Counter Steering: Does Anybody Have An Explanation? - Demystification Required

[oexing]

Norman, did you look up the link in my post above ? The BMW bearing is 34-51-12, so I do not think you can get any closer to old sizes for replacement. 30 mm i.d. would not work with Vincent stems as these are something like 31.5 mm or so. I had some alternatives from Jap bikes 30 years ago as I had no info of later specials for BMWs and more. These are close enough for your mod as I did a few years ago.

Vic
BMW tapers

 

[timetraveller]

Vic, if you look at the original Vincent steering head it is 1.25" (31.75 mm) at the bottom, where the lower bearing fits, and then the tube is 1.125" (25.875 mm ) all the way up to, and including, the top nut. When I designed the new system for CNC machining I designed the bottom to be the same 1.25" where it fits into the lower block, through the washer FF36 and the bearing and then has a slow taper (no stress concentration points) over more than one inch down to the 1.125" diameter which then continues to the top. My idea for the new dimensions was that the lower part where it is an interference fit into the lower block and where it passes through the washer FF36, would stay the same as original, 1.25", and then would reduce the diameter down to 30 mm all the way up to where the nut is. The tube would then reduce to the correct diameter for the nut, 1.125". That way the same size taper roller bearing could be used top and bottom with no shims etc. [ I have to measure the inside of the top FF1] to see what OD is needed there. I note that the bearing you used is12 mm deep so how did that compare with the original total depth of the cup, cone and balls? It is possible that there are some advantages with your system and I will have to think about it for a while. Remember that we are making a new part so that there is no problem designing to fit a new size of bearing. It is the OD and depth which are potential sources of trouble. I can see that there would be some savings in both time and money to keep the top cup and cone bearing if it is in good condition but I really do not like having to be so careful to capture all the grease covered balls when working with the original bearings. Plus they cost about six times the cost of the taper rollers.

 

[Cyborg]

With a 3D printer you could print a cage for the ball bearings? I believe some of the Moto GP bikes use a caged ball setup, but don’t have any info to back that up.

So how many balls are folks normally using? 20 seems a little crowded to me.

 

[Keith Martin]

Cyborg, Your post reminded me of the bearings fitting to Triumph Triples in the early 1970's. Triumph part number 97-4034 is a caged ball set up that just so happens to fit the Vincent races perfectly. The bearings are hard to find nowadays but I stash them every time I see one. I think I will try them in the touring Rapide going together with the JE steering stem.
16 balls that will not fall out during assembly.

 

[John Reynolds]

Caged balls are not a good idea for a headset bearing. The advantage of a caged bearing is that the rubbing speed of the balls (or rollers) is halved but this is only significant with bearings which are rotating at high speeds. Obviously this does not apply in the case of head bearings, the primary role of which is to resist axial loadings. In this role, the greater the number of contact points, the better. So more balls! Again, it is obvious that the races must not be overfilled or the balls will not be able to rotate freely.

 

[oexing]

Norman, I had the standard forks in mind for mods and taper roller types. So with these I believe the BMW replacement is not to beat at 34-51-12 mm . I would never want more than 51 mm in the head casting for fear of cracks there. So alternatively there are bearings with 50 mm o.d., problem is the very thin adapter from 50.5 to 50 mm - not great. So next size is 48mm , allright for adapters but not stronger than the BMW size. But you don´t need to machine the head casting. Anyway, you have to keep 12 mm depth due to recesses in head lug. I do not know if bearings with 14 mm height would work out with your parts. So see my links below , scroll down for getting sizes and motorcycle types for ordering samples. Some sets may be useful when just having one bearing for the mod and bin the other, cheap enough.

Vic
Yamaha bearing

Yamaha No 2

Honda

A great thing with the BMW type is the 34 mm i.d. and adapters loctited on the standard stem - which is typically a banana shape and bushes not perpendicular to stem. So you get the press for rectifying the plane of link bushes to be perpendicular and checking by having the stem on the lathe between machined centers. After you are happy about that matter you can loctite premachined adapters for upper and lower taper bearing on the stem and turn them to minimum press fit below and light slide fit of upper adapter, 34 mm here. Another matter on Bramptons is the fit of top yoke which has the pinch bolt for tightening the lot onto the stem. This yoke will possibly need a boring head job and sleeving for restored snug fit again.
Having races from different types of taper roller bearings does not work mostly as taper degrees are different, depending on cross sections of races and load requirements.

Vic

 

[Bill Thomas]

With taper rollers, Could you use an inner bearing from one set and an outer from another,
I know a man who did.

 

[Cyborg]

Cyborg, Your post reminded me of the bearings fitting to Triumph Triples in the early 1970's. Triumph part number 97-4034 is a caged ball set up that just so happens to fit the Vincent races perfectly. The bearings are hard to find nowadays but I stash them every time I see one. I think I will try them in the touring Rapide going together with the JE steering stem.
16 balls that will not fall out during assembly.

This is a steering head bearing for a 2021 Ducati Panigal. I just picked a new bike at random. OEM part number is 70241231A which is a NTN SF07A17P. If OEM’s (Japanese, Italian etc.) are using them on large displacement sport bikes, they are probably ok. If I understand correctly some of the GP riders didn’t like the way the taper rollers reacted under very heavy load. I don’t have any data to back that up and don’t feel like searching… I have to go powder coat my seat frame. Also nothing wrong with using taper rollers on a Vincent …. if you reach loads high enough to cause a problem…. you’d likely be more worried about how long the ambulance is going to take to arrive. I don’t doubt taper rollers would last longer in a Vincent, but not a factor for me give the amount of riding I do. Anyway… just my opinion.

 

[Cyborg]

With taper rollers, Could you use an inner bearing from one set and an outer from another,
I know a man who did.

Not that I know much of anything about bearings, but for something that rotates as much as a steering head bearing… why not as long as the rollers are contacting the cup at the correct angle and are lined up properly. If there is enough meat, turning the outer race isn’t an issue either. I thought they would be harder than the hubs of hell, but chucked one in the lathe… used a carbide insert and it cut without any fuss whatsoever.

 

[oexing]

That Ducati ball bearing is 35-55-14.5 mm . Now imagine turning down the outer race for 50.5mm there will not be left much of the race, in any case very thinwalled. Not to speak of total height of 14.5mm that will not fit well in head lug recesses. One critical place is the recess for lower bearing which got a step of clearance of about 51 mm . So I see not much choice for taper types of turning down outer races for 50.5mm so as not to have the lug machined somehow. I surfed Ebay for some time and did not find suitable bearings for the standard stem of around 31.5 mm . There are Timkens of 48mm o.d. and 30mm i.d. suitable for the new Norman type stem, from Jap types, no old ball bearings on these, unless small and light bikes.
Anyway, the relieved recess of lower bearing is far from ideal for having a turned down taper type in there as it is not supported well . So far I can only see the BMW replacement 51-34-12 mm to go in there but with machined lower recess 51mm all the way for good support. And maybe the 48mm type with 30 mm i.d. suitable for the new stem to go with a decent adapter 48/51.5 mm . The BMW size is not suitable for turning down the o.d. as it is very slim already !

Vic