SOHC.co.uk Forums > CB750
Front Axle query
Lobo:
Hi,
Reassembling the front end of the K2 with a couple of questions.
(1) never particularly noticed in the past, but the axle is about 3mm short of flush with the axle holder. The axle is in the correct orientation (ie hex side by the disc) and looks normal wrt the various clearances. Notably though the 400F’s axle is flush in this respect. Comments? (the forks were removed off the bike)
(2) the fork seals have been replaced; and I note the ‘book says 225ml of oil to replace for the K2..... and other volumes for K3 blah blah. Q. The bike is nearly 50yo.... how can I tell what forks are on it... they may have been changed out in the past?
Ta.
S
Bryanj:
Try rotating the fork tubes in the yokes and see if the gap varies indicating slightly bent tube, fairly common.
As to oil pick a quantity and make sure both are same thats more important than exact quantity
SeanFD:
From what I have read, if you have a back-up ring under the circlip, chances are you have early forks. Another external test is whether there is a bolt at the bottom holding the damper in. If no bolt, you have very early forks; I believe the bolt appeared at K0/K1.
The outside appearance of the lowers gives another clue:
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If that doesn’t help, you can tell by the innards.
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It says original because that was what in there when I dismantled them. Later contents:
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When I replaced my springs with IKON progressive springs, this was the advice I was given by IKON rep:
As prior I suggest you remove the springs and fill with about 400cc oil, stroke the fork slowly to bleed, then measure the height of the oil from the top of the tube, with the fork collapsed. Looking for 140mm of space between the top of the fork tube to the top of the oil. Add or remove oil till you get that set evenly, then install the springs and cut spacers as needed to get a total of 25mm of preload on the springs. Measure preload by placing the fork cap on top of the spring and spacer, measure the distance between the top of the fork tube and the sealing surface of the fork cap. Do this measurement with the fork assembly fully extended. [/i]
The preload bit may be specific to the springs, so take the above as a suggestion only.
I’d be interested to hear what others think of this, because after replacing the springs and shocks (IKON also) the bike developed a severe head-shake at about 35-35kph if I took one hand off the bars. This quickly settled and at higher speeds it was fine. I have yet, 20,000km later, to solve this problem, so any ideas welcome. I have just rebuilt the forks completely while replacing the seals, so here’s hoping 🤞
Lobo:
...aah thanks Bryan; that makes a lot of sense; didn’t occur to me. (tho’ the stanchions are new’ish / DSS pattern & I’d bloody hope true!)
Thanks too Sean; your info does indeed suggest my forks are K2. The forks are now buttoned up with the spec 225ml of W5; I’ll road test it before going the slightly more tech route you outline. (kinda want to see the back of the front end so-to-speak! 😂)
Cheers,
Simon.
Bryanj:
I have seen bent yokes cause the same problem but that is rarer though as you say new tubes ought to be true!! I have never checked but i would think its possible that axles may vary. Cant be arsed to go through parts books at moment to check
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