Engine Mounting Bolts Destroyed

[kmon]

Three out of four of my engine mounting bolts have been cut clean off from just riding.. I have no idea why! I have a skyhawk frame gt2a with a silver slant 66cc. The bolts are now flush with the engine and impossible to get out. The only fix I can think of is drilling out the spots and trying to drive new bolts in. Please help with any suggestions. I can take pictures. Thanks

 

[butre]

are you using rubber between the engine and frame? if so, stop. that's what breaks those studs.

as for getting those studs out, go at the area with a cutoff wheel on a dremel and then back it out with a flathead screwdriver

 

[KCvale]

...Or get an easy-out and corresponding drill bit and drill little pilot holes into each broken bolt and back them out that way unless you put them in with locktite, if that's the case you'll need to put the engine in a drill press, drill them out, and then re-tap bigger threads.

That is really messy and hard to do.
The soft engine case will give quicker than the bolts themselves so it can get messy real quick trying to do it freehand.

Using a grinder or dremel you can X the bolt for a center mark to hold the drill bit in the center.
Ya, it will cut the case some but that's OK, there is enough material there.

When you do get them out and re-mount the engine do 'The Test'.
A well mounted engine won't just shear all the studs, it HAD to be way loose and rode anyway to do that.

 

[crassius]

if drilling and/or extracting by one or the other method won't work, search for "80cc alternate engine mount" and you'll see some ways to bolt a piece of angle iron to the case to hold it well

 

[kmon]

Thanks so much guys, the dremel and cutoff wheel worked great. I haven't been using rubber or anything, I think the problem was with looseness. Thanks again for all your ideas!

 

[crassius]

when you remount, remember that the goal is not to make the mounting bolts tight, but to make the motor tight - this means adding whatever amount of spacers that may be needed to get the motor to fit snugly in the frame before the bolts are ever tightened

 

[Tauseef]

are you using rubber between the engine and frame? if so, stop. that's what breaks those studs.

as for getting those studs out, go at the area with a cutoff wheel on a dremel and then back it out with a flathead screwdriver

Hey , i was planning to add rubber(cut piece of car tyre TUBE ) as shock absorber at the engine mounts with cycle frame.
SO i shouldnt do that ??

 

[skyash]

I have tried rubber be for and it let's the motor move under load my friends bike worked for a long time like that but in the end it came to lose all the time and had to hold the motor on with his foot to ride it I think it's better to be solid on the bike.

 

[butre]

Hey , i was planning to add rubber(cut piece of car tyre TUBE ) as shock absorber at the engine mounts with cycle frame.
SO i shouldnt do that ??

definitely not. rubber in the mounts is the single biggest cause of failure

 

[Learner4life]

when you remount, remember that the goal is not to make the mounting bolts tight, but to make the motor tight - this means adding whatever amount of spacers that may be needed to get the motor to fit snugly in the frame before the bolts are ever tightened

I cant agree more here!!! This is SO important. I am a noob that learned the hard way. The comment also before about the engine case being soft is so true also.

What I do now when its engine mount time is this:

- First, make sure bike frame is secure, upright and level/close to final riding position etc(meaning if the wheels arent on it, just make sure the frame is not rotated way forward or back etc if that makes sense), best to have the front and rear wheels on bike and tight, I dont worry about getting the chain over the rear sprocket etc until after the engine is mounted perfect.

-Now find the sweet spot for the engine. Without any rubber or anything at all between the frame and engine (metal to metal) I lower it into the "V" trying my best to keep the frame tubes as perpendicular and flush as possible on either side. I want to gently shimmy it back and forth into place, NOT force it(this can cause frame stretch which is very, very bad!) Tap the engine a little on each side, rotate it, etc. try a few different angles and take your time. Every engine/frame combo "should" have a sweet spot, or at least a best position possible.

- After I have the engine perfectly wedged between the two frame tubes, making sure im fitting flush on both sides, hopefully have 0 or as little gaps as possible between frame and engine mounts. Its ok to have small gaps though if you cant avoid it. Now I JBWeld (2 part epoxy resin dries hard as metal) and literally fill in between the frame and engine mounts anywhere its not perfectly flush. This welds the engine in place.
This is all before I attach a single bolt or u clamp.


The next time I do this I want to use those awesome muffler u-clamps and fabricate stronger mounts like ive seen on some other bikes. Relying on the standard engine mounting brackets/bolts etc even if you do all of this perfect still can have issues/fracture/fail etc. I end up using no rubber/insulator at all except for a small thin layer with the u-brackets where they make contact with the frame to keep it from scratching it up.
Please share any other suggestions/tips.

First build/bike. "Funhog"