Case Reed 125 Hodaka Project

[viclioce]

Third. Why does one create such a large air box, to put such a small filter in it? Just curious. I was expecting something more on the scale of the box itself. Is all that extra just for the splash guard protection? Guess I just don’t understand, but would appreciate enlightenment... Victor

[thirdstone]

Hi Victor I’d love to tell you that I calculated the amount of cubic air required for 49 HP at 20000 RPM and that the cubic volume of the airbox was accurately calculated to supply that air but alas no such thinking. The Airbox is actually not that big but I think it’s big enough not to be a restriction , Crikey I’ve run a pod hanging out in the breeze and it works fine , it does get dirty quickly and forget about riding around water. In truth the filter in the pictures is the one I had hanging from the back of the carby uncovered, it wasn’t a hinderance on performance that I could tell. I do have a larger POD But it’s a bit squashed up in there.
The goal of this airbox was give my filter some protection from the elements. The only issue I had was what size of entry would I need. I put a round hole on the right hand side to give a bit more flow, but I probably didn’t need to.

[thirdstone]

Pipe all tacked up , now back to the real welder to TIG up. Starting to think I’ve gone a bit big on Volume but then I see pipes like this

[thirdstone]

Ready for the welder

[ossa95d]

I vaguely remember reading (probably 50 years ago) that the airbox should have enough clearance and volume so as to allow unrestricted laminar flow to the whole filter at full throttle, as if there was no airbox.

[viclioce]

Thanks Third! I was just curious. We don’t have a lot of water to ride thru here. Closest water we have to ride near, is the Rio Grande! Definitely too deep for a water crossing!!! There are a few mountain streams, But, except with the Early Spring melt off, most are not more than an inch or two deep, except in small pockets where there are little pools. So water protection never occurred to me in the high mountain desert! Thx for the explanation! Victor

[thirdstone]

I now have the pipe tacked up (except the stinger) and mounted on the bike. I decided to raise the tank a few mm to give more clearance than it had , it was clear but maybe vibrations would have made them contact. The seat is now ready for foam. On the rear of the seat base I made a grab handle cut out because previously I had cut off the loop and welded it back internally, purely for looks.

[Bullfrog]

Got a photo of the seat grab cut-out feature?

Ed

[thirdstone]

Here you go Ed . It’s just somewhere to grab when you put the bike on a stand. The seat bolts take the weight. Still in production.

[Bullfrog]

All right! It is good to have a place to grab. You never know when you might have to push the bike off a muddy track after demonstrating how to do a feets-up J-turn! (Don't ask how I know. )
Ed

[thirdstone]

My Shocks are 13.5 in long , the fast boys use 14.25 inch shocks so I’ve found. I’m too tight to buy $600 Shocks so I’m looking at relocation of the ones I have to give a bit more travel and more importantly better balance front to back. Move the bottom forward or lay the top Down ?

[ossa95d]

Laying the top down mechanically provides a rising rate for the springs as the shocks compress due to the decreased mechanical advantage applied by the swing arm. This is caused by the shocks becoming more perpendicular to the swing arm as they compress due to the geometry of the configuration. This allows the suspension to be more supple and reactive to small bumps while still being able to absorb large jump landings without bottoming. Works really well!

[matt glascock]

Just wondering here, Pop. If you lay the shocks down, I would think that would change the vector of force acting on the swinging arm pivot point. In other words, as the angle between the shock and the arm becomes more acute under compression, the force on the pivot point would be more aft than it would with a more upright shock configuration. Does this suggest the need for some additional bracing of the swinging arm pivot point? The forces acting on it are different than those of its original design.

[thirdstone]

After many changes of heart I went with lay down the top. My main reason was that it was easier to do from a fabrication point of view but also I think the result is structurally stronger. It’s easy to reverse should I A. Be gifted some longer shocks or B. have chain issues due to the changed angle of the swingarm, I don’t have a chain tensioner fitted (yet).
There was also memories of bike from the 70’s with upright shocks that handled like pogo sticks. We are not talking a huge change here , it’s just 1.75 inch . This is enough to make a difference. Staticly the once over firm shocks are a bit more supple requiring spring tension adjustment of two notches.
Too early to see if the chain requires a tensioner.

[Bullfrog]

I think you selected the correct method Kev.

Ed

[ossa95d]

Note that on this particular frame the swing arm has already been extended between the shock mounts and the wheel. Also the top shock mount has already been modified to accept a more forward location than stock. Both of these modifications add a slight amount of travel to the rear wheel and increase the force applied to the shock absorbers and springs. Along with the longer travel comes a slightly softer ride. The vector forces on both the swing arm pivot and the swing arm itself have been increased as well as to the frame at the top mount. As Thirdstone has suggested, moving the shocks forward on the swingarm increases the strain on the swing arm itself exponentially. Also because of the lack of progression in the geometry, it tends to cause harshness in the initial part of the stroke of the shock itself, and at the same time causes the suspension to blow through the rest of its travel too quickly on big hits. Hence the "pogo effect." That's why in the late 70s all the manufacturers gravitated toward a layed down configuration prior to adopting a linkage system that provided built in progressivity. Joe Bolger invented a linkage system for twin shocks in 1976 that was later copied by Suzuki in their single shock application. I could go on but this is too much history already I'm sure.

[ossa95d]

I know it's not a Hodaka but Here's my modified CR125 back in the day with layed down piggyback Marzocchi's. Note the hot wheels track fork guards!

[thirdstone]

Nice Picture Pop

I had the hot wheels set as well although mine was in my bedroom not on my bike.

Any welders on this forum now is the time to look away.

This is what I came up with.

[thirdstone]

Side shot

[thirdstone]

A small but significant change in the seat pan. I rounded the rear end , widened the front and increased the front side section to align with the side plates and tank better.

Merry Christmas everyone

[thirdstone]

A few more tweaks done to the rear mud guard mount , much better balance .

[Dale]

Already looks fast just sitting there! Striking for sure.

[thirdstone]

During the Shocks fitting I noticed that the stock wombat swingarm flex is quite a lot .
I did a bit of stiffening .
What are people doing to stop the chain rubbing the swingarm pivot shroud ?

[thirdstone]

For the swingarm arm Schroud I came up with this bit of chopping board shaped with a heat gun. I’m sure the wife won’t miss it.

[ossa95d]

That should work nicely!