Cobb 155mm crank.. should there be play when installed?

[cpml123]

Hi all,
I just installed Cobb 155 50/34 crankset on my S40. I had Sram Rival crank and BB. Since it's GXP compatible, Robert said I should be able to take off the Rival crank and install the new crank easily. It did install fine. However, I found the new crank has a little play, my guess about 1 or 2mm. Is that normal? I did torque it to 35 ft lb as instructed. Is this manufacturing issue? Help!

 

[ratz]

Hi all,
I just installed Cobb 155 50/34 crankset on my S40. I had Sram Rival crank and BB. Since it's GXP compatible, Robert said I should be able to take off the Rival crank and install the new crank easily. It did install fine. However, I found the new crank has a little play, my guess about 1 or 2mm. Is that normal? I did torque it to 35 ft lb as instructed. Is this manufacturing issue? Help!

Sounds like you need to add a wave-washer to get the proper torque.

24mm
http://www.enduroforkseals.com/id435.html

These are also helpful
24mm x 1mm
http://www.enduroforkseals.com/id433.html

 

[ReklinedRider]

Just from experience with Cobb cranks: remove the crankset from your bottom bracket and shell. Put the crank arm on the spindle as if you were installing it on your bike. Torque to spec, then torque it some more. Ditch the torque wrench for the moment and tighten it down **unreasonably** tight (remember this is with it off your bike). Disassemble and reinstall on your bike. Should tighten down nicely with no play. I recently installed two Cobb cranksets and I had the same amount of play you are describing. Tightening the arm on the spindles really tight, off the bike, worked well. I don't know why this seems to be a problem with these now; I have installed Cobb's in the past with nary a hitch.

Before I did that extra-tight maneuver I had called Cobb; the person answering the phone didn't have an answer and said "hang on". The next voice on the line said, "Hi, this is John Cobb". He was perplexed and sent me a new crank arm the next day. Same problem with it, though. I admit I was frustrated when I took it apart and tightened it down <excessively>. But it worked. {The point of this paragraph is that Cobb offers great customer service. Maybe give them a call and see what they say.}

(I'm assuming you didn't use any spacers on your bottom bracket. Using the MTB spacers creates a problem too. More experience)

 

[cpml123]

No I didn't add any additional spacer. I just left the little gasket as is from the Sram BB.
I did find a wave-washer in the box with Cobb BB that I did not use.

Kline - did you install a wave-washer with your crank or you just pre-tightened and re-installed the crank without the wave-washer?
Bob - if I were to use the wave washer - do I use on the drive side or non-drive side?

Thank you!

 

[cpml123]

OK. I clicked on the link that Bob has for wave-washer. It says it can be used for threaded GXP drive side. So I tried to get the wave washer that's included in the Cobb BB box onto the spindle, and the tolerance was so tight that I couldn't get the washer onto the spindle. So I gave up and tried Kline's method of pre-torquing the crank arm and reinstalling it. Now the crank arm went on with no left-right play (along the spindle axis) and tightened onto the BB at 35 ft lb torque. However, when I tried to rock the crank rotationally (imagine if you look at the bike head-on, hold crank arms with both hands, and try to twist the whole bike clockwise/counter-clock wise using the crank arms), there was a slight play. It seemed to come from the BB itself. I don't know it's normal but I am thinking it's probably good enough for now, I hope.

 

[ReklinedRider]

i didn't use a wave washer.

i see what you mean about the rotational play. mine doesn't do that.

not familiar with the little gasket from the sram bb. i used the bb that came with the cobb crankset.

 

[cpml123]

Kline.. Thank you for the pointer that yours doesn't have rotational play. I went back and loosened the crank arm by a few rotations. I then tightened it again to 35 ft lb, and now the crankset and bb are completely tight.

It's kind of odd that the crank has to be tightened, loosen, and tightened again vs being tight and no play the first time.

 

[ratz]

The wave washer is for bearing life it preloads the torque so the bearings stay in the races; goes on the crank side. You don't need it but your BB will wear our sooner without it

 

[cpml123]

Hi Ratz... does the wave washer go on the drive sprocket side or the non drive side?

 

[ratz]

Hi Ratz... does the wave washer go on the drive sprocket side or the non drive side?

Chain Ring side, the non drive side on a GXP is self aligning self torquing. If should be noted if you are using a $30 BB don't bother. If you are using a $125-200 BB don't skip it.

 

[cpml123]

Noted. When my current cheap BB gets replaced in the future with a better BB, I will put that in.

It's just that washer was so impossible to get on the spindle due to tight tolerance. Any tips on getting the washer onto the spindle? Or just get a bigger washer?

 

[ratz]

Noted. When my current cheap BB gets replaced in the future with a better BB, I will put that in.

It's just that washer was so impossible to get on the spindle due to tight tolerance. Any tips on getting the washer onto the spindle? Or just get a bigger washer?

make sure it's a 24mm one and grease.

 

[ReklinedRider]

It's kind of odd that the crank has to be tightened, loosen, and tightened again vs being tight and no play the first time.

I agree. SRAM cranks....no such problem.

 

[cliff oliver]

I have same issues. Tighten (over 35lbs) loosen, re-tighten. I have enduro BB use the washer on drive side they provide. The SRAM cranks no problem, but I sure like this shortened COBB crank. What a difference 15mm makes.

 

[cpml123]

Oh good. I guess it's a "feature" we pay for. I won't bother to call to complain then.

I will save the washer for the future BB.

 

[ReklinedRider]

Oh good. I guess it's a "feature" we pay for. I won't bother to call to complain then.

I will save the washer for the future BB.

It can't hurt to call and complain--tell them you know two other people who have had that problem. Maybe it's something fixable. As noted, I've installed a couple before without any issues. So maybe it's a recent mfg problem, and fixable. Anyway, it can't hurt to call. When I called, they sent me another non-drive side crank arm. Better to fix the problem than send out extra crank arms!

The wave washer supplied with the Cobb cranks--I could not get it to go over the spindle to the drive side either, so I now wonder if Cobb intends the wave washer going on the non-drive side? When the BB supplied with the Cobbs wears out, I'll replace with Enduro and use their wave washer.

Mine are 145mm on both V20 and DF bikes. Got the recent two sets on sale so they were only a negligible amount more than going with Bikesmith Design. Either way, I sure like the shorter cranks too.

 

[cpml123]

Here is what I got, after chasing down Scott, the production manager. I think other folks with the same issue should complain to them as well. Or maybe this is a non-issue.

-----Original Message-----
From: Scott Warren <scott.w@cobbcycling.com>
To: Michael Lo <cpml123@aol.com>
Sent: Wed, Jan 24, 2018 12:55 pm
Subject: Re: Question about the 155mm alloy compact crank installation issue

The only possible situation that I can see is that if the outside bolt cover that uses a 10mm allen head is tight against the 8mm crank bolt it creates a false torque reading. After repeated use maybe it reduces the pressure. I'm not sure to be honest, This is the first I've heard of this situation and you are telling me there are three of you with the same symptoms. I've installed several and we've sold thousands but I havent heard this issue before.

Scott

On Tue, Jan 23, 2018 at 5:57 PM, Michael Lo <cpml123@aol.com> wrote:
Hi Scott,

Any solutions to this issue?

Thank you,

Michael



-----Original Message-----
From: Michael Lo <cpml123@aol.com>
To: scott.w <scott.w@cobbcycling.com>
Sent: Fri, Jan 19, 2018 09:39 AM
Subject: Re: Question about the 155mm alloy compact crank installation issue


Yes threaded.

Thank you, Michael


-----Original Message-----
From: Scott Warren <scott.w@cobbcycling.com>
To: Michael Lo <cpml123@aol.com>
Sent: Fri, Jan 19, 2018 09:07 AM
Subject: Re: Question about the 155mm alloy compact crank installation issue


Michael,
What type of BB is in your bike? Threaded?

Thanks,
Scott

On Thu, Jan 18, 2018 at 2:07 PM, Michael Lo <cpml123@aol.com> wrote:
Hi Scott,

This is Michael Lo. Your sales department gave me your email about my question about the crank.

I had Sram Rival compact crankset (GXP bottom bracket). I took it off. Installed this crank. First time I tightened it to 35 ft lb (with torque wrench), there was a gap of 1-2 mm between the non drive crank arm and the BB. I had to loosen the crank and re-tighten the crank arm to the right torque, This time the arm touched the BB. So no gap, but the BB is a little wobbly. I loosened the crank arm again and re-tightened it again to 35 ft lb. The third time finally it's solid with no play or wobbliness. This is opposed to the Sram crank where it gets tightened with no play the first time.

I have a Cruzbike, so I asked if that's normal on the cruzbike forum. Two other members said they recently bought the alloy Cobb cranks and had to same issue of having to repeat tighten, loosen, and re-tighten. They asked me to represent three of us to ask you if this is a manufacturing problem or if it's normal. Also, we did not install the wave washer, which was impossible to get on the crank spindle anyway as the tolerance was so tight or a little too small for the spindle.

Thank you,

Michael

 

[Jeremy S]

FWIW, the instructions for my SRAM Rival crank instructions said to expect play at first (but not to live with it). SRAM's recommended procedure was torque down, check for play; if play is found, remove, retorque, check again. Repeat until no play. I've put Rival cranks on a several times and I've always had to go through this process.

 

[cpml123]

Ok thank you Jeremy. I guess it's a feature we paid for then .

 

[ccf]

I put a 145mm Cobb crank on my V20 a few months ago, and I had the same issue. I "solved" it by using the spacers. But the crank keeps coming loose. If I really tighten it tight, then the bearings feel way too tight; the cranks don't spin much when the chain is off. I have the RWC BB with ceramic, angular bearings. Should I take the cranks off, torque it unreasonably tight, then re-install it without the spacers? BTW, I have the wave washer on the drive side.

-Cliff