loosen the pinch bolts on the GSXR yoke and carefully slide both fork legs out. To press the old stem out of the bottom yoke you will need a good hydraulic press. For those doing this at home without a press, you will probably want to find a workshop that can perform this task for you. With the right equipment, it’s a quick job. For this ‘how to,’ we will assume you have had a professional do this for you. If you’re going to do it yourself you can watch the full process in our instructional video here.
Preparing the frame for the install
With the Cognito Moto stem installed into the GSXR clamp, you need to prepare the frame for the install. Inside the neck of the frame are racers which the old bearings sat in. These have to come out. This process involves hammering the old racers out using a blunt edge. This could be a steel bar, large flat head screwdriver (note: this could damage your screwdriver so only use tools you aren’t precious about) or anything that you can use the get purchase against the inner lip of the racer inside the neck of the frame. Be careful to not damage the frame while hammering. Work your way around the inner edge of the racer a bit at a time until each racer (upper and lower) pops out of its seat. The key is to be methodical and to not rush things.
With your Cognito Moto steering stem conversion kit, you will have received new bearings, spacers, and racers. With the old racers out you can now install the new ones. Once again work methodically in order to seat them evenly. With the racers installed you can go ahead and pack the new bearings with grease. Be sure to press the grease in-between the roller bearings and rotate them in your hand to get full coverage.
Seating the lower stem bearings at the correct height
Now place the lower bearing up inside the racer you’ve just installed and check which steering stem spacer is required to provide sufficient clearance from the edge of the frame. Once you have determined which one to use slide the spacer on to the steering stem followed by the seal and the lower bearings. To seat the lower bearing on the steering stem you can use an Arbor press or even a piece of tube the same diameter as the bearing collar. Be sure you have the bearing sitting level before you begin seating it on the steering stem. The key here is once again taking your time and checking how things are looking as you go. With the bearing seated on the GSXR stem, you can install the upper bearing in the frame.
Installing your new forks into the frame
Now that we have the upper and lower bearings installed, we’re going to go ahead and push the steering stem up through the neck of the frame. Now using the original GSXR lock nuts you can attach the triple tree to the frame. The first nut is to set the tension for the bearings and should be torqued to the factory spec of your donor forks. The second nut is to lock it down. Always use both.
Next, you will either install the original GSXR top clamp using the top nut it came with or one of our Cognito Moto top clamps. If you are using the original clamp it may need to be modified to clear the steering stops on the Honda frame. If you’re using one of our Cognito Moto top clamps it will bolt straight on. We also sell retro styled nuts to fit GSX-R, R6 or CBR forks. These will also need to be torqued to OEM spec.
You can now slide the GSXR fork tubes back up into the triple clamps. You will notice that the clamp will sit lower on the fork legs. Check that the lower clamp is only sitting on the flat area on the fork leg. If it is sitting on a tapered section it can’t be clamped down. This shouldn’t be an issue with the fork types we’ve mentioned here, but you could run into issues with bikes that have longer stems such as the Nighthawks or the nineties CB750s. If you’re unsure feel free to contact us before you begin. We also sell products to get around this issue.
With the forks in place, you will notice that the factory steering stops on your frame and those on the GSXR forks won’t work together. This means your handlebars will hit your tank which isn’t ideal or advisable. So you’ll either need to fabricate a solution which may involve welding on the frame. Alternatively, we offer fixed offset triple clamps for this kind of fork conversion. They are a great solution as they look better than the OEM Gixxer clamp and they include adjustable steer stops.
To offset or not to offset?
The last thing I want to talk about is fork offset. Fork offset is the position of the centre line of your fork tubes to the centre line of your steering stem. On a GSX-R, and most modern inverted forks you’re going to have a 30-millimetre offset. If you’re planning on running a larger wheel such as a 19-inch one the distance should be 50, 55 or 60mm depending on the bike. As wheel size increases, you want to increase your fork offset to have the correct trail. If you run a 30 mm fork offset, with a 19-inch wheel, the bike is going to be more in line stable and less nimble. So, in other words, it’s going to take more effort to get the bike to lean. In order to correct that, you need to increase fork offset. To do that, we offer complete Cognito Moto triple clamps. These will push the offset out for the top and the bottom equally, and that will correct your trail. It’s not something that is essential but to optimize your bikes handling with your new fork, you want to have the correct offset. If you’re running a 17-inch wheel the stock GSXR 30mm fork offset will be fine.
Fork conversion finished!
So that’s it. If you follow these basic steps you should have your fork conversion done. With the forks in place, you can move on to setting up your front wheel. For our full video demonstration of this process and other guides be sure to check out the Cognito Moto Youtube channel. If you have any questions about any of our products, which forks to use on your project or other technical queries you can contact us via the Cognito Moto website.”
WARNING:The information in this article is designed to give you a basic overview of this modification. Tampering with or modifying any part of your motorcycle can render you motorcycle unsafe. Return of the Café Racer always recommends having an experienced mechanic work on your motorcycle.