Topic: '75 750F: Three Sprocket Questions

[cabrala]

While working on the new 750 this evening, I ran into some obstacles with the front sprocket; three obstacles to be exact. I would very much appreciate some help.

Here's the backstory:

The bike is a 1975 750F with 1978 750K motor. I bought a 17T front sprocket, 48T rear sprocket and a 530 chain because, from what I understand, the conversion is supposed to be pretty straight forward. I am aware that the '78 motor with '75 swingarm causes an offset issue and will wear the chain unevenly; at the moment I am not worried about that.

Issue 1:



What is the sizing of the central bolt? The one I removed had a head size of 13mm which struck me as being very odd. I had imagined that it should've been a 12mm.


Issue 2:



This sprocket (existing) sits flush against the shaft end.



This sprocket (new) sits proud of the shaft and will not pull in any closer.

What do I do about this alignment? To do this conversion, does the counter sprocket have to be milled down? Maybe I read the wrong threads.


Issue 3:

Do I reinstall the washer (in first picture) after the conversion? It's very possible that this is a stupid question, but I am wondering if the 1975 sprocket fixing plate works instead.

[crazypj]

Sprocket needs to be ground so there is 0.010" or so sticking out so washer doesn't bear on sprocket, it will come loose if that happens.
The bolt is 8x1.25 which is a standard thread but not a standard grade
I can't remember if it has a built in washer/flange, I think it depends on the year
You won't be able to use mounting plate unless you have sprocket far enough inboard to fit into the groove in shaft you probably don't have?

[seanbarney41]

I ended up in a similar situation and don't totally remember all the in and outs of it...I ended up having a buddy mill my new sprocket to match the old one...and Cyclex offers(or at least they used to...) a 10mm offset rear sprocket to match your engine to your frame, but it is only available as a 46 tooth.  You may have slight clearance issues with your sprocket cover(I just allowed the steel chain to "self clearance" old scruffy aluminum cover) and your rear shock (if you have aftermarket shocks that are even slightly wider than stock in the path of the chain)  Stock shocks will clear...barely.

[70CB750]

The sprockets is held in place by single bolt?  Loctite or not?  Compare to K0 sprocket it seems to be unsafe

[cabrala]

The sprockets is held in place by single bolt?  Loctite or not?  Compare to K0 sprocket it seems to be unsafe

It did seen funny to me, especially when only familiar with the 550's which have the fixing plate with two bolts. According to the fiche this is the stock setup for the late model K motor; one bolt and a large washer.

Barney and PJ, thanks for the replies. I was hoping the offset problem was something I could live with for now but it seems as though removing material is integral into making my setup work. Not what I wanted to hear, but what I asked for. In terms of the offset rear, I believe the clearance at the swingarm will cause all kinds of problems. I'll take a shot at getting this front milled down properly.

[andy750]

Found some good info here:

http://forums.sohc4.net/index.php?topic=87372.0

and here - rear sprocket conversion

http://forums.sohc4.net/index.php?topic=103649.25

and finally here - all about 530 front sprocket conversion;

http://forums.sohc4.net/index.php?topic=37174.15;wap2

Cheers
Andy

[70CB750]

Thank you, Andy.

I am rather inclined to believe that sprocket can be turned in lathe, the center should not be hardened.  Anyway, will try it with an old one, just need to know 

[754]

If you grind it the part against shaft must be flat, and parallel to teeth , outer side matters less. You could make a stepped washer for the bolt.

[cabrala]

Thanks guys. I am looking into the options right now and am hopeful to get it figured out soon.

To further clarify where my thoughts were/are at and to hopefully learn a bit more from you guys about what is correct or incorrect, read the following (an excerpt from an email just written to Mike R. who runs a similar setup):

I was under the impression that the 17T 530 sprocket would slip right onto the counter shaft and bolt up using the existing retainer washer and bolt. I knew I would encounter an offset issue, but believed it was due to the '78 K counter shaft matching up to the '75 swing arm and rear hub (you know, just a matter of one sprocket sitting a bit differently than the other; both sides ares seated properly but the chain is running slightly off-center so uneven wear occurs)? It seems however that machining of the counter sprocket has to happen regardless just to get this setup to work.

Maybe that helps someone else understand the problems as I see it; maybe it just makes this all a bit muddier; either way that's how my brain is working...

[Jerry Rxman Griffin aka MuthaF'er]

I contacted Sprocket Specialists. They SAY they have a conversion sprocket so I ordered one. I got a call back saying they were out of stock and would let me know. Months later no word. Try them and post back up. Tell em I'm still waiting  Much less trouble that way! There is a diagram on one of the sprocket sites that provides dimensions. You can see the offset on both sides of the 75 and only one side of the 78. I'll be doing the same thing on #2 as you are. 

[cabrala]

I contacted Sprocket Specialists. They SAY they have a conversion sprocket so I ordered one. I got a call back saying they were out of stock and would let me know. Months later no word. Try them and post back up. Tell em I'm still waiting  Much less trouble that way! There is a diagram on one of the sprocket sites that provides dimensions. You can see the offset on both sides of the 75 and only one side of the 78. I'll be doing the same thing on #2 as you are.

Just got off the phone with them, Jerry. Assuming you ordered a 17T front sprocket, that is the only one out of stock due to it just going into production. The kind lady on the other end of the line informed me that production will take 2-4 weeks but normally becomes available within week 3. So that will be your backorder time. They do have an 18T available

Their conversion sprocket is shouldered only on one side; the new JT I have is shouldered on both sides (hence the material removal needed).

[Jerry Rxman Griffin aka MuthaF'er]

Exactly on all accounts. Thanks for the update.

[andy750]

Alex Ill buy the 17t sprocket off you if you want to re-order the 18t from Sprocket Specialists.

Andy

[crazypj]

It's been a long time but doesn't the CB400F have same splines but much 'thinner' sprocket?
Also, the center has to be hardened or you would very quickly end up with a round hole instead of a splined one 

[70CB750]

It's been a long time but doesn't the CB400F have same splines but much 'thinner' sprocket?
Also, the center has to be hardened or you would very quickly end up with a round hole instead of a splined one 

How is it about peeing on electrical fence?     I will give it a shot tonight.

[70CB750]

I was able to take some meat off the old sprocket - with carbide - but it was not worth the effort and expense.

[lucky]

The 1977-78 models also had the sprocket held on with one bolt.

[cabrala]

I was able to take some meat off the old sprocket - with carbide - but it was not worth the effort and expense.

As crazypj mentioned, about .010" needs to be removed and due to it being hardened, carbide will be needed. If sprocket specialist carried the 17T then I would be all over it. I don't really want to over-gear the bike with the 18T so this is my only option.

The 1977-78 models also had the sprocket held on with one bolt.

I'm aware of this. The bolt is 8mm X 1.25 at 20mm long. I think the PO might have used a 5/16 X 18 SAE.

Now a general question: if the sprocket is milled down, or the proper conversion sprocket is bought, is the 77-78 retainer washer used or the earlier two-bolt clip?

I think it was mentioned above that the washer is used, but what is all this talk about fitment? Does the washer sit up against the sprocket? Is there a gap? Is this in the manual? Maybe I'll go check...

[70CB750]

I understand that the sprocket needs to be narrow so the round washer under bolt rests against the shaft and the sprocket itself is to some extent free floating.

The two bolt washer K0 style can not be used because the shaft - at least my F2 - does not have a groove in shaft. See the picture.

It looks like the PO run 530 sprocket in full thickness.

[HondaMan]

It's been a long time but doesn't the CB400F have same splines but much 'thinner' sprocket?
Also, the center has to be hardened or you would very quickly end up with a round hole instead of a splined one 

Yep!
The 350F/400F sprocket looks just like the 750/550/500 sprocket, but without shoulders. When used on the bigger bikes, the lack of shoulders causes the sprocket to sit further outboard, wearing both the final drive splines and the inside of the 750 case. These sprockets are widely available, even from JT and EMGO.

That said, it also makes a decent conversion for the late "F" bikes, though. Just be sure to make the sprocket TIGHT against the end of the countershaft: if it is free to wiggle, it causes increased wear on the splines due to the smaller surface areas, as compared to the wider shouldered sprockets.

The wide-shoulder sprockets appeared when the 17T/48T sprocket combo came out to replace the early 16T/45T of the K0 bikes (which had the narrow sprocekts in the beginning). It was a way to reduce the wear on the splines, as well as the chain. When the 630 chain/sprockets appeared on the 1976 "F" bike, the countersprocket was locked down solidly with the big bolt and washer. This created a precise chain path through the swingarm & chainguard mounts for the extra-wide chain and helped prevent it from hitting the inside of the engine cases. It stopped the spline wear that was found on the K6/F0 bikes, but that mostly came from Honda having removed the chain oiler as a cost savings measure.

[crazypj]

Thanks HM, in the late 70's I was something of a Honda specialist, but, ended up working at a Suzuki dealers so became something of a Suzuki specialist although I've forgotten a bunch about them as well
When 'we' were Yamaha, BMW, Vespa, Triumph, Ducati, at various times, things got real confused 
Everything kinda gets blurred together but it was fun at the time 

[HondaMan]

Thanks HM, in the late 70's I was something of a Honda specialist, but, ended up working at a Suzuki dealers so became something of a Suzuki specialist although I've forgotten a bunch about them as well
When 'we' were Yamaha, BMW, Vespa, Triumph, Ducati, at various times, things got real confused 
Everything kinda gets blurred together but it was fun at the time 

Yeah!
My shop was Honda/Suzy/BMW/Harley. The Hondas were 60% of everything, the Suzys were 30%, and the Beemers and Harleys split the rest. I enjoyed the Suzy Triples (waterbike, GT550 and GT380), especially the GT380, but when they got old, they were tough to get 'right' again. It is interesting to see that 40 years later, the only ones still on the road are those same Hondas:750/500/550/350F and 350G (and K) twins, 450 twins, all of them! I got so attached to the 750 in those days, it just became an appendage.

[crazypj]

 
 Last Suzuki GT550 crank I rebuilt was in 1985
They lay down a heck of a smoke screen after running round town for a few hours 

[lucky]

" I am aware that the '78 motor with '75 swingarm causes an offset issue and will wear the chain unevenly; at the moment I am not worried about that."

It will not just wear the chain unevenly it would cause several other problems which cannot be overlooked.

The sprockets MUST line up.

[crazypj]

Guess we are now back 'on topic' 
Yep, chain could easily break or derail which isn't any fun
Have you ever seen a side plate pop off the rivets?