80cc happy time broken mount. again.

Discussion in '2-Stroke Engines' started by solitus3989, Aug 27, 2009.

  1. solitus3989

    solitus3989 Member

    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.

    Here you can see how crooked the tap was.

  2. Just_Gasit

    Just_Gasit Member

    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.
  3. Hawaii_Ed

    Hawaii_Ed Member

    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 :)

  4. linnix13

    linnix13 Banned

    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,
  5. Handyguy2have

    Handyguy2have New Member

    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.
  6. Al.Fisherman

    Al.Fisherman Active Member

    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.
    Last edited: Sep 11, 2009

    TREEWK Member

    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
  8. Al.Fisherman

    Al.Fisherman Active Member

    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.

    Attached Files:

    Last edited: Sep 11, 2009
  9. EnFlaMEd

    EnFlaMEd Member

    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.

  10. MikeJ

    MikeJ Member

    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.

  11. MikeJ

    MikeJ Member

    Hi Solitus -

    I was thinking some more. Here is a thought that may be an improvement over the previous suggestion. I was thinking the wire may continue stretching over time. The tightness will have to be tested and adjusted frequently for a while.

    Instead of the heavy wire (I am thinking of #9 wire; its diameter is about 1/8th of an inch in diameter; it is still hard to manipulate), I thought maybe a steel rod would be better.

    Many hardware stores sell 1/4 inch diameter threaded rod. I am thinking of purchasing a piece (it is inexpensive) and cut it to length to wrap around the base of the cylinder jug and have the two arms extend to beyond the bottom of the downtube. (An anvil will be a big help. And if you can heat the rod with a torch to red-hot to orange-hot at the area where it is to be bent, that is recommended.) So the rod will be shaped like a square-ish letter "U". The muffler clamp comes with a stamped piece of steel. I am thinking to form the threaded rod to extend through the stamped steel piece. (Must verify this can be done before purchasing the threaded rod.) This idea would require some multiple bends in the threaded rod, but none of the bends between the cylinder and the downtube should be sharp. As before, tighten down the nuts onto the threaded rod just tight enough to keep the engine and downtube from shaking separately.

    On the opposite side of the cylinder, a file or a grinder can cut down the sharp peaks of the rod so the peaks will not dig into the softer aluminum.

    Another thought... Because this is experimental, I am going to place some rubber pieces, such as scraps from a cut-up inner tube, between the engine mount and the downtube. The intent is to prevent the engine mount and the downtube from banging together while the engine is running at higher speeds. There is a property of all solid stuctures called resonance that, if not avoided, can break the strongest of structures. The idea is to avoid resonance from developing when the engine is running. A physics or chemistry instructor or industrial arts instructor can better explain.

    I am open to all ideas from anyone that does not involve JB Weld or any similar product. Though good stuff, that is of no value to me in my case. I am going to try something soon.

    Last edited: Sep 15, 2009
  12. Luka

    Luka Member


    I believe this mount is pretty much 'pot metal', isn't it ?

    Or aluminum ?

    In either case...

    Find a piece of fuel line, or similar steel tubing, that is just slightly larger than the stud.

    File saw teeth into the end of the tubing. What you end up with, should look like a holesaw.

    Now use that to cut out the stud. Center it on the stud, and start drilling. It should work exactly like a holesaw, cutting outside the stud/broken off extractor.

    Once the bad parts come out...

    Get a 'helicoil' kit, and install it in the hole.

    If done correctly, you should actually end up with a stronger connection there, than you had in the first place.
  13. MikeJ

    MikeJ Member

    Hi Luka -

    I see you are relatively new here... Welcome! There is a lot to learn and opportunity to report back on any attempt to make this hobby more fun and less expensive.

    I finally looked up the definition of "pot metal":
    Pot metal is a slang term which is used to refer to cheap metal alloys with a low melting point. The low melting point makes pot metal very easy to cast, but the generally low quality can cause problems during casting and at a later date. Because there is no formal definition of pot metal, it can be hard to determine its contents. Some common metals included in pot metal alloys include: zinc, lead, copper, tin, magnesium, aluminum, iron, tin, and cadmium, among others.

    The mixed contents of pot metal make it highly unpredictable, which can be a problem for people who are trying to create specific items. It has a tendency to become very soft and porous, and over time, it is subject to deformity. Pot metal also tends to break or bend easily, making it unsuitable for many tasks, and because some of the metals commonly included are toxic, pot metal can also be hazardous to human health.

    Yes sireee.... That describes the metal these engines are made of.

    Your intent of making a hole saw is good, but there is at least one weakness in your thinking: I don't have the raw materials to make one. Maybe the holesaw concept will work, but for now, I want to try a couple of other less elegant workarounds.

    Last night I formed an 18-inch-long, 1/4 inch diameter non-threaded round steel rod from Home Depot into a shape that looks like an oil filter remover, one with parallel handles and a round grip that wraps around the filter. The rod is relatively soft hot-rolled steel. It can be bent into multiple 45-degree angles without the need for a heating torch.

    The ends have one inch of 1/4 - 20 NC thread cut into them. I shaped it and wrapped it around the engine block as I described in a previous post. The ends are below the downtube, held in place by the stamped steel piece from a muffler clamp. It doesn't look too bad either. With washers and nuts on the ends, I can pull the engine and downtube together so there is no relative motion whatsoever.

    Maybe tonight, I can give the bike a run and see if this jury-rigged setup will hold together.

    In the future, I may re-think this again. Instead of a solid rod, maybe use a short length of braided garage door cable wrapped around the back of the engine block; maybe 16 inches long and looped back on itself. Have the guys at Home Depot mash down a press fit onto both ends of the cable after forming the loop. Then use eye-bolts to hook into the loops, and use the muffler clamp steel piece under the downtube, and use nuts to pull the eyebolts downward, tightening the braided cable around the back of the engine block. That would be easier than multiple bending and constantly test fitting a solid rod. The tensile strength of a heavy braided cable is well above that tension needed to fix the engine into place. Just check torque on the nuts (should be very low) frequently for a while until the braided cable has stopped stretching.

    I will post my observations again in a few days. Thanks for writing!
    Last edited: Sep 16, 2009
  14. MikeJ

    MikeJ Member

    I went for a ride tonight with the work-around steel rod in place. Positive results so far... no shaking; my bike rides just as if the motor mount never broke in the first place. The ride was short because of increasing rain; maybe seven minutes or so.

    The formed steel rod I used was a pain to put into place. I had to remove the carburator and the clutch handle. IN THE FUTURE, I would use a heavy garage door braided cable with loops on the ends, two eyebolts through the loops, and the muffler clamp steel piece holding the eyebolts. It will be easy to put on, have much more than enough holding power, and will be easy to adjust at any time.

    I am hoping for make a 120 mile ride this weekend. Whether my work-around remains in place or not, I will post results.

  15. Stink Bike

    Stink Bike Member

    I did a temporary repair on one of my old bikes by wrapping a length of threaded rod around the motor.That was about a year ago and I still haven't replaced the threaded rod.I guess I'm just lazy.
  16. MikeJ

    MikeJ Member

    Hi Everyone -

    I tried to attach pictures of my mount that is on my bike. This is my first attempt, so overlook any failures.

    The first picture shows an 18 inch long rod bent to fit around the base of the cylinder. I cut the threads with a die from a tap and die set that I have.

    The second picture shows the left side of the engine.

    The third picture shows the right side of the engine. Note the steel shim is positioned right over where the stud should be. It is to relieve high-pressure points on the down tube. Note also the wires, how they are heat-shrink-wrapped over soldered connections.

    I rode the bike a total of 31 miles since placing on this broken mount workaround. It took all the normal stress that hills and high speed present. I am going to call this workaround successful, but still leery that the nuts can snap off the rod at some unknown time in the future.

    The only reason why I did not put 50 miles on my bike since installing the workaround is because my rear tire got speared tonight while doing 26 mph by a huge framing nail into my back tire. It went completely through a kevlar puncture-prevention liner and completely through both sides of a puncture-resistant thick-wall inner tube. The bike was completely controllable, but no fun to ride on the metal rim.

    Oh, well. I made two steps forward and one step back. This gives me a lame reason to buy a real road tire to replace knobby mountain terrain tire.


    Attached Files:

    Last edited: Sep 17, 2009
  17. solitus3989

    solitus3989 Member

    to revive an old forum.. Sorry it took so long!

    i finally got around to trying something. since the drill and tap was real jagged, i tried just lots of JB weld to hold the entire stud in place.

    Worked fine on a shorter ride, but i tried taking it on a 10 minute ride to my friends house, and the whole JB weld/Bolt popped right off the engine. it didn't really bind well.

    Mike, i like your idea of how you mounted that on there. it looks pretty solid! is that still holding well?
  18. MikeJ

    MikeJ Member

    Hi Solitus and Everyone -

    I'm happy to see you are back. The 1/4-inch rod is holding quite well. I have 275 miles of hard hill pulling and high speed runs on that workaround. Checking that all bolts and nuts are tight, the engine vibrates very little in the low-4000 rpm range under full load. I seldom run above 4400 rpm.

    I suggest trying the braided cable, eye-bolts (or J-bolts if you can find them), and the steel piece of a muffler clamp. Any good hardware store that sells garage door cable should be able to make the short cable with loops on each end. A special pressing tool that applies several thousand pounds of pressure to a cable collar (for lack of better terms) is needed to assure the cable will not loosen.

    Notice I double-nutted the ends of the work-around. Neither end has moved one bit. Tighten the nuts until the engine does not move. Braided cable will stretch a little over time, so check nut tightness before each ride for a while.

    I will bet a well-constructed braided cable will work for you. Get a hefty cable if you can find one. Also, if deemed needed, double-loop the cable so that two passes of the cable exist behind the base of the cylinder. I will bet your engine will not move after that!

    Let us know what you end up doing!

  19. TREEWK

    TREEWK Member

    Stink, Sometimes Temporary Can Last 20 Years!! Lol. Ron
  20. dudeimarobot

    dudeimarobot Member

    Hey guys. I just wanted to share my broken mount experience.

    Both front studs sheared flush with the engine case. I was able to remove only one. So after some thinking, I came up with this...


    I found the metal strap in the back of my bike shop. Its comonly used to attach racks, fenders, random stuff. So, I bent them to the correct shape, enlarged the holes. Drilled out the other side of the case mount, tapped it for the next size up stud. Used an 8.8 automotive bolt+locktite. I used a hardened homedeopt bolt on the right side. Seems to work fine. Has gone through 50 miles of commuting so far. each strap is an 1/8" thick. I used two.