Fork mods

fastharry · Post by **fastharry** » Thu Dec 05, 2013 7:42 pm

I have recently bought a B50mx, i have read somewhere that there are modifications to the front forks that can make a great improvement. Has anyone got any idea what they are,

Post by **minetymenace** » Fri Dec 06, 2013 2:05 am

to the forum fastharry.

I'm going to move this to "Tech" as is is more of a technical question rather than a write up (don't be put off, it is what I do)

Would you also update your profile and let us know where you are please?

gunnag · Post by **gunnag** » Fri Dec 06, 2013 8:55 pm

Not sure about MX bikes but certainly one improvement for BSA forks is to change the springs to progressive types. This will help the forks to be more sensitive on smoother surfaces, absorb shocks on rougher surfaces an prevent bottoming out/diving. You can get progressive springs from SRM, Hagon and other BSA suppliers.

The other modification is to change the damper valves to improve compression and rebound damping. This is more of a specialized modification which may need an expert in suspension like Maxton though it may be possible to do on a diy basis using Racetech cartridge emulator damping see http://racetech.com/HTML_FILES/DampingRodForks.HTML

fastharry · Post by **fastharry** » Fri Dec 06, 2013 9:52 pm

Yes, progressive springs are one of the mods i have in mind, i was hoping someone might have had a positive experience to pass on, I did talk to maxton and i was a bit shaken at the price of a revalve on what is a fairly simple fork design, £450 + vat at 20%, im hoping some one has tried things like the raceteck valves and give us there veiws.

roadplough · Post by **roadplough** » Fri Dec 06, 2013 11:32 pm

When I bought a pair of legs last year the seller mentioned a damping mod, supposed to be a vast improvement.
I didn't quite get what he meant so he sent some pics but I still don't understand and can't offer any further info but here are the photos:

: T160

No idea of the relationship of the T160 legs to these next 2 pics:

Some one else may be able to explain.
Another (easy) mod is to replace the damper o-rings with the split metal type which along with progressive springs I got from that mob in New Zealand.

gunnag · Post by **gunnag** » Sat Dec 07, 2013 1:26 am

My understanding is that the Racetech cartridge emulators provide much finer and accurate control of compression and rebound damping as commonly found on modern bikes and therefore give much better control of the ride. I believe the cartridge emulators can be purchased and retro fitted to some BSA's, but I dont know how its done.

Regarding the progressive springs, I have a set fitted on my 68 A65 and they have made a big improvement in the ride quality, so I can recommend them. I have also fitted a pair of Hagon adjustable 2810 shocks which are also very good and improved the rear end damping no end, these are similar to the old koni dial a ride dampers.

Norman_John · Post by **Norman_John** » Sat Dec 07, 2013 9:49 am

The same for me as Gunnag - progressive springs in the otherwise bog standard forks on my 1968 B44 made me happy enough to looking for modern forks I could bolt on.
John

fastharry · Post by **fastharry** » Sat Dec 07, 2013 7:45 pm

Fantastic, just what i was after. Can you tell me the make of the the progressive springs as there are many out there, Thanks again.

Norman_John · Post by **Norman_John** » Sat Dec 07, 2013 11:10 pm

If you can make your way over to Nuneaton from Leicester I have an unused pair in the cupboard you can have... PM me?
John

Post by **minetymenace** » Sun Dec 08, 2013 12:16 am

Leicester to Nuneaton is less than 20 miles and most of it is motorway!

fastharry · Post by **fastharry** » Mon Dec 09, 2013 12:22 am

I certainly will. Its the A5 for me.

blaise · Post by **blaise** » Wed Feb 05, 2014 12:58 am

I am scheming to make some modifications to the front forks of my 1969 BSA B25 (B44 motor), as I am unimpressed with the stock forks. I most certainly will keep this great forum posted on my progress, but am just drafting out my plan for now. It involves grafting in some modern cartridge forks to the stock BSA hub. This likely will be my first attempt at making custom yokes.

Would any of you know the OD (outside diameter) of the steering head bearings outer race that fits into the frame. I am trying to source a good set of tapered bearings, but did not want to take the whole fork apart on my bike during this planning stage (If I can avoid it).

I found a measurement of 1.78386" (45.31mm) doing an internet search, but this may just be for an oil in frame set up (part number 97-4031).

I think that the stock part number for my steering head bearings is 99-9913 and just the outer race is 66-4149.

Thanks in advance.

blaise · Post by **blaise** » Wed Feb 05, 2014 1:28 am

Oh, I just got some information on this, with a measurement of 2.125" (2-1/8").

HPbyStan · Post by **HPbyStan** » Wed Feb 05, 2014 1:42 am

I just today turned out two adapters to mate TT500 Y*maha taper bearings to the '67 C25 frame I'm putting the '71 B50 engine in for my NZ mate to ride in the int BSAOC rally in Petaluma in May. I made the steering stem from Aluminum bar stock to fit Ceriani clamps although I made my own clamps as well.

blaise · Post by **blaise** » Thu Feb 06, 2014 8:14 pm

HPbyStan wrote:I just today turned out two adapters to mate TT500 Y*maha taper bearings to the '67 C25 frame I'm putting the '71 B50 engine in for my NZ mate to ride in the int BSAOC rally in Petaluma in May. I made the steering stem from Aluminum bar stock to fit Ceriani clamps although I made my own clamps as well.

Stan,

Hopefully we can meet in May in Petaluma. I plan to be there.

Blaise

gpvictor · Post by **gpvictor** » Thu Feb 06, 2014 8:30 pm

Hello Stan,
I am pushing my nose in un-invited but is an aluminium stem going to work ok?
Co-efficient of expansion of a steel headstock and an ally stem and all that implies. You could use a bit of 1/2 inch steel rod with ally inserts to pack out to the bearings if you haven't got a piece of inch steel tube - you only have to clamp the bearings in the headstock - the stem doesn't take a lot of force.
Sorry, if you have discarded this idea already.
Mike

blaise · Post by **blaise** » Mon Feb 10, 2014 8:31 pm

Here is my first lower yoke design drawing. It is basically inspired by the stock yoke, but meant to grasp a larger fork tube (1.690").

This is my first time making a yoke, so am wondering if anyone has tips on making the steering stem.

How is it typically secured to the yoke? This yoke will be made of 6061 aluminum. I think that on my BMW, it is simply pressed in (actually expand aluminum to slip steel stem in).

fastharry · Post by **fastharry** » Thu Mar 06, 2014 6:56 pm

I have several spondon engineering steering sets, they are all alloy and the stem has a small top hat at the bottom to stop it pulling through the bottom yolk, it is just pressed in,

blaise · Post by **blaise** » Thu Mar 06, 2014 7:43 pm

fastharry wrote:I have several spondon engineering steering sets, they are all alloy and the stem has a small top hat at the bottom to stop it pulling through the bottom yolk, it is just pressed in,

Thanks

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