Topic: front sprocket source and dimension - help solve an argument

[greenjeans]

1969 CB750K 

Need new front sprocket.   I know I can get one from Honda but it's twice as much as an aftermarket.

I picked up a JT sprocket at a local dealer.

Looks like this:



However, it will not fit.   The bolt pattern is correct, but the plate that goes on the spline and then rotates to enable the bolts to thread into the sprocket to keep it in place won't go.

The sprocket has a lip/shelf that is approximately the width of the plate.   

http://www.westernhillshondayamaha.com/fiche_section_detail.asp?section=125962&category=MOTORCYCLES&make=HONDA&year=1969&fveh=2998

The guy swears to me he sells them all the time and that they fit my bike.    JT sprockets web page also shows it to fit my bike.    However, the locking plate WILL NOT fit.

Everything is clean as a whistle.     What gives ?    Do I just need to spring for the more expensive Honda sprocket ?     Surely there is an aftermarket option.

[brooze72]

Measure up the old & new sprocket thickness.  Your drawing shows a width of 12.7 mm or 1/2 inch, is the old one the same?  As CycleRanger said too, is the new retainer plate the same thickness as the old?

[greenjeans]

The retainer plate was on the bike.   The sprocket, however was not useable.     I have an old sprocket off my 72 that fits with the plate but it has a tooth broken off so it can not be used either.
It is just under 10mm thick

The parts fiche drawing looks the same to me - flat sproket - no raised portion in the center where the bolts are.

The new sprocket did not come with a plate of any kind.   He did offer a fat c-clip, but that won't work either as the sprocket covers the groove.


*Also -  I'm using a new stock 530 chain

[brooze72]

Seems like the extra 2.7mm thicker sprocket covers the groove, therefore no way to install the retainer, correct?

[greenjeans]

exactly.    I just don't want to order another until I can get proper dimensions from the part supplier.

Or.....   is there something that I'm missing here ?

[greenjeans]

Here's what I have.    The parts fische doesn't show any additional spacers etc...   definitley flat.
The small plate the the bolts go through on won't work with a thicker center.

[greenjeans]

Success - just got off the phone with DennisKirk - One of their guys actually took 3 different sprockets out of their packaging and measured them.   Problem solved.   Customer service is refreshing.

It is amazing how I can overthink the simplest things.

In case anyone is interested, this sprocket is the same dimensions (8.7mm thick) as the type in my photo.

https://www.denniskirk.com/parts-unlimited/sprocket.p8254.prd/825415.sku

Parts:     

825416 (16T)
825417 (17T)
825418 (18T)

[chickenman_26]

I don't know what's going on with JT Sprockets lately. Cycle gear here in Phoenix dropped the line, because they were having so many returns due to fit issues. I bought a JT counter shaft sprocket for my 750A that wouldn't go on the shaft. It pushed on about 3/4 the depth of the splines in one direction. Flip it over, and it wouldn't go on the shaft at all. The bore was conical.

Stu

[ekpent]

Success - just got off the phone with DennisKirk - One of their guys actually took 3 different sprockets out of their packaging and measured them.   Problem solved.   Customer service is refreshing.

It is amazing how I can overthink the simplest things.

In case anyone is interested, this sprocket is the same dimensions (8.7mm thick) as the type in my photo.

https://www.denniskirk.com/parts-unlimited/sprocket.p8254.prd/825415.sku

Parts:     

825416 (16T)
825417 (17T)
825418 (18T)

Guess I am dense but what did you overthink and what was the solution to your problem ? Did the JT sprocket work or was it too thick.

[CycleRanger]

Here's a shot of a JT and a "generic" I have.  Both of these fit on my K5 no problem.
The generic sprocket is flat and requires the extra spacer.

The JT is 13mm thick. The locking ring is 2.3mm thick.

[scottly]

I just replaced the 16 tooth sprocket on my K1 with a 17 tooth I got through the local Honda shop. The 16 tooth was flat, while the 17 tooth had the raised hub. The 17 fit fine. Maybe Honda changed the design of the counter-shaft after '69?

[754]

 Man am I glad I got a Browne and Sharpe surface grinder for Chistmas,...no such problems..
 Beware of the flat ones, check them often.. I tore the middle out of mine..but when it happened it welded itself up. ( that held till the tree showed green, and I let thre clutch out!). lot of work changing the output shaft......

[greenjeans]

The originals were flat correct ?      I ended up ordering the flat one from Dennis Kirk.   

The JT sprocket I had definitely won't work with what I have unless modified.

[754]

 Looked at a very late KO today, had a 16 Tooth on it, flanged both sides..approx .50 thick just under 13mm...had the lockring retainer on it...

[Cqyqte]

1969 CB750K 

Need new front sprocket.   I know I can get one from Honda but it's twice as much as an aftermarket.

I picked up a JT sprocket at a local dealer.

Looks like this:

Have you researched the serial numbers on your bike, including the engine numbers?  Interesting enough a K7 CB750 uses a similar sprocket to the old one you said came on the motor, 10.7mm thick sprocket.  All other CB750's are listed using the wider sprocket on the JT Sprocket site.  Just wondering?

[ekpent]

He's working on a Sandcast Cqyqte, Lucky Bugger.

[CycleRanger]

He's working on a Sandcast Cqyqte, Lucky Bugger.

Oh, well that's very different!