1971 CL450 Front Fork Casing Questions

[KnuckleBustingTwin]

Hello All,

I have a few questions regarding a pair of '71 CL450 fork casings ... would any know why the pair would have different diameter oil lock bolt at the bottom of the casing? One is 8mm and the other is smaller (not sure what size, but suspect 6mm) ... see photo ... I'm going to try and "carefully" drill the smaller hole.



There are different markings stamped on the casings, though I don't know what they mean; on is marked 4G and the other X6



Last question ... is there any reason that this (see picture) 47mm circlip won't work vs the OEM spec? The one I have is from a CB200T ... seems to fit, though shape is a little different ... the pipes do seem to clear the "rounded" ends of these circlips. I've been waiting months for the spec'd clips to arrive via David Silver spares ...

Spec'd part for CL450

The one I have originally for the CB200T

As always ... thanks for the advice gang ... hope everyone is staying well! Bill

 

[ancientdad]

The width of the bottom of those lower forks in the first picture is different, which could have an effect on spacing with the axle. If those are the ones you got with the bike, it sure looks like more mix and match pieces you inherited unless they've all been that way and I just never noticed. The clue is probably in the different diameter holes for the allen bolt, and I know those should both be the same. I'd be concerned about the differences. As far as the circlip is concerned, I might grind a tiny bit off the inner rounded edge of the clip ends to be sure but do it gently and don't overheat it in the process. The allen bolt holds the forks together on this design so it isn't like the circlip is carrying the load of assembly like the circlips in the older forks did

 

[Jays100]

Re the lower bolt for the damper rod, check the fiche for bolt p/n and description but I don’t recall 2 diff sizes.

the brake stay arm on the other hand, does have a mix of m6 and m8 sizes. Gotta keep you on your toes!

 

[KnuckleBustingTwin]

Thanks for the thought guys ... I actually measured the channel on the bottom of the two casings and (despite the picture) they are the same size. Must have been the way I was holding them when I took the pic.

Tom ... as you know, I have a bit of a frankenbike front end on this thing ... using a '71 CL450 drum brake and lower casings, new down pipes that are a touch longer than the originals, etc ... every time I think I'm close some new challenge shows up ... but that's OK, it's why we do this right?

I like your idea to gently grind off the round nubs on those circlips ... I'm also going to "carefully" drill out the smaller hole so it can fit the 8mm allen bolt ... that should solve the issue (providing I can get that hole as straight as possible).

Jay ... I did check CMSNL on the bolt sizes but couldn't discern two different bolts from the fiche ... believe me, this project is keeping me on my toes!

Thanks for the help guys ... photos coming soon ... Bill

 

[LongDistanceRider]

Looking at the Partzilla fiche for forks it appears the '71 K4 doesn't have those bolts, different fork design, and they only appear with the K5 listed as 8mm. Makes me wonder where a 6mm version came from.

 

[ancientdad]

Yes, the K4 had the older version external springs and bolt-through top bridge, K5 got the CB750-style forks like on my red bike and those have the allen bolts in the bottom that hold them together. K4 version was held together by the seal circlip

 

[66Sprint]

Looking at the Partzilla fiche for forks it appears the '71 K4 doesn't have those bolts, different fork design, and they only appear with the K5 listed as 8mm. Makes me wonder where a 6mm version came from.

The sliders using the 6 mm bolt (JIS head) had a damper tube that did not need to be removed/unbolted to extract the fork tube (which had its valving on the tube's OD)....
IIRC, this also means the internal bore of the K3/K4 slider is likely larger or at least different than the bore of the K5/K6 type fork slider.......

I'm NOT convinced that simply enlarging the bottom bolt hole and "pocket" are sufficient for proper functionality, particularly speed at which the assembly can/will compress......

 

[ancientdad]

I share those concerns. If the one leg had the 6mm JIS screw in it, that means the internals are different.

 

[66Sprint]

Even should you swap out the internals, if the bores are different, they will compress at differing rates.....

 

[Jays100]

um, not to get too technical but some of that is needed here. If he has two of the same springs (free length, wire diameter, number of coils etc.), they will compress at the same, exactly same, rate. There may be uneven loading side to side - do both springs stick up out of their respective tube evenly? In any case that will not affect handling, you won't even feel it. Generally compression dampening is non-existent on this type of fork so that's not part of the equation. Hydraulics only apply at the topping and bottoming extremes.

simply stated: Load=deflection * spring rate

which brings us to oil level and diameter. if the levels/diameters are different, Steve's point is that the change in air volume will cause a modification in the rate calculation and can be significant enough to impair handling if extreme enough. Boyle's law of combined gas starts like this: V1P1T1=V2P2T2
ends like this P2=(V1P1)/V2
where V=Volume, P=Pressure and T=Temperature. in this case temp is not considered and so cancels. it's essentially a sum/difference calc. P2 in this case is the compressed pressure in psia (absolute) or P1 is 14.5 psia. notice i'm using English units so your measurements should be in inches, or, convert it all to SI or metric units.

so, spring load + air pressure load (remember, volume is a function of the surface area the air acts on) * stroke, is the true investigative path.

Bottom line is, if the fork sides are profoundly different, well, they need to match.