A real swinger

Reading the rules before attempting to follow them is just boring so let us get stuck into some hard thinking and work to sort the swing arm out on the VFR.

I had a small dilemma with my VFR750 RC24 6x [rep] build: The swing arm didn't look much like what it was pretending to be.
The caliper was all wrong and on the wrong side of the swing arm which itself was the wrong shape and looking no better for it.
Changing the swingarm was going to be a lot of work but, conversely, modifying the original for racing then upgrading again later would be a great way of throwing money away so I decided to try and find something more suitable looking.

** Spoilers** I ended up not carrying out the swing arm swap due to not being able to for CRMC eligibility. I am going to leave the process in here however for anyone else trying to do this to their own machine so they can have an idea of what will be required to achieve such a swing rm upgrade.
If you're not bothered about this, then scroll down a bit to see what race prep is needed for the stock swing arm.

If you look online you will find a few people have gone out there and found a way to put the right looking swing arm on their VFR750 RC24.
The one way I saw of doing it with the best description was using the arms of an NSR250 MC18 swing arm welded onto the body of a VFR750 RC24 swing arm. This has the advantage of customisability, using the original shock and it will end up being prety dam light.
The down side of an NSR swing arm was it uses the original shock (yup that can suck too), MC18 swing arms aren't exactly common anymore making it is a lot of work and money just for the look.

The other option that I found out about was; using a CBR600 f4 swingarm.
These are cheap, look the job and have a better designed suspension linkage than the VFR's.
From what I had read (Looking back I might have seen someone getting an RC24 and early RC36 muddled up), it was a case of a bit of machining and the thing will drop in, allowing for a simpler rear brake in the mix too.
I managed to get one with all the extra bits for £30 in fair condition but nowhere near as clean as you can see on the left!

Out with the old..

Taking the rear shock off is straight forward. 

You will need some monster allen keys though so I got a box of sockets on order as I had nothing that size.

With the wheel already out; the shock unbolted from top and bottom without too much arguing. Then with the remote preload adjuster freed from the frame, it could be dropped out the bottom of the swing arm. 

With the correct allen keys in hand I could undo the two swing arm pins. The left side threads into the chassis and right has a captive top hat nut.

Both undid with out too much fuss then could be pulled out to allow the swing arm to be worked out of the frame.

Before you can do that however you need to release the swing arm lincaging.

Unlike most modern bikes; the VFR's is under the swing arm to ensuder it really gets covered in crap!

Thankfully, with a long soak in penetrating oil and the help of a rattle gun, all of the bolts came out with little to no fuss.

The only thing that wouldn't come out was the pin holding the cast linkage to the swing arm.

I took this opportunity to give the back end of the bike a really good clean.

30 years of road grime and chain oil were scraped out and the rest wiped up to find gleaming metal underneath. A real testiment to Honda castings and the preservative properties of caked on oil!

The rear exhaust shield had corroded completely through so this was removed and binned. If I was running this machine on the road I might have been tempted to copy it and make a new one but for racing I wouldn't be too worried.

In removing this I did manage to retrieve a second right swing arm top hat nut (!?) and both of my 10mm sockets that had gone exploring the week before.

The CBR600 swing arm was offered up for a test fit (I told you it was grotty) which looked really prommising.

If this wasn't good enough, a CBR600 f3 shock I had lieing about (wich is the same as an f4's) also dropped into the top shock mount with no arguments at all. This was a big deal for me as this shock is very common and thus has lots of aftermarket options for me to run a high quality yet very affordable rear shock.

The F3 wheel would fit in with some minor spacer modifications and I could use the f4's rear brake caliper for tidiness (no tie bar) or weld a tab on and run a more authentic under slung caliper if preferred.

Some close up views of the swing arm located in the chassis give you an idea of what will be needed to get these two components to work together.

Lugs on the inside of the chassis will need to be removed first.

If I were to run the adjustable swing arm spindle that the CBR runs, I would then need to drill the centre section of the chassis to allow it to pass through then drill and tap the outside for the adjusters. Some shims might be required but that was basically it.

The rear shock lower lincage uses an aluminium dog bone to tie it to the chassis. I thought I might need to make one of these but passing a bolt through seemed to be the linkage to roughly the right place.

This did highlight a problem I was anticipating. The shock was far too long for the current mounting points.  Custom lower linkage plates are easy to make for some adjustment but wouldn't get me out of this problem. The top mount would need to be cut off and relocated higher to allow me to run a full length rear shock.

If you have read the spoiler you know what is coming.

Whilst procrastinating the work required I hit the RC24 facebook group to see what I could gain form them. The response I got from them was a general slating, telling me it was impossible and reminded me why I didn't go on forums till Jos Hammer dropped this image on the tread, dropped the mic and walked off.

Climbing out of dejection, I was over the moon to see that it was indeed possible and looked bloody class. He gave me a few pointers in broken English which I ferrited away for future reference.

Procrastination continued till I decided to read the eligibility rules for the CRMC's 750 superstock class to see what I could do to my subframe for the rear seat fit. It was then that I spotted that, after all this fiddling about, I was not allowed to change my swing arm.

Bugger!

...And in with the.. erm... old again

In going back to the standard swing arm; I was saving myself from a boat load of work if nothing else.
The jobs that would need doing involved welding on some tabs for bobbins and a sharks fin. These were cut out of aluminium sheet, shaped and drilled before welding them on with my R-tech digital tig 170.
Doing this with the swing arm off was a lot easier than previous efforts with swing arms in situe. That and the fact that the VFR's Aluminium swing arm wasn't a rotten old piece of Yamaha steel that I had become accustomed to welding recently.

The results were fairly tidy allowing me to bolt on some off the shelf aluminium bobbins to support the bike then get to making a shark fin.
I chose to make this sharks fin out of 1.5mm alloy as it would be quicker to fabricate than previous efforts.
The result is pretty tidy and remarkably subtle addition to the machine.

Shocking

The biggest drawback of the standard swing arm wasn't it's looks but the fact that I would have to use a rather dated shock and linkage system. This dramatically limits me in shock choices with the ever popular yet rather expensive Nitron being the one I had been looking at before I had crazy ideas of changing the swing arm.

Now much further down the road and not exactly swimming in money; I managed to get a good deal on a YSS rear shock for my bike. It was listed for an RC24 86-89 with adjustable preload and rebound for around £300.

Faced with the choice of this or the old one, I went for the newer shock to tide me over till I came up with some more money for a full race shock.

As it happens the YSS item is a pretty nice shock and I hope will offer me some good performance against the nackerd stock Showa item.

 Featuring preload and rebound adjustment, I would be able to make a few adjustments to the rear suspension I couldn't previously too.

I used the stock rear brake tie bar and location point for the time being so as to save on time and money this late into the build.
I may not have quite managed what I set out to do but the results were quite usable and I hope this blog entry will assist anyone attempting the slightly more radical (and quite possible) CBR600 F4 swing arm mod to a VFR750 RC24.