Removing outer chain ring from a Shimano M739 crank

[Woodyuk]

Hi All


I need to remove the outer chain ring from my Shimano M739 cranks as rings look worn out and pointy. (or would they still be OK to use ?? :? )
I have a replacement ring but having issues removing the old crank ring. It is the Outer ring that is one piece which fits to the Crank. It looks like I need a special tool? but was wondering if there is a trick to remove it without a special tool
PHot below ...any help would be appriciated :roll:

 

[mattr]

From memory, it uses a thin snap ring that snaps into a groove, can carefully pop that out with a small screwdriver.
Then the actual lock ring uses the same tool as the early octalink bottom brackets. (I have the xtr equivalent). Using a normal lockring spanner might work if you can get it in past the profiling on the back of the ring, failing that you might be able to drift it round (screwdriver/punch and hammer) that might be an option.

Or try and borrow the right tool, someone local to you is bound to have one. (I'm not local, but do have the tool........)

 

[Woodyuk]

Thanks for the reply..
I have managed to get the snap ring off
I will now see if I can find a lockring spanner to see if I can rmove the lockring

 

[Spudly]

If not, then a flat blade screwdriver and a hammer will be able to undo the lockring, as long as you dont get too excited tapping the screwdriver that is!

 

[gtRTSdh]

I suggest not trying to bodge that one, there's only a couple of threads, and they are at the best of times very fragile.

 

[gdb2b]

Woodyuk,
I've learned the hard way (and at some expense). A couple of recommendations...

The special Shimano tool mentioned above is probably hanging wall at your local bike shop. I've attached a couple of pics of it. See if you can borrow it, or rent it. Due to the age of the M739 groupo, this tool probably hasn't seen use in that shop in 5 - 10 years. Who knows they might even give it to you!

1) Don't try the hammer/drift/punch/flat bladed screw driver technique. Steel impacting aluminum alloy will damage the lockring, and likely render it unable to be reused. There are prescious few replacements to be found!
2) Use penetrating oil to assist in removing the lockring. Given the age and ride miles needed to make the 42T big ring look like that, my guess is that it has never been apart before. Penetrating oil will help.
3) Fabricate a clamping jig that will allow you to securely mount the crank spider in it without damaging it. This is very critical! The crank spider must securely clamped immovably before attempting to remove the lockring.
4) Use a 2 foot long crescent wrench or breaker bar to gently loosen the lockring from the spider. Easy does it. Those teeth look sharp. A slip and they they bite!

I run the M739 drivetrain almost exclusively and have learned to service the components myself. One other thing. Get yourself a complete set of chainring bolts. Age, use, and corrosion might have yours a challenge to get loose.

If you get in a pinch, the lockring from the M569 crankset (Deore LX) is compatible....

Here are some reference pics...

 

[trail_head]

I always clamp the tool in a vise and use the crank arm as lever to loosen or tighten these.

Stop by your local bike shop, I can't imagine they'd charge for this.

 

[Twister]

The Shimano tool (TL-UN96) is usually about £25-35 new. I bought a bought a used one for £6. However, there are compatible versions available.
Here's an ice tools version on eBay for £9.99,
http://shop.mobileweb.ebay.co.uk/search ... eburn+tool
They fit xtr 95* and middleburn rs7 cranks as well as your 739s and of course octalink bottom brackets. So IMHO they're more versatile than first appears and well worth investing in.

 

[FluffyChicken]

Just buy the tool. Shimano used it for their chainsets of that era form STX-RC up. Also used for the early 00's until the all in one axle things came out.
Middleburn use it for their spider as well.

Also used for the M95x bottom brackets and various ISIS bottom brackets.

Should be able to pick it up for <£7 on ebay


The one I bought was this one
http://www.chainreactioncycles.com/Mode ... elID=74221
I think you can still get them.

 

[Woz]

"I always clamp the tool in a vise and use the crank arm as lever to loosen or tighten these."

ditto....plus a nut, bolt and large washers through the tool and taper hole to stop it slipping.