Bicycle Mechanics - 10 speed top cog on 7 speed cassette?

I'm trying to build a "custom" cassette.
I've "found" a 13T "top" cog from a 10 speed and, with its' built in spacer, it's about 1MM "thinner" than a 7 speed top cog (12T that I want to replace).
Can a 1MM spacer be used behind the top cog, or would that result in other problems?
If OK, is the spacer readily available?

The only problem is that I'm not sure you will be able to use a spacer in that position. It won't fit in a way that will allow you to slide in the top cog and lockring.

A 1mm cog spacer should work OK. I'm thinking you may be able to run it without the extra spacer if the lockring will tighten down enough. The high limit screw sets the derailleur for the first position cog, set the indexing for the other cogs with the barrel adjuster.

Al

Thanks for the response.
I was looking at it again and I fear there may not be enough engagement with the splines if I added a simple spacer. It looks like the "proper" top cog has pretty minimal (to me) engagement.
I'd hate to mess up the FH body.
What I was trying to accomplish was convert a-
12-14-16-18-21-24-28 to a
13-14-15-16-18-21-24.
At least the 15T will still be quite useful (I tend to "cruise" between the 14 & 18). I wouldn't use the 13 that much, but it would still be used more than my "unused" 12.

A 1mm cog spacer should work OK. I'm thinking you may be able to run it without the extra spacer if the lockring will tighten down enough. The high limit screw sets the derailleur for the first position cog, set the indexing for the other cogs with the barrel adjuster.

Al

The 13T sits too close to the 14T. I'd have to get a 10 speed chain for my 7 speed cassette. Budget prevents that. I'm not sure if that wouldn't also result in other drive train problems, with my stock 7 speed mountain triple.
I think I'll have to just use the 12T and "enjoy" having the 15T added. If I happen to run into a 13T top cog from a 7 or 8 speed, at a later time, I'll try that.

The bike is an 86 Rock Hopper w/ friction shifters. I can handle a LITTLE bit of irregular cog spacing. Especially if to the top, seldom used, gear.

I'm trying to build a "custom" cassette.
I've "found" a 13T "top" cog from a 10 speed and, with its' built in spacer, it's about 1MM "thinner" than a 7 speed top cog (12T that I want to replace).
Can a 1MM spacer be used behind the top cog, or would that result in other problems?
If OK, is the spacer readily available?


http://www.loosescrews.com/index.cgi?d=single&c=Cassette&sc=Loose%20Cogs&tc=Shimano%20Hyperglide&item_id=SH-11F1312.2&id=186037319618

http://www.loosescrews.com/index.cgi?d=single&c=Cassette&sc=Loose%20Cogs&tc=Shimano%20Hyperglide&item_id=SH-11F1312.2&id=186037319618

Your link refers to a 2nd position 13T. IF I used it with the 12T top cog, I'd have to give up a more useful cog elsewhere. I didn't see a 13T 1st position listed.

Why not just buy the regular 13-23 7 speed cassete? Pretty close. Lickbike sells them for $25.

I currently have a 12-28.
I was doing some "horse trading" and got the 15T and 13T cogs. Had the 13T worked, I would have had a 13-24 with a little better selection for the gears I use the most.
13-14-15-17-19-21-23 (std 13-23)
Mine would have been-
13-14-15-16-18-21-24
The 24 works very good for a start gear on the middle ring for my riding (flat). The 23 is slightly "steeper" than I want, although it would work.
I tend to run between 14-18 for most my "cruising". Usually, the 14 is just a bit too steep where the 15 would fit perfectly. I still want the 1 tooth drop to the 16, since that gear is also used a lot. After that, 2-3 tooth changes are no big deal since I only use those gears for getting up to speed.
Ideally I guess I would like a 13-14-15-16-17-18-21-24/5. But that's 8 speeds!
Anyway, I got the 2 cogs virtually free and the 15 WILL still be useful, plus I drop the 28, which is too low on the middle ring. Friction shifters! It's just a lot easier to shift down to 1st instead of 2nd when you have to make a quick stop.

Your link refers to a 2nd position 13T. IF I used it with the 12T top cog, I'd have to give up a more useful cog elsewhere. I didn't see a 13T 1st position listed.

http://www.nashbar.com/profile.cfm?category=600087&subcategory=60001109&brand=&sku=6213&storetype=&estoreid=&pagename=Shop%20by%20Subcat%3A%20Freewheels