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Discussion Starter · #1 ·
Hi all,
My '71 CB450 is leaking fork oil from the right fork tube. It seems to be coming out of the very bottom of the tube into the cylindrical cavity (pictured) in the front axle. It then makes its way out of that, drips down the two bolts securing the lower cap on, and onto my garage floor. You can see the red fork oil in the attached picture pooling inside the axle and on the lower cap nut.

I'm assuming that I will need to disassemble this and tighten *something* at the lower end of the fork tube. I have never torn apart the front shocks before. The bike has been leaking like this since I bought it from the previous owner.

Has anyone encountered a similar leak before? Any tips or pointers? Any parts I should buy in advance of tearing it down?

Another thought I had is that possibly the previous owner overfilled the oil, and there's too much pressure causing oil to overflow... Perhaps this is just wishful thinking for an easy fix. I've seen the Clymer's manual spec on volume of fork oil, but is there any "fill line" or oil height that I can measure without draining all the oil and refilling the measured amount?

Thanks all!
Max
IMG_4447.jpg
 

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From looking at the parts fiche and the fresh looking atf leaking there I'd guess that someone rebuilt the forks but didn't manage to seal the drain bolt in the bottom of the forks.

It could be loose or it could need a new copper washer. Either way hopefully that's all it is and it should be pretty simple. If it's anything like the cb400t forks you won't even have to take the forks off.

Someone who knows 450 forks better will probably be able to confirm this.
 

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Discussion Starter · #3 · (Edited)
Update: I searched for the exploded parts diagram on CMSNL.com and found the following picture attached. It looks like Bolt #18 protrudes into the oil reservoir - is that correct? If so, perhaps that bolt has gotten a little loose and all I need to do is tighten it. Can anyone confirm if this bolt does indeed plug the end of the oil reservoir, and if it were a tad loose, would it cause a leak like mine?

Link to full-res pic - see bolt 18 on the lower right corner: https://images.cmsnl.com/img/partsl...-k6-c5-k7cl450-k5-k6_big3IMG01171602_9ca3.gif

(Edit: Looks like 80cb400t suggested the same. Are there two drain bolts on this fork design? One on the side (#23), and then another one at the bottom (#18)?)

Screen Shot 2019-02-05 at 9.22.16 PM.jpg
 

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I think bolt 18 screws into part number 7, that's how it works on later forks. I think the side drain screw is so you can change fork oil without taking the front wheel off which is quite useful.

Only one way to find out what is going on (take it apart), I would also look up the fork assembly section in the cb450 service manual and see what it says about that bolt.
 

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I agree that 18 screws into 7.
You may simply need to remove your front wheel and torque 18 to spec. Clean, reassemble and test ride before inspecting for further leakage.

You may have to get creative to keep the fork lower from turning, and you may have to remove your front fender to reduce risk of flexing its mounts. You could put the fork bottom caps back on and slide a long 1/4" socket extension (or something) through them, something thin enough to allow your 6mm hex driver access to the screw head.

Most manuals will tell you to clamp the fork lower in a vice with padded jaws, after powder coating the PO probably wasn't interested in that at all.
That's why I suspect lower than spec torque on that bottom bolt.
 

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Discussion Starter · #6 ·
Awesome advice. Thanks guys. I'll pull the wheel off, torque #18, and report back here.

Since I've lost some fork oil, is there a way to top it off to the correct amount, or do I have to drain it all and refill the measured amount? Seems like there should be a way to measure a fluid height from some reference at the top of the fork tube, no?

Thanks!
 

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Yes, fork oil level is easily measured from the top of the fork tubes to the top of the oil level. Do you suppose you've really lost enough oil to warrant draining and refilling?

If we're talking less than an ounce of oil I personally might wait few thousand miles.
 

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Is this a K4? That was sold in the US in 1971. The image above is for the K5-7 front shock and they are different than the K2-4 shock. The K2-4 shock does not have the bolt in the bottom of the slider. From what I can see from the picture the sealing washer is missing from under the drain bolt. This is a soft copper washer and is required to keep the drain plug from leaking. This is the same principle as the sealing washers on brake banjo bolts and the two right hand acorn nuts on the head. The washer is #25 on the attached image. Copper sealing washers should not be reused unless they are annealed. Back in the day Honda would just replace them. They can be annealed by holding them in a gas stove flame or propane torch. I usually bring them up to a glowing red color. After they cool I flat file the faces to ensure they seal.

CB450 K4 Front Shock.jpg
 

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James 71 forks have the bolts in the bottom. I know I've had mine apart. Reason far as I know they don't show on the fiche is because they are not supposed to be serviceable, not to be taken apart. At least that is what I was told on here a few years ago. Should be pics in my build log somewhere.

Cap needs to come off anyway, it's on backwards, the shorter side goes towards the rear of the bike if I recall.

Copper washer under that bolt maybe bad. You may get lucky tightening that on the bike, I had to rig a holder to hold the valve in place at the bottom of mine when I put them back together. Mine had had to come apart they were so full of rust from sitting outside it was nasty.

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Can you loosen the lower clamps and orientate the hole in the axle allowing access to the Allen bolt? Perhaps the po didn't want to risk clamping and it's not tight. If it seems to just spin put weight on the forks. The added spring pressure on top of the threaded damper piece may help keep it in place enough to get the job done without total disassembly which can be a pain without a good lift arrangement.
 

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Discussion Starter · #12 ·
Yes, fork oil level is easily measured from the top of the fork tubes to the top of the oil level. Do you suppose you've really lost enough oil to warrant draining and refilling?

If we're talking less than an ounce of oil I personally might wait few thousand miles.
Hi Alan, I'm not sure how much oil I've lost. I also am not sure if the previous mechanic got the oil level right in the first place. Do you know what the measurement from the top of the fork tubes to the top of the oil level should be?
 

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I don't know if Alan knows, but that isn't a spec anyone would provide - you'd just have to measure the one that isn't leaking and compare it to the one that is. I'd drain and refill both with the proper fluid and amount once you get the leak solved, based on it being done previously by a PO
 

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Tom's right I don't have that measurement, it surprises me that this isn't commonly known info especially on a bike of this age and popularity.

At this point I'd also recommend comparison between the two forks and go from there. in my opinion it likely hasn't lost enough oil to be concerned with, but of course it's your bike so your comfort is key.

For most bikes there are fill amounts for forks that have just been assembled and are dry inside, and there are fill amounts for a quick drain - pump a few times - drain some more - and refill, which are lower amounts to compensate for the amount of oil that clings to the internal fork parts. Full forks will have a measurable distance from the top flat of the fork tube and the top of the oil level, if you measure this, write it down for next time.
 

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Most likely the copper washer needs replacing. Order new seals and just plan on rebuilding the forks. It’s an easy job. The bolt in question fastens to the inner fork tube. If you need guidance, feel free to ask. It can easily be done, both sides in an afternoon
 

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Make a holding tool, a suitable strip of metal with 3 holes, 2 for the fork studs and the other for the allan key tool to reach the damper rod allan bolt, and a handle to stop the tool and fork from rotating. I would slacken the damper rod allan bolt with the fork in the yokes, as well as the top nut, rather than gripping the fork tube in a vice, no matter how ell protected.

The top internal nut, is that a special shape. It looks as if it screws onto the threaded end of the damper rod. I wouls also slacken that with the forks in the yokes, in frame.
 
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