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  1. #126
    RysiuM's Avatar
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    RE: Poulan 25 from FL trimmer


    ORIGINAL: diablo_r
    Looks like this one will be glow only until I get another engine sorted!
    I don't remember, did yo try running glow on it? I mean 50/50 gas/methanol mix on glow plug. You may get even better result than spark plug. At least mine did.

    RysiuM
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  2. #127
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    RE: Poulan 25 from FL trimmer

    I tried glow very quickly, using an OS type F plug (the 4 stroke one) and 70% petrol, 5% oil, 3% nitro and 22% methanol with the glow powered all the time, it ran okay but I did not have enough time to set it up properly. I also know the fuel pressure is set too high on the carb but again time has stopped me playign with it. Its 25psi, it should be 15 and ideally 11. Bit of spring and needle arm fiddling required, that should improve the bottom end mixture too.

    Cheers,
    Rich

  3. #128
    diablo_r's Avatar
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    RE: Poulan 25 from FL trimmer

    I took the engine out of the plane tonight and stripped it totally. its going glow only so I'm going to trim absolutely eveything off that is not required, I've made a new inlet manifold to tip the carb so no bellcranks are required, and I've marked the piston skirt to cut it under the gudgeon pin as (as was mentioned earlier by Rysium I think) the crank web and the back plate block the transfers at BDC. I'm aiming for about 1300g all up including exhaust, prop adaptor, glow plug and adaptor, carb and trumpet. And 9500 on the APC 16x8. Hopefully I'll get all the machining done tomorrow and can test it over the weekend.

    Cheers,
    Rich

  4. #129
    RysiuM's Avatar
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    RE: Poulan 25 from FL trimmer


    ORIGINAL: diablo_r
    I'm aiming for about 1300g all up including exhaust, prop adaptor, glow plug and adaptor, carb and trumpet. And 9500 on the APC 16x8. Hopefully I'll get all the machining done tomorrow and can test it over the weekend.
    I'm still gathering the currage to put a dremel inside the cylinder I have measured all angles, and dimmensions and all is like you said. The most critical part is transfer ports size and timing. Together with that the exhaust port timing should be extended (this is easy job).

    The engine is already cut for either glow or electronic ignition. I made a prop hub the way I can easy put 2 magnets here. I would use Vlach ignition that requires 2 magnets, but is cheapper than CH. Vlach II has also nice feature that stops advancing timing when battery voltage is low. This way the engine still runs about 4000-5000 rpm for safe landing but you know that something is going on. Also with lower rpm ignition takes less current so the baterry even at low level last long enough for stress-free landing.

    But before I start with that I need to stop the shaking of my hands every time I think about dremelling

    RysiuM

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  5. #130
    diablo_r's Avatar
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    RE: Poulan 25 from FL trimmer

    just make sure you tape up the bore before dremelling, if in doubt do a bit of practise in an old engine or bit of pipe or something, or have a drink first to stop the shakes

    do you have a web link or something for the vlach ign, it sounds interesting as I wanted to try electronic but its $200 over here, thats 10 engines!!

    Cheers,
    Rich

  6. #131
    RysiuM's Avatar
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    RE: Poulan 25 from FL trimmer


    ORIGINAL: diablo_r
    do you have a web link or something for the vlach ign, it sounds interesting as I wanted to try electronic but its $200 over here, thats 10 engines!!
    Pe from MVVS.NL has it in stock for 123.81 Euro (including VAT - UK is part of EU, so you pay it).

    You may also try Jenny and Paul from JustEngines - thy are in UK and very nice and friendly to deal with.

    One more thing about Vlach is safety shut-off. If you leave the ignition powered for more than 90 seconds without moving the prop it will shut itself off. It's just safer in the shop. I have always buzzer in the circuit, so when ignition is hot, I can hear it well.

    RysiuM
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  7. #132
    diablo_r's Avatar
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    RE: Poulan 25 from FL trimmer

    cheers, I bought my last saito and all my engine bits from just engines but could ony find the MVVS with the ign, not the ign unit by itself. I mght call them tomorrow!

    Rich

  8. #133
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    RE: Poulan 25 from FL trimmer


    ORIGINAL: diablo_r
    could ony find the MVVS with the ign, not the ign unit by itself. I mght call them tomorrow!
    They say, they do parts too. Let me know what you find. I'm also looking for spare Vlach ign (but not decided to spend over 100 bucks yet). I got my MVVS gas from justengines - was much cheapper and faster than trying to buy it here. And very friendly to talk to.

    RysiuM
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  9. #134
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    RE: Poulan 25 from FL trimmer

    well today I got angry with power tools[>:]

    Seeing as the original coil mount was now no good I stripped the engine to remove all metal that is not needed. This included the lower crankcase which every bit possible was cut/powerfiled off, and the cylinder which I mounted in the lathe and turned all the draft off the top 5 fins with a rounded off parting tool. I left nothing it did not need! I also cut the transfer passages in the piston under the gudgeon pin area. I also wanted the weight and complexity of the throttle bellcrank off so I made a new inlet manifold to turn the carb about 50 degrees round to allow direct connection of the throttle snake to the throttle am on the carb.

    Total weight of the new glow or elec ign version, including exhuast, prop adaptor, carb, bellmouth, mount and all bolts is 1220 grams. Add 166 grams for 2 3000 NiMh cells for onboard glow and its pretty light!

    I've put the pics on so you can see, I'll test it tomorrow hopefully. I need to sort out the carb pressures too but need to make a test gauge first!

    Cheers,
    Rich
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  10. #135
    RysiuM's Avatar
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    RE: Poulan 25 from FL trimmer


    ORIGINAL: diablo_r
    Seeing as the original coil mount was now no good I stripped the engine to remove all metal that is not needed.
    One thing I see you can cut off is the original fuel tank mount. You use it for your upper (in inverted) mount. If you can change the mount you can use smaller possts (under the fuel tank mount) drilled and threaded (i.e. M4). See the picture How I cic the back mounting holes - the original fuel tank mount is already cut off Just few grams less



    RysiuM

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  11. #136
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    RE: Poulan 25 from FL trimmer

    One more thing - I didn't do much cutting in lower case and cylinder as I didn't know how strong shoud it be. So I left all pieces (kind of fins) in lower case just to make sure it will not blow up or crack when running.

    RysiuM
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  12. #137
    diablo_r's Avatar
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    RE: Poulan 25 from FL trimmer

    well if it goes pop, it goes pop! Its kind of a development engine anyway so if it does not go pop I've not pushed it far enough!

    I have already drilled and tapped M4 those bits you talk about but did not have time for making another mount today so stuck with the one I already made. Another job for the future.

    My main worry with the lwoer crnakcase would be flexing of the case making the bearings go tight but using my highly trained engineers eye I reckon it has enough ribs to keep it all in line. Only more flihts will tell though, but first I've gotta get it running on glow. I emailed Just Engines too to ask about buying the ign, if they cannot supply I'll buy one from Holland.

    Cheers,
    Rich

  13. #138
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    RE: Poulan 25 from FL trimmer


    ORIGINAL: diablo_r
    Total weight of the new glow or elec ign version, including exhuast, prop adaptor, carb, bellmouth, mount and all bolts is 1220 grams.
    Are you sure about that? 1220g = a little over 43oz.
    My rough cut engine including original carb and adapter, custom muffler, mount and prop adapter is 37.5 oz. See the post #15 in Step by step converting Poulan 25cc FL trimmer

    RysiuM
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  14. #139
    diablo_r's Avatar
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    RE: Poulan 25 from FL trimmer

    its the exhaust that makes all the difference, the one I have right now is all steel hence the 5oz weight difference.

    Maybe I'll get sorted out and either get a tig, or buy a wacker engines one.

    Cheers,
    Rich

  15. #140
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    RE: Poulan 25 from FL trimmer

    forgot to ask, how much does the wackerengines muffler weigh...?

  16. #141

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    RE: Poulan 25 from FL trimmer

    Hi,
    Nice trim job. Is the notch in the thrust face of the piston stock?

    Dave

    Every day above ground is a good day.

  17. #142
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    RE: Poulan 25 from FL trimmer

    ORIGINAL: diablo_r
    forgot to ask, how much does the wackerengines muffler weigh...?
    That's the one on the picture


    This one has not cut engine holes yet becuse I wanted to do it myself. Also the weight does not include 2 screws that are about 1 oz. So the final weight is about 4.5oz including bolts, but if you can get tytanium bolts you will save some weight.

    I found, that actually the original gutted muffler with drilled two 14mm holes in outer case weight the same and performs the same - just looks ugly. And both are loud anyway. But I would rather have some long aluminum tube instead that would sound like Harley. I'm going to make or order something like that for my Wilga.

    RysiuM
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  18. #143
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    RE: Poulan 25 from FL trimmer

    ah, that explains it. The exhuast I have right now is 313g (about 11oz) and the wacker engines one is 110g. With one of those mufflers and a bit of tweaking I might be able to get this under 1kg, that would be an achievement.

    Best get one order next week then!

    Dave, the piston as standard is circluar at the base, I have cut all the notches. The front one for the intake timing, the side ones to open the transfers with the piston at BDC.

    Cheers,
    Rich

  19. #144

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    RE: Poulan 25 from FL trimmer

    Hi Rich,
    That intake notch really is large. How many degrees is the intake duration? My stock blower engine is 132 degrees duration or 66 degrees before TDC. The tranfer notches should help a lot.

    Dave
    Every day above ground is a good day.

  20. #145
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    RE: Poulan 25 from FL trimmer

    Hi Dave,

    I've read some of your other posts, you've played with a few engines! Your numbers do not make sense though, do you mean your blower is 132 degrees duration...? 66 deg BTDC and 130 total duration do not add up.

    As standard my engine had 122 degrees, but the key numbers are the port time area and the port angle area, both of which were woefully low, in the end its a mass production 6000rpm trimmer engine not intended for turning a 16" prop at 9000rpm[:-]

    To get it to those revs it needs a load more transfer, a bit more exhuast and a mid amount more inlet. Sorry for the SI units, but as standard the engine runs a PTA of 0.000063 sec-cm^2/cm^3 but given Jennings data for 8000rpm it wants to be 0.00014 to 0.00016 IE its half what it should be. The port angle area as standard is 3.01 and it should be 6.7 to 7.7, again half. Well I cut the port as high as I could without it exposing the inlet to the cylinder over the top of the piston at BDC, but that only gave 126 deg duration, PTA of 0.0001 and PAA of 4.5 so the next step was to cut the piston skirt to increase the figures, so now it runs 156 deg duration, 0.000138 PTA and 6.6 PAA. Its on the low side still, next step will be to widen the port to get the figures up a bit more but seeing as a reed valve motor runs 180 deg inlet timing the size of notch in the piston is not so critical, the thing that is important is the port is open long enough to let the engine take as much as it wants to.

    Of course there is more than one way to skin a cat, or even tune an engine, this was just my take on this engine and I'll probably port the next one a little different, ie more area and less duration. The disadvantage of large area ports is obviously the lower air velocity which in itself can cause problems with fuel falling out of suspension etc etc.

    Cheers,
    Rich

  21. #146

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    RE: Poulan 25 from FL trimmer

    Hello Rich,
    Thanks for pointing out my typographical error. You were right, it should have been 132 degrees. I didn't mean to put you into attack mode. I take modifying my engines seriously and don't consider myself playing with them. It won't happen again.

    Dave
    Every day above ground is a good day.

  22. #147
    diablo_r's Avatar
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    RE: Poulan 25 from FL trimmer

    Sorry Dave, my coments were meant only as a compliment to you and your obvious experience.

    Cheers for the info on Mufflers Rysium, I ordered a wackerengines one today so should have it in a week or so. I also talked with a couple of electronic wiz's at the patch today and between us we are going to have a go at building an electronic ign, maybe even PIC, with a nice small coil specifically as light as we can. Will keep you updated.

    Cheers,
    Rich

  23. #148
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    RE: Poulan 25 from FL trimmer


    ORIGINAL: diablo_r
    Cheers for the info on Mufflers Rysium, I ordered a wackerengines one today so should have it in a week or so.
    One more thing about this muffler. I have two of them. It is designed so tubes are screwed in to the muffler body. I tried different things and still didn't sucseed with keeping them in place. Even muffler-pipe sealer doesn't keep them in place and tey are always shaken loose. A think the second one I will just weld in place (maybe this 'magic rod' that can weld aluminum).

    ORIGINAL: diablo_r
    I also talked with a couple of electronic wiz's at the patch today and between us we are going to have a go at building an electronic ign, maybe even PIC, with a nice small coil specifically as light as we can. Will keep you updated.
    Please do.

    Thanks
    RiysiuM
    Visit my site at www.rysium.com

  24. #149
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    RE: Poulan 25 from FL trimmer

    I've heard about the alu welding stuff, you can buy it here but I've heard that with an engine runnign in a cowl it can get hot enough to remelt the magic stuff and the pipe falls to bits. I'll see when I get mine but maybe I'll find a way to lockwire or pin/grubscrew them in place.

    Cheers,
    Rich

  25. #150
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    RE: Poulan 25 from FL trimmer

    The magic stuff melts at 750F and there is no penetration..Think of it as solder...It should work OK if the tubes are screwed in first..[8D]
    RC Ignition


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