Chain Sizing for '83 Suzuki GN125

[Guest]

OK, I know it's not a GS, but it's a little Suzuki and it was neglected and in bad need of somebody to restore it, so I brought it home.

Most everything on this little bike is original, including the totally dry rotted tires! The chain is toasty rusted, so she needs a new one (in addition to the $250.00 of new and replacement parts I've already bought).

The existing chain has 113 links plus the connecting link. An odd number of links is sure unusual, but I counted them three times and still came up with 113 plus the connecting link. It's a non o-ring 420 chain (4/8" pitch x 2/8" width).

So, what length chain to buy? I see lots of 420 chains available in 110 link length, but that would be three links short (1 & 1/2 inch short). It looks like I have only about 1/2" of forward travel left on the chain adjuster with the old chain on it, so that would only make up for two 4/8" links on the chain. So, still one link short at least.

Are my calculations correct here, or am I missing something? If correct, looks like I will have to buy a 120 link length chain and cut 7 links off of it.

Chain adjuster picture attached. I'll post up another reply with pictures of the little bike.

[WingMan71]

Here's a picture of when I first got her home. Looks pretty good from a distance, but lots of stuff messed up badly by a previous owner or two.

Several stock Honda parts removed, including air box, grab bar, rear turn signals, and more, plus lots of rust and dirt under the body work. Frame rusty in spots, chain toasty rusty, inside fenders all rusty. Fenders will go in EvapoRust baths.

QUIZ:

What's "wrong" with the bike in this picture? Stands out like a sore thumb to me, but take a look and see if you find something just plain wrong!

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[fbody_mike]

Two right hand switch clusters.

[WingMan71]

Two right hand switch clusters.

You win! Now answer my drive chain question in post #1.

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[fbody_mike]

No answer there, but the chain is still available from Suzuki though and it will have 124 links.

[RichDesmond]

...The existing chain has 113 links plus the connecting link. An odd number of links is sure unusual, but I counted them three times and still came up with 113 plus the connecting link. It's a non o-ring 420 chain (4/8" pitch x 2/8" width)...

Not "odd" at all. The connecting link is part of the total count, so you're at 114. Has to be an even number.
I never bother with pre-cut chains, I always just by the 120 link ones and size to fit.

[WingMan71]

Not "odd" at all. The connecting link is part of the total count, so you're at 114. Has to be an even number.
I never bother with pre-cut chains, I always just by the 120 link ones and size to fit.

Thanks Rich.

I found an RK 420 Chain with 124 links on Amazon. I'll order that one and remove some links to fit.

Heck... just noticed that I'm listed as a Forum Newbie. I probably have a couple hundred posts on this site from a year or more back when I was restoring an '83 GS650L. Exact same forum name too. Wonder why that got messed up. I did have to re-register just recently when my old login wouldn't work.

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[Corvette95]

Hi, kinda off topic, but my first street bike was a new GN125, would love to see a picture!!!

[bwringer]

Not "odd" at all. The connecting link is part of the total count, so you're at 114. Has to be an even number.
I never bother with pre-cut chains, I always just by the 120 link ones and size to fit.

Same. Even in common chain sizes, I just buy 120 and lop off what I don't need. No counting needed.

I'd definitely upgrade to an o-ring chain.

[Gorminrider]

Consider new sprockets too.... Worn sprockets will ruin a new chain.

However, if they look "pretty good" just get a normal chain until next time when the price of a fancy chain AND New sprockets is justified by your use and love... by the way, The Fancy chains seem quite a bit heavier, and well, I just buy a decent normal Dido or similar, new sprockets or not. They last a long time with oil on them.

[bwringer]

I've encountered a few of the smaller GS/GN models, and most seem to be wearing corroded crappy roller chains, very low mileage, and virtually pristine sprockets.

Situations vary, but in any case, I've been fairly comfortable replacing chains but keeping stock sprockets when it's a low-powered bike without a lot of miles and wear.

[John Park]

Consider new sprockets too.... Worn sprockets will ruin a new chain.

However, if they look "pretty good" just get a normal chain until next time when the price of a fancy chain AND New sprockets is justified by your use and love... by the way, The Fancy chains seem quite a bit heavier, and well, I just buy a decent normal Dido or similar, new sprockets or not. They last a long time with oil on them.

I've not seen 420 o ring but 428h o ring exists. The sprockets shouldn't be hard to find and usually there's enough clearance to switch. That motor is an ancestor of the DR200 so the countershaft sprocket may fit, and the rear should be some sort of recognizable hole and pattern that Sunstar [JT] makes. OTOH if you're not going to Guatemala on it, just oiling up a 420 regularly will suffice.

[RichDesmond]

Sprocket Specialists used to be able make anything you needed for the rear. Been a lot of years since I needed something oddball, so don’t know if they still do that sort of thing.

[John Park]

Sprocket Specialists used to be able make anything you needed for the rear. Been a lot of years since I needed something oddball, so don’t know if they still do that sort of thing.

I'm spoiled by having two good friends who are machinists; doesn't take that long to open up the center to fit and redrill the hole pattern, but you need a lathe and a milling machine to get the result round and true. I just did a Hodaka rear sprocket which has become unobtainable.

Moving an old 420 bike to 428 may open up possibilities of supply that aren't there for the original parts. Finding out what modern stuff will retrofit is the part that requires some sleuthing. I don't know what the sprocket I modified fits; doesn't matter as long as the center hole is smaller and there's room to put the new holes. Countershaft sprockets are more involved. My usual method is to cut the center out of the donor and trim the outside off the original, using a step on each so that they can be clamped and welded together, with a V channel to accept the weld.

[John Park]

According to the Canadian supplier Fortnine.ca the listed sprockets are 428 not 420 and the JT numbers are JTF522 - XX and JTR810-XX with a few size options. And cheeeeep at $34 CDN for the pair which is about $27 USD.