The little monster is officially outta commission

[Skin Mechanic]

The bike has had some vibration when decelerating thru 6k-5k rpm range. It got progressively worse on the 128 mile ride today. I started checking the bike out after it had cooled down. The only thing loose was the chain, like "I'm surprised it didn't fly off the sprocket" loose. The swing arm bolts were tight, so I decided to pull the front sprocket cover and found the problem. The head sheared off the lower motor mount bolt. Story of my life

[iparks81]

Wow! Im'a pull the cover off mine and check this tonight! are you able to find a replacement? does the motor "rock" at all if you push pull on it in the frame?

best of luck!

[Skin Mechanic]

I ordered some replacement bolts from McMaster-Carr. The engine is hanging loose at the top motor mount. I'm gonna replace both bolts and use fender washers at both ends.

[prismways]

Holy crap. Good thing you weren't injured. I will consider changing mine out too!

What was the size and type of bolts did you order?

[lildew]

Originally Posted by prismways

Holy crap. Good thing you weren't injured. I will consider changing mine out too!

What was the size and type of bolts did you order?

for the bolts on the Vader it is 4 1/2" by 5/16 for the bottom and 5 1/2" for the top engine mount bolt.

[Skin Mechanic]

Originally Posted by lildew

for the bolts on the Vader it is 4 1/2" by 5/16 for the bottom and 5 1/2" for the top engine mount bolt.

That's odd that a Chinese bike would have SAE fasteners. The monster's bolts are 8mm x 1.25mm x 120mm. I ordered 130mm length to make up for the thickness of the fender washers.

I've been doing a little reading on bolt failure and this is common when a bolt has to hold a part in place as well as setting it's location. If shims were used to align the motor and mounting bracket, this probably wouldn't have happened. Isolating engine vibrations with bushings in the mounting brackets would probably have prevented the break as well.

[BlackBike]

The old timers on normal bikes have also warned about out of box loose mount bolts too.

[lildew]

Originally Posted by Skin Mechanic

That's odd that a Chinese bike would have SAE fasteners. The monster's bolts are 8mm x 1.25mm x 120mm. I ordered 130mm length to make up for the thickness of the fender washers.

I've been doing a little reading on bolt failure and this is common when a bolt has to hold a part in place as well as setting it's location. If shims were used to align the motor and mounting bracket, this probably wouldn't have happened. Isolating engine vibrations with bushings in the mounting brackets would probably have prevented the break as well.

they are metric but i used the 5/16 size.

[2LZ]

Looks like it was WAY over-tightened at the factory. These motor mounts on most CB's only take about 18-22 ft lbs, depending on bolt thickness. Having them all torqued evenly is far more important than "bear down tight".
Better check the rest. On Mrs. 2LZ TT250, it had a bad vibration and I found the motor mounts in all different torques. I evened them up and the vibe went away.

[ben2go]

Originally Posted by Skin Mechanic

The bike has had some vibration when decelerating thru 6k-5k rpm range. It got progressively worse on the 128 mile ride today. I started checking the bike out after it had cooled down. The only thing loose was the chain, like "I'm surprised it didn't fly off the sprocket" loose. The swing arm bolts were tight, so I decided to pull the front sprocket cover and found the problem. The head sheared off the lower motor mount bolt.

Over torquing a bolt causes it to stretch. Vibrations, plus torque from the engine trying to move, will cause the mounting bolts to break like this.

[Bruce's]

purchasing anything because it was 1/3 the cost of an original is also the reason bolts break like this .Instead of real butter ,they use the I can't believe it's not butter bolts to sell at the price point that gets them out the door .

[Skin Mechanic]

I've bought a lotta crap from China, with emphasis on "crap". It's to be expected. I wasn't surprised that the naugabutter bolts were pitted with rust, like the original gas tank. I guess their parts department is on a flood plain. There's also too much side play in the mounts. I'm not gonna bother buying real shims, I've got a coupla PBR cans that will work just as well.

[prismways]

not sure what all these acrononyms and jargon is about, but interested to see how you secure the motor and mounts.

Originally Posted by Skin Mechanic

I've bought a lotta crap from China, with emphasis on "crap". It's to be expected. I wasn't surprised that the naugabutter bolts were pitted with rust, like the original gas tank. I guess their parts department is on a flood plain. There's also too much side play in the mounts. I'm not gonna bother buying real shims, I've got a coupla PBR cans that will work just as well.

[sshevie]

Lol real pbr can shims on a China bike.....here hold mah beer!!!! I do love the way we all jerry rig our CBS to make them work

[jsumd]

Well damn! At least you weren't hurt. I'll have to keep an eye on mine.