I bought one!- Yamaha Moto-bike build idea

[Walker]

Looks like only only 10 places to have possible frame alignment risks. it would be a whole lot less work to start with a 26, or even a 24 to keep the size down..IMHO

 

[outskirtscustoms]

Looks like only only 10 places to have possible frame alignment risks. it would be a whole lot less work to start with a 26, or even a 24 to keep the size down..IMHO

Not really, the seat tube is straight down, The back legs are straight, the rack bars are straight, the other two (top tube and down tube) you can heat where the bends are (4 inches from the seat tube and BB) and make them line up pretty easy. Just try to keep everything straight.

 

[Walker]

But you have to separate the front triangle to make those changes..lots of pieces to put back together is all I'm saying..

 

[outskirtscustoms]

But you have to separate the front triangle to make those changes..lots of pieces to put back together is all I'm saying..

True, but it looks more intimidating than it really is. The finished product would be worth the headache.

 

[Fisch]

Looks like only only 10 places to have possible frame alignment risks. it would be a whole lot less work to start with a 26, or even a 24 to keep the size down..IMHO

Frame alignment risks? I would think that straight bars like this would be easier than curved. But I am far from an expert. I have seen CRAZY builds on this site, curves and swoops and frames without down bars. By comparison this seems pretty straight forward.

If I use inner sleeves, wouldn't that alone keep things pretty straight? Plus clamping it to a jig.

IDK honestly, this is new for me, but the swoopy stuff scares me a lot more. My bro-in law is a classic car restorer. I would have him do all the welding.

Modding something new, I would still have to fab the cross bar and entire back end. Swing arm, stays, etc. The stays would have to be custom cut as would the shockmounts if I wanted them to look like the Moto-bike.

Also not a lot of current manufacturers make a bent back frame. Many that do have a curved down bar. (At least curvier than the Motobike.) But I'd love to hear f some if y'all know of any!

Just seems like a lot of work any way you slice it!

 

[kram]

I say go for it! It's your bike and who cares about purist. You have the bike already and it sounds like you got a good deal on it. If it had original paint and in perfect condition then maybe it would be different. I personally think taking that tiny frame and making it bigger is a cool idea.

 

[outskirtscustoms]

Might want to talk to uncle stretch, he's the in house guru on the subject.

Looks like only only 10 places to have possible frame alignment risks. it would be a whole lot less work to start with a 26, or even a 24 to keep the size down..IMHO

Frame alignment risks? I would think that straight bars like this would be easier than curved. But I am far from an expert. I have seen CRAZY builds on this site, curves and swoops and frames without down bars. By comparison this seems pretty straight forward.

If I use inner sleeves, wouldn't that alone keep things pretty straight? Plus clamping it to a jig.

IDK honestly, this is new for me, but the swoopy stuff scares me a lot more. My bro-in law is a classic car restorer. I would have him do all the welding.

Modding something new, I would still have to fab the cross bar and entire back end. Swing arm, stays, etc. The stays would have to be custom cut as would the shockmounts if I wanted them to look like the Moto-bike.

Also not a lot of current manufacturers make a bent back frame. Many that do have a curved down bar. (At least curvier than the Motobike.) But I'd love to hear f some if y'all know of any!

Just seems like a lot of work any way you slice it!

 

[yardsaleman]

tell you what if you need funds to buy a 26 I would like the 1st yamaha if you want to sell I have always loved/wanted one of them thanks and good luck

 

[Fisch]

Might want to talk to uncle stretch, he's the in house guru on the subject.

I will PM him and see if he will check into this thread!

And thanks for all the advise guys, both directions!

 

[Fisch]

tell you what if you need funds to buy a 26 I would like the 1st yamaha if you want to sell I have always loved/wanted one of them thanks and good luck

Appreciate the offer! But this little dude is missing a bunch of stuff and by the time you get it all you might have been able to buy a complete one. These forks are not original, and the tubes I do have that are OEM, are are pretty shot and non functioning. Also missing the top mounting plate for the original forks. Missing the cranks (but this is easy because they are the same ones on almost any 70's Raleigh 3-speed). Missing the original wheels too.

The original banana seat is really hard to find and big $ usually. (Mine is a generic one.)

Plus I guess the point of this has evolved into actually building a Moto-bike. Almost like a tribute. All that stuff about making it a cafe motored bike on the first page would be way down the road. And if you took all that stuff off it would still look just like a Motobike underneath.

Stage one- build a moto-bike and ride it. (Possibly scaled up)
Stage 2- Motorize it if is big enough. (But much later.)

 

[Dr. Tankenstein]

Your rendering looks great! Instead of new shocks, why not just weld on some lowered mounting plates (you got the welder out to stretch the frame anyways, right? :wink: )

Cheers,
Dr. T

 

[Uncle Stretch]

I see lots of problems already. One is when you stretch the top tube the angle on the downtube will change. If you cut it where it connects to the BB then when you lengthen it the new angle will show up. Your going to do 10 tube welds. There will need to be a tube slid inside each tube you lengthen with a 1/16th apart to weld to both tubes and the one inside for strength. The other angles should be ok .For what your going to do you could take some 1'' tubing ...stick a picture of you frame in an overhead projector, and back it up till the tires are the size of a 26'' one and then tape some large paper on a wall and draw out your new creation. It will be less work and a lot stronger than all the tube inserts your going to put in. I know I could do it , but for the amount of work involved , I wouldn't. This is just my 2 cents so take it with a grain of salt.
If you do move forward, cut the down tube completely out and use a piece of 1'' angle a foot or so long clamped to both tubes your going to weld to keep them straight. Never and I stress never add a piece by just welding one against the other without putting another tube inside. Good luck.

 

[Fisch]

I see lots of problems already. One is when you stretch the top tube the angle on the downtube will change. If you cut it where it connects to the BB then when you lengthen it the new angle will show up. Your going to do 10 tube welds. There will need to be a tube slid inside each tube you lengthen with a 1/16th apart to weld to both tubes and the one inside for strength. The other angles should be ok .For what your going to do you could take some 1'' tubing ...stick a picture of you frame in an overhead projector, and back it up till the tires are the size of a 26'' one and then tape some large paper on a wall and draw out your new creation. It will be less work and a lot stronger than all the tube inserts your going to put in. I know I could do it , but for the amount of work involved , I wouldn't. This is just my 2 cents so take it with a grain of salt.
If you do move forward, cut the down tube completely out and use a piece of 1'' angle a foot or so long clamped to both tubes your going to weld to keep them straight. Never and I stress never add a piece by just welding one against the other without putting another tube inside. Good luck.

Thanks so much Unclestretch! I will certainly take your word for it!

I am curious though. Why when I did the photochop did none of the angles change? I thought for sure they would just like you said. I was shocked they didn't actually. I realize photoshop is far away from the real world, but man it looks close.

Sorry if I am sounding stupid here guys!

 

[Dr. Tankenstein]

I'd take Uncle Stretch's word for it brother. He's forgotten more things about stretching a frame than I'll ever learn! :mrgreen:

He's got a point that it wouldn't take much to make a 26" clone. Then you could have matching daddy/daughter bikes!

Cheers,
Dr. T

 

[Fisch]

I'd take Uncle Stretch's word for it brother. He's forgotten more things about stretching a frame than I'll ever learn! :mrgreen:

He's got a point that it wouldn't take much to make a 26" clone. Then you could have matching daddy/daughter bikes!

Cheers,
Dr. T

Oh I take his word for it for sure! I have much respect for the Uncle Stretch! Just trying to learn!

 

[outskirtscustoms]

I'd take Uncle Stretch's word for it brother. He's forgotten more things about stretching a frame than I'll ever learn! :mrgreen:

He's got a point that it wouldn't take much to make a 26" clone. Then you could have matching daddy/daughter bikes!

Cheers,
Dr. T

Oh I take his word for it for sure! I have much respect for the Uncle Stretch! Just trying to learn!

Aren't we all? :mrgreen:

 

[Uncle Stretch]

Its not really that you have to take my word for it. If you take a perfect triangle and lengthen each side the same amount it will become a bigger triangle. What you have is not a perfect triangle. Something will have to change , and I'm betting it will be the down tube. Even if your a really good welder , and you find tubing that will match what is on the frame originally ....same od and id it will be a bunch of work and you will end up with and less than perfect frame. Lots of frame builders use what someone will supply them with. It could be any size. There was no set standard on frame material. I have cut them apart and they would be some crazy size and thickness. Now if you have a lathe and can match the OD of the tubing and then turn down some 2'' inserts to go in each place you want to weld where they are pretty tight, you can do a pretty good job. It won't look as good as a piece of untouched tubing. Its really hard to sand the welds down to the perfect size. There is a fine line between sanding down flush with each side and removing too much weld and having your beauty crack on your first bunny hop. :wink:

PS in reality this site is about following your dream ....not the norm or what anybody says you can do or not do. If its metal and you want it to look different , it can be changed . If you hit a snag...change it. Sooner or later you will get it done.

 

[Fisch]

Its not really that you have to take my word for it. If you take a perfect triangle and lengthen each side the same amount it will become a bigger triangle. What you have is not a perfect triangle. Something will have to change , and I'm betting it will be the down tube. Even if your a really good welder , and you find tubing that will match what is on the frame originally ....same od and id it will be a bunch of work and you will end up with and less than perfect frame. Lots of frame builders use what someone will supply them with. It could be any size. There was no set standard on frame material. I have cut them apart and they would be some crazy size and thickness. Now if you have a lathe and can match the OD of the tubing and then turn down some 2'' inserts to go in each place you want to weld where they are pretty tight, you can do a pretty good job. It won't look as good as a piece of untouched tubing. Its really hard to sand the welds down to the perfect size. There is a fine line between sanding down flush with each side and removing too much weld and having your beauty crack on your first bunny hop. :wink:

PS in reality this site is about following your dream ....not the norm or what anybody says you can do or not do. If its metal and you want it to look different , it can be changed . If you hit a snag...change it. Sooner or later you will get it done.

Fantastic advise Uncle Stretch! Thanks for that. So even the seat tube may be different than the top bar and down tube tubing within the same bike?

I guess when I thought about making stays, notching tubing, head tubes, bottom brackets, and making lugs (if going that far)- adding 5 or 6 inserts to a moto-bike felt so much easier. And so much more affordable!

On the flip side, like you guys are saying, if I get a 26" frame with a bent top bar, and straight bars almost everywhere else, all I would have to do for the front half of the bike is remove the middlebar and fab up one to match the motobike. Then scratch build a swing arm OR snag one from a 26" suspension bike and add the shock mounts.

So to explore all the options before I chop a Moto, the new question would be, are there any new frames with a bent bar top? I guess I could chop a classic but....

 

[Uncle Stretch]

You will find the top tube and the down tube will probably be out of the same size tubing. The seat post tube will probably be a different size.
The answer to you problem is pick up a girls frame. They are cheap and everybody here chops and changes them. You could build you a top tube like the one on the bmx bike and have all the parts for a 26'' already there. Real cheap and you get the bike you want without destroying what you have.

 

[Fisch]

I think I answered my own question. Seems like the Worksman cruiser frame would be the closest without going antique. I wish the seat tube were just a little longer though. (Kicken myself because a frame just sold on ebay little bit ago for $60!)

The moto for reference.

The Nirve B2 was interesting too, but the top bar seems to hit the seat tube too low.

I am going to the monson swap meet this Sunday, I will keep my eyes out there for a mystery bent back frame.

Now I will start looking into swingarms.