Hi all,
I have fitted the top and bottom cones into the steering head cups but the "stops" that provide a steering lock (bottom yoke to frame) just do not seem to be lining up correctly (see photo). The top cone is a modified Triumph one and the bearing profile just does not match the original. I feel that the bottom yoke should sit higher in the frame (this is why I asked the question about the seating of the head cups). This doesn't look right to me - any thoughts?
Kevin
The inner bearing cones should sit proud of the steering column which seems to be the case here - you are only talking about the odd mm or two which is neither here nor there in terms of the bigger picture.
I don't have a pre-OIF B25 but, looking at my B44, there is about 1/2" of bottom yoke projecting below the bottom of the steering column that looks to be similar to what I see in the above picture. However, I will need to wipe off some grease before I can see exactly where the lower bearing sits to compere with this B25.
In the mean time, it would be helpful if you can clarify what has been done on the bike. Have you simply replaced the steering head bearings and, if so, have you not compared the old and new bearing geometries to see what is different? When you mention that the top cone is a modified Triumph one, does that mean that the bottom cone is a modified Triumph one?
Hi Spaceman,
thank you for once again responding with helpful comments.
The frame had been completely stripped for powder coating. The engine, frame, etc are 1967 C25. The forks are (I think) from a 1969-70 B25. I have fitted new top and bottom steering head cups. The bottom cone is a BSA part (number 40-5144). The BSA top cone (part number 40-5143) does not seem to be available from anywhere I have looked and so a Triumph top cone which integrates a dust cover is offered as a suitable alternative. To make this part suitable for BSAs the dust cover is cut off. In the attached photos you can see that the geometry of the bearing surfaces are different but whether that is significant, I don't know.
Any help and advice is really appreciated,
Kevin
I've just had a close look at my B44 that uses essentially the same frame and fork yokes as the C25/B25. On my B44, the lower bearing cup also projects 1-2 mm below the bottom of the steering column but, where this C25 appears to differ with my B44, is how far the lower cone projects below the cup. On my B44, it projects only about 1 mm whereas, on this C25, it seems to project down about 5 mm and this may be what is causing the steering stops not to line up.
If the lower cone is the correct one, I assume the ball bearings used are 3/16" in diameter and not 1/4"?
We checked the "new" bottom cone against the original one and they were very similar in thickness. I'm sure that we have 1/4" ball bearings which is as stated in the later parts book. Why do you assume the the ball bearings are 3/16"?
Thanks again for you help in this,
Kevin
I was going by the size listed on a particular web site under part 89-5015 that was clearly wrong - they are 1/4".
However, looking in RR Vol 2, it states the bottom cone flange is 1/8" thick - it would be interesting to know the thickness of your flange.
The thickness of the flange is 23/128th. I've also measured the original cone's bottom flange and this measures 25/128th
I've also dry fitted the original top cone (without the bottom yoke in place) to see how this differs from the new Triumph cone, there is no discernible difference. The original cone is pitted in places so not an option.
Quote from: KCF21 on 05 Jun, 2023, 20:23
The thickness of the flange is 23/128th. I've also measured the original cone's bottom flange and this measures 25/128th
If I interpret you measurements properly (where does 128th of an inch come from?), the correct thickness should be 16/128" and so your flanges are a bit thicker than they should be by about 1.5 mm. The picture below is of my B44 set up.
The 128th measurement is just what my callipers measured when the measurement gauge was set to fractions of an inch. What I fail to understand is that the new cone is slightly less thick than the original ones (probably what was fitted when it was made) are just as thick.
OK, so I've explored the possibility of not having the correct parts to the correct dimensions and it seems that the replacement parts I have are not significantly different to the originals. The forks are held in place by the pinch bolts on the bottom yoke and the top nuts on the top yoke so does it matter that the bottom yoke sits slightly lower than I would like to see it?
I think the bearing thicknesses only differ by about 1.5 mm which is neither here nor there for the steering column or the forks.
It looks as though the main problem is with the steering stops not lining up. For reference, the flanges on the lower yoke that contacts the stops on the frame are about 3/8" thick on my B44 and the top of each flange is 3/8" below the bottom of the steering column.