If you are happy with a bandsawn one for the easy cut then a hacksaw should do the others

Two hacksaw blades in one frame is common tip for wider slot. But I could never get a pair to work properly to cut a neat slot.

Put it down to the blade tensions being a bit different. The mounting pins on all my frames have significant angle pointing out of the ends of the frame to ensure the blade doesn’t ping off when tightening. So the inner blade carries less tension.

When the Rapidor power hacksaw broke a blade I said “Ah ha” and made half into a knife and half into a slot widener. The knife is great, takes a really keen edge. The slot cutting thingy gets used about once in 3 years!

Clive

Hi Ian,

My suggestion would be to  invert a jigsaw and mount on a wooden platform. Use a metal cutting blade and cut the necessary slots using a guide to keep slot in correct place.

NimbleNeil.

If you go to rsonline and search for locking bush you will find clever taper affairs that might obviate the need for slots. You’d need to bore the holes bigger, looks like there is some scope as wall thickness appears greater than original

Correct me if I am wrong but those slots dont look symmetrical, the one at the top looks to be the one that is right as its angle has thinned the material to be pinched by the bolt. Just an observation.

I imagine that the considerable reduction in thickness over the central potion of the original, cast or forged, yoke compared to the outer web and the immediate surroundings of the holes influences the ability of the slot to close up when clamped.

My one and only experience of making special triple clamps (yokes) was well over a decade ago but, as I recall things, the first test with the material still of constant thickness was very unwilling to clamp up. I think it sort of did but the bolt torque needed seemed dangerously high. For reasons I can no longer recall it had to be thinned down in a manner very similar to a standard cast yoke. After thinning the clamp bolt torques dropped to more reasonable levels.

Factory pinch bolt torques are quite low. For example the manual for the rotary engined Norton Interpol 2 that I have immediately to hand recommends 22 to 24 ft lb on the tube pinch bolts and 18 ft lb on the stem pinch bolt. Which seems fairly typical for modern alloy yokes. So clearly things are inherently fairly flexible.

Back in the day, before (apparently) all the world and his wife had a CNC mill in the garage and the billet craze undreamed of, many aftermarket top yokes seemed to be basically a quite thin plate with slotted tubular extension affixed below to actually grip the fork tubes and stem. Which always seemed a bit scanty to me. But BMW used what appeared to be a chromed off-cut of 3 mm (or thereabouts) sheet steel as their top yoke on the R series airhead twins so presumably the engineering worked out.

Clive

Ian

Given that what you have isn’t working it seems worth thinning out the middle in the hope that my experience transfers to you.

Alternatively if you do fancy trying a simple BMW style flat plate top yoke I have vague memories of one of the non-accredited BMW dealers (Benrae?) offering an improvement kit based on a double thickness alloy plate. My recollection is that tis kit used cylindrical slugs screwed into the tops of the forks with the top end made as a smaller diameter spigot to fit in the holes in the top plate. The slug being tapped to take a smaller diameter bolt to hold things together. I imagine the screwed slug had narrow land for the fork tubes to screw up against and the replacement cap bolts were around M14 or M16 (fine?) so clamping took place on an area something like 5 mm wide. Presumably special bolts with built in annular flange to ensure that clamping loads were properly applied through the plate to the top of the slug. New centre nut too.

That said I don’t recall being particularly impressed by the various improvement options on display in a nicely lit up glass cabinet. More influenced by marketing than engineering I felt. This was in the days when high quality, shiny anodising was somewhat rare and pretty components priced accordingly. Well outside my pocket for sure. 1984 (ish) I guess as I had my first K100RS at the time.

It may, or may not, be relevant to note that aftermarket “flat billet” yoke suppliers cut the fork tube clamping part free of the main yoke rather than replicating the slot. This gives 180° or more of flexible wrap to clamp. The stem surround area is frequently shaped so as to give perhaps 90° each side of relatively narrow material to flex and clamp.

Clive

On 8 January 2025 at 16:19 Neil Wyatt Said:

I think you have a decent chance of the slots being adequate if you try to emulate the original part by recessing the underneath of the yoke, the top can still be flat. I assume you have the right grade of alloy and awareness that this is safety critical should go without saying.

All good points. Home made parts could perhaps invalidate insurance if the worst were to happen?