Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board '71 front forks on a dry frame A65?

Can this be done? If yes, what is involved? I've just purchased a '71 A65 basket case, and I'm investigating the possibility of using the front forks on my dry-frame A65 bitsa, so I also have the '71 yokes and front wheel.

The quick & dirty way is to get some custom bearings and fit the entire front end
However doing this changes the steering geometry and makes the steering ponderously heavy at low speeds
A flat mate had an OIF front end on a dry rear
Seemed to run OK at speed but it was never registered so the test rides were some what limited in duration.

I can't speak for A65s, but I have a later set of forks on my 441. There are kits for installing tapered roller bearings in the fork neck precisely for that purpose and the forks just pop in place. It didn't make the 441s steering heavy, although I can't compare since I built the bike out of a basket case. I would be surprised if there aren't similar kits for the A65.

Ed from NJ

I found earlier suspension better working than my later 73 oif type front end on my Trident.

G'day Trevor, Do you recall if the later front end raised the front of the frame? That would definitely be a non-starter.

If the length is the same then I would guess the change in steering geometry would be due to the offset of the yokes.


Hmm, I don't know, my 1966 rod-damper forks leave much to be desired.

I suspect custom bearings is far more expensive than making a new stem to fit the headstock bearings.

Wasn't my bike so never bothered to measure it
It was the flat mates bike and we were actually fiddleing with the gear change at the time.
The custom bearing was a drop in off the shelf part from one of the BSA specialist, most likely the one Jon mentioned a couple of replies ago .

Perhaps try to find 69 / 70 front end, I was quite happy with it.

I’ve found the 69/70 front end great on an A65 but lousy on the 100lb heavier rocket 3, likewise with the oif forks. The late forks are great on an A65.

Mark Z: I found the damper rod forks to be rubbish on my 68’ after trying lots of other variations and eventually decided to completely rebuild the forks. Even though the stanchions looked perfectly fine and the seals didn’t leak I changed everything regardless. What I think made the biggest change was replacing all the damper rod components. Including the rods. I bought some 5/16” drill rod from your side of the pond and turned them until all the threaded portions matched the original units (drill rod is expensive but an exacting size and perfectly straight) The original rods had worn a lot and were pitted. Added some progressive springs for good measure and it’s now a really good front end.

Adam, the thing here is that I've just purchased about 80% of a '71 Firebird Scrambler. The frame has been sitting in a damp cellar for about thirty years and may not be worth saving. There is no fuel tank or exhaust system, and the wheel rims are quite rusty, but it has a complete engine and almost-new condition front forks. So I'm considering options for what to do with the engine and front end.

I came across this picture of a dry-frame A65 with a '71 or '72 front end. The length of the front end looks right.

Short term memory loss, forgot about it writing my post Mark. In this situation go for it, I'd go for tapered bearings with it, I have them in my Trident and they work very well. Quality of aftermarket ball bearings is low, and price wise they are now the same with tapered bearings, or very close. If this new front end feels good for you great, if not ask what to do, I constantly work on it to make it more compliant on my bike. It will be striped again this fall to make some change to the dampers.

It isn’t the length (I don’t think) that is different between the pre oif forks and the oif forks. But the yokes.

The yokes on the oif are parallel. So if you placed the top yoke all the way down the stem on top of the bottom yoke it would line up with the bottom yoke. Do this on a pre oif yoke and it would not. The top yoke is pulled back closer to the stem compared to the bottom yoke and increases the fork rake

Amusing title - "How Choppers Work". Sort of an oxymoron?

Right, it should have been titled "How to Compensate for an Abysmally Long Front End"

Allan, I do get it, and I will examine the yokes. So apparently, the resulting rake of the OIF setup is steeper. This would seem to contradict Trevor's observation that the steering on his mate's bike was "ponderous at low speeds" - that is, I would think a steeper angle would make the steering more "flickable". But then, what I know about steering dynamics would fit in a thimble.

I've never experienced a pre-conical front brake, but I agree with your assessment.
I had the drum on my '72 T150V, totally inadequate. I swapped the disc front end from my A65 onto the Trident. Conical was just fine on the A65.
BTW: The Trident still features the caged ball head bearings. So far so good, but those bearings are very expensive. I'll convert to rollers when they wear out. The OIF already has roller bearings.

Yes it works just fine. SRM has the bearings you need. Not hard to do.

The hardest thing will be steering stops and adapting the OIF steering damper to the early frame. You have to find a dry frame plate that will fit. Probably the best steering stops if you can find a set will be the chopper type that attach around the fork tube that have a rubber tip pointing back at the frame. I haven't seen one in years.

My 67 race Hornet runs just fine with its OIF front end and brake. Steady and straight with no complaints under heavy braking or leaned into the corners.

These are the bearings I think...

https://shop.srmclassicbikes.com/product/t140-disc-or-conical-hub-conversion-steering-bearings

Sadly I didn’t choose the chopper title, but it was the best image comparison google had to offer lol.

I’m not sure what the oif rake is. As it’s not just the yoke but the actual rake of the steering head and the rear suspension which will change the rake again. Then you have all the other factors in place like trail, castor(?) etc. I’m far from an expert infact I know very little. I know however that the oif bikes handle really well especially at speed. A tighter steering angle will make it turn tighter but less stable at speed. This is noticeable just by shortening a standard set of forks by an inch and making no other physical change, however other changes like trail etc will change.

There was an article in one of the classic bike mags (CBG? I think) explaining it all.

From factory manuals.
1970 Dry frame 27 degrees rake.
1971 OIF 28 degrees rake.

Low speed heaviness is a lot worse with a soft front tyre, my 71 feels very different if the front drops a few psi.

Quoth Allan, "As it’s not just the yoke but the actual rake of the steering head and the rear suspension which will change the rake again. Then you have all the other factors in place like trail, castor(?) etc."

Ok, but I'm talking about putting an OIF front end on my dry-frame A65, so the steering neck remains the same. It would seem then that the only change would be in the yokes. As I understand trail, I think that as long as the axle is in line with the fork leg, as it is in both cases (dry frame & OIF), there is zero trail.

My take, based on all of the above, and in particular Semper's reply, is that this is worth trying. I'm getting awfully tired of trying to get my rod-damper forks not to leak, and trying to keep the same amount of oil in both sides.

I could not find "rake" mentioned in any of my books. I am more familiar with the steering angle referred to as castor and the difference between the steering angle and the fork legs as rake. The Trident Workshop manual shows the angle between the steering stem and stanchion but does not call it rake.
Anyway, the angles are referenced to the frame zero line and have nothing to do with the rear suspension. Yes, the angles change with suspension movement but it usually measured relative to a reference line. Otherwise the castor angle would have to be given as a range from *** to *** depending upon the suspension position and tyre deflection.
Trail is the distance from where the steering pivot line meets the ground and the tyre contact point. Moving the fork tubes forward from the steering pivot reduces the trail. Placing the axle on the front of the slider also reduces the trail. You can have the axle in line with the fork tubes which are in front of the steering axis or put the fork tubes in line with the steering axis and have the axle in front of the sliders and end up with the same trail.
To have zero trail the fork tubes would have to be far in front of the steering axis (for a standard 28 degree head angle) or the head angle would have to be nearly vertical with the stock fork tube to steering axis distance.
You can quicken the steering by changing from a 19" rim to an 18", or, with the later straight top stanchions, slide them up through the top triple clamp.
The Wenco race frame has a 26 degree head angle.

OK Steering head angle dry frame 27 degrees, OIF 28 degrees referenced from vertical with bottom frame rails level horizontal.

Ok, but again, these numbers may reflect a difference in the angle of the steering neck between the two frame types. Since I'm talking about putting OIF forks onto a dry frame, if the steering angle as affected by the yokes is as Allan states, steeper, than the resulting angle will be less than 27 degrees, not more.

The total rake will be, yes.

The headstock is not being altered, so as long as the fork legs are the same length and the front rim is the same size then the headstock angle is the same. So that leaves 2 possible new variables, the offset between the yokes steering stem and the holes for the fork legs and any angle added to the fork legs taking them away from the pre OIF parallel legs.