Chainline Help for 93' GT Karakoram

[Moondog]

I've been building up this GT with similar parts to a few 90's mtb restorers - such as the Shimano Deore crank. I sent the bike in to my local shop on the weekend to install the chain and cables. The chain falls off the crank ring in first gear, and the chainline (FCL) is around 55mm. They're recommending a new crankset, but I'm hoping I might be able to salvage it by removing the 2.5mm BB spacer, and maybe spacing the crank ring 2.5 / 3mm or so? Has anyone had similar issues? From what I've read it should be okay if I get the FCL to around 49 / 50mm?

The crank ring is a cheap narrow-wide from eBay.
Rear derailleur is a Sram X-4.
Chain is a Shimano HG 8 speed.
Cassette is a Shimano HG 8 speed.

Any help much appreciated!

 

[Black_puma]

I have had the same issue with my 1998 GT Tempest. I have had to fit some 2mm spacers between cranks and chainring.
I am running a Shimano XT Hollowtech chain set with a 34 tooth narrow wide chainring, which helps to keep the chain in place.
Not fitted any spacers on the drive side of the bottom bracket, btw.

 

[Dface]

First thing I’d try is a narrow wide chainring.

 

[Imlach]

First thing I’d try is a narrow wide chainring.

That is a narrow wide.

 

[Imlach]

I've been building up this GT with similar parts to a few 90's mtb restorers - such as the Shimano Deore crank. I sent the bike in to my local shop on the weekend to install the chain and cables. The chain falls off the crank ring in first gear, and the chainline (FCL) is around 55mm. They're recommending a new crankset, but I'm hoping I might be able to salvage it by removing the 2.5mm BB spacer, and maybe spacing the crank ring 2.5 / 3mm or so? Has anyone had similar issues? From what I've read it should be okay if I get the FCL to around 49 / 50mm?

The crank ring is a cheap narrow-wide from eBay.
Rear derailleur is a Sram X-4.
Chain is a Shimano HG 8 speed.
Cassette is a Shimano HG 8 speed.

Any help much appreciated!

I've had issues like that and like the black puma I've had to use spacers on the spider to offset the chainring. Once I did that, moving the right further in towards the frame. That corrected my issues on a 1x11 setup, which were also in the high cogs.

That combined with making sure the b screw adjustment is solid and that the chain isn't too slack will hopefully do the trick.

Also you don't have to be bang on the money, chainlines don't have to be an exact science. Try to get it closer to manufacturer spec and see, I'm slightly off on both my Cross Check and Kocmo but have zero issues now.

 

[donnie]

Calculating the chain line for a 1 x drive train on a bike depends on the rear drop out spacing.
If you were using a frame with a 135mm rear drop out spacing the chain set would a chain line of 45mm.

 

[Imlach]

A lot more crucial with narrow spaced 10/11/12 than anything lesser.

 

[donnie]

A lot more crucial with narrow spaced 10/11/12 than anything lesser.

Absolutely I found the best chain line to run with a 1 x 11 drive chain with a rear drop out spacing of 135mm was 46mm.
when I tried to run the chain set with a 45mm chain line and the chain was on the smallest sprocket it would rub slightly on the next sprocket.
It’s difficult to find a modern hollow tech type chain set that will run in a 1 x congratulation with the correct chain line for older drop out spacing standards like 135mm.

 

[Imlach]

Absolutely I found the best chain line to run with a 1 x 11 drive chain with a rear drop out spacing of 135mm was 46mm.
when I tried to run the chain set with a 45mm chain line and the chain was on the smallest sprocket it would rub slightly on the next sprocket.
It’s difficult to find a modern hollow tech type chain set that will run in a 1 x congratulation with the correct chain line for older drop out spacing standards like 135mm.

Yeah, similarly I had issues with the high gears. Playing around with some chainring spacers got me to a setup that works. Had to do it on both my 1x11 bikes, as they used to sometimes upshift in the high end. I run square taper mostly so I don't have the ability to adjust chainline without replacing BB. I ran 1x9, 1x8 and 1x7 for an eternity before I eventually moved into the 10 speed territory and I was always amazed and how fecking wonky I could have things and it just worked perfectly. One of the great benefits of older drivetrains, far less finicky.

 

[donnie]

I've been building up this GT with similar parts to a few 90's mtb restorers - such as the Shimano Deore crank. I sent the bike in to my local shop on the weekend to install the chain and cables. The chain falls off the crank ring in first gear, and the chainline (FCL) is around 55mm. They're recommending a new crankset, but I'm hoping I might be able to salvage it by removing the 2.5mm BB spacer, and maybe spacing the crank ring 2.5 / 3mm or so? Has anyone had similar issues? From what I've read it should be okay if I get the FCL to around 49 / 50mm?

The crank ring is a cheap narrow-wide from eBay.
Rear derailleur is a Sram X-4.
Chain is a Shimano HG 8 speed.
Cassette is a Shimano HG 8 speed.

Any help much appreciated!

Hi is the chain set a deore 12 speed?
55 mm must be optimised for boost drop out spacings.
If you remove a bb spacer you need to check your Q factor is not on the piss as this may cause knee issues.