Topic: K1 CB750 Fork parts Question

[ZTatZAU]

Many here know I'm still learning and just feeling my way along on my K1 (s/n 1072186) CB750's resurrection.   But, at the moment, I'm quite confused and could use some learnin' here.

When I first posted about rebuilding my forks, I remember either Newday77 or BenelliSEI suggesting I order new crush washers for the hex bolts at the bottom of my lower fork sliders.

This is where the plot thickens and I don't know if my question is really about the forks on my bike or about the K0-K1-K2 Parts book I have "Courtesy of honda4fun.com.

The pictures below show the relevant fork diagram from my parts book and my still disassembled forks on the bench.





When I looked in the parts book for the crush washer for a K1, the diagram didn't show a hex bolt or the crush washer at the bottom of a K1 slider.  Neither did it show the inner lower piece that the hex bolt threads into; like the parts I've enclosed in the red and blue boxes in the K2 diagram above.

As far as I know, my forks are original K1 forks but my fork parts in the picture above look like a hybrid of the K0-K1 forks and the K2 forks.

I ordered new crush washers with the part number shown on the K2 parts diagram which seem to be correct and fit the hex bolts that came out of my lower sliders when I took the forks apart.

My question is, was there a transition period where the earlier forks shared some components with the later forks?  Or is the parts book I have and the diagram for the K0 & K1 forks just wrong or at least incomplete?

I asked my local Honda Dealer parts guy what his books showed and he said they show the same as mine.  Can anyone tell me what's going on here?

Thanks for any info anyone can provide!  ZT

[Don R]

 I think the K0/K1 drawing fails to show the internal bottom parts. They probably come assembled in the lower fork as a replacement part.
 Put a new copper washer on the allen bolt that holds the lower fork innards in place and re-assemble what you have.
 What you have is more accurate than that drawing is.

[ZTatZAU]

I think the K0/K1 drawing fails to show the internal bottom parts. They probably come assembled in the lower fork as a replacement part.
 Put a new copper washer on the allen bolt that holds the lower fork innards in place and re-assemble what you have.
 What you have is more accurate than that drawing is.

Thanks Don!  I appreciate your reply!

During reassembly of the forks, what's the correct sequence and the best way to secure that inner lower rod assembly (not sure what it's called) in order to tighten the bottom hex bolt?  Should I assemble every thing except the bottom hex bolt, including the top "bolt" (filler plug), and rely on the spring pressure to hold the inner lower rod from turning when tightening the bottom hex bolt?

And do I then remove the filler plugs while still on the bench and fill the forks with the correct amount of oil?  Or should I fill the forks with oil after the fork tubes are installed on the bike?

I appreciate the guidance!
ZT (CB750 Apprentice)

[BenelliSEI]

I usually do as you suggest; assemble everything and then tighten that bottom bolt. The spring pressure is usually enough (with the cap on). I add oil when everything is assembled, but thinking about it, you can do it anytime.

[ZTatZAU]

I usually do as you suggest; assemble everything and then tighten that bottom bolt. The spring pressure is usually enough (with the cap on). I add oil when everything is assembled, but thinking about it, you can do it anytime.

Thanks John!

Emphasis added to your reply!  You say the spring pressure is usually enough... what do you do if that lower piece spins when tightening the hex bolt?

I'm not looking for trouble... Just asking!
ZT

[BenelliSEI]

Assuming the inside the fork tube bottom, and all the other parts are clean and dry, it won’t spin. It “often” spins on disassembly when the internals are still sitting in a pool of oil.

[newday777]

I usually do as you suggest; assemble everything and then tighten that bottom bolt. The spring pressure is usually enough (with the cap on). I add oil when everything is assembled, but thinking about it, you can do it anytime.

Thanks John!

Emphasis added to your reply!  You say the spring pressure is usually enough... what do you do if that lower piece spins when tightening the hex bolt?

I'm not looking for trouble... Just asking!
ZT

Fully assembled dry you won't have any worries. The same with taking the bottom bolt out to rebuild. It takes the pressure of the cap pushing on the spring to properly do it.
Too many people don't do this of getting the allen bolt out or back in and that is where the problem happens. 😕

[ZTatZAU]

Thanks John!  Thanks Stu!
I appreciate you sharing your experience and expertise.
ZT

[HondaMan]

The fork's lower part differences were more of an "Old factory vs. New factory" situation. The Old Factory (where the sandcasts came from) supplied those forks where the lower SHCS bolt and the lower internal damper arrangement were missing: in fact, my K2 (Old factory) has none. They intermittently appeared/disappeared in production, too, as I discovered when doing a friend's K2 not long after mine: his has the lower bolt and the associated inner damper, yet his lowers use the same shaft seal as mine. By the K3, all those I have worked on had the bolt. On my K1 I never had a chance to change the seal, so I didn't notice: other K1 bikes I've serviced had both types.

One way I've often used to hold that lower damper rod in place while tightening the bolt is: I have a long tapered metal rod that I wedge into the top of the lower damper tube to hold it still, then tighten the bolt. My rod has a conical tip on it and is slightly larger than the ID hole of that lower damper tube. It holds it from turning, well.

[BenelliSEI]

I also have an “emergency tool”. It’s a broom stick with the top end whittled down to fit snugly in the rod. Rest of the time the other end is screwed into my shop broom.

[HondaMan]

I also have an “emergency tool”. It’s a broom stick with the top end whittled down to fit snugly in the rod. Rest of the time the other end is screwed into my shop broom.

That's probably a smarter approach than my steel rod!

[Johnie]

I also have an “emergency tool”. It’s a broom stick with the top end whittled down to fit snugly in the rod. Rest of the time the other end is screwed into my shop broom.

I use the same broom stick...works slick.

[ZTatZAU]

The fork's lower part differences were more of an "Old factory vs. New factory" situation. The Old Factory (where the sandcasts came from) supplied those forks where the lower SHCS bolt and the lower internal damper arrangement were missing: in fact, my K2 (Old factory) has none. They intermittently appeared/disappeared in production, too, as I discovered when doing a friend's K2 not long after mine: his has the lower bolt and the associated inner damper, yet his lowers use the same shaft seal as mine. By the K3, all those I have worked on had the bolt. On my K1 I never had a chance to change the seal, so I didn't notice: other K1 bikes I've serviced had both types.

Thanks Mark!  Once again, I appreciate the historical information you can always provide!

One way I've often used to hold that lower damper rod in place while tightening the bolt is: I have a long tapered metal rod that I wedge into the top of the lower damper tube to hold it still, then tighten the bolt. My rod has a conical tip on it and is slightly larger than the ID hole of that lower damper tube. It holds it from turning, well.

I also have an “emergency tool”. It’s a broom stick with the top end whittled down to fit snugly in the rod. Rest of the time the other end is screwed into my shop broom.

I use the same bloom stick...works slick.

And once again, I appreciate you guys sharing the solutions you've found for the common, as well as the not-so-common, problems encountered on these old bikes.

In the case of a fork is assembled with clean and dry components, I can only assume the cause of some lower damper rods spinning (and others not) when tightening the bottom bolt, depends on the amount of pressure exerted on the damper rod by the fork spring.  That is to say that a fork spring in good condition will normally apply enough pressure to keep the damper rod from spinning, while a worn fork spring may not apply enough pressure to keep the damper rod from spinning.  Is this assumption correct?

If so, in pondering this new found knowledge and how it might apply to my K1's resurrection, I revisited the measurements I made when disassembling my forks.  The FSM calls out the "standard" free length specs on the fork spring as 19.075" with a "Serviceable Limit" of 18.11".  I measured the free length of both of my fork springs as 18.8125" (18-13/16").  Accordingly, I did not plan on replacing my springs.

But in light of this discussion, and the measurements noted above, I am curious about any predictions you may have as to whether or not my fork springs will exert enough pressure to prevent the lower damper rod from spinning when I get around to tightening the bottom bolt?

ZT (CB750 Apprentice)

[seanbarney41]

You just have to try it.  If you got 'em apart without resorting to a broom stick, than I doubt you will have trouble getting 'em back together.  Keep in mind, according to Honda manual, this job MUST be done with the special tool (or a broom stick lol)

[ZTatZAU]

You just have to try it.  If you got 'em apart without resorting to a broom stick, than I doubt you will have trouble getting 'em back together.  Keep in mind, according to Honda manual, this job MUST be done with the special tool (or a broom stick lol)

Thanks Sean!  I appreciate you candid and pragmatic reply!

  ZT

[BenelliSEI]

“Just do it”.

[ZTatZAU]

“Just do it”.

Will do John!
ZT