Head bearing top yolk nut replacement. - Page 3 - Triumph Forum: Triumph Rat Motorcycle Forums
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post #21 of 23 (permalink) Old 08-17-2019, 08:19 AM
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Hi Gary,

Originally Posted by Code Man View Post
I tried to get some space between the steering stem nut and the top of the top yoke today but no success. I also don't have any space between the bearing dust cap and the bottom of the top yoke.
I think that because I installed tapered bearings in the steering head that the top yoke will not have space between it and the stem nut like the original ball bearings would have had.
called it good.
Nope, you haven't understood what's wrong with your bike. It isn't "good".


. If your bike "don't have any space between the bearing dust cap and the bottom of the top yoke", how can you expect "to get some space between the steering stem nut and the top of the top yoke"?

. Ian's bike doesn't/didn't have "space between the steering stem nut and the top of the top yoke" but it does/did have "space between the bearing dust cap and the bottom of the top yoke".

. Otoh, because your bike doesn't have space above and below the top yoke, the problem with your bike is the tubular part of the steering stem nut isn't longer than the depth/thickness of the top yoke which it must be for you to know the steering bearings are adjusted correctly.

. Your bike has exactly the same forks as my T150; as I posted earlier, my T150 has a 1/32" gap between the underside of the stem nut hex. and the top of the fork yoke.

. I haven't yet had a chance to check whether the T150 also has a gap between the underside of the top yoke and the top steering bearing dust cap. So:-

.. it might be these forks only have a very small gap, that Meriden increased on later bikes/forks;

.. otoh, it might be a PO of your bike misunderstood the design and shortened the tubular part of the stem nut so the hex. hit the top yoke.

. It's only possible the bottom of the stem nut on your is reaching the top bearing and adjusting both bearings correctly; nevertheless, even if it is, friction between your bike's nut hex. and top yoke makes it harder for you to judge when the bearings are adjusted correctly; bear in mind that, if anything, correct preload is more important on taper-rollers than it is with the original balls.

. For those reasons, I advise you to unscrew the stem nut on your bike and measure accurately both the tubular part's length and the depth/thickness of the top yoke and top bearing dust cover. Then buy a new steering stem nut with a greater tubular length than that total depth/thickness.

Secondly, "because [you] installed tapered bearings in the steering head" has nothing at all to do with "the top yoke will not have space between it and the stem nut":-

. If the tapered bearings you installed are deeper/thicker than the original balls-'n'-races, only the yokes can be further apart vertically, because the bearings are the same - fixed - distance apart in the frame.

. As I posted earlier in the thread, the steering stem is through both steering bearings but attached to the bottom yoke. So, if the yokes are further apart vertically, only less of the steering stem protrudes through the top bearing.

. As I also posted earlier in the thread, the top yoke is nothing to do with the top steering bearing; the top yoke should still sit on the top bearing's dust cover and the stem nut - being correctly longer than depth/thickness of the top yoke - should still have a gap between the underside of the hex. and the top yoke.



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post #22 of 23 (permalink) Old 08-17-2019, 02:53 PM
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Hi Stuart,
Everything you said above makes perfect sence to me and I agree with you that the steering nut seams to be the thing to check regarding its depth. I wonder if the steering stem nut could be just the perfect length to put the right load on the bearings and have no space under the head of the nut and the top of the top yoke!? I know, it's probably a million to one chance and more likely the nut is to short. It's very likely that nut came off a different model Triumph or the previous owner cut its original length thinking it should push down on the top yoke.
To really know the answer I'll have to pull the nut and check its length like you said.....Gary
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post #23 of 23 (permalink) Old 08-17-2019, 08:20 PM Thread Starter
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Thanks Chris and Gary,
Really useful and respectful input.

Hi Gary, I am not close to the bike for a few days but if you want to measure your nut, I am happy to measure my original Triumph T140e and replacement to see how they compare. I want to double check my setup anyway, so plan to unclamp everything, remove the nut, make sure everything is correct (referencing the original workshop manual that came with the bike, rather than any potential confusion due to online misinformation). It sounds like we have a very similar issue so I am sure we can work this out between us.

Hi Chris, much of what you say makes perfect sense. As Triumph manufactured the headlamp support tubes for this specific bike, then it makes absolute sense to use them as a guide to initial fitting/positioning of the top/bottom yolks. In fact, with my factory-set yolks and bearings, the headlight support tubes were pretty much a snug fit between the yolks, as they are with my new bearing nut setup. Of course, the bearings have to be set correctly (no binding and no free play) but it makes no sense for Triumph to engineer the relationship incorrectly between yolk distance and headlight support tube length, albeit with sufficient wiggle room for minor specific bike differences.

However, I do agree that replacing the original 1970s ball bearings with modern tapered roller bearings, introduces the real chance of a difference in head bearing setting, even the most inexperienced of us should realise that there is a likelihood, due to the different nature of the bearings (let alone manufacturing differences between balls, rollers, tapers and races etc), of changes in dimentions, no matter how small. IME even fitting new factory bearings, like for like, has impact due to the wear in the old bearings.

Thank you for correcting me on the whole head bearing / yolk fitment setup, all makes sense now. I will follow your advice when I strip, check and rebuild my setup in a couple of days and report back.

Cheers Chaps!
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