analretentive

I inherited a Specialized Stumpjumper (late 90's model I believe) from my son who was going to junk it some years ago. The chainrings were in bad shape, and eventually I found new exact replacements. They were Shimano Hyperdrive-C. There was no chain on the bicycle. I purchased a 6-7-8 Shimano chain (7.3mm width), and it is not even close to a fit on the chainrings, but fits the rear cassette just fine. The spacing between the rings looks like it would take a chain of about 5 or 6mm width. I re-assembled the old set, and the spacing is exactly the same. One of the compatibility tables I consulted lists all the different chain and chainring/ cassette compatibilty with the various widths given, then says Shimano Hyperdrive is the exception, with no widths given for the chain. The bike is 21 speed 3 front , 7 rear.


What width chain do I need, and where do I find it?


Thanks in advance. Gerry

Unca_Sam

What do you mean when you say it doesn't fit the chainrings?
Does the chain fail to engage the teeth fully (you can see the space between the teeth under the chain rollers with the chain on). Does the chain drop between the chainrings when you shift? Is there insufficient room to use the middle or smallest chainrings? You didn't replace the crank spider, right?

A 6/7/8 speed chain should work with a 7 speed cassette. chainrings from that era used the same dimensions and spacing from 5 speed through 8 speed.

analretentive

The chain seats perfectly on the large chain ring and the rear cassette gears. There is not enough space between the 2 inside chain rings to allow 7.3mm chain to fully seat on the teeth of the intermediate and small rings. It would bind immediately if I forced it into the gap. I don't believe anyone has ever changed anything on the bike, but it looks like a 10 speed chain would work (5.88mm). I hate to buy another not knowing if it will work.

Thanks for your help.

Gerry

70sSanO

First step... What crankset do you have on the bike?

Not just the name, but look on the back of the crank arms for a model number.

An original 21 speed Stumpjumper is from the late 80’s/early 90’s and was running XT. The crankset was likely an XT FC-M730.

However, 30 years later, who knows what is on that bike now.

John

analretentive

Not late 80's or early 90's. I believe it is late 90's or early 2000. Deore LX Fc-m 563

70sSanO

If the crank is a 563, I can’t think of a reason the chain would not work.

FWIW, Specialized didn’t make 7 speed Stumpjumpers in the late 90’s/early 2000’s.

The LX 563 crank goes back to the early 90’s, not that it matters to your issue, but I had LX 563 shifters on my early 90’s GT. Really surprised Specialized didn’t use an XT crank.

John

Edit: I think my GT was early 90’s and the 563 came out in the early 90’s. There was an MT-60 and I think M560 in the late 80’s.

70sSanO

But... it could be a late 90’s/early 2000’s frame. But that crank should not have a rub problem that prevents it from seating with a 7 speed chain. You can try an 8 speed, or 9 speed chain.

Everything I run that has late 80’s to late 90’s drive train I run KMC 8.93 chains whether it is 7 or 8 speed.

John

70sSanO

FWIW...
A KMC 8.93 (X8) is 7.1mm wide.

I also use a KMC 9 speed 9.93 (X9) on newer drivetrains including a 10 speed crank (8 speed cassette) that is 6.6mm wide.

Needing to have a 5mm-6mm wide chain for that crank just doesn’t make sense.

Now if the middle ring was reversed and the attached nuts are not countersunk there could be rubbing in the small chainring, or the wrong chainring spacers (or no spacers), but those are the only scenarios I can think of.

John

Unca_Sam

analretentive,

Shimano is a rare corporation in that they have an online catalog of specifications and installation manuals for as far back as I cared to look. If you know the part number for the crank (which isn't always easy) you can look up how it was to be assembled with the chainrings, spacers, and bolts.

I found this at Shimano Technical Documents.

analretentive

That's where I'm headed.

Thanks