SOLVED: Sprocket alignment for K6 engine & K7 frame.

[Qaxe]

What tool can I use to check my sprocket alignment?

My CB750 consists of a K7 frame with a K7 swingarm and rear wheel, and a K6 engine. Both sprockets and chain are K6 too.
EDIT: My rear sprocket carrier was K7 also.

I have read that the K7 swing arm, and both sprockets are out to the left by 1cm compared to older years. People who mix and match K7/K8 frames or engines with K6 or older engines or frames, end up with some sprocket alignment issues. I'd like to check this, but I don't know what sort of tool to use.

I don't have a laser-guided surveying scope, but looking at it, my sprockets sure look aligned. The rear sprocket certainly doesn't look to be a full centimeter further to the left.

 

[Old_Crow]

Wow, you just gave me an idea. I've got a little laser pointer (the kind that people use to annoy cats) that came with my last pair of eyeglasses. I might give that a try the next time I adjust my chain.

 

[Qaxe]

- Apparently, there is a $170 ~ $190 laser chain alignment tool by "Profi-Cat" (which I'm not going to buy).
- I heard from a guy who bought a cheap chain alignment tool, then zip-tied a laser pointer onto it. Sounds funny, but he said it worked for him...
- And finally, I recently learned about "offset" front sprockets. I swear that my chain doesn't look off at all. When I turn the wheel the chain goes around right in the center of each sprocket. But if it turns out to be off a full 1cm, I may have to fork over $130 for an offset front sprocket. Sheesh. Never-ending story enit?

 

[brettp]

If your front sprocket isn't supposed to be offset, but you find it 1cm off, you have a part to replace that isn't the sprocket.

 

[Qaxe]

When I put this K6 engine in this K7 frame, I didn't know that Honda had made the K7 front sprocket shaft 1cm longer than previous years. There were tons of changes to the K model in 1977, and I've dealt with them, but this one... this certainly is annoying.

I've read conflicting opinions online. First was that all I need is the rear sprocket carrier from a K6 and it would all line up. Somebody said that idea won't work, and what I actually need is a new 10mm offset sprocket. Neither mentioned whether they have actually done the job, or they are just sayin'. (That happens quite often) The 3rd bit of advice was not to worry about it and just ride it.

I have been talking to a guy who has a K4, who also has a different rear end. He bought the 10mm offset for $90 Euro (that's $98? plus shipping from Europe). The bad news is that he had to chop 3-4mm out of his front sprocket cover because the chain was grinding on it. Cripes. Chopping... I actually have a spare front sprocket cover... sh*t. Or as my kids say "Bruh".

Before I go any further, I've ordered a chain alignment tool off Amazon. I'll try the laser method and see if it looks like it's off at all. It may not be exactly calibrated, but it's better than me looking at it with my wishful gaze, and making a visual judgement.

 

[Qaxe]

Not sure why I thought that would work. I got the chain alignment tool, and a laser pointer. I attached them to the chain. Well... the chain draws a line straight between the front and rear sprocket. It doesn't matter if the front sprocket is 1cm left, or 1cm right, the chain goes straight between them. Similarly, anything attached to the chain (like this tool) is going to follow the line of the chain.

I suppose I could remove the chain, get a rigid straight edge, lay it across the rear sprocket and see if it points to the front sprocket. That seems... I dunno, pretty sketchy. Like something a guy who went to art school would do.

 

[brettp]

I hated art class. But that sounds like something I would do. A new chain should not have side to side flex, so if a new chain is on the rear sprocket and going to the front sprocket just fine, I'd say case closed (until there is a reason to reinvestigate).

 

[Old_Crow]

I suppose I could remove the chain, get a rigid straight edge, lay it across the rear sprocket and see if it points to the front sprocket. That seems... I dunno, pretty sketchy. Like something a guy who went to art school would do.

I don't know. I didn't go to art school, nor do I play an artist on TV, but a straight edge is exactly what I used when I was putting together an old hardtail Ironhead Sportster that came in a series of boxes when I bought it,
You aren't actually trying to align the chain, you're trying to align the sprockets. The chain just gets in the way of seeing the sprockets.

 

[Qaxe]

"...play one on TV" heheheheh

Yeah man. Art school. Lots of money and what did it get me? (aside from cute art school girls) My degree got me a job teaching English in Japan. WTH? What a goofy world.

So. I have been studying this, and talking to all the people. I came to the conclusion that I don't like the idea of having to cut up my front sprocket cover to make space for a 10mm offset sprocket. So I paid $34 on Ebay for a K4 sprocket carrier / final flange, and I'm gonna slap that bastard on there, and see what the bike says. Might be an issue with axle spacers, but I'll jump off that bridge when I come to it. Since I'll have 2 parts, I'll go ahead an make measurements between my rear sprocket and the shock, and the chain and the tire. And then, the next guy who comes along with this issue, I'm gonna shout "Don't do it bro! It's a trap!"

And you know? 20 years ago I put my K7 engine in a K6 frame (the exact opposite of what I'm doing now) and I didn't know about any of this. I just rode it, and it was good. The chain never flew off or killed me even once.

 

[Qaxe]

BrettP: Art class brought my GPA up and helped me graduate. I got a F in math and a D in "power tech" which was the class where you measure valve seat clearances and change piston rings.

And THAT'S why my bike is pretty, but runs like shit. HA!

 

[dirtdigger]

If you rode it without issue and the sprocket and chain are not running off to one side or showing a weird pattern then I think you are overthinking it. Cycle x used to have info up on their site about the offset carriers and what combinations to run but I couldnt find it anymore on the site. They also had various offset sprockets but dont show them anymore. If you want some confirmation Ken at cycle x would be able to tell you 100% what parts will make correct alignment. No offset sprocket should be needed, the correct oem parts should get things in line.

 

[Old_Crow]

BrettP: Art class brought my GPA up and helped me graduate. I got a F in math and a D in "power tech" which was the class where you measure valve seat clearances and change piston rings.

And THAT'S why my bike is pretty, but runs like shit. HA!

I was just the opposite. Flunked Algebra I once and made it through with a C- the second time, but passed Geometry with straight A's. It bored me to learn out of books but put a wrench in my hand and something broken in front of me and look out Jack. Now I've reached the stage in life where I pay somebody to do most of it because my body's worn out.

 

[Qaxe]

DD: Overthinking is my curse. I used to say that the only time I wasn't talking or thinking was when I was asleep. My wife said, "No, you talk in your sleep too". Poor gal.

I've got an older model sprocket carrier coming from Ebay, so I'll throw that on and see what happens. If it is any better, I'm going to declare it awesome and move on.

My pitiful tuning skills are more concerning than sprocket alignment right now actually. But I've still got a couple things I have to do with my carbs before I come back here crying about my farting cylinder #1. I forgot that I had to redo the vaccum sync after I tore apart and reassembled the carbs. Done everything else, so hope that's what I missed.

 

[Qaxe]

Got my older model sprocket carrier in the mail today. (Ebay) It's 1cm shorter all right. Gonna have to find a machine shop to make me a spacer though. The new-old part came with a spacer which I don't need so I'm hoping to find a machinist to cut it down to 1cm.

The right side remains unchanged, and with a 1cm spacer on the left, the wheel will remain in its correct alignment with the bike. Hopefully it will all be done sooner than later.

 

[Qaxe]

I just called a machine shop...
To cut an existing spacer for my axle would $60 and a 2 week wait. WTH?
Guess I'm going with plan B, which is to try and find a 10mm spacer that fits my axle. Cripes.
(No, I've never had anything machined, hence the surprise.)

 

[brettp]

That's a lot. They must have a shop minimum charge. Keep looking

 

[Qaxe]

You're right. They had a minimum 30min. charge. I should have been a machinist...

 

[Qaxe]

Hey, you guys weren't kidding about CycleX being helpful.
I decided to call them up and see if they could help me out. Ken is going to make me a 10mm aluminum spacer for $25.
He and his wife were really friendly too... Wisconsin. Figures they're Wisconsinites. The only friendly people in my family are from there.

 

[Qaxe]

Just to wrap this up, I had two options to chose from in properly aligning my front and rear sprockets.
1.) Buy a $100 10mm offset front sprocket, and potentially have to cut into my sprocket cover to create clearance for the drive chain. The chain would certainly drag on that part without modding. I opted to avoid doing this, because next time I or a future owner has to buy a front sprocket, somebody is going to have b.s. to deal with.

2.) Buy a used rear sprocket carrier from an older K model, and add a 10mm spacer on the left side of the axle to tidy up the gap. I chose this way. The sprocket carrier cost $30 on Ebay, and Ken at CycleX made me the spacer for $25. Everything fits and there will be no future b.s.

The chainguard can no longer be used as-is, because of course the chain and chainguard touch now. Some people might choose to go without a chainguard. It actually mounts up on the opposite side of the usual mounting points in back quite nicely. In front, I just needed 1 extra nut as a spacer to align it all with the chain.

Easy peasy, nice n' greasy.