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uclj

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Reply with quote  #16 
There is a big difference between bending a coat hanger back and forth and a reed valve.  Totally different type of metal.  Consider  valve springs in a 4 stroke.  Those springs are compressed and released about 1/2" on each intake and exhaust stroke.  I have heard of valve springs getting weak, causing valve float and getting 'set' so that they do not exert enough pressure on their valve, but I have never heard of one actually breaking, although I am sure that they do.


olypopper

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Reply with quote  #17 
Quote:
Originally Posted by uclj
There is a big difference between bending a coat hanger back and forth and a reed valve.  Totally different type of metal.  Consider  valve springs in a 4 stroke.  Those springs are compressed and released about 1/2" on each intake and exhaust stroke.  I have heard of valve springs getting weak, causing valve float and getting 'set' so that they do not exert enough pressure on their valve, but I have never heard of one actually breaking, although I am sure that they do.




Here is a little more theory for you on why reeds break.  The reeds don't simply open and close on a flat plane.  As the crankshaft spins around the inside of the crankcase there is a large amount of directional turbulence that actually causes the individual reed petals to open and close from one side to the other.  This is why the tend to break off the corners early on and then larger parts will start to come off and cause potential catastrophic destruction of moving parts inside the crankcase and or cylinders themselves.  

Other causes of reed failure can also be attributed to fuel inadvertently entering the crankcase (only talking about DI 2 strokes here) and causing a backfiring event.  This can happen from flooding VSTs and also from lift pumps failing and leaking fuel into the crankcase through the pulse line.  

Factory Evinrude reeds are very tough and I normally don't recommend changing them until around the 500 hour mark OR if a customer insists on lugging his engine.  Lugging can also lead to early reed failure depending on some other factors.

It's more of a preventative measure in the end as when a composite reed breaks and the engine digests it no harm will be done.  If you break a factory BRP reed on a high time engine...........it's a roll of the dice in my experience.  _reed.jpg 
This was a 90 Etec that had been used in a village nearly it's entire life and lugged to death with poor quality fuel most of the time.  It only had 600 hours on it and when this entire reed petal failed it took out the piston AND cylinder as the reed shrapnel lodged itself between the piston skirt and cylinder wall becoming a saw.    

And you are correct, valve springs on 4 stroke engines can and do break.  My latest broken valve experience was on a brand new Honda 30.  Didn't run right during PDI and a broken spring was the result..........I've also seen it on modern Hemi engines from Chrysler and 5.4 liter Ford V8's.  


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olypopper

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Reply with quote  #18 
I will also add that part of the reason Evinrude reed petals are so durable compared to other brand 2 cycle engines is the curved design vs square reed.  The way reeds open and close from side to side applies significant forces to the corners of a square reed and the round style of the Evinrude reed tends to cope with this operation better over time.  
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Hydrasports2150

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Reply with quote  #19 


"Factory Evinrude reeds are very tough and I normally don't recommend changing them until around the 500 hours"

Oly: I am not a mechanic by trade but have been working on engines both two and four stroke for 30 years. While I have seen a fair share of broken reeds and even some broken springs, I have never considered this to be a regular maintenance item. My last engine was a 1995 200hp oceanrunner with over 2000 hrs on it and still had original reeds in it and It was still running great last year when I sold it to upgrade to a new Etec 225hp. If 500 hrs was the average life of a reed valve I would think Evinrude would call for their replacement as part of regular reccomended maintenance. I am a big fan of preventative maintenance but for the most part I would expect reeds to last for the lifetime of the engine unless it was used for heavy commercial or racing purposes. Not questioning your qualifications or experience, just offering my opinion on the subject.
boscoe

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Reply with quote  #20 

Quote:
Originally Posted by uclj
There is a big difference between bending a coat hanger back and forth and a reed valve.  Totally different type of metal.  Consider  valve springs in a 4 stroke.  Those springs are compressed and released about 1/2" on each intake and exhaust stroke.  I have heard of valve springs getting weak, causing valve float and getting 'set' so that they do not exert enough pressure on their valve, but I have never heard of one actually breaking, although I am sure that they do.



It was just an example. Metal fatigue is metal fatigue.

And yes, valve springs can and do break from fatigue.

olypopper

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Reply with quote  #21 
Quote:
Originally Posted by Hydrasports2150


"Factory Evinrude reeds are very tough and I normally don't recommend changing them until around the 500 hours"

Oly: I am not a mechanic by trade but have been working on engines both two and four stroke for 30 years. While I have seen a fair share of broken reeds and even some broken springs, I have never considered this to be a regular maintenance item. My last engine was a 1995 200hp oceanrunner with over 2000 hrs on it and still had original reeds in it and It was still running great last year when I sold it to upgrade to a new Etec 225hp. If 500 hrs was the average life of a reed valve I would think Evinrude would call for their replacement as part of regular reccomended maintenance. I am a big fan of preventative maintenance but for the most part I would expect reeds to last for the lifetime of the engine unless it was used for heavy commercial or racing purposes. Not questioning your qualifications or experience, just offering my opinion on the subject.


I understand what you are saying.  For me and more importantly, my customers, the recommendation is made as we often times boat several hundred miles from civilization here in Alaska and have such a failure in a remote area could cost tens of thousands of dollars to rectify.  Having a replacement powerhead flown in by bush plane and performing the work with only basic hand tools doesn't sound like fun.  

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Hydrasports2150

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Reply with quote  #22 
Quote:
Originally Posted by olypopper


I understand what you are saying.  For me and more importantly, my customers, the recommendation is made as we often times boat several hundred miles from civilization here in Alaska and have such a failure in a remote area could cost tens of thousands of dollars to rectify.  Having a replacement powerhead flown in by bush plane and performing the work with only basic hand tools doesn't sound like fun.  



Point taken, I guess individual circumstances dictate the course of action taken. While I run miles from shore as well there are very few times a break down could actually be a life threatening event or would cost tens of thousands of dollars to repair. For me It would be more of an inconvenience than a disaster. I guess if I had that much at stake, reed valves would be on my maintenance schedule as well. Of course with my luck I would end up replacing old reeds with a new defective set that would fail two hours after I changed them.
boscoe

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Reply with quote  #23 

Quote:
Originally Posted by olypopper


I understand what you are saying.  For me and more importantly, my customers, the recommendation is made as we often times boat several hundred miles from civilization here in Alaska and have such a failure in a remote area could cost tens of thousands of dollars to rectify.  Having a replacement powerhead flown in by bush plane and performing the work with only basic hand tools doesn't sound like fun.  


Good point. What is sufficient for the ordinary boater is not sufficient for an extraordinary boater. One size does not fit all.

Same thing with airplanes. A twin jet liner that flies over the US is held to one standard. The same airplane, when flown over water, far from shore, is held to a much more stringent standard. 

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