Topic: Front sprocket: JT versus original

[rivetslag]

I'm doing a 630 to 530 chain/sprocket swap on my '78 750K. I am using this post from the FAQ as reference: http://forums.sohc4.net/index.php?topic=372.msg249900#msg249900

I ordered those JT sprockets, wanting the 17/48 setup. The front sprocket is, as that post mentions, thicker. The actual gear is the same thickness, but it has shoulders the original sprocket lacks:




This does move the sprocket outboard a tiny bit (probably 1/16", omitting the original spacer). My actual concern is more with this:


The output shaft is now "recessed" within the sprocket, such that I think putting any real torque on the bolt would squish the washer into concavity. The washer won't really present much surface to the face of the gear.

Should this be an issue? I suppose there isn't much lateral force on that sprocket, so it's not like the bolt really needs massive torque to retain the gear.

Should I have the shoulder on the front of the sprocket milled flat? Or not worry about it?

Thanks for any advice you guys might have.

P.S. I cleaned all of the gunk from in there after the photo was taken :p

[Hasenkopf]

thats funny, the sprocket on mine has the shoulder on it, and it sits flush.... but not sure if it's original or not, it still has the 630 though....

[rivetslag]

Upon further research, various parts guides seem to indicate that the JTF288-17 is for 70-76 750K bikes, not 77-78. I guessed as much when I was at the shop. The guy's Parts Unlimited catalog listed NO 530 front sprockets for 77-78. There was a rear, but no front.

I think i'll just get the shoulder milled off.

Sometimes I feel abandoned by the aftermarket with a K8. Why the hate!

[dave500]

yeah thats wrong,some guys would just wrench it up,how would the locking tab engage though?ah,the later models have a centre bolt?ive got jt on my 500,they have a good name here.

[hondaface75]

Just installed a chain and sprocket set from them on my K5 yesterday. Flawless. Looks great and is WAY quieter than my ratty old one. Had no issues w.ith the front sprocket as mine is earlier. But mine had a shoulder and fit as well

[rivetslag]

Just a quick update on this. I did end up getting the shoulders milled off that 530 sprocket, which did make it the same dimension as the stock 630 gear. I suppose knowing about this "much more difficult than it had to be" swap could possibly help someone in the future, especially w/r/t cross-compatibility? 

I guess if you didn't mill it, the sprocket wouldn't be able to "follow" the chain if it moves slightly in a lateral direction. It does have some ability to move side-to-side.

[754]

Why would you take both shoulders off?

 The shoulders increase load carrying capability..

 If you ever tore a center out of a thinner style sprocket, and had it WELD to the sprocket shaft, causing you to miss a days racing, and have to re & re the motor, and split the cases... you would probably leave them on..

[Hasenkopf]

they should  fit as described..... not everyone  has a milling machine in their basement, and years on valuable racing exp. to draw on 

[rivetslag]

754: this is why I asked the question in the first place. I didn't get any response warning me not to, though, so...

I understand that the shoulders would increase the gear's capacity for torque. It's too bad I've lost that, but: is the design of that other sprocket, which my new gear now matches, not the Honda original design? I have not seen too many cases on this board where re-engineering Honda's work has resulted in tangible gains, without some kind of compromise (excepting some of Hondaman's thoughtful mods).

If the gear matches OEM design, and the whole setup is actually stronger than before (530 vs. ancient 630), I'm still happy.

If you say my original problem w/r/t changed profile on the shaft is not actually a problem...well then, next time I'll leave the shoulders alone :p

Understand that my motivation to mill off the shoulders was the thought that I had gotten a sprocket for some other bike, and was making it work on mine. I couldn't find a 530 conversion front sprocket for my bike, so I just got one and made it work.

[Zaipai]

Seems to me that what you did should be fine, you don't have a massive engine mod and the pressure on that sprocket should not be much different then the stock one.. In short, I bet you are fine with that setup, given all things being equal I would have done the same thing..

Now should you soup up that motor, you could have an issue.. even then unless your getting on it hard all the time you should be ok.

.: Scott :.

[754]

I think i explained it badly..
 The 630 SPROCKET (not a gear) is thicker I think so the 530 may be oK with shoulder (this may or not not be, if you actually checked aligngment it could come in handy).. but at any rate that small difference should not hurt.  Part of what I meant though was if you did take it iff, you only had to remove the inboard side.

[rivetslag]

754: it is actually the same thickness as the 630 sprocket, once the shoulders are discounted. I did consider leaving one of the shoulders. I decided that, not being super familiar with all of the ins and outs of the chain/sprocket system, I'd just match to the old setup. Now that I think about it, though, I should have thought about the fact that the 530 chain itself is nowhere near the width of the 630 chain.

I may well update this in 1000 more miles. I've got about 200 miles on the swap now, and I've been disheartened to find that the chain needs tightening already. I set it to ~3/4" slackness, it's out to over an inch now (numbers are not exact, just going by memory from looking at it a few days ago). I'm wondering if something is out of whack.

I'm a newbie to motorcycles (although not mechanics in general), so I'm greatly appreciative of everyone's advice so far. Thanks.

[Zaipai]

Some one can correct me if I am incorrect, however with a new chain there will be some adjustment as the chain stretches.. At some point however it will stop and become more normal.. That seems to be what happened with mine..

.: Scott :.

[754]

Unless its a pre-stretched chain, it will generally run in and loosen off in the first few hours..

[madmtnmotors]

The last time I replaced the chain and sprokets on my CB750K8 I made the 530 conversion as well. The information was difficult to interpret and the stock (630) tooth counts were not available with the 530 so I consulted the ratio charts to get the tooth count/ratio that I wanted. The new front sprocket fit like it should so I'll do some research and see if I can dig up some part numbers. As for the width of the chain, I put a caliper to both my old 630 o-ring chain and my new 530 o-ring chain and they were almost identical widths. The 530 has a shorter distance pin-to-pin (shorter links) and the side plates aren't as tall, but the widths are nearly the same. Think about it, if the sprockets are the same thickness, the chains would have to have a similar width to fit their respective sprocket.

[rivetslag]

madmtnmotors: did you ever find a part number for that sprocket you used?

I've put about 1000 miles on the swap now, everything seems smooth and well suited. The chain did stop stretching, as you guys said it would.