OC fronts forks

[Chris (Sprinter)]

Morning all,

I am trying to find out if there are any differences between OC and later (possibly later 20s early 30s 600 sidevalve) front forks. I am aware of the brake anchor being moved to the opposite side. Any advice greatly appreciated.

I am looking to mount the later forks into an OC frame with this in mind; however, the forks i have need re-tubing. Are there any drawings available for these forks (OC or later sidevalve)? Also any comments/advice about dimensions for jigging if no drawings are known.

Thanks in advance,
Chris

[Doug]

Chris,

The OC used fork girders the same as the 600EWthrough E/F29; except the brake drum being on the opposite side as you noted. The same girders were also used on the TT, thought the brake anchorage and cable terminus are different again. Then when you get into the mid-thirties you cannot separate the girders and you are stuck with the central spring design. Not sure how authentic you are trying to get it. The only thing you need beware of are the forks used on the T6. These were a hold-over from the twin extension spring suspension of the 1929 600s, where as the S5/S6 got the new central compression spring forks (and different girders and link arrangement). However the T6 girders while looking identical to the OC/TT/600EW girders, are slightly longer to suit the change to welled rims and balloon tires. I think about 5/8" longer, if I remember correctly. Useful perhaps if you are making a mild trials version of the OC...

I think there is some info on the individual girder tubes floating about (bend info), but no general arrangement drawings that I know of.

-Doug

[Chris (Sprinter)]

Doug,

Clearly I am slightly confused about the forks I have. I assumed they were S6. The forks are the correct shape for OC and have the detachable fork blades and twin springs. I note that the OC frame is built for taper roller headstock bearings. The forks also had the remains of a taper roller when i purchased them. Is this a good sign? Please excuse my naivety. Trying to learn and get a useable, sporty/racey road bike at the same time.

Thanks,
Chris

[Doug]

Chris,

The S5/S6 girders will have tabs on the front face of the lugs for the four headlamp stays. It will not have the ears to the rear for the upper end of the suspension springs (since it has a central compression spring). The T6 girders will have those ears for the two extension springs, but will not have the tabs for the headlamp stays, as it retained archaic headlamp irons (attached at the base of the steering stem). I have not checked, but I suspect both the T6 and the S5/S6 girders share the longer length for the balloon tires. So the only way to determine a T6 from the earlier 600EW is the length, and from the OC by the side the brake was on.

The T6/S5/S6 also had taper roller bearings top and bottom.

In 1934 you start to have heavyweight models where the girders cannot be dismantled.

-Doug

[Doug]

I have measured the girders on my F28 and compared them to the girders for a T6. As it might be useful for determining the difference I am posting it here for posterity.

600EW~F28.  From wheel spindle to the lower fork pivot: 15-3/4 inches.
T6. From wheel spindle to the lower fork pivot: 16-1/2 inches.

-Doug

[Chris (Sprinter)]

Doug,

Thank-you for the information. I will check the forks and let you know of my findings. I have attached some photos of the forks for reference.

Chris

[cardan]

I'm sure you could do something with those. At least they've got the early style headlight brackets.

Cheers

Leon

[Chris (Sprinter)]

Hello again,

Just to comfirm I have the longer T6 (16.5 inches) forks. I believe this should work in my favour for well rims. This bike will not be very standard unfortunately but I shall keep my eyes peeled for correct OC parts. Until then it will be a usable ALL Douglas motorcycle.

Thanks,
Chris

[cardan]

What have you got for the motor and gearbox Chris? I doubt if OB stuff is going to look out of place.

Leon

[Chris (Sprinter)]

Leon,

I have a tall airbox DT motor and a complete UG gearbox.
There is lots that I will need to find with time. The largest part i need is a petrol tank. I am thinking to fabricate a new tank if necessary. I have an 8inch front brake and 9 inch rear brake to build into rims. I think I have a good basis for building a usable machine.

Chris