1937 Girder Fork Barrel Spring

[Ian.Cockshull]

When I ride my 1937 VH over poor road surfaces it feels much more uncomfortable than I think it should, the ride is jerky and uncontrolled to the point where any speed over 40mph feels unsafe and makes you slow down. The ride over good road surface is OK. I have tried tyre pressures in the range 20 - 24 psi in the ribbed Avon front tyre with no significant improvement. I am now wondering if I have the correct front spring, it has 12 complete turns and the wire diameter is 0.350 inches. I have checked for excessive play in the fork bushes and spindles - all seems good there, also the friction dampers. Is my ride experience normal for the 1937 frame? Any helpful suggestions you can offer would be appreciated, Ian

[chris.shearwood]

Hello Ian,
I'll paste below a message I sent to the AOMCC e-mail chat group last year and also Paul Jamieson's spot-on reply:

Ever since I first put my 1946 girder/rigid Sq4 together I haven't been happy with the way it handles potholes or bumps in the road surface. The rigid rear causes no problems, it's the front suspension which gives me grief. Crossing a set of railway tracks at 30mph results in jolts to my shoulders and at higher speeds one would seem to be risking a total loss of control.
I have installed new spindles, bushes, knurled washers and friction disks with no detectable improvement. Likewise loosening or tightening the dampers. The spindles, which are kept well greased, are a nice sliding fit in the bushings. The spindles end play adjustments are such that all knurled washers can turn with at least one washer per pair turning easily. The spring wire diameter is .344" which I understand to be right for a solo Sq4. The installed spring length is 7 3/4" with no weight on the saddle which is probably pretty close to the specified 9 1/2" no-load length. The pressure in the Avon Speedmaster Mk11 front tire is maintained at 20-24 PSI. With the bike on the rear stand and the front brake applied, a push on the handlebar reveals a smooth up and down movement of the rest of the bike relative to the forks.
I'm wondering if it is not just the nature of the beast. I've never had the opportunity to ride a similarly equipped bike so I don't have much to which I can compare. However, in the November 1995 issue of Classic Bike magazine there is a road test of a '38 Sq4 which David Jones, who knows much more about Sq4's than I, restored. Some of the writer's comments are not encouraging: "Minor road imperfections jar the wrists. If the front end hits a pothole it can really hurt and the plot will shake its head alarmingly."
Perhaps a member of the chat group knows the owner of this road test bike, Cynric Richardson? If so, could you ask him if he ever solved the problem?
Any opinions, advice, etc. will be greatly appreciated.
Thanks in advance, Chris Shearwood

Reply from Paul:

Geoff Brown of the Gloucester Branch recently bought Bob Brassington's old 1938 VH and had similar problems. In his case, the jolting affected an old arm injury quite badly. He came over here on the bike and then took out my 1937 VH while I rode the ex-Brasso one. The difference was marked, with my 1937 model being far better than the ex - Brasso model. Apart from greater wear in my forks and enough grease having come onto the dampers over the years to render them totally ineffective, the main difference was the spring wire diameter. The spring on my 1937 is 0.312 diameter, while Geoff's was 0.344 diameter. He took my spare 0.312 diameter spring, fitted it to the bike and found it completely transformed such that he can now ride it in comfort. Last weekend we had a barbecue run with about 6 girder fork Ariels on it. All were fitted with the thin wire spring (0.312 diameter), including Editor John Mitchell's 1939 Square Four.
I can only think that the thicker springs were for sidecar use.
Paul

[Ian.Cockshull]

Hi Chris
Many thanks for such a quick and comprehensive reply. Your experience on your Sq4 sounds identical to my experience with regard to the front forks, the rigid rear feels well planted but the front end seems to have a mind of its own. My front spring measures 8 inch with the bike on the rear stand and 8.5 inches when all weight is taken off the front fork. Did you manage to source a thinner spring for your Sq4? Ian

[chris.shearwood]

Hi Ian,
Yes, I did buy a 4606-34 light duty .312" spring from Draganfly which much improved the ride. On the dirt road where I live, the bike was very rough to ride at a speed just faster than stalling in first gear before I changed the spring. Now I can come up the same road in third. The suspension is still rougher than those on my teleforked bikes and if I could I would buy an even lighter duty spring. The 4606-34 is a bit short too as the top links are far from being parallel to the ground (perhaps a thirty degree angle). As a result the ground clearance is reduced. At some point I intend to look into having a longer spring with thinner diameter wire made up. Anyone know of a spring manufacturer?
Regards, Chris

[nevhunter]

Most of my recent experience with the type of forks discussed is on my W/NG but I have many miles on girder forks. The W/NG is fine but it is a lighter than normal spring that easily responds to road undulations. IF you forks aren't showing much travel consider using a light spring. This seems to be the consensus of opinion with which I agree. If it is too light it may bottom out, but I haven't had that happen much over the years. You certainly need stronger springs when an outfit is fitted as there is much more weight on them. Nev

[Ian.Cockshull]

Many thanks for all the helpful comments. What is the procedure to remove the girder fork spring? Even at full droop it looks to be under some considerable compression so potentially dangerous with all that stored energy! Any advise you can give would be appreciated, Ian

[Steven.Carter]

Yes you definitely must be careful with it, I've never done it myself but it hospitalised my mate Alan!

[chris.shearwood]

Hi Ian,
To remove or install the fork spring you could try Mr. Nicholson's method. In the third edition of his "Modern Motorcycle Mechanics" he suggests the following:

"...use of a carpenter's gooseneck, levering under the rear top fork spindle housing and prying down on the spring mount top flange, will enable easy fitting."

I don't know what a carpenter's gooseneck is and I suspect that his definition of "easy" is dramatically different than mine. Once the bike is jacked up such that the front wheel is off the ground and the top securing bolt is removed, I use a couple of hookless ratchet straps, looping the straps through the spring on either side and then tightening them such that the anchorage fitting clears its hole in the top rear spindle housing. Then undo the ratchets, remove them and unscrew the spring from its bottom mounting flange. The use of a hammer and a punch might be required to start the unscrewing. At best this is a fiddly job and one has to be careful not to scratch the tank. Sometimes it is easier to pull the headlight up out of the way and put a third strap through the front of the spring. I obtained this kind of ratchet strap from a Harley dealer as HD ships all their bikes from the factory secured to pallets using this kind of strap. At least they did a few years ago.
Good luck. Slow and steady is the right approach.
Regards, Chris