Topic: 1977 Honda CB750K Rear Wheel Fitment

[Ellz10]

Bike is a 1977 Honda CB750 K.

I've spent over 2.5 years rebuilding this bike. Countless hours, money, ect.

I'm finally in the home stretch and this is what I run into. I am BEYOND crushed. As lame as it sounds, I want to seriously cry. I was told a 4.25" rear rim would not be too big for the larger '77/'78 swingarms. The tire is a 140. I don't understand how this could be.

Anyone have any helpful words please, I could use them.

[Ellz10]

I want to point out that you can see the whole wheel isn't centered correctly. There's 4 or 5 times more room on the left than on the right. I've installed everything correctly, both spacers, ect.

Any thoughts on what I could've missed or how to go about spacing the right side more and reducing the left side?

Could it be that the swingarm got bent out of whack? Hondaman did a full service rebuild on it, if something was amiss, I figure he would've noticed. Here's a pic.


Edit:  After looking over everything 3 more times I noticed that the right hand side spacer in front of the drum doesn't look as big as the parts fiche does. So I googled the part number and the correct part number spacer looks quite a bit longer. However It was a very snug fit getting everything in there now, so I'm just confused all over again. Maybe it's a mix of having a bent swingarm AND the wrong spacer?

[bryanj]

First check is are the sprockets on engine and wheel in line, that sprocket looks a long way away from swingarm to me

[RAFster122s]

If you had the wheel built or built it I would say the offset or dish on the assemble could be contributing to the issues you are seeing. The hub often is not exactly centered in relation to the rim. This offset allows for proper alignment of the chain and the tire within the fender and within the swingarm with the stock spacers.
The offset is adjusted when building the wheel and tightening the spokes.

The assemble with the wheel spacers is usually a pretty snug fit.

I will let others more talented than myself address your concerns and fitment issues...

[Ellz10]

First check is are the sprockets on engine and wheel in line, that sprocket looks a long way away from swingarm to me

Used an alignment tool with laser and they're dead center of eachother.

[denward17]

I don't know if this helps, but here are a couple of pics on a K8, using a 120 tire.

The wheel is located about half way up on the chain adjustment.

[Stev-o]

Is the motor also a '78?  Honda made chances in '77 to the final driven shaft, sprocket carrier and 17" wheel.
Just throwing this out there to rule out that possibility.

I had a 130mm on my K8 with no issues.

[Ellz10]

I don't know if this helps, but here are a couple of pics on a K8, using a 120 tire.

The wheel is located about half way up on the chain adjustment.

Denward, you helped more than you know. It's quite possible you helped solve this mystery/issue by providing those pictures (assuming that everything installed on your K8 as shown in the pictures is all correct oem stock parts).

So the previous owner of this bike, as many can attest, was a complete Dumbo. He should never be allowed near a motorcycle.

So upon doing my research this morning, comparing and contrast reference photos, cross checking part numbers across the fiches, I've learned that not one, but BOTH of the spacers in the rear that came installed on this bike are incorrect. I know this for fact now. One of them is for the FRONT wheel and the other is from what I assume is a K0-K6. I just ordered both of the CORRECT spacers and will be giving an update when they arrive. It all makes much more sense now.

Is the motor also a '78?  Honda made chances in '77 to the final driven shaft, sprocket carrier and 17" wheel.
Just throwing this out there to rule out that possibility.

I had a 130mm on my K8 with no issues.

My motor and frame are both 77.

And yeah I had made sure to do my homework and was sure the 140 on an 4.25x18 rim would fit before I spent ALOT of money on everything. Pretty sure you can go up to a 150 max on the 77/78 swingarms without problems.

[denward17]

Yes Ellz, everything is stock on mine, as far as I know.  It was like that when I purchased, but don't think the PO did anything different than stock.

[grcamna2]

subscribed

[Ellz10]

So problem solved - to a point.

I wish I could just cower and hide from this thread, but I've always faced my own idiot mistakes, not going to stop now. If Frank were here, I'm sure he'd have some remark about my dimwitted mistake lol

I had the unpleasant stupidity of installing the 2 rear spacers (left and right side) wrong. I installed the right one on the left and vice versa. Suffice it to say I'll never make THAT mistake again.

As soon as I figured that out and switched them into their correct places, I could see the whole rear assembly shifted to the left by about 3/8" which was great.

So I proceeded to throw my shocks on, took the front sprocket cover off, and installed my chain.

Once that was all done I stood back and dialed in the chain bolt adjusters, and much to my suprise and annoyance I found that the tire shifted back towards the swingarm. I've still got clearance between the swingarm and the tire, but not as much as I'd like. There's about 1/4" of space between the two. Should I be concerned or am I safe as long as there remains that clearance?

I'm able to gain more clearance the farther back the tire goes, however with the 88P chain, I'm back as far as I can go with barely ANY slack at all in the chain.

[denward17]

Is it a new chain ?  If so, it will stretch with a few miles and you can re-adjust.

How true is the rim?  If true, then 1/4" should be ok.  I'm not sure how much these rims flex during hard cornering though.

[RAFster122s]

Frank was never a dick...he wouldn't seriously rip on you. He might tease you, but nothing you couldn't take...

[Ellz10]

Is it a new chain ?  If so, it will stretch with a few miles and you can re-adjust.

How true is the rim?  If true, then 1/4" should be ok.  I'm not sure how much these rims flex during hard cornering though.

Brand new chain, yep!

And the rim is a brand new Sun Buchanan rim. After having it mounted and balanced, he only had to add one small.1 ounce weight.

I suppose we'll see how it handles in the corners - if it rubs at all or not.

Frank was never a dick...he wouldn't seriously rip on you. He might tease you, but nothing you couldn't take...

Oh Raf, I meant that in the most wholehearted and genuine way possible! He could be straight to the point and no nonsense at times but was kind and pretty damn smart! We were talking about having a dust shield made for my triples, but then the accident happened 💔

[newday777]

How true is the rim?  If true, then 1/4" should be ok.  I'm not sure how much these rims flex during hard cornering though.

I agree that a 1/4" will be good if the rim runs true.

[rotortiller]

Spacers AFU. Also the stock 77 does not have the wheel centered in the swing arm. More room on the left side, way more. 7mm difference between tire and swing arm with 130 tire at the widest tire point. Spacer position 13.5 and 37.5mm.

[rotortiller]

long spacer position. For ruff appraisal only.

[Ellz10]

Spacers AFU. Also the stock 77 does not have the wheel centered in the swing arm. More room on the left side, way more. 7mm difference between tire and swing arm with 130 tire at the widest tire point. Spacer position 13.5 and 37.5mm.

I saw that when I first threw it in and thought "Oh s***!" I thought something was wrong, but nope that's just how the 77 is!

[rotortiller]

When Honda lengthened the transmission output shaft they frankengineered the swing arm and rear sprocket hub area to line #$%* up. That threw the above mentioned visual symmetry out the window. I was kinda surprised what they did with the methodology reminding me of a Harley abortion, but being at the end of the production run they likely would have given a rats ass. lol