Crofter
Addicted to ArboristSite
I wonder how many times they had to change the engine on those reeds during their 3 months continuous operation at 20,000 plus rpm?
Reed Valves
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amissionaryman
ArboristSite Lurker
Crofter,
No engine used. The testing equipmet is kind of interesting. Used compressed air as a source of power to creat pulses per second. I am not saying that reeds are the answer. Just that the technology is constantly chainging and that to count them out as the next good inovation for chainsaw use would be a mistake. And to answer Timberwolf's question about what happens when a polly or fiber reed goes through an engine. Not much. In the old days of steel reeds it would trash the cylinder and piston most of the time. I can only remember one case of having to replace a cylinder and piston in an engine using polly or fiber reeds.
God Bless,
Brent J Cox
No engine used. The testing equipmet is kind of interesting. Used compressed air as a source of power to creat pulses per second. I am not saying that reeds are the answer. Just that the technology is constantly chainging and that to count them out as the next good inovation for chainsaw use would be a mistake. And to answer Timberwolf's question about what happens when a polly or fiber reed goes through an engine. Not much. In the old days of steel reeds it would trash the cylinder and piston most of the time. I can only remember one case of having to replace a cylinder and piston in an engine using polly or fiber reeds.
God Bless,
Brent J Cox
timberwolf
Addicted to ArboristSite
It would not be the next good innovation for chainsaws, an innovation by definition is "The act of introducing something new". Reeds have been done before, the saw industry moved away from the idea, why?
Sure maybe with new reed products it could be done again, but does the cost and associated service problems justify such a nostalgia trip?
Sounds by your post you have great experience with broken reeds, could they be subject to frequent failure? Clever thing about transfer ported saws with timing done by the ports, the ports don't fail.
Sure maybe with new reed products it could be done again, but does the cost and associated service problems justify such a nostalgia trip?
Sounds by your post you have great experience with broken reeds, could they be subject to frequent failure? Clever thing about transfer ported saws with timing done by the ports, the ports don't fail.
Timberwolf, Yes, that was tried and it did work , but thats not what Deans claiming.
Piston ported engines work fine with pipes. Instead of the read valve controlling the intake the psiton skirt does. Both types close of the intake, but work in slightly differant ways. The read valvesallow for more midrange, and low end power becase they reduce spitback out the exhaust and rough running at low speed due to excessing intake timing. The actually make slightly less power than a piston port though as reed are another restriction to air flow.This effect is slight.
Timberwolf... just fyi
A dirt bike being ridden around a field by a novice doesn't spend much time at max rpm, but small bore one being ridden by a pro on a sand track or desert race does. They also last an amazingly long time doing so. Also interesting, ultralight aircraft (PPG's to be specific) folks are starting to use 100cc dirt bike engines for power. They set them to run at 13k rpm full throttle for hours on end with no ill effects, especially not from reeds. Reeds have very very little inertia and are capable of very high sustained rpm's for long periods of time. In general reeds will last at least as long as the piston.
BWalker - interesting info - I've never messed with piston port engines much. Just some older ski's (which did all have expansion chambers, but still made very little hp for their displacement). I was under the impression that piston port engines generally require much more mild port timeing than a reed valve engine which generall more than off-sets the potential gain in power due to better flow from not having a reed valve in the way. Again, I'm no expert just trying to understand.
Just for those who haven't seen a reed valve recently. Here's a pic of a popular one.
A dirt bike being ridden around a field by a novice doesn't spend much time at max rpm, but small bore one being ridden by a pro on a sand track or desert race does. They also last an amazingly long time doing so. Also interesting, ultralight aircraft (PPG's to be specific) folks are starting to use 100cc dirt bike engines for power. They set them to run at 13k rpm full throttle for hours on end with no ill effects, especially not from reeds. Reeds have very very little inertia and are capable of very high sustained rpm's for long periods of time. In general reeds will last at least as long as the piston.
BWalker - interesting info - I've never messed with piston port engines much. Just some older ski's (which did all have expansion chambers, but still made very little hp for their displacement). I was under the impression that piston port engines generally require much more mild port timeing than a reed valve engine which generall more than off-sets the potential gain in power due to better flow from not having a reed valve in the way. Again, I'm no expert just trying to understand.
Just for those who haven't seen a reed valve recently. Here's a pic of a popular one.
timberwolf
Addicted to ArboristSite
Right, but the pro rider taking the bike to the line will be doing reeds or a rebuild every how many races?
From what I have found the life expectancy of read valves is in the range of 100,000,000 cycles, sound like a lot. But at 20k that works out to about 80 hours or about as long a 100$ green Poulan. The reeds alone are worth more than the saw.
From what I have found the life expectancy of read valves is in the range of 100,000,000 cycles, sound like a lot. But at 20k that works out to about 80 hours or about as long a 100$ green Poulan. The reeds alone are worth more than the saw.
Chopwood
ArboristSite Guru
I've got a 3120 that does quite well with a reed set on it, hopefully it will do even better after a visit to uncle Ed.
i have had reeds go 5000 miles on a snowmobile.
I wrenched for a pro privateer racer for a little bit. Engine re-builds in the 250cc class were usualy every 3-4 races, but the parts looked perfect when they came out. Racing advanced amature stuff, I usually go two full years on a 250cc motor and at least one on a 125cc motor. Even then, there is negligible wear. On small bore practice bikes I've logged around 1000 hours before a re-build was actually needed based on piston/ring wear. These wear figures are for 27hp 100cc engines, 35hp 125cc engines and 50hp 250cc engines. The 250's turn less rpm (max power between 8 and 9k) and need maintaince somewhat less frequently.
FYI a new set of carbon fiber reeds for my CR250R is ~$40 and takes 10 minutes to install. Doing an entire top end takes less than an hour and costs $100.
Double FYI - two stroke single cylinder race bike's are not rpm limited, i.e. no rev limiter all that keeps them from reving higher is simply how much air they can move. In the course of a race they are frequently reved much higher than the rpm at which max hp is acheived for various reasons, yet I've never seen an rpm related vailure (now when a long time two stroke racer gets on a fancy new thumper watch out).
FYI a new set of carbon fiber reeds for my CR250R is ~$40 and takes 10 minutes to install. Doing an entire top end takes less than an hour and costs $100.
Double FYI - two stroke single cylinder race bike's are not rpm limited, i.e. no rev limiter all that keeps them from reving higher is simply how much air they can move. In the course of a race they are frequently reved much higher than the rpm at which max hp is acheived for various reasons, yet I've never seen an rpm related vailure (now when a long time two stroke racer gets on a fancy new thumper watch out).
The average pro racer in the 250 class is only at full throttle about 30% of the time. This figure was related to me by a man the wrenched for several of the low level factory teems(Noleen, Plano Honda, ETC).
I would never go over a year on a 250cc bike used for MX. Its not the wear that will bite you it the service limit of the parts.
I would never go over a year on a 250cc bike used for MX. Its not the wear that will bite you it the service limit of the parts.
timberwolf
Addicted to ArboristSite
good point ben, the sevice limit of the parts, fine if your just going out riding to have ho humm reeds, but if you wanted to win races you would need to replace them more often. Your snowmobile example supports exactly what I was saying, 5000 miles, say 50 mph (I am sure you would be no granny on the gas) =100 hours. The RPM for the snowmobile would be half a saw so it's like 50 hours for the saw in terms of how many times the reeds would cycle.
bikepilot sure the reeds for 10k rpm or less CR 250 can be had for 40$, higher end reeds or reeds deigned to do twice that rpm are a bit more.
What, do you guys think that the all the mechanical engineers, engine builders, and marketing specialists working for Stihl, Husky, Dolimar have never asked the question, could we put some new fangled carbon reads from a motorbike in the saws to make more HP. Sure they have, but obviously up to now anyway, the idea has been nothing more than that!
Why, who knows, there can be no argument, reeds are moving parts that do fail. they would add to the cost, 40-50$ even if it was possible would still be 10% on the cost of a saw, space and weight, thought this could be argued if the saw produced more hp with reeds the displacement and weight could be reduced to give the same output, though I don't know how it would market, I think a lot of the market share talks CCs not HP.
bikepilot sure the reeds for 10k rpm or less CR 250 can be had for 40$, higher end reeds or reeds deigned to do twice that rpm are a bit more.
What, do you guys think that the all the mechanical engineers, engine builders, and marketing specialists working for Stihl, Husky, Dolimar have never asked the question, could we put some new fangled carbon reads from a motorbike in the saws to make more HP. Sure they have, but obviously up to now anyway, the idea has been nothing more than that!
Why, who knows, there can be no argument, reeds are moving parts that do fail. they would add to the cost, 40-50$ even if it was possible would still be 10% on the cost of a saw, space and weight, thought this could be argued if the saw produced more hp with reeds the displacement and weight could be reduced to give the same output, though I don't know how it would market, I think a lot of the market share talks CCs not HP.
bwalker said:
That's racing supercross, Dez or an open sandy MX track is a different story as is small bore class racing (i.e. 125cc 2-T or 250cc 4-T)
After a solid year of riding/racing none of the top end parts on any of my 250cc bikes have been anywhere near the service limit. I do pull them down and inspect from time to time, even ring end gap doesn't change measureably in a year. Admitedly, a pro woudn't go a year on a top end, it just doesn't make sense at that level. But many amatures will, I race B/A class and this works fine for me.
Timberwolf, the reeds on smaller higher rpm engines (i.e. 85, 100 or 125cc class engines) are no more expensive, usually less. As for higher end reeds, I don't know of any higher end reeds than good boysen carbon fiber units.
Its entirely possible that a saw might benifit from a motorcycle like reed/cylinder/port design, but that the initial R&D costs + the increased production costs make it uneconomical even though such a design may make a superior saw.
bugfart
ArboristSite Operative
A set of aluminum reed valves in an older saw will outlast us all. You can make new ones pretty easilly I bet. Never even heard of one going bad before this discussion.
Crap lodged inside, yes. Reed failure? Total ingorance to it.
Thanks for getting me all freaking paranoid.
Crap lodged inside, yes. Reed failure? Total ingorance to it.
Thanks for getting me all freaking paranoid.
Mange
Addicted to ArboristSite
I have at least 10 saws here that need new reed valves. 4 of them HVA'sbugfart said:A set of aluminum reed valves in an older saw will outlast us all. You can make new ones pretty easilly I bet. Never even heard of one going bad before this discussion.
Crap lodged inside, yes. Reed failure? Total ingorance to it.
Thanks for getting me all freaking paranoid.
The service limit for a 250 if memory serves me correct is about 25 hours. If you road it for a year you surley exceded the service limit.
And for FWIW the comment I made on pros, 30%. The guy was tlaking about national MX, not arena cross or supercross. The desert of course would be differant.
Crofter
Addicted to ArboristSite
I am surely not up to date on reed valves but they used to be mostly steel. Aluminum is not often used as a high cycle spring material because of the much lower fatigue cycles to failure as compared to steel. Have they come up with a new alloy?
Yes, the service manual for a 250cc bike usually recomends either inspecting the top end or replacing the ring and piston at 25 hours. I don't know anyone (outside of factory teams) that actually replace the piston every 25 hours. I've talked to a few former factory race mechanics (tom morgan, eric gorr...) and a respected local engine builder. They all recomend inspection at the recomend intervals at least untill you get comfortable with the engine, but said there is no reason to replace a piston that is well within the clearance spec. Dito for the rings. At 25 hours there isn't even a measureable amount of change in ring end gap, much less piston to cylinder clearance. I guess what I am saying is that the specs for replacement intevals are very much suspect and not a good indication of actual replacement requirems due to wear or fatigue. You'd really be amazed how long even a small bore modern 2-stroke bike engine will last if moderately well maintained.
Here's a fun (and true story). Years ago I bought a KX100 (100cc liqued cooled, 2-stroke mx bike) in moderate condition at best. It obviously had high hours and the previous owner had never done a top end. I rode it for 2 seasons without touching the inside of the motor. The bike was then handed down to my sister (who is an experenced racer and just as hard on a bike as most guys) who rode it for a full season. Then my family took a month-long trip out west for some dez and dune riding. We spent 3 weeks in the dunes and rode at least 5 hours a day (really closer to 8 I belive). Now a 100cc bike with an experenced rider in sand dunes spends the vast majority of its time at high rpm and full throttle and this is at a minimum 105 hours of hard use preceeded by at least 3 seasons of hard east coast use (much less hard than the dunes though). Once we got home from the dunes I tore the top end down on the little KX just because it had been so many hours. The piston was a the loose end of the spec, but still in spec, dito for the rings. We went with a bored and ported cylinder/piston at that time as she needed a bit more for the upcomming racing season (she ended up winning the championship on that 107.5cc engine).
I haven't seen a metal reed on anything other than an early 1980's yamaha YZ80 and IIRC it was aluminum. I replaced it with a two-stage fiberglass reed which improved the throttle response a bit.
Here's a fun (and true story). Years ago I bought a KX100 (100cc liqued cooled, 2-stroke mx bike) in moderate condition at best. It obviously had high hours and the previous owner had never done a top end. I rode it for 2 seasons without touching the inside of the motor. The bike was then handed down to my sister (who is an experenced racer and just as hard on a bike as most guys) who rode it for a full season. Then my family took a month-long trip out west for some dez and dune riding. We spent 3 weeks in the dunes and rode at least 5 hours a day (really closer to 8 I belive). Now a 100cc bike with an experenced rider in sand dunes spends the vast majority of its time at high rpm and full throttle and this is at a minimum 105 hours of hard use preceeded by at least 3 seasons of hard east coast use (much less hard than the dunes though). Once we got home from the dunes I tore the top end down on the little KX just because it had been so many hours. The piston was a the loose end of the spec, but still in spec, dito for the rings. We went with a bored and ported cylinder/piston at that time as she needed a bit more for the upcomming racing season (she ended up winning the championship on that 107.5cc engine).
I haven't seen a metal reed on anything other than an early 1980's yamaha YZ80 and IIRC it was aluminum. I replaced it with a two-stage fiberglass reed which improved the throttle response a bit.
Wanna know how many hours are on my 02 cr 500 AF??
how many?
FYI watch the CR5 motors, mine (had an 87' 90' and 92') always seamed to eat top ends more quickly than even my 125's. I don't know if its becuase of the iron cylinder or the somewhat questionable factory squish dimensions but I never got great life out of them, especially considering its such a large, low rpm, low hp (for its displacement) motor. I owned a 93' KX250 at the same time as the 90' CR5 and with both of them stock, the piston to cylinder clearance on the CR5 would go in less hours than the KX. I never messed with modding the CR5 motor but did port the KX motor which didn't have any affect on top end life that I could tell.
Here's a pic of the 93' KX that lasted so well.
How about some pics of the CR5AF? Is it a Service Honda unit or did you build it yourself?
FYI watch the CR5 motors, mine (had an 87' 90' and 92') always seamed to eat top ends more quickly than even my 125's. I don't know if its becuase of the iron cylinder or the somewhat questionable factory squish dimensions but I never got great life out of them, especially considering its such a large, low rpm, low hp (for its displacement) motor. I owned a 93' KX250 at the same time as the 90' CR5 and with both of them stock, the piston to cylinder clearance on the CR5 would go in less hours than the KX. I never messed with modding the CR5 motor but did port the KX motor which didn't have any affect on top end life that I could tell.
Here's a pic of the 93' KX that lasted so well.
How about some pics of the CR5AF? Is it a Service Honda unit or did you build it yourself?
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