Topic: Anybody know what this rear sprocket side plate is for? '71 CB750

[ksmith0034]

I am putting new front and rear sprockets on my '71 CB750 cafe project and found this in my "here's how it came off" pile.  My manual doesn't show it, but I found it in an IPB online.  It is a rear sprocket side plate.  But what is it for?  Do I need it, or can I ditch it?

[ksmith0034]

I have a 140/90-16, so I am a bit concerned about clearance.  However, this is how it was mounted on the stock setup.  I don't see how this setup would make any difference on tire clearance.

[Stev-o]

No, it won't. I thought it was mounted on the inner side of the sprocket.

Maybe that's not the original hub?
I'm almost certain the 71 did not come w/a 16" rim.

[kmb69]

The early Sandcast chains had a master link with a removeable clip so you could "open" the chain to remove the rear wheel. The guide on the rear sprocket was implemented to accomodate removal of the rear wheel with the "riveted" and subsequent "endless" chains. Instructions were to loosen the axel, spin the chain tensioners down, push the rear wheel all the way forward, move the chain from the sprocket to the guide, and then pull the rear wheel out. The rear sprocket guide was used to hold the endless chain from getting in the way with enough slack in the chain to get the wheel out. Reverse the process to reinstall.

[HondaMan]

That plate is a part Honda called a "splash guard". It was supposed to help reduce the oil slinging from the chain at the rear and help keep the bike cleaner. This was due to the early 750 having a high oiling rate from the countershaft's oiler, due to lower gearing and larger oil settings than the later bikes.

If you have a genuine Honda rear sprocket, that sprocket has a recessed face that is the same depth as the thickness of the stamped steel used for this splash guard, so the overall sprocket thickness with the plate installed is the same as the width of the sprocket teeth. Aftermarket sprockets, including the current crop of JT/EMGO units, do not have a correct recess: it is too small in OD (or nonexistant) and the guard ends up too wide from being stacked on top of the sprocket, often scraping the inside of the chain gaurd. Many have thus been removed. 

[kmb69]

Respectfully Mark, You may want to rethink this one. Official Honda part numbers and descriptions are:

K1     41211-300-000 Plate, Sprocket
K2-K6 41211-341-000 Plate, Sprkt.Side
K7-K8 41211-405-000 Plate, Sprkt.Side
F0     41211-392-000 Plate, Side
F1-F2 41211-405-000 Plate, Sprkt.Side

Centrifugal force slings the chain oil out, not in. Honda issued a service bulletin with pictures on how to use the plate as described in my post above. I do agree with you about the recessed faces on the sprockets.

[KingCustomCycles.com]

Now you got me wondering.  I can't imagine a plate helping remove the wheel in the way described.  I also remove these all the time caked in old grease.  That grease came from the chain in defiance of the centrifugal force. Common sense says it is a "slinger" due to the thinness of the metal and the shape.  However, the documentation points to the disassembly aid.  Anyone work at Honda in 1970 on here?  (you never know)

[05c50]

I think I read somewhere that the plate was there to keep the chain from wrapping around the axle in case it would break or come off the sprocket. I could be wrong...........and I'm wrong 99% of the time.

................Paul

[ksmith0034]

Well you guys aren't much help.  
I'm building a cafe racer so I don't care about looking stock.  Basically, do I NEED it or will I be safe without it?

[MCRider]

Well you guys aren't much help.   
I'm building a cafe racer so I don't care about looking stock.  Basically, do I NEED it or will I be safe without it?

I have always taken it off and thrown it away (frisbee style). It is not necessary and as you can see its original purpose is controversial. I ran without it for more than 20 years.

On my new project i am using it. Had it colored the same as my frame (gold) so its a cosmetic piece to pull the color scheme together, along with a gold chain. I didn't want to color the sprocket itself. I've seen some people chrome it which looks nice also.

But if YOU have no need for it, the BIKE has no need for it. IMO

[Hinomaru]

I could be wrong here ...  I thought the sprocket plate acts as a vibration / noise dampener working in conjunction with the hub rubber cush drive assembly. Perhaps this being one of the features that Honda incorporated for a smooth & quiet ride? The early bikes had a small diameter sprocket plate and this was later increased in size beginning with the K2 thus adding to the mystery. Regardless of their true purpose, they do look good when chromed.   

[ksmith0034]

Wow that looks nice!  But since my swingarm is chrome, maybe I should go with black powdercoat...  Has anyone seen a picture like that?

[MCRider]

Wow that chrome one does look nice! Since we're showing off, here's a long shot of my gold powder coat one, matching the frame and the front discs:

and a close up


Black w/ a black frame would be nice.

[MCRider]

And yours is the smaller early one.

[kmb69]

Yeah, I'm old. I was a Honda mechanic at Pasadena Honda and SouthWest Honda from 1968 thru 1974. Got to see the introduction and the early refinement of these fours firsthand. Got my certificate for Honda Technical Training in Atlanta in 1970. Road a Sandcast to the Daytona 200 in 1970 and saw Mann win that one. Supported my family working on them until changing to a Machinist career in 1975. Enough for the resume.

The Plate in question is NOT required and can be tossed if you desire.

Chains in the day did not have the tensile strength of today's chains and the side plates and pins would stretch quickly from the 750's power. The Sandcast and early K0 chains had a master link with a removeable clip so you could "open" the chain to remove the rear wheel. The removeable clip was supposed to be installed in one direction per chain rotation. The clip could be slung off if the chain side plates stretched longer than the clip could accomodate or if the removeable clip was installed backwards. Many of the "broken chains" were not actually broken but rather the master link would fall out. Honda introduced the "riveted" master link to prevent this. The plate on the rear sprocket was implemented to ease removal of the rear wheel with the "riveted" master link and subsequent "endless" chains. Sure, you can move the chain to the inside of the sprocket and accomplish the same thing and score up the aluminum sprocket carrier. Or, remove and replace the riveted link with Honda Special Tool 07062-30050. The plate was implemented beginning with SN CB750-1026845.

All the gunk that accumulates on the rear wheel is comprised of chain lube, tire rubber, brake shoe dust, road grime, metal particles from chain and sprocket wear, and who knows what else.

[HondaMan]

Respectfully Mark, You may want to rethink this one. Official Honda part numbers and descriptions are:

K1     41211-300-000 Plate, Sprocket
K2-K6 41211-341-000 Plate, Sprkt.Side
K7-K8 41211-405-000 Plate, Sprkt.Side
F0     41211-392-000 Plate, Side
F1-F2 41211-405-000 Plate, Sprkt.Side

Centrifugal force slings the chain oil out, not in. Honda issued a service bulletin with pictures on how to use the plate as described in my post above. I do agree with you about the recessed faces on the sprockets.

Well, my comments about the "cleanness" this plate was supposed to bring to the bike are a parrotted statement from Honda in the 1970s. I never understood it, either, and removed mine when I changed the first rear sprocket. For resto-riders, though, it is an important piece. 

While the part changed from hole sizes and colors, the thing still appeared on all the CB750s. They do not fit well when using aftermarket sprockets, though. 

[HondaMan]

I think I read somewhere that the plate was there to keep the chain from wrapping around the axle in case it would break or come off the sprocket. I could be wrong...........and I'm wrong 99% of the time.

................Paul

That was the front one on the K1 bikes. 

[Henning]

Yep, I can confirm that the plate is really useful for supporting an endless chain when you're trying to get the rear wheel out - this was on an early K1 with stock pipes and an oversized rear tyre. There's not a lot of space in there. If you're running a different setup like 4 into 1 you probably don't need it.

[ksmith0034]

I soda blasted it and rattle canned gloss black on it.  Tomorrow i'll mount it up and see how it looks.  Dont't worry, i'll take a picture! 

[ksmith0034]

Here it is with a rattle can paint job.  I like how it's a contrast piece.  At some point I would like to try the DIY powdercoating, but for now I need to spend my money on the things that actually make this bike function.  I'm still waiting on my X chain from KSC Direct.
Now to rebuild and repaint the shocks...

[HondaMan]

Here it is with a rattle can paint job.  I like how it's a contrast piece.  At some point I would like to try the DIY powdercoating, but for now I need to spend my money on the things that actually make this bike function.  I'm still waiting on my X chain from KSC Direct.
Now to rebuild and repaint the shocks...

Wow, that's a really small one! Like, from a different bike?

[MCRider]

Here it is with a rattle can paint job.  I like how it's a contrast piece.  At some point I would like to try the DIY powdercoating, but for now I need to spend my money on the things that actually make this bike function.  I'm still waiting on my X chain from KSC Direct.
Now to rebuild and repaint the shocks...

Wow, that's a really small one! Like, from a different bike?

I was just in my shop looking around...and I have one that size as well. Surprized me.

[Grnrngr]

The plate is actually there to provide two more guys with jobs..one guy to make it, the other to bolt it on.....