Topic: Will a JTF338 16t front sprocket work on K7 750

[Pielz]

Since converting a k7 750 to a 530 chain is impossible to find info on, I think I have it narrowed down by cobbling together info. I've read that the 79 CB650 has a similar front sprocket to the k7 and k8 and is interchangeable. I ordered this:

http://www.jtsprockets.com/catalogue/sprocket/JTF338/

It says it works for the 79 650 and the measurements seem the same as the stock ones for my k7 750 except for the shoulder extending out further. Can anyone definitively tell me whether or not this will work before I wait 2 weeks for it to come and have it not work? They're both 10.7mm thick and have the same measurement for the cog in the middle.

Here's the page for the stock one with measurements

http://www.jtsprockets.com/catalogue/sprocket/JTF331/

[seanbarney41]

yep, that is the one you want...although 16 tooth might be stunt bike territory as far as acceleration...slight exaggeration...17 front 48 rear makes for good acceleration and reasonable revs on the freeway.  16/48?...if your motor is making some power, might be a little wild.  If you want to compare ratios, just divide the rear tooth count by the front...that way chain size does not matter.  If you like the stock gearing of our k7/8, just pick the 530 sprockets that most closely match the ratio.

[Pielz]

Awesome, thanks! Yeah it's all bone stock and feels a little sluggish on the take off. I rode my buddy's GS850 and its shaft drive but has a final drive ratio of about 3. It feels a good bit peppier and was hoping to get a little closer to the feeling of that bike!
 
I did some calculations and it should only shave about 10 mph off the high-end. It's not gonna be on any tracks and barely on the highway so that's not really speed id be using anyway. I'll keep the old stock sprockets anyway just in case it's a little much!

Heck, they're only like 12 bucks. Maybe I'll just get the 17 as well and see what's better

[seanbarney41]

yeah, well?...those gs' make some much better low end torque so don't compare apple's to oranges and we need a little more gear to keep up.

If that is how you ride, 16/48 can work.  Oh, and rear tire o.d. can be played with too.  130/90/17 is a lot different than 130/80/17.  And don't be afraid to cruise on the freeway at 6-7000 rpm.  These bikes eat that #$%* up.

[PeWe]

836cc with a good torque cam to keep up with the other bike.
17:48 work well on CB750.
16 front, what about clearance to swingarm?
My K6 has 18:48 since it has much more torque thanks to 1005cc.

[Pielz]

yeah, well?...those gs' make some much better low end torque so don't compare apple's to oranges and we need a little more gear to keep up.

If that is how you ride, 16/48 can work.  Oh, and rear tire o.d. can be played with too.  130/90/17 is a lot different than 130/80/17.  And don't be afraid to cruise on the freeway at 6-7000 rpm.  These bikes eat that #$%* up.

Would playing with that OD change the handling of the bike much? That's actually something I was toying with the idea of. mainly because I'm 6 ft tall but my seat foam is pretty tall as well (someone re-upholstered it) and I wouldn't mind a slight drop in height.

[Pielz]

836cc with a good torque cam to keep up with the other bike.
17:48 work well on CB750.
16 front, what about clearance to swingarm?
My K6 has 18:48 since it has much more torque thanks to 1005cc.

I haven't read anything about being mindful of clearance to swingarm.. is that an issue when changing front sprockets?

[PeWe]

836cc with a good torque cam to keep up with the other bike.
17:48 work well on CB750.
16 front, what about clearance to swingarm?
My K6 has 18:48 since it has much more torque thanks to 1005cc.

I haven't read anything about being mindful of clearance to swingarm.. is that an issue when changing front sprockets?

If sprocket diameter is smaller, chain might scuff the swingarm.
16 might be OK, one thing to verify.
The bike might not run quicker wirh that gearing, just a pathetic screamer.
I knew one guy in the mid 80's with a CB750 he revved very high. It did not accelerate much, just screamed as it was zero torque and totally wrong gearing. D cam ported head, maybe 812, 820 or 836.

If you need to keep up with other bikes, 836 and more is needed.

I have a stock K2, it runs fine with 17:48 gearing.

[Pielz]

I was probably just going to order a 17 as well and see which one feels best for me. They're so dirt cheap it makes sense to just get a few

[seanbarney41]

yeah, well?...those gs' make some much better low end torque so don't compare apple's to oranges and we need a little more gear to keep up.

If that is how you ride, 16/48 can work.  Oh, and rear tire o.d. can be played with too.  130/90/17 is a lot different than 130/80/17.  And don't be afraid to cruise on the freeway at 6-7000 rpm.  These bikes eat that #$%* up.

Would playing with that OD change the handling of the bike much? That's actually something I was toying with the idea of. mainly because I'm 6 ft tall but my seat foam is pretty tall as well (someone re-upholstered it) and I wouldn't mind a slight drop in height.

yes, shorter rear tire will increase trail/make bike turn slower.  Taller tire reduces trail/makes bike turn quicker.  By how much?  hard to say.  If you are sensitive to such things, the difference is noticeable.

[HondaMan]

836cc with a good torque cam to keep up with the other bike.
17:48 work well on CB750.
16 front, what about clearance to swingarm?
My K6 has 18:48 since it has much more torque thanks to 1005cc.

I haven't read anything about being mindful of clearance to swingarm.. is that an issue when changing front sprockets?

The K7's bolt-down front sprocket (which most of them have, not all) makes a 530 sprocket sit slightly closer to the engine. That's where the clearance issue in the chain guard might come up.

[Pielz]

Sprockets came in the mail today. They seem really nice. The machining seems like good quality.

[HondaMan]

That front sprocket from JT is 100% cast (injection-molded) and will have a lot of "grit" in the teeth. That's why I recommend running the (or AN) OLD chain for a while (100 miles or so) if possible, to remove that grit into something that won't wipe out your nice new chain. BUT...I think the 530 chain on a K7 is something longer, like 104 links, than most of the used chains I have here, or I could send one to you to 'sacrifice'. That's why I keep them around. I think all of the ones I have are 100 or 102 links.

[Pielz]

Unfortunately I only have the one 530 chain 106 links to be sure. Is there any way I could knock that down? Maybe use a brass wire wheel or something to smooth it out?

[Pielz]

Hey Hondaman, this front sprocket goes stepped side facing outward, correct? The thicker side is what contacts the washer that holds it on?

[madmtnmotors]

Hey Hondaman, this front sprocket goes stepped side facing outward, correct? The thicker side is what contacts the washer that holds it on?

I'm pretty sure the stepped side faces the engine with the flat side out. I believe this was to provide extra clearance for the 630 chain on the later models. I know you're not using the 630 chain, but the stepped side to the inside in order to maintain proper alignment with the later model (wider) rear sprocket carrier. I am using the JTF338 front sprocket as well on my K8. 

[Pielz]

Awesome thank you so much. I had off today and was wrenching on the bike and I'm glad someone responded so I could flip it the right way around.
 
Haha side note: the previous owner did such a #$%* job of peening over the rivets on the old chain I was able to pop off the master link with a flat head. Good thing it's getting tossed out haha. Only miles that were on it were a few from testing the rebuilt carbs.

[scottly]

Wilbur, the 630 chain is the same width as 530 chain; the 30 is the width is 1/8" increments, or 3/8", and the 5 and 6 is the pitch in 1/8" increments, so 5/8" and 6/8" (3/4"). I don't recall which side of the sprocket faces out...

[Pielz]

Any chance one of you fine folks would snap a pic of it if possible? I'd love to know for sure since I can't find anything on the interwebs

[scottly]

Sprockets came in the mail today. They seem really nice. The machining seems like good quality.

The markings face out, so they can be seen with the sprocket installed.

[scottly]

Some related pics on this thread:
http://forums.sohc4.net/index.php/topic,180796.0.html

[Pielz]

Oh okay great! Thanks! Gosh they can't make this easy, eh?

[madmtnmotors]

Wilbur, the 630 chain is the same width as 530 chain; the 30 is the width is 1/8" increments, or 3/8", and the 5 and 6 is the pitch in 1/8" increments, so 5/8" and 6/8" (3/4"). I don't recall which side of the sprocket faces out...

You are correct, my bad, the "30" portion of the "X30" chain size is indeed the width. The "5XX" and "6XX" designation is the pin to pin spacing. I'm pretty sure the shoulder goes to the inside, though I've been wrong before!   

This genuine Honda sprocket has the tooth count stamped on the flat face:

https://www.ebay.com/itm/NOS-Honda-Sprocket-15T-1977-1978-CB750-750-FOUR-23801-405-010-/192349374896

[madmtnmotors]

Here is my logic:

>The early models front sprocket had a shoulder on both sides
>The later K7/K8/F2/F3 moved the rear sprocket out 10mm and also have a 10mm longer output shaft
>If you flip the front sprocket with the flat face towards the motor then the front sprocket is only moved outward by 8mm if you put the 2mm shoulder to the outside

[scottly]

Wilbur, you are correct: the flat side faces out. I checked my original K7 sprocket and it's also stamped on the flat side. I measured both ways and compared to my K1 to verify. Perhaps the shoulder side faces out when installed on a 650?