rear engine bolts

G

glenz

New Member
i have an 80cc jet kit installed on a diamondback v-frame. i'm having a cronic problem with the bolts shearing off at the engine block at high rpm. i've had to remove 3 times with an easy-out and replace the bolts. anyone experiencing the same? any solutions? thanx-g.z.
 
I haven't experienced the bolts shearing off.. But what I did do on my bike was get beefier US made bolts instead of the cheesy stock ones.
 
6mm bolts worked just fine for me, although if you have the time and tools to drill and tap I think that would be better. But like I said 6mm worked just fine for me, never had any issues of bolts breaking off ect. Just make sure you get some of the good quality ones or you'll have the same issue again in the future.
 
have you tried mounting the engine on rubber or something to get rid of the vibration? i think thats why they shear off. what kind of bolts did you replace them with?-like grade 8 or something?
 
Does the rear mount sit securely on the frame, with no spaces top and bottom? What type of front mount did you use? Though it works for some, the least stable would be the one bolt drilled through the frame type of mount.
Should'nt this post be in "troubleshooting"?
 
glenz,
Welcome to the forum. I would keep away from mounting the engine in rubber. Sounds like you're already having vibration issues and the rubber mounting idea will only make it worse. You need to check to see that you have good, (total) contact area in the motor mounts. If the motor doesn't fit the frame tubes snuggly then you are asking for trouble in the way of broken studs or bolts and vibration. The motor must fit the frame and should fit without movement in any direction. Try replacing the motor mounting bolts with grade '8' Allen head capscrews available at Ace hardware. The front will be 6mm X 20mm, the rear bolts 6mm X 55mm. Those lengths are good for a standard bicycle frame. If you have larger seat and down tubes then you'll need to adjust the lengths. Don't overtighten the bolts. Torque them down until the lockwashers are flattened then give them a small amout more. Use new lockwashers. Keep us informed and post the results in the forum under the appropriate heading. 'Trouble Shooting"
Tom
 
thanx for the help bro's-where do i find this trouble-shootlng heading? i'm new and not really a computer-whiz, i'm just an old-school welder and fabricator. i appreciate the advise about not mounting on rubber-it does seem to worsen the vibration. yes, it is a standard frame with no modifications to the factory mounts.
 
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