what did you do to your motorized bicycle today?

Discussion in 'Motorized Bicycle General Discussion' started by Skarrd, Oct 25, 2010.

  1. Davezilla

    Davezilla New Member

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    That could very well be the problem... either they never put a key in it on the assembly line and somehow it held this long or the last guy lost it, these things will go for a while without a key if the gears and sprockets are a nice tight fit... but not very long.
    I know on the centrifugal clutch kits the key can't be used at all on the crank because with the bevel gear removed and the shaft extension installed, all that keeps the shaft extension from slipping on the crank is just that slight taper on both parts, then when torqued down it don't slip. I've had my bike up to 38mph without a slip at that connection, but what did make it slip was when the gear separated from the clutch bell.

    I would buy a replacement key, but buy a few more just to keep on hand as spares in case one goes flying out during disassembly or reassembly, they hold just fine once installed, but get lost real easy.
     
  2. GoreWound

    GoreWound New Member

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    I doubt a cut-off piece of coin would work, would it?

    Edit: I sent an email to the vendor asking if he might just send a replacement.
     
    #7722 GoreWound, Jan 20, 2015
    Last edited: Jan 20, 2015
  3. mapbike

    mapbike Active Member

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    I've made half moon/woodruff keys from Grade 8 flat washers before and from grade 5 flat washers which is probably best since you don't want the key to be so hard that it destroys the shaft its in rather than just shearing.
     
  4. GoreWound

    GoreWound New Member

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    that's a good tip, I will wait to see what the vendor does first, but will probably make use of this tip if he doesn't pull through, thank you.
     
  5. Davezilla

    Davezilla New Member

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    That's a good point...

    I was going to suggest borrowing the key from the bevel gear and putting it in the missing spot on the clutch shaft, the bevel gear won't slip without a key due to it's taper fir, but it needs to be torqued down to about 10 lb/ft using a bolt and washer in place of that screw.
    When I put the centrifugal clutch on mine (until I broke it) there's no key for the shaft extension so just the torque on the bolt and the taper fit holds it and keeps it from slipping. I doubt you could get the screw that's in it now tight enough so if you do try this, find a bolt with the right thread size and a washer, it does need to be fairly tight.
     
  6. Davezilla

    Davezilla New Member

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    After a little more work on mine measuring and all, the mountainbike caliper got reworked and it's gonna be the one I use, the pocketbike caliper is nice, but replacement pad availability and a few more measurements swayed me into liking it more, the reason it wasn't stopping as strong as it should for the kid who owned that bike before me was because he didn't have it adjusted or aligned right, and only about half the inner pad was actually making contact with the rotor, I also found by moving the rotor to the other side the caliper will bolt in very close to the fork leg and out of the way even better.
     
  7. redneck82

    redneck82 Member

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    i've got 3 keys in my motor right now all made from welding rod i put in the vice and just used a file to cut it to shape... they seem to work pretty well... no issues yet and over 500 miles on them...
     
  8. redneck82

    redneck82 Member

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    ok... so... took my bike out on the sled trails again today... unfortunately where i went there is heavy foot traffic as well... all the trails were frozen solid (which WOULD be a good thing)... with all the rain we recently got, combined with people tramping all through the trails, made for an almost impossibly bumpy ride :/ safe to say, i came down a frozen hill bout 150' long of hill and a good 40' drop in elevation... made the hill ok, but the trail bent to the left and safe to say, not much turning on the ice, so naturally, i took a digger... the fall didn't bother me any, i had plenty of gear on... BUT... i bout tacoed my back rim and when i got home, i noticed that BOTH of my rear motor mount bolts had broken off inside the case...
    now i'm kinda screwed... the left side bolt didn't drill out centered therefore did not want to back out and with limited tools on hand, it's stuck where it is and at this point, i think i need to just order a new left side case and seals... UGH!!!
     
  9. mapbike

    mapbike Active Member

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    Here ya go, Best deal I've seen on a new case.

    http://www.ebay.com/itm/181474273792?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT
     
  10. Davezilla

    Davezilla New Member

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    Ouch... did you drill into the aluminum when trying to drill out that left bolt? And how deep in did you drill? You can probably save it if you take the engine off the bike (if not already) and steady it in a vise or whatever you can come up with so the broken stud is Real easy to get to with the drill. Start the drill again but angle it opposite the way you were drilling at first until the bit has dug in enough that it won't slipp off, then while drilling gently bring the bit inline with the stud and it should drill out straight.... This is a lot easier showing somebody than telling them by the way...
    I got other tricks to get one out if it's been drilled in deep already, you'll need a dremel and a rather small carbide burr then you carefully eat away the part of the stud that's stopping you from drilling the hole straight, then make a "start" in the middle of the stud to prevent the drill bit from slipping off... again... easier shown than told...

    Anyway, if it is a total loss, at least empty cases are cheap at most online places, and on a better note, this is a real good time to slip in some of the good bearings on the crank and clutch shafts... Every time I've split cases the bearings looked so bad there was no way I could put the thing back together without replacing the bearings. I also keep at least 4 bearings in my parts stash just in case I have to open one up and don't like what I find inside...
     
  11. Davezilla

    Davezilla New Member

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    That IS a good price for that case....
     
  12. mapbike

    mapbike Active Member

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    I need one myself so I can pull all the guts out of an older BGF engine that had the crank walk over and caused the mag rotor to eat up the seal and into the case on the mag side, been planning to get it apart to see if a main bear spun I the case and caused to problem or what actually happened, this was a smooth running engine at about 36-38 mph with nothing done to it but a well tuned NT carb and a free flowing exhaust pipe.

    if crank is still good in it Id probably just chuck it up in lathe and get it as tdue as I can to help it even more and then slap all the guts in a new case, it has the round clutch pucks which I like better than the squarish ones they all have now, its easy to make really high quality round pucks that work better than the others I think.
     
  13. Davezilla

    Davezilla New Member

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    That's the same exact reason I originally tore into my first engine... it had about 1/8" of crank walk and I just happened to notice it one day when I had the mag cover off, the crank moved really freely then felt like it was locked up, then next time I tried to move the crank I noticed it was moving side to side a lot.
    I took that one all the way apart to get the crank out and everything looked just fine, the crank was sliding side to side on the bearings, they were ok too, just felt a little rough due to being so cheap. After I trued the crank I put the bottom end back together temporarily to see what things were like and saw where the play was. I was going to make a few washers to keep the crank centered but at the time i had a lot of other stuff going on so I bought a new Dax lower and put my top half onto, bought a new jug but decided the old jug had better looking ports, the new one was one with smaller transfers that were slanted across the top instead of straight, and the old one already had the transfers cleaned as well as everything else opened up really nice so it would take less time to just make the old jug work on the Dax lower, the old jug only had about 30 minutes of run time on it anyway so it was practically new anyway...

    What I think was going on with that setup was maybe they were relying on the crank being a tight fit on the bearings to keep it centered or they machined the steps off the crank or it was missing the spacers or washers... or who knows what they were thinking, and I was surprised it ran so well like that...
    Hopefully yours is the same way and you find nothing wrong but the crank walk and can make or get some spacers for it, and also, when I temp installed it again with the crank straight and true it slid side to side even more freely...
     
  14. mapbike

    mapbike Active Member

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    Yeah I have two engines that do this, the latest to start this side to side mess is one of my dax engines, it's the one I actually ended up GPS'ing 52.0 mph out of on the old western flyer bike, I think I got it a little hot and trashed the temper in the rings because it lost power big time as if it had no compression, i pulled the jug and the cylinder bore and piston were both in good shape but the skirt on the piston is really oily black carboned up from the serious blow by from the lack of ring seal.

    While I was looking at that issue I just happen to push the piston to the side and thats when I noticed the crank had all the side to side movement and I though, well this ain't good....!

    I set that engine aside until I can take it down and see for sure what's going on, but i would imagine its just as you found with yours and the crank is just sliding in the bearings.

    Maybe if I could find a brass bushing that had the right iD that was at least very close to the size if the shaft and not to thin, a fella could make a couple spacers for each side of crank between it and the bearing and resolve that problem.

    I found out after it was a little late of the old BGF engine, I was on my way back from about a 10 mile ride, I was cruising smoothly at about 36 mph and all the sudden the engine had a slightly different sound, my first reaction was to let off the throttle, but much to my surprise when I released the throttle nothing happened,it's like I was stuck on cruise control, bike was just zipping right on down the road... I thought the carb slide had stuck wide open at first and just continued for maybe another mile or so, I reached down and even closed thr choke and it actually seemed to run a little better and thats when I knew what it was...HUGE air leak, long story short... I had to shut it down and peddle for about 5 miles up and down hills all the way home, and when I pulled the mag cover I saw aluminum shavings all in there, I pull the rotor and then seen where it had rubbed into the seal until it ruined it and there my HUGE air leak was.

    Sad thing about all this was that this engine had just got to the point to where it was smoother running than ever and was such a pleasure to ride.

    The case may actually be savable since it just barely shaved enough material until the rotor contacted the seal and ruined it, if I can save the case and reuse it that will be nice since it's a large from mount case and these sure work out nice on the cruiser frames.




     
  15. Davezilla

    Davezilla New Member

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    What I was planning on doing was to try and find some brass washers that would slip over the crank that were like. 040" to. 050" thick to limit the side play to. 040" or .020" crank to bearing clearance on each side but any washer that would fit would also block off the fuel/oil mix from reaching the bearings so it was back to the drawing board and I need to make a mandrel that's the same diameter as the crank and then punch some small pieces of sheet brass in the right thickness then cut it so the outer diameter is the same as the bearing's inner race. That would eliminate the slop in the crank but also leave about .020" side play to keep it from going too tight after the engine is fully warmed up. I'm not sure how much the crank and all expands from heat fully warmed up compared to cold, but at .020" there should be plenty enough room but drastically reducing the side play. This side play as you saw can cut into the case, ruin the seals, or even short out the mag if enough tiny shavings are in there floating around when the engine is running which would just feel like a hickup or a small miss every now and then, but could eventually ruin a mag by shorting it out on and off while riding.
     
  16. mapbike

    mapbike Active Member

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    Using a brass bushing like I was thinking of and just chucking it up in the lathe and then slicing off the thickness you need for the right spacing wouldn't interfere with bearings getting lube since the OD would likely be roughly the same size as the bearings inner race OD, the spacer would just kinda act like and extension of the bearing inner bearing race that is on the crank shaft.

    This was my thinking, instead of making a shim washer, this would be what I would call a spacer on the shaft.
     
  17. mapbike

    mapbike Active Member

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    since we both have a lathe handy how about just getting a piece of bronze bar, bore it to the correct ID turn it to the desired OD and then mark thickness needed and slice a couple spacer off and bingo...



    [​IMG]
     
  18. Davezilla

    Davezilla New Member

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    That would work just as well... I think boring out the center hole first then slicing off the needed thickness would be the easiest way. The spacer needed in this case is more like a precicely sized ring than a washer because we need to make sure we don't block off the bearings from getting the proper amount of lube. Now if I can find a piece of silicon bronze bar stock that's about 1" diameter.... finding it isn't too hard but getting somebody to sell just a small piece of it like maybe 3" or so may be...
    Brass or other types of bronze would work just fine too I'm sure, even annaluminum alloy like 6061 or 7075 T6 would work and hold it's shape for the life of the engine.
     
  19. Davezilla

    Davezilla New Member

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    Now you got me thinking... brass tubing with the right id would be as easy as facing the end then slicing off what,s needed. It just needs a wall thickness of .080 to .120" to work.
     
  20. mapbike

    mapbike Active Member

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    #7740 mapbike, Jan 22, 2015
    Last edited: Jan 22, 2015

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