1974 Yamaha RD250 street rod build

[NobNoc]

Hello again! This is NobNoc Motorsports with our fifth build! We're trying to get this one done in the week lull while Old blue's frame is at the powdercoater. This is a 1974 Yamaha RD250 with 5xxx miles on it that we did a frame off restoration on a few months ago, and now it's back in again for some more custom work! Thanks to our friend Chance for poking around with his photography skills.

1. This is where we're starting out.

2. The bike gets half stripped (motor on, plugged up to prevent contamination) and the back end gets a nice diet...

3. Whilst work commences on some brackets for the swingarm.

4. Adding support gussets to the upper frame (where the seat will be)

5. Better view as we fabricate brackets for the shocks. Plan is to mount them under the seat, similar to our other build going on at the moment

6. We're not sure what this style is, so we're calling it a streetrod. But here it is in loose mockup.

7. Aaaand with some new paint, still in mockup.

Stay tuned!

 

[teazer]

Why take a really nice looking bike and make it unfunctional? The swingarm is not designed to work like that and is weak enough stock. Hopefully the owner will find the back end so bad that he doesn't ride it much because if he does he is in for a nasty surprise.

Have to call it like I see it. WTF were you thinking? Step away from the motorcycle before anyone gets hurt.

 

[NobNoc]

Why take a really nice looking bike and make it unfunctional? The swingarm is not designed to work like that and is weak enough stock. Hopefully the owner will find the back end so bad that he doesn't ride it much because if he does he is in for a nasty surprise.

Have to call it like I see it. WTF were you thinking? Step away from the motorcycle before anyone gets hurt.

We own it, it's an experiment, we like the look, and we want to see if it works. If it doesn't we can always build something different. That's half the fun of these bikes, getting an idea, giving it a shot, and working out the kinks. If something goes wrong, we can always bob it or build a new frame. This little guy is just a kickabout we wanted to have some fun with it and figured others may like to see it and learn whether it does/doesn't work and if it does what we did to make it work but it seems not. Geez.

 

[teazer]

Actually you make a really good point that style changes and color schemes and minor changes - go for it. Major changes to the basic design - not so much - unless you happen to be an engineer and understand the issues involved.

Second issue is that unless you declare the modifications to your insurer the bike cannot be insured. If you tell the insurer that the bike is stock, that's illegal on a major scale and if someone gets hurt on it you have no coverage for when they, or their loved ones, sue you.

Are you licensed engineers and motor mechanics? If not you might want to check the laws in the great state of Texas. I'm not an attorney, but I did stay at a Holiday Inn Express last night............................

 

[novacafe]

Is it just me or did anyone else notice the front end of the ford is dinged up pretty good...and there are small chalk marks on the fender? looks like hes up to ten hits id say ???

 

[NobNoc]

Is it just me or did anyone else notice the front end of the ford is dinged up pretty good...and there are small chalk marks on the fender? looks like hes up to ten hits id say ???

It's just dusty.

 

[teledan]

Yeah that geometry looks really scary man, especially with the back of the frame sitting right above the tire. You mention "if something goes wrong", be careful because that could mean you get injured or even die.

 

[Rich Ard]

You are building a folding bike

 

[bradj]

Wonder how many pounds of ass the rear tire will eat

 

[Rich Ard]

Jesus - you're doing the same with a DOHC CB750 as well?

Look around here for a bit - you'll note that this is not the standard reaction to a bike getting cut up. What you're doing is bad news: you make clear in your 750 thread that these bikes are being built to support a new shop - and getting somebody hurt or killed is a bad way to get press for a small biz...

 

[Floegstad]

IMO:Insane stupidity.
Its not all looks,be careful!

 

[DeanJ]

That poor little RD.... this makes me very sad.... :'(

 

[VonYinzer]

That's the problem... You're just "seeing if it works" instead of listening to people who KNOW for a fact that it won't. Nobody can or will fault you for trying to strive for something new and interesting. That's part of the fun. But, there's a limit. Especially when the plan is to put this bike out there for others to purchase.
The builder has to assume that the customer is brain dead stupid when selling them a bike, and therefore needs to ensure that everything on said bike is at minimum, safe. That poor RD is not safe.
I'm sure you're thinking "fuck these guys" about now. That's a really irresponsible stance to take, if you are. The members here are trying to help you become a better builder and doing so for nothing in return. Take heed in their warnings. They're based in decades of real world knowledge and experience.

That said...

What the fuck man? You took what was essentially the closest thing to a street legal factory race bike that the average guy could afford and turned it into a death trap for the sake of "experimenting". Which brings me to my next point. When undertaking an "experiment", you need to look to past builders and the science behind you. Otherwise you're just pissing in the wind. There's a difference between finding a better way and just running areound with a hard on trying to find a wet spot. Listen to those guys up there. They're giving you the advice in a few sentences that most folks would need a lifetime to accumulate.

Good luck bud, and I hope to see the bike get the work it deserves and the engineering it needs.

 

[clem]

That's a good two part post there Von. Why try and experiment with this by doing? You can easily find the proper mathematical calculations that will prove the points spoken here. It's simple leverage dude. Just to take a swag at it, I'd say that the shocks will move slightly within the radius of the swingarm before actually being compressed but that's a simpletons guess. A crusted up, non-titled rat frame would have been better to "experiment" on than this bike. Like said above, there are some here that really know there stuff(like the guy with the first reply) that are more than willing to help.

 

[NobNoc]

Nah, don't mean to come across as not listening or thinking I know better, we signed up here to learn and hear from the community and I'm very glad we posted, looking back, not sure how we thought that would end up working, I guess we never thought the swingarm on the bikes would be as weak as they are, all of our other builds have been bobbers so we've never worked much with them, or suspension on the whole, haha. The original plan was to just build a new frame and bob this one, so this frame isn't really worth that much to us in the long run, and we can still always bob it and we were having some fun with the old frame before we bobbed it. Either way, feeling stupid. But I am glad the general opinion is that the bike started off looking great, it was my second frame off awhile back that I brought back from a basket case.

Anyway, here's an update on the build. Still playing around with the monoshock idea but doing something a little more conventional.

Donor swingarm and 1/4" thick frame bracing plate tacked on, with a shock we had laying around for reference. Our idea is to keep the monoshock linkage as shown and replace it with a stiff shock, connected to the frame via brackets welded to the mounting plate holding the shock at a 45 degree or so angle, not as shallow of an angle as it's pictured, and some gusseting to the upper frame rails and in between the brackets for strength. Other idea is to re-use the monoshock linkage and a vertical monoshock like the bike the swingarm came off of. I like the first way, and we've found a supplier with shocks from 500-800lbs that will fit, and the frame brace is already on (we are going to use it to either hold the battery or a flask of oil, so we needed it either way). I've seen the second way tauted though, so I'd love to hear the community's opinion. The swing arm is from an XT660R, which outweighs the RD250 by about 50lbs, so it should be strong enough, eh? Stretches it by a few inches, which is nice, too. Chain fits no problem and the swing arm has a chain tensioner built in, but it's off in the pictures.

As always, comments welcome

 

[bradj]

Ill give you 50 bucks for the head tube and title. i think you should take it

 

[Rich Ard]

I think what you have there will shear the shock mounts off the swingarm pretty readily.

Look at where stress will be transferred to the frame as the suspension moves around.

 

[NobNoc]

I think what you have there will shear the shock mounts off the swingarm pretty readily.

Look at where stress will be transferred to the frame as the suspension moves around.

Here is a better picture of the swing arm shock mounts...

We were thinking they seem decently beefy and the whole bike would struggle to weigh 350lbs wet, and for the frame mount we are planning on building brackets to hold a shorter shock at a more closer to vertical angle and gusseting to support the brackets and make sure the stress is distributed to the frame evenly... We were eyeballing this bike:

Still no? And thanks for your input!

 

[bradj]

That dirt bike swingarm is ten foot too long and acting like a big lever. One 40 year old shock that was designed to work in pairs, when nixon was in office is not gonna work. your putting that shock through twice the abuse to do twice the work. 50 bucks my offer stands

 

[bradj]

A few rds have been mono shocked on this site i dug a picture of one up for you to see the differences in building a bike and pulling random shit outta a pile of dirt bikes and bolting it to your frame