80cc happy time broken mount. again.

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solitus3989

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So i posted before, when the bolt broke off inside the engine. My dad successfully drill and tapped a new bolt hole.

the problem is, he tapped it a little sideways, i guess.

I was riding today, and the metal on the bottom engine mount started rattling. i babied it home, and found out that the new bolt was just loose. i tightened it, which is when i found out that it was tapped sideways, because the little bit of casing that was holding the bolt came off in my hands...

Is it time to buy a new engine, or is there some other way of mounting? :( i was thinking of putting the bolt in the right spot and loading it with quicksteel? If its already broken, i figure i might as well try something before i buy a replacement engine.

You can see what's left of the broken off bolt here.
mount1.jpg


Here you can see how crooked the tap was.
mount2.jpg
 
I hate to say it but the drill and retap was not well done. It can be a hard thing to fix if tools are limited and the engine was left in the bike frame for the repair. I had a rear mount stud break and removed the motor, blocked it up in a drill press for the stud removal. Not easy for the average person. A second problem I see with your mount is the frame tube doesn't fit the engine and you should have used a "big front tube" mount kit. If the tube doesn't fit correctly into the mounts, the vibration will work it loose and either break the bolt/stud or the engine casting itself. If an engine kit isn't mounted with care and attention to the small details, it won't last long and will give you problems eventually. Lucky for us, engine kits are fairly cheap and bikes are nearly a dime a dozen too.

You could make another mounting system such as a "U" shaped piece of steel and drill a couple holes side to side though that front mount casting for the bolts. That could buy more time for that engine and bike.
 
Quicksteel or JB weld might work, not a lot of stress on that point.

I do have a good bottom end, you can swap your jug and piston onto it if you'd like. I think I can fix it in a flat rate box to ship if needed :)

Ed
 
yeah just get some jb weld and cover the whole thing with an entire tube! hopfully it works, dont forget to let the jb weld fully cure though,
 
If your near a Tech School with a welding class and a Machine shop. They might be able to take on a project. I was able to get my custom made mounts welded right to the engine after I snapped off the Grade 8 bolt inside one of the holes that I re-tapped. Good luck.
 
I don't think JB Weld would hold but a try won't hurt anything. Since these engines are so cheap I'd experiment. What I would do if it was mine (off the bike) is to fill the hole (both) with JB Weld. Then with either a grinder or sander I'd grind both sides flat. (I just looked at mine and I'd have to remove the nylon plug where the coil wire comes out and reroute them, to cut that section out) After shaping the sides square I'd drill a hole from right to left through the mount, insert a bolt and nut to bolt on some flat metal and fabricate a bracket. One thing that could be used is something like the end of a turnbuckle, a eye bolt. Run the bolt you drilled the hole for and bolt on two of them. Just a thought. Another thing about doing it this way is that when it is put together you can shim the eye bolts with washers thus wider to match the frame, if need be.
 
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Part Of Your Problem Is Using A Bolt. It Looks Like It Was Way To Short. Not Enought Threads Used In The Block. That Is Why Studs Are Used With Nuts. If The Metal Is Good Enough To Clean, Fill In With Weld, Redrill And Tap In New Threads. Then Get Good Quailty Studs (all 4 Of Them). "sbp" Sells Acomplete Bolt (fasterners) Kit For About $10. Good Luck With Your Build. Ron
 
Part Of Your Problem Is Using A Bolt. It Looks Like It Was Way To Short. Not Enought Threads Used In The Block. That Is Why Studs Are Used With Nuts. If The Metal Is Good Enough To Clean, Fill In With Weld, Redrill And Tap In New Threads. Then Get Good Quailty Studs (all 4 Of Them). "sbp" Sells Acomplete Bolt (fasterners) Kit For About $10. Good Luck With Your Build. Ron

Just noticed he used bolts...good call as studs need to be used as you don't really know how tight vs bottoming out.

5/16" with nylon self locking nuts would work fine.
 

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Hey dude. This is far from the ideal solution and your mount maybe more far gone than mine but I basically cleaned up all the damage, leveled the bottom of the cast mounts and then drilled and retapped the threads further into the block. Ide say Ive done around 300kms on my bike as it is now with no problems so far. I guess what I am saying is, before you bin the block completely, try drilling the holes further into the block and then retapping.

 
Hey Solitus -

I just encountered the same problem you have.

It was my turn the day before a planned long ride... The front downtube mount snapped a stud right at mount surface level. Bummer. I got the needed drill bit and extractor from Ace Hardware. The stud drilled out alright, but even after heating the mount, the stud would not budge with the extractor. That blue Locktite works wonders, even when you don't want it to do so. The extractor snapped in two at mount surface level. There is no option to drill that out. The mount is unsalvagable.

Now, both our options are to remove the engine and replace parts; either the entire engine or just the case. Alternatively, find some other method to hold the front engine mount to the downtube. The bikes are still kinda ridable as is, but because the front mount is dangling, severe engine vibrations set in at a low rpm.

Now, let's put our brains in gear and keep money mostly out of sight. My mount broke because of pulling stress placed upon the studs. It looks like your mounting bolt tore out the side of the mount because your downtube is too wide for the mount. IN THE FUTURE: if you replace the engine, borrow and use a big set of Vise Grips and a lot of muscle to squeeze the downtube in the area of the mount to a racetrack shape, top to bottom. That will squeeze in the sides of the downtube to be at or just below the width needed by the engine mount. That will prevent the problem you encountered.

There are multiple things we can try at this time, keeping in mind that if we fail, we did not lose anything more except time from this point on. We are going to engineer and test our own solution. Here is my first thought, as far-fetched as it is: get a big-diameter wire (as big as you or your dad can handle; steel is preferred) and car muffler clamp that will just fit your diameter of downtube. Measure the wire and cut, making a loop on each end of the wire. Wrap the wire back up on itself three or four turns. Big wire is needed and is very hard to work with.

The wire, when finished, will be just long enough to wrap around the base of the cylinder jug (avoid wrapping around the jug, else the cylinder studs may break prematurely), and reach just over the tops of the threaded portions of the muffler clamp U-bolt. The U-bolt is placed under the downtube; the threaded arms pointed upward toward the engine. Place washers and the nuts over the wire end loops, which are pushed down on the U-bolt arms. Turn the nuts onto the U-bolt arms, drawing the wire down on the arms. That, in turn, will draw the engine case tighter to the downtube.

Try to form the wire to the shape of the engine case to eliminate slack. With luck, the wire wraps will hold, and the tight wire will prevent the engine from bouncing around while running. If you remove the other mount bolt, the engine will self-center on the downtube. Tighten the nuts just tight enough to keep the engine in place. How tight will be a judgement call. You won't know the nuts are too tight until the wire breaks or the ends unravel. When that happens, you try again.

As I stated, this is a far-fetched idea, but it is cheaper than a new engine. This is the best idea I came up with so far. This is what I am going to try.

Keep in mind that downtube squeeze with the Vise Grips if you get a new engine. That technique worked for me. Be sure to stop when the mount bolts do not touch the downtube. Don't oversqueeze. And use multiple layers of paper in the jaws to avoid excessive nasty-looking impressions in the paint.

Let me know what you do.

Thanks,
MikeJ
 
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