XK120 Clutch Operating Shaft

Guys, in typing this up I see here from past postings that the shaft, fork and tapered pin for this assembly have been problematic. So I’ll mention my current scenario and if you have any suggestions then please dive in:

The clutch operating shaft bushings at each end of my bell housing have some wear. I’ll be heating the housing up in the oven (girlfriend is gone for the weekend) prior to knocking the old bushings out with a drift sized on my lathe to fit. The replacement bushings lack the cutouts that secure them in place with bolts. Perhaps I can file cutouts but I have a vertical mill so I guess there’s no excuse not to use it for that.

The operating shaft has some visible wear at the end where it rotates in one of the bushings (bell crank end). Would it be better to turn it down on my lathe and fit a sleeve with an interference fit (restoring the outside dimension) or just buy a replacement shaft?

Finally, the whole tapered pin thing. The throw out bearing fork over time must have turned just enough to bend the pin slightly because it was exceedingly stiff upon removal. So much so that despite many attempts to carefully start to unscrew/ screw back and forth, it still sheared off where the threads meet the taper. As this seems to be a weak spot in the overall design, would it be a good idea to drill a second hole/ pin combination? Weld the fork to the shaft? Cut a keyway? In short, if you were to do yours over again what might be done differently with the benefit of experience and hindsight?

I only want to have to repair this assembly once.

Thanks.

When I recently bought a new fork from one of the major suppliers I noticed the new part was reinforced where my old part had been repaired. I wish I could say who the source was. I think you should look for a new one at this point. Someone on line should know who has these.

I don’t think it will be necessary to heat the bellhousing. If you have a suitable drift they shouldn’t be hard to remove. I think I used a piece of threaded rod, a couple of nuts and an appropriate sized washer to remove mine.

I bought standard, industrial grade, high-load, oil impregnated, SAE 863 iron-bronze plain bearings for the shaft. And I’m pretty sure I used bearings that were longer than the originals, under the theory that more load bearing surface area would slow the rate of future wear on the shaft. Other than the original length made the bearing idiot proof to install (cut-out same distance from each end) there was no reason not to fit a longer bearing.

Not having a mill (jealous!), I pressed the bearings in place using the same threaded rod, then used the holes in the bellhousing as a drill guide to make the half-moon cutouts for the shaft lock bolt.

I bought replacement taper pins (part number C.568) from virtually every supplier in this side of the Atlantic and found a stupefying variance in length and taper. I wound up using the least-ugly original pin I had. And same for the clutch fork.

Personally, I would not drill any new holes in an old shaft. The one hole is already a weak point.

If you weld the fork to the shaft, you will never be able to remove it without cutting it into pieces.

Somewhere around here I still have a ziplock bag of broken pins. I looked at everything you mentioned above, and came to the conclusion that each of them made a marginal assembly weaker by removing metal where it was sorely needed.

In the end, because I had a bunch of aftermarket taper pins that were just stupidly too short, the only change I made was to tap the blank hole on the back side of the actuating bellcrank (C2483, “Lever On Clutch Shaft”) arm (outside the bellhousing) and install a second taper pin from the opposite side, (see photo bottom left. The heads of both pins safety wired together) putting the pins in double shear. If you have original style pins, this is not necessary.

Mike, I’m in agreement with using longer bushings in each side of the bell housing. What I’m assuming to be the originals measured some 7/8" in length. My replacements are 1" in length. The bore on each side of my bell housing measures about 1.5". So, there’s still quite a bit of room to go longer with each bushing. I will be ordering a nominal 3" length from McMaster-Carr, facing the cut ends and milling the slots. For anyone simply following this, it’s also important to note that there are oil holes on each side of the housing above each bore for the shaft ends. Mine were covered over by hardened dirt/ grime. So easy to overlook. I might possibly drill out these holes slightly and press in a pair of small Gits oilers to keep the dirt out – assuming there’s enough parent metal to do so.

I also compared the replacement taper pins to my broken originals and yes, they too are ridiculously short. My originals measure around 1.75" in length and the replacements: around 1.4". So, a shortage in length of 3/8". That doesn’t inspire confidence. At this point I’m thinking of rooting around for some Grade 5 bolts and using those as stock for making my own on the lathe. I believe these were made to a Number 6 pin taper. Someone please correct me if I’m wrong.

Thanks.

I did a search of my McMaster-Carr parts orders, and I can see that I bought two SAE 863 plain bearings that were 3/4" x 7/8" x 1-1/2" long.

Hi Christopher
Here is the small weld I made on the fork retaining taper pin, hopefully enough to prevent it from moving (I still wired it up afterwards), and to make it easy to dismantle with a bit of grinding.
HTH, Francis