O'hara Reed Cage Modification

[Dennis Detweiler]

What is the process used in reshaping the thingamajiggers that hold the reeds in place? Is there a certain curvature tool/diameter that is used to get the proper contour? Do you heat the thingamajigger?
Thanks

[Jeff Campbell]

... I did a similar reed guard modification back in the 70's, I think you can do this by hand with the help of things like a big vice and a little patience. The idea is to get a uniform arch/radius, where the reed guard still fits in the stock manifold. I would arch mine so I had to push the guards in a tad to get the reed block assemby into the manifold. Since the reed guards have to fit in the manifold, you are somewhat limited on how the guards can be reformed.

Jeff

[jmendoza]

I beleive the poop you are looking for is on John T's site. Basically, you bend the reed stoppers so that they only contact the reed near it's base, by the screws holding the reed on. The idea is to minimize the amount of stopper that is in contact with the reed when it is closed.

[John Tzortzoudakis]

Dennis, The reed block modification is in my website. No real explanation on how to bend a piece of steel. But any simple tool like a vise and hammer or pliers or metal shaping tools should do the trick. Visit your local library for books on metal fabrication to learn how to shape metal or a autobody book. Let us know how it turns out. See the link below to get to the website. Sorry about the funny domain name (actually it's just the IP address) but for now thats all I can do. Good Luck.

[Dennis Detweiler]

Thanks John,
I read through the website article, but didn't see a specific method. I thought there may be a tried and true method to get a consistent shape. I have several large wrench sockets. I might try one and see if the curvature and manifold fit matches up. If I find a match, I'll post it. I'm a body shop graduate and have experience working with sheet metal and frame straightening.
I'm always interested in engine function and experimentation with performance options or alternatives.
Thanks for everyone's input.

[steveohara]

Back in the 70s I had access to different shaped mandrels and made many different arcs and tested them all. The process typically involved taking the original part and flattening it in a mill vise first and then re-shaping around a large radius form. The effect you want to achieve is to cause the guard to separate from the reed approximately .1" from the center of the screw holes and draw away from the reed in a slow continuous arc. The correct radius is around 6" but it is not important for the entire guard to have that shape. Only the section starting from the center of the screw hole and running about half the length of the guard makes a difference. The reeds only open about 2mm at the tip so the proximity of the guards to the manifold is of no consequence as long as they are don't limit the opening of the reeds to the 2mm range.
The modification allows the reeds to respond to much lower pressure delta between the case and throttle body so it will begin moving air into the case sooner and the reeds will remain open longer as the rate of expansion of the case slows when the piston nears TDC. The result is a larger charge in the case that leads to more HP.
A 5 gallon fuel can is pretty close to 12" in diameter so it has a 6" radius.... if you can make your reed guards fit uniformly to the side of a 5 gallon fuel can you are in the ballpark and final adjustment can be done with a gentle tweak once the guard is mounted and the screws are tight.
Good Luck!
Steve O'Hara

[Dennis Detweiler]

That's what I needed. Thanks Steve.

[jmendoza]

I know this is crude, some may chastize me, but hey, it has worked for me and is very simple:

Take the reed stop, and note the area near the screw holes. Clamp it in a vise so that the jaws cover the screw holes. Now bend the reed stop a bit, and try test fitting it with the reeds and cage. This does not change the radius, but it does move the base of the stop away from the base of the reeds, allowing the reed to uncover more of the hole in the cage.

Alternatively, you can just bend the reed stops open a bit with the whole cage assembled, this is what we do on Yamaha RD 250/350/400 twins, we bend open the reed stops 10mm, and it lets the reeds uncover more of the openings as the reed stop now does not pin the reed at it's base as much as before.

I know this is crude, but it does work, and I have never seen a steel reed damaged as a result of doing this.

I have also seen the stops removed altogether, but sometimes the result is chipped tips of glass/phenolic/composite reeds.

I have also seen the reed stops spaced off the reeds with a .010"- .025" thick shim right under where the screws go. This keeps the stop from touching the reed until it opens. I don't know if this is such a good idea though, as the base of the reed may be more stressed as a result of no support....experts can add more knowledge here........

[John Tzortzoudakis]

Steve, There you go again, Kicking in to help at the right time. You CAN be sure I'll add bending tips to your section in the website.
Every time I saw Steve in the pits in the last Adams event he was drilling or wrenching on someone else's kart to help him get going. He is an 8 time National Champion...
Good going Steve...your a great asset to us.