motor mount bolts

[caprirs302]

Okay, so i had replaced the factory studs with American bolts, but nonetheless the torque of the motor managed to shear off one of the mounting bolts.

Now I am in the midst of finding a stronger replacement bolts so that hopefully this doesn't happen again, but when I went to my local hardware store, they said that they didn't carry any "grade 8" metric bolts. Is there such a thing? If so, where can I track down some hardened metric bolts?

[tonytt98]

SickBikeParts.com has a grade 5 set that can be purchased for $9.95. I haven't seen Grade 8 anywhere. If anyone knows of a place let us know. I'm interested. If someone has time, they could possibly try to find someone at mfg.com.

[Bikeguy Joe]

Grade 8 is total overkill, the threads will pull out of the aluminum before grade 5 will strip.

The "torque of the motor" didn't shear off the bolt, look for other causes.

[xlite]

Originally Posted by tonytt98

SickBikeParts.com has a grade 5 set that can be purchased for $9.95. I haven't seen Grade 8 anywhere. If anyone knows of a place let us know. I'm interested. If someone has time, they could possibly try to find someone at mfg.com.

McMaster Carr has grade 8 allthread for pennies per foot. No a good idea for motorized bikes though. It's far more brittle than grade 5 and when this stuff snaps off you got REAL problems.

IMO the stock chinese hardware is best and most problems are caused by noobs not knowing when to stop torquing. A stubby ratchet handle is your friend.

[Bikeguy Joe]

Originally Posted by xlite

McMaster Carr has grade 8 allthread for pennies per foot. No a good idea for motorized bikes though. It's far more brittle than grade 5 and when this stuff snaps off you got REAL problems.

IMO the stock chinese hardware is best and most problems are caused by noobs not knowing when to stop torquing. A stubby ratchet handle is your friend.

I'm thinking you haven't examined the threads on the nuts very closely...

The stock studs can be "o.k." but a lot of the nuts are absolute junk.

I do agree that a "stubby" ratchet (and some blue loctite) are better than the gorilla technique for tightening all fasteners.

[Pitchfork311]

I heli coiled all my mounts to 1/4- 20 and got some grade 8 american bolts. Have not had a problem since.

[2door]

And ignore those who tell you to tighten fasteners after every ride. What a bunch of bull hocky. Tighten them once, check and snug after they have reached engine operating temp the first time...then leave them the heck alone. Any fastener or threaded casting can be broken if they are tightened time and time again. Torque them until you flatten the lockwashers then give them just a slight twist more. These aren't semi tractors or bulldozers. Look at the size studs/bolts you're dealing with then tighten them accordingly.
Tom

[tonytt98]

I broke a motor mount bolt also. It was factory bolt from a Grubee 50cc engine. I was a newbie and I'm sure the bolt was to tight. IT was just plain wide open throttle vibrations that did it. It would be nice to find a source that has grade 8 bolts and nuts at a good price for an overkill so one could sleep easier at night.

Tony

[tonytt98]

I got an account with mfg.com. I could do a request for some grade 8 motor mount bolts if there are enough people interested in going in on some. let me know how many sets you would be interested in. The more sets that people want the cheaper we could get them at.

Tony

[xlite]

Originally Posted by Bikeguy Joe

I'm thinking you haven't examined the threads on the nuts very closely... The stock studs can be "o.k." but a lot of the nuts are absolute junk.

Never really inspected them but haven't had trouble. Guess I've just been lucky. However having gone through a bag or two of McMaster Carr 6mm nuts found a couple that, when viewed from the side, looked like they been hitting the bottle.