Author Topic: Offset sprocket? (Read 6373 times)

climbingaz · « **on:** November 06, 2011, 03:34:17 PM »

Can you take a look at this sprocket and tell me if you think it is offset? I'm getting ready to buy a new chain and sprockets for my bike and want to make sure I get the correct countershaft sprocket. The reason I'm unclear whether it's offset or not is because I'm running a '70 750k motor in a '78 frame and I've heard there could be some alignment issues. What is on the bike now seems to work fine, but I don't know if this is a regular or offset sprocket.

WHAT DO YOU THINK?

Tree · « **Reply #1 on:** November 06, 2011, 04:34:03 PM »

From what I can tell from the pictures, to me it looks like a standard sprocket for a 530 chain. I recently converted a '78 K from a 630 to 530 chain. I bought the standard sprocket for a 76K (It's the same part number for a 71 K, 23801-300-620). There is a shoulder on each side of the sprocket, but the teeth are centered, so I don't think it would be called offset.

I would order a standard sprocket with either 17 or 18 teeth.

Retro Rocket · « **Reply #2 on:** November 06, 2011, 05:01:35 PM »

That is a standard sprocket, but if you have an early K engine in a K8 frame then your chain is out of alignment. The K8 has a bigger offset on the rear sprocket carrier, 10mm to be exact, you can either use an earlier K model rear sprocket carrier to fix the problem or get a 10mm offset front sprocket from Cycle X.

scottly · « **Reply #3 on:** November 06, 2011, 05:18:00 PM »

Quote from: Retro Rocket on November 06, 2011, 05:01:35 PM

The K8 has a bigger offset on the rear sprocket carrier, 10mm to be exact, you can either use an earlier K model rear sprocket carrier to fix the problem

I'm wondering now if an earlier K carrier has already been fitted? I have a K7 carrier I can measure...

Tree · « **Reply #4 on:** November 06, 2011, 05:52:20 PM »

Retro Rocket - Thanks for pointing out that CycleX site (http://www.cyclexchange.net/Chain%20Sprocket%20Page.htm). The pictures really help demonstrate the sprocket carrier differences and the need for the offset sprockets to compensate.

You should be able to tell the K7/K8 rear sprocket carrier just by comparing it to the picture below. I believe the K7/K8 is the one on the right.

Retro Rocket · « **Reply #5 on:** November 06, 2011, 06:20:24 PM »

Actually, i need 2 K8 carriers to use on my bikes because of the wider wheels i am using. I also think that the K8 output shaft on the gearbox is 10mm wider. Hmmm, now if i use the K8 output shaft with a 10mm offset sprocket i could get 20mm wider.....Interesting.....

scottly · « **Reply #6 on:** November 06, 2011, 06:24:11 PM »

Well done, Tree! Here is a pic of a K7 assembly; in your pic, the early carrier on the left has ribs, while the late carrier on the right is smooth.

climbingaz · « **Reply #7 on:** November 06, 2011, 06:37:07 PM »

I had a feeling this was going to be a learning experience for me in what exactly I have for a bike!

Problem is I literally pulled this thing out of the weeds of the seller's backyard where it sat for almost 20 years rotting. And he didn't know anything about the bike other than he wanted $100 for it.

Anyway, the reason I believe I have a '70 motor in the '78 frame is because of this serial number on the engine just above the front sprocket cover. Sort of hard to see in the picture below, but is says:
CB750E-1090125

Can you first confirm my suspicion that it is in fact a '70 motor?

Next, I can almost certainly tell that the rear sprocket is not offset by 10mm, but can you confirm by these photos?

And finally, by looking at the pictures of the two rear carriers Tree posted, it looks like my carrier is a K8 because it doesn't have those ribs. It has the smooth curves.

So what the hell do I have going on here? hahaha

Retro Rocket · « **Reply #8 on:** November 06, 2011, 06:50:32 PM »

The offset is in the carrier, not the sprocket, and it looks like you have the later 10mm wider rear sprocket carrier. Reread the last few posts, its explained well there.

ekpent · « **Reply #9 on:** November 06, 2011, 06:59:11 PM »

The engine is a 1971 which was a very good year.

scottly · « **Reply #10 on:** November 06, 2011, 07:00:21 PM »

You have an early motor in a late frame, and the PO didn't know about the 10mm offset. (I wouldn't have known if not for the forum.

) When you remove the chain, you might see more wear on one side of the rear sprocket than the other, another clue of misaligned sprockets.

Retro Rocket · « **Reply #11 on:** November 06, 2011, 07:01:42 PM »

Quote from: scottly on November 06, 2011, 07:00:21 PM

You have an early motor in a late frame, and the PO didn't know about the 10mm offset. (I wouldn't have known if not for the forum. ) When you remove the chain, you might see more wear on one side of the rear sprocket than the other, another clue of misaligned sprockets.

The wear would be on the inside of the sprocket, no good for the chain either....

climbingaz · « **Reply #12 on:** November 06, 2011, 07:09:19 PM »

You guys rock!

Two mysteries about my bike solved in one day.

So as far as I can tell, this is the current setup:

'71 motor
'78 frame
'78 rear carrier
530 chain with 104 links
530 (not offset) sprockets (18 teeth up front, 48 on the rear)
and most importantly....I'm probably 10mm out of alignment.

Is all my thinking correct so far?

Now, my real goal for the day.....I want to order some new sprockets and chain. What should I buy??

ekpent · « **Reply #13 on:** November 06, 2011, 07:18:18 PM »

Does the bike still have the 17 inch rear tire which I think is 77-78 or the earlier 69-76 18 inch rear? If it has the 17 then I would stick with the 18/48 combo.

Tree · « **Reply #14 on:** November 06, 2011, 07:22:14 PM »

I would buy the cycle x offset 18 tooth front sprocket, a 48 rear sprocket, and a good O ring chain. Sprocket and chain I bought recently are at links below. You can get a clip type master link if you want. You said 104 links. You could buy that length or something a little longer and shorten it, to be safe.

http://www.z1enterprises.com/530-JTR284-series-48T-Rear-Sprocket-1793.aspx

http://www.z1enterprises.com/530-Chain--RK-104-link-X-Ring-378.aspx

climbingaz · « **Reply #15 on:** November 06, 2011, 07:24:09 PM »

Quote from: ekpent on November 06, 2011, 07:18:18 PM

Does the bike still have the 17 inch rear tire which I think is 77-78 or the earlier 69-76 18 inch rear? If it has the 17 then I would stick with the 18/48 combo.

Has the stock 17" rear tire.

scottly · « **Reply #16 on:** November 06, 2011, 07:45:09 PM »

As far as the off-set issue, the preferred solution would be to swap in an early rear carrier, if they are, indeed, a direct swap. The k7/8 had more substantial bearings on the primary shaft to support the outboard mounted front sprocket.

Tree · « **Reply #17 on:** November 06, 2011, 07:55:21 PM »

Wow, that's something I never would have thought of. So, I wonder if you can't get an older sprocket carrier, would you be better off leaving it 10mm out of alignment, or using the offset front sprocket?

scottly · « **Reply #18 on:** November 06, 2011, 08:04:32 PM »

Personally, if I had this problem, I would try to machine 10mm off the late carrier, but I think it might be a real pain to do it accurately. I'll scope it out, but I still think swapping the carrier is the easiest, and best solution.

ekpent · « **Reply #19 on:** November 06, 2011, 08:04:58 PM »

E-bay or someone here probably has an early carrier,should not be a rare or hard part to source.If not go with the offset,alignment is important.

scottly · « **Reply #20 on:** November 06, 2011, 08:15:03 PM »

Quote from: Retro Rocket on November 06, 2011, 06:20:24 PM

Actually, i need 2 K8 carriers to use on my bikes because of the wider wheels i am using. I also think that the K8 output shaft on the gearbox is 10mm wider. Hmmm, now if i use the K8 output shaft with a 10mm offset sprocket i could get 20mm wider.....Interesting.....

Hey Mick, want to swap Shawn an early carrier for his K8? I'll throw in my K7!

Retro Rocket · « **Reply #21 on:** November 06, 2011, 08:19:43 PM »

Quote from: scottly on November 06, 2011, 08:15:03 PM

Quote from: Retro Rocket on November 06, 2011, 06:20:24 PM
Actually, i need 2 K8 carriers to use on my bikes because of the wider wheels i am using. I also think that the K8 output shaft on the gearbox is 10mm wider. Hmmm, now if i use the K8 output shaft with a 10mm offset sprocket i could get 20mm wider.....Interesting.....
Hey Mick, want to swap Shawn an early carrier for his K8? I'll throw in my K7!

I don't have any mate, i only have 2 F1 spoked rear disc hubs, no carriers.....

climbingaz · « **Reply #22 on:** November 07, 2011, 06:32:58 AM »

Just did a quick search on ebay and looks like I can get an early model carrier for $30-40. So you guys think that would probably be the better option vs. buying the offset front sprocket? Are the carriers a direct swap?

Toxic · « **Reply #23 on:** November 07, 2011, 07:34:43 AM »

So you have a 71 motor in a 78 frame and a 78 swing arm if you change to a 71 sprocket carrier to get your chain lined up, will you not need to fab a spacer? The 78 swing arm is wider.
Would you not need a 71 sprocket carrier in a pre 77-78 swing arm.

The simpler solution would be the offset front sprocket.

climbingaz · « **Reply #24 on:** November 07, 2011, 09:37:19 AM »

Never would have even occured to me to ask about the need for a spacer.

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Author Topic: Offset sprocket? (Read 6373 times)