Reeds

[Larry Mac]

When the reeds begin to go up and down faster (higher RPM) than the resonant frequency of the reed, then the reeds begin to form into an "S" shape and the tips begin to hit the reed block first (where and how depends upon the center of gravity of the reed petal and the pinch point). One could rubber coat the reed blocks to "soften" the surface. Stiffer reeds can help slow down the damage since there would be less time the reed spends beyond its resonant frequency.

-Paul Fuchslin

I have made reeds form motorcycles that turn a lot more rpm than we do. So I think some of the issues are what you say but I think the reed block design is also in the mix.
Larry Mac

[deverhart1]

I wonder why everyone is so concerned about the longevity of the fiber reeds. Most racers that are "in the hunt" so to speak work on their power head keeping it fresh more often than I do. My line of thinking is that a fiber reed faulting doesn't do any damage to the very valuable block and pistons which we have spent so much time and money on. The fiber reed is a wear out item as are the rings. The block and pistons are what I try to save and reuse. And on top of all that thinking I still try to go as fast as I can get the motor to go.
David Everhart S52

[trident]

Plastic Reeds in 4 cylinder Mercs

Very valid point. Yes, plastic reeds fail. They are a consumable part, and cheap insurance from causing expensive damage to other parts.

Then again, we don't want them to fail prematurely...

Geez Louise, we've been running plastic reeds, since what?, the early 1980's?
What's the mystery?

Biggest factors I've seen in failures, given the reeds we have and the reed block design we're stuck with is 1) too high reed stop setting, 2) too long a reed opening (same as too short a reed), and 3) bad drivers.

Someone else correctly made the point that reeds, under some conditions, can curve down at the tip or even 'snake'. Both situations allow the reed to come in tip first, having, in effect, shortened itself and sort of 'stub its toe in the hole'... yes they can do that.

Abusing the reeds by needless over revving, burping the throttle because it sounds neat (it doesn't) tears up reeds. Sharp edges on reed openings tears up reeds (radius the edges, plus it flows better). Insufficient reed overlap tears up reeds. Too high a setting on stops allows the crank to 'rotary lawnmower' the tips. Slightly too high, I suspect also contributes to that 'stubbing' the tip in the hole problem.

So, I think you'll find, as so often is the case, that there is no one Magic Answer; its really a combination of a bunch of little seemingly insignificant things that make a difference.

BTW, quick way to tell reeds are going away, is first, motor gets harder starting. Then, performance starts to fade... the good news is even when they fail, there is no other damage. A failed steel reed will trash a motor.
Do you want to replace reeds or pistons?

Hope this helps.

Jerry

[Eric Engler]

That does not explain why the exact same reed tip fraying occurs on motors where the tips are not in the same area as the crank.

If you "goose" your throttle like some drivers like to do after they cross the finish line the tip of the reed can bend down and snag the end of the cage opening and snap off. Used to happen in our 25s Then I learned and they would last several seasons.

[ram95]

You guys are on the right track - but just for the sake of the discussion...
Anna Nicole has the kinda tips I'm willing to guard. I don't know if they're phenolic or what. But, I'll bet that the tighter you turn em the more you might fray em. On Mercs with round reed cages, you need to look at the action of the crank cheek as it rotates clockwise. Look at the reed cage. Half of the reed tips, if they are allowed to open TOO far can stick right up into the path of the 'on-coming' crankcheek. And, the crankcheek smacks it head-on! Sooner or later the reed chips, or breaks. Maybe it even takes the reed stop with it - your engine becomes a hand grenade!! BUT, as the crankcheek passes the adjacent reed, there is no "head-on" collision. Instead, the crankcheek action is to smoothly contact the reed as it passes over it. How smoothly is questionable if your reed stops are set high, but it is not a "head-on" collision. But, this is no secret.. is it? Everybody knows this... right?
Setting the reed stops to the factory spec is smart, and when using the merc steel reeds, it will probably save your bacon. Also, centering the crank in the block, by properly arranging the end cap shims, will also served to prevent crank-to-reed or reed-stop contact.

Even so, racing engines need to be taken apart and inspected at least seasonally.........and NEW parts installed. Remember how you used to drag race you dads Oldsmobubble???? Yeah... and your Dad (or mom) traded the pelican in every year or two.. right? WELL Dude... guess what. THIS aint yo momma's Oldsmobile.... It's yo race motah!! INSPECT IT - or pay someone to do the job for you.

Alex, 12A