Chain Conversion Conundrum!!!!

[portdave]

Just practicing my fancy words and alliteration..

Went to put my new chain on last night and it was too long...

1978 GS750EC
Original sprockets/chain - 15 front - 41 rear/96 link 630 chain
PO put a 15 front - 42 rear with a 530 chain 110 links(figured out the links last night)

I called Z1 and ordered a 530 RK(XSO?) chain. Rob was really helpful. We looked up the original sizes and did the conversion. 15/5=3 times 6 = 18 front, 41/5=8.2 times 6 = 49.2. The chain - 96/5=19.2 times 6 = 115.2.

So we went with the 18/48 (48 for a few less RPM at higher speed) and a 530 chain that was 116 links.

Too long. When I layed both chains on the floor next to each other the old chain was about 3 inches shorter. 110 links. They are both 530 chains. I didn't realize the old one was a 530 until I took it off and saw the 530 marking in the light.

I called Rob and he is confused as am I. This should be the right configuration for this bike.

Could the PO but a different swingarm on the bike? Were there shorter swingarms for this model?

Does anyone have a 750 that could measure their swingarm for me from front bolt to back end?

I can make it work cutting it down but I would like to know. I plan on laying the old chain on the new sprockets tonight and see how many links I need to make it work.

Thanks so much.

[JHawkins]

Here is what I ordered, per their recommendations (wanted to lower the RPM, so added one tooth in the front) They said 17/47 stock with 114 link chain. It worked out perfect on my '79 750L.

Product Name: 530 (SS514 series) 18T front sprocket
Quantity: 1 Product ID: EM95-47318 Price: $18.93

Product Name: 530 Chain - RK 114 link 'X' Ring
Quantity: 1 Product ID: LA530XSOZ1-114 Price: $92.05

Product Name: 530 Chain - RK split link 'X' Ring
Quantity: 1 Product ID: LA530XSOZ1-CL Price: $4.05

Product Name: 530 (JTR816 series) 47T Rear Sprocket
Quantity: 1 Product ID: TU24-9742 Price: $31.84

[portdave]

That is interesting. I wonder if your stock sprockets were different sizes. I know the L model is diff up front with the forks but not sure about the back. If you get a chance maybe you could measure your swingarm length.

Thanks for the info.

[JHawkins]

That is interesting. I wonder if your stock sprockets were different sizes. I know the L model is diff up front with the forks but not sure about the back. If you get a chance maybe you could measure your swingarm length.

Thanks for the info.

Stock was 15/41 with 96 link 630. If yours was the same, then it should have been the same conversion.

[portdave]

Stock was 15/41 with 96 link 630. If yours was the same, then it should have been the same conversion.

Mine should have been the same as yours stock but the PO had changed it by the time I got it. I just removed a 15/42 setup with 110 link 530 chain.

That is why I think maybe my rear swingarm was swapped with one from a different bike with a shorter swingarm, but I am not sure if other models had a shorter swingarm or not.

Thanks again.

[JHawkins]

15/42 530 sprockets would be smaller than 15/42 630 sprockets. That is the reason that during the swap you increase the size of the front sprocket, you want to keep close to the same diameter so the chain doesn't have to make a much tighter bend because of the smaller size of the 530 sprocket.

Your new sprockets will be bigger than the old, you added 3 teeth in the front, and 6 in the back, so you will need more links than your current 530 chain.

i think the guys at z1 might have just got the chain estimate wrong. You may be able to just take a couple of links off the chain and be fine. Note: I wouldn't cut anything till I mounted the sprockets and checked everything out for size.extra

Edit: actually, the new chain sounds pretty close upon further thought, about half your sprockets have chain on them at any time, so if you increased by 9 teeth then you need 4.5 more links. You have 6 extra links, so it sounds to me like you will be really close. Mount that baby up and have a look!

[portdave]

15/42 530 sprockets would be smaller than 15/42 630 sprockets. That is the reason that during the swap you increase the size of the front sprocket, you want to keep close to the same diameter so the chain doesn't have to make a much tighter bend because of the smaller size of the 530 sprocket.

Your new sprockets will be bigger than the old, you added 3 teeth in the front, and 6 in the back, so you will need more links than your current 530 chain.

i think the guys at z1 might have just got the chain estimate wrong. You may be able to just take a couple of links off the chain and be fine. Note: I wouldn't cut anything till I mounted the sprockets and checked everything out for size.extra

Edit: actually, the new chain sounds pretty close upon further thought, about half your sprockets have chain on them at any time, so if you increased by 9 teeth then you need 4.5 more links. You have 6 extra links, so it sounds to me like you will be really close. Mount that baby up and have a look!

I just went out and looked some more. I also took some measurements. 21.25 inches from center of swingarm bolt to back of swingarm. Also 25.25 from center of front sprocket to rear axle center. When using this site (http://www.sprocketspecialists.com/S...ptimizer2.aspx) and plugging in my sprocket numbers they said probably a 114 link would do it.

I need to go back out there and check it out again but right now I am rocking my 11 month old girl to sleep.

I had it all together last night and that is when I noticed I couldn't pull it back far enough to take up the slack. It might just be a few links.

Thanks again for your time. Sure would be curious to see how the measurements compare to someone else.

[portdave]

A little update. I ended up using the formula from http://www.sprocketspecialists.com/S...ptimizer2.aspx
to calculate what I thought I needed. The odd numbers were confusing. I did a rough fit and figured where I needed to cut the chain. I marked it with a piece of chalk and got out my cutting disc. Cut the head off the pin and punched it out. Duh. I did it on the 113. The chart from the formula confused me and I forgot that I needed even numbers to put on the master link. Went down to 112 links and I was still able to make it work. Just a little closer to the front.

Just wanted to pass along this info for anyone else having a similar problem. The formula worked great with measuring the front sprocket to the rear axle. It gave me the original links and what was on there previously. Test it out. Pretty accurate.

Rob was also a huge help at Z1. He was also perplexed with why the basic divide and multiply didn't work right for the chain links on my bike when converting from 630 to 530.

David