2017 Bulls crank arms coming loose ***warning***

[Craig Crowder]

I've had my Bulls SIX50+ E FS 3 about 3 weeks now and I've ridden it about 16 times for a total of 170 miles. I've been very happy with the ride and performance. Luckily for me the LBS notified me that the manufacturer notified him of the crank arm bolts coming loose. I checked them and they were very loose and I tightened them. About 4 rides later the left crank arm came off while I was riding and I was lucky to be sitting on the saddle when it came off. I was able to find the bolt and put back together. The LBS had said that he was waiting for a "Bulls" fix but I guess they haven't got back to him yet. I'm thinking of using blue loctite after I clean the threads, what do you think?

****UPDATE 8/4/17****

SR Suntour has a "corrective action" on the cranks depending on the Bulls bike model number and the model number of the crank arm. From Suntour:

"SR SUNTOUR has found that the cranks supplied on some BULLS E-Bike Models(See attachment for complete list) tend to loosen over time.
Re-tightening the crank only works for a short time then becomes loose again. SR SUNTOUR has therefore decided to have all crank arms and bolts
replaced."

Affected models:

-2017 BULLS E-STREAM EVO 2 27.5 PLUS
- 2017 BULLS E-STREAM EVO 2 FS 27.5 PLUS
- 2017 BULLS E-STREAM EVO 3 27.5 PLUS
- 2017 BULLS E-STREAM EVO 3 29
- 2017 BULLS E-STREAM EVO 45 FS 27.5
- 2017 BULLS CROSS LITE E
- 2017 BULLS DAIL E GRINDER 45
- 2017 BULLS SIX50 E 1.5
- 2017 BULLS SIX50 E 2 STREET
- 2017 BULLS SIX50+ E FS 2 27.5
- 2017 BULLS SIX50+ E FS 3 27.5

 

[Sonoboy]

Loctite Blue 242 is a solid choice. Glad you were able to find the fastener out on the trail.

 

[Craig Crowder]

LBS said Bulls is sending replacement crank arms...I'm curious....anyone know what the problem is?

 

[JRA]

Usually if your cranks get ridden enough while loose, sq. taper, isis or octalink, they will wallow enough to lose their taper and not want to stay tight no matter how much lock tite and ft. lb. of torque you apply to the bolt. The only solution is new cranks.

Word to the wise it is good to keep an eye on the crank bolts, especially when the cranks are new, as they will not fully seat until ridden a few times.

 

[Craig Crowder]

Usually if your cranks get ridden enough while loose, sq. taper, isis or octalink, they will wallow enough to lose their taper and not want to stay tight no matter how much lock tite and ft. lb. of torque you apply to the bolt. The only solution is new cranks.

Word to the wise it is good to keep an eye on the crank bolts, especially when the cranks are new, as they will not fully seat until ridden a few times.

What I found interesting was that Bulls already knew about the problem and had warned the LBS who informed me. I had ridden the bike about 20 miles before I checked them and they were loose. I tightened them pretty tight and they came loose again after another 40-50 miles. The bolt had teflon tape on it (photo on my original post) and I assume it was put there by Bulls...I wonder if that contributed to the problem?

 

[Sonoboy]

Teflon tape? You're talking about the off-white band in the threads? There are several manufacturers of anaerobic thread lock compound; they don't always have to be blue. That's what you're seeing.

 

[Craig Crowder]

Teflon tape? You're talking about the off-white band in the threads? There are several manufacturers of anaerobic thread lock compound; they don't always have to be blue. That's what you're seeing.

Yes, the off-white band. I pulled a little off with a toothpick and it felt like "teflon tape". I had no idea they made anaerobic thread lock in white. Thanks for the info.

I just found what you were referring to:
LOCTITE® 592 Slow Cure Thread Sealant locks and seals threaded fittings. Parts may be repositioned up to 24 hours after application. Slow cure, high temperature.

 

[Sonoboy]

Great! That's probably what you should use. Not to go off topic but another brand I use allows removal and repositioning of items several times per application. It doesn't go rock-hard like the Loctite 242. I use it on 6mm size screws on my PCP Air rifle.

https://www.vibra-tite.com/products...GW7Z_C5XosM036QqlXOS2HKCyPqpp533omxoCIgrw_wcB

 

[Craig Crowder]

I've had my Bulls SIX50+ E FS 3 about 3 weeks now and I've ridden it about 16 times for a total of 170 miles. I've been very happy with the ride and performance. Luckily for me the LBS notified me that the manufacturer notified him of the crank arm bolts coming loose. I checked them and they were very loose and I tightened them. About 4 rides later the left crank arm came off while I was riding and I was lucky to be sitting on the saddle when it came off. I was able to find the bolt and put back together. The LBS had said that he was waiting for a "Bulls" fix but I guess they haven't got back to him yet. I'm thinking of using blue loctite after I clean the threads, what do you think?

SR Suntour has a "corrective action" on the cranks depending on the Bulls bike model number and the model number of the crank arm. From Suntour:

"SR SUNTOUR has found that the cranks supplied on some BULLS E-Bike Models(See attachment for complete list) tend to loosen over time.
Re-tightening the crank only works for a short time then becomes loose again. SR SUNTOUR has therefore decided to have all crank arms and bolts
replaced."

 

[Craig Crowder]

Affected models:

-2017 BULLS E-STREAM EVO 2 27.5 PLUS
- 2017 BULLS E-STREAM EVO 2 FS 27.5 PLUS
- 2017 BULLS E-STREAM EVO 3 27.5 PLUS
- 2017 BULLS E-STREAM EVO 3 29
- 2017 BULLS E-STREAM EVO 45 FS 27.5
- 2017 BULLS CROSS LITE E
- 2017 BULLS DAIL E GRINDER 45
- 2017 BULLS SIX50 E 1.5
- 2017 BULLS SIX50 E 2 STREET
- 2017 BULLS SIX50+ E FS 2 27.5
- 2017 BULLS SIX50+ E FS 3 27.5

 

[rich c]

I'd say they have a crank alloy issue, not a bolt issue. All the torque and stresses go through the taper or what ever drive style they use. The bolt only keeps the crank tightly against the drive. Once the alloy yields and looses the grip, that's when you have a bolt issue.

 

[Robie]

Another bolt that has been loosening on my FS Bulls MTB is down near the rear sprocket. There is a small resessed plate on the suspension on the inside that keeps working loose , a spinning , from movement . I will try correct torque , if that doesn't work might put a little blue loctite.