frame design questions regarding tanks, motor

Discussion in 'General Questions' started by still2nu2no, Sep 8, 2011.

  1. still2nu2no

    still2nu2no New Member

    new to the forum, so please be a little patient (particularly if this is posted in the wrong section).

    One think that continues to bother me is the styling and location of many of the tanks included or used in doing a conversion. They look horrendous. I understand they may be similar to the old Whizzer style tanks, and that's OK if you're building a Whizzer look-a-like, but many of the powered bikes seen here (and elsewhere on the Internet) have been custom constructed. Doesn't it make sense for some of the kit makers to offer a tank option or the kits without a tank?

    I'd riden a Sachs rear motor/hub/rim conversion years ago and it used a 1 litre MSR backpacking fuel container for fuel, which was mounted in a bottle cage. I have to believe that something can be accomplished that looks better than the Whizzer tanks. Why not mount a tank below the top tube? It would look cleaner.

    I feel the same way about motorcycle tanks: on choppers there is always a huge amount of space under the top tube.

    Obviously those bikes designed and built to emulate board trackers often use tanks hung from the top tube. This just makes more sense to me.

    Regarding motor locations, I see several types of mounting: rack mount, "high mount" where the engine is well above the crankset, and "low" mount, where the downtube is modified to allow the motor to be mounted slightly above or inline to the crankset. (as referenced to the centre-line of the output sprocket). I guess my question is that if a dedicated design is used rather than a retro-fit, why wouldn't the downtube/motor mount location be made to lower the centre of gravity. I understand that in the case of mountain/offroad bikes the need for ground clearance affects motor location, but what about street/cruiser bikes?

    Again, these questions and comments are not meant to inflame anybody, but rather to help educate myself. No offence is intended towards anyone or any particular bike style.

    thanks for your patience with a noob

  2. motorpsycho

    motorpsycho Active Member

    i agree with you on the gas tank design, but with a little work, they can look really cool.
    on the other hand, you can make your own custom gas tank if you know how to do it.
    I'm not talking about a water bottle or p.v.c. made gas tank...I'm talking about a full custom frame mounted tank that actually looks like a gas tank.
    my lowrider gas tank, which is the stock kit tank, painted metallic white with pearl clear, ivory and purple pinstriping.

    the tank on my o.c.c. chopper, custom made from a jesse james bicycle gas tank.
  3. Porkchop

    Porkchop Member

    Keep in mind, most of the engine kits come from China and I imagine they're disigned and made for their market, not ours or the rest of the world. Keep wandering around here on the forum, espeically the photo gallery. There are some good looking tanks around. Find something you like and start asking questions.
    Last edited: Sep 9, 2011
  4. Porkchop

    Porkchop Member

    As far as some of the things you mentioned about "Center of Gravity" I personally have a friction drive set up, with the engine hanging on one side above the rear wheel. I have never noticed being off balance. The engine weighs only maybe 15 pounds or less. I don't think it's of any real concern. If we were talking a mega dollar high performance machine of some type, yes, it probably would be. Not trying to talk you into a friction drive, just saying I think balance is a critical issue here. Just use good sense and most of all, at least try to be safe. Welcome aboard the forum !
    Last edited by a moderator: Dec 18, 2015
  5. still2nu2no

    still2nu2no New Member

    guys, thanks for the replies

    Yes, on the right bike, some of the engine kit tanks look right. Yours looks very good.


    I guess the CofG thing is my background in physics. It makes sense to keep it low, but the point made regarding the mass of the engine , and its distance to the CofG vs. mass of bike/rider and their CofG isn't wasted. I guess if "custom bikes" are being built from scratch or if one is modifying a existing bike, it seems to me to try to optimize this in the design. In the gallery I saw a bike that started as a "ladie's" bike and ended up as quite a nice board tracker, with low-slung engine as per many of the originals.

    The current bike in my garage is a WCC/JJ "chopper" with gas tank. It looks very good and will not need much in terms of modifications to have functional. This bike belongs to a friend who has lent it to me . It's a 38cc Poulan Pro 2stroke single from a chainsaw with a centrifical clutch It is currently friction drive, using a welded mount for a jackshaft/roller, and the engine. I'd like to make a new engine mount. Chain is far more efficient at transfer of energy (obviously "reduced friction). Peak power in the 6000 RPM range (I'll see if I can get specs from Poulan). I'd like to gear it for maximum efficiency at 25 mph (40 kph), to try to keep it somewhat "legal". I may not even be permitted to use it on the street after all is said and done.

    motopsycho: Your bike looks excellent, what I hope to end up with (and maybe a "board tracker" style one too) :)
    Last edited by a moderator: Dec 18, 2015
  6. still2nu2no

    still2nu2no New Member

    found the gallery of the simple board tracker I liked.

    the board tracker I saw was from James65. The gallery here sucks! Why not just a photobucket type "thumbnail?

    motorpsycho: 3 piece cranks on the OCC? if so stock? if not, just a common bottom bracket?

    About your chain drive, motor to jackshaft (inner) and crankset (chainring) to jackshaft and sprockets (rear)? Am I seeing this right?

    Last edited: Sep 9, 2011
  7. Big Red

    Big Red Active Member

    Tanks, motors.

    I'm also building a Jesse James M.B. Almost finished, just waiting on carb jets to get the engine running right. But I'm the old school guy. I like it to look like an old school motorcycle with the engine set high in the frame and the tank mounted on the top bar. Mounting the engine high required me to put a side draught carb on it, but it looks cool. I'll try to shoot pics when I'm done.
    So fabricate away bro, Make it YOUR bike. The only real requirement is that it's safe. I don't know what state you're in, so I can't comment on the law for you. In California it's 49cc and 30mph limit. Look up the law for your state and follow it as closely as possible.(or not?).
    Good Luck,
    Big Red.
  8. motorpsycho

    motorpsycho Active Member

    yes those 3 peice cranks are stock, and the bottom bracket is small in diameter, much like some mountain bikes with 3 peice cranks.
    I have no idea of the diameter, but it's very small compaired to the bottom bracket on bikes with one peice cranks.
  9. motorpsycho

    motorpsycho Active Member

    the gas tank on my o.c.c. is from a Jesse James chopper.
    There is A LOT of work involved in making these gas tanks functional.
    You have to weld up, braze or silver solder all of the holes and gaps closed.
    then you have to make fuel outlet tubes (one on each side of the tank).
    You have to put one on each side because the tank tunnel is so high inside the tank, there's no way for gas to get from one side to the other. It's actually like 2 tanks inside a single tank. Then you have to run 2 fuel lines out of the tank with a filter in each line. Run the lines into a T fitting so that you have 2 lines in and one line out. after the T fitting you can put an in-line fuel shut off valve on the single gas line, and then run a line from it to the carb.

    you have to pressure test the tank with compressed air and water to make sure there are no leaks at all. If there are leaks, then you have to go back and re-seal them by welding, brazing or silver soldering them. Then test it again....and repeat if necessary.
    cut a hole in the top for a gas cap, and then figure out a gas cap that will work (i have a simple solution for this), paint it, and figure out a way to mount the tank to the frame (i made a hidden mount).
    if you want to go a step further like i did, grind down the big ugly weld in the front of the tank where the peices are welded together, fill that area in with bondo, smooth it out and slightly re-shape the front of the tank.
    you can also fill the little dents in the tank with bondo to smooth them out, These tanks ALL have little dents from when they were made.
    the steel that these tanks are made out of is very thick and heavy, so they do make excellent real gas tanks.
    Last edited: Sep 11, 2011
  10. Big Red

    Big Red Active Member

    Gas Tank

    Hey Moto, When I first hit this site and saw your bike, I asked where you got your tank. Further investigation showed me it came 0ff a Jesse James and that you're a pretty fair fabricator. As you know, I'm doing a JJ now, but it had no tank on it when I got it. The stock tank fits it perfectly and wish I had one. But, I just don't have the welding equipment even if I did.
    I think you have one of the best looking OCC Choppers around, in large part due to the tank. I would just have to change the seat to a larger, more comfortable one,(Couse I'm old). I might also find a fork set with the brake setup on it. Put on a dual pull and yer done. I had one setup like that and the braking was incredible. Still, Great job on the bike.
    Big Red.
  11. motorpsycho

    motorpsycho Active Member

    well thanks for the compliments.
    I never said that my seat is comfortable...but it looks good.
    sometimes looks win over

    yeah i sold my j.j. bike (no engine on it) but i kind of wish i would have kept it.
    I wanted to motorize it this winter, but someone made me an offer on it that i couldn't refuse.
    If i had a spare j.j. tank, i'd sell it to you, but i don't have one right now.
    I know that you've probably already seen my j.j. bike, but here it is for old times sake.
  12. still2nu2no

    still2nu2no New Member

    very nice so far...

    motopsycho, very nice so far. (oops, I guess that's the JJ/WCC 'sold' bike...)

    Yes I know the tank takes a fair amount of work to actually use it.
    What style of drive do you guys use on the OCC and WCC types out there? The one in the garage is friction drive via a jackshaft/roller, with the mount welded to the frame. Not very fuel efficient, but no chainline troubles.
    When looking at the bike above the LHS, it appears there would be a fair amount of work to drive the rear wheel by chain (a re-dished wheel might help), unless I turn the motor around and put a drive sprocket on the LHS and drive it via the jackshaft (which would be driven from the RHS). Seems kind of tight to get a good chain angle if driving from the LHS.

    Any comments?
    Last edited: Sep 12, 2011
  13. Big Red

    Big Red Active Member


    I do my OCC's like this. I'm pretty old school and like my bikes to look as much like motorcycles as possible. The engine sitting on top of the tire just don't look right to me.
    OK, I'm still a dummie. I just noticed I'm using this pic for my Avitar. You can see better pics in my album.

    Attached Files:

    Last edited: Sep 12, 2011
  14. motorpsycho

    motorpsycho Active Member

    I'm not really following you....
    if you turned the motor around (a h.t. motor anyway) it would spin the rear wheel backwards.
    I just use a regular sprocket (41 tooth) on the rear wheel, and the stock chain drive (single speed) on my o.c.c.
  15. still2nu2no

    still2nu2no New Member

    no transmission...

    I want to drive the rear wheel from the motor. This particular motor spins clockwise. If I attach the output sprocket from the motor to a rear sprocket mounted on the LHS of the wheel, then I get brakes, not drive (as the motor is currently mounted). If I drive a jackshaft from the other side, and drive the rear wheel (with sprocket on LHS) from a sprocket mounted on the LHS of the jackshaft, then I will get forward motion.

    I am assuming that many are using a transmission of a sort, which may output in the correct direction. One of the biggest issues is to get a suitable chainline to drive the rear wheel using a sprocket on the LHS of the wheel.

    hope that clarifies the problem...
    Last edited: Sep 13, 2011
  16. motorpsycho

    motorpsycho Active Member

    If you have a happy time (china) 2 stroke, they all spin clockwise.
    You can not run a standard bicycle wheel sprocket on the left side because it will not spin forward (forward would be brakes if it has a coaster brake, or freewheel if it has a freewheel hub.)
    You have to get a secondary sprocket for the wheel that gets mounted on the left side. This sprocket bolts directly to the wheel.
    You keep the original sprocket on the right side of the wheel for peddling, and you add a secondary sprocket to the left side of the wheel for the engine. The secondary sprocket should be in the 36-44 tooth range depending on your wheel size and if you are looking for top speed or low end power. This set up will allow the bike to be one speed only.

    If you want to run a shift kit, then you would have to run a jackshaft and a freewheel crank sprocket.
    The jackshaft diverts the chain over to the right side and it drives the pedal crank sprocket. The pedal crank sprocket has a chain that runs to the rear sprocket on the right side of the wheel (a standard bike sprocket, with either 3, 5 or 7 speeds.)
    The crank sprocket freewheels so the pedals don't move while the enigine is powering the bike. When you want to pedal, you just pedal as normal and the freewheel locks up and supplies pedal power to the rear wheel.
    This set up will allow you to add shifting capabilities for more power/speed.
    Last edited: Sep 13, 2011
  17. Big Red

    Big Red Active Member


    Check out Sick Bike Parts. Very cool jackshaft/shift kit.
  18. Big Red

    Big Red Active Member

    Jesse James

    Hey Moto, Here's the bike that was giving me so much trouble. It's got a side draft(sp.) carb. OCC drag bars and OCC rear fender. I built the engine mount myself because I wanted the engine to sit high in the frame. That forced me to include a sprocket roller, not for tension but only to keep the chain off the frame. What do ya think?

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  19. motorpsycho

    motorpsycho Active Member

    I like it, i like it!!
    Nice work!
  20. Big Red

    Big Red Active Member

    Jesse James

    Thank's Bro, I think I like it just a little better than the OCC bikes. The metal seems thicker in the frame. I guess Huffy just makes a heavier bike. The next Jesse James frame you get you should go for it. With your ability I think it would be one BAD A bike.
    Big Red.