graeme jones Posted January 25, 2014 Share Posted January 25, 2014 Colin - if Brian Winch is to be believed, you have water in your fuel. See various articles in RCM&E over the years and previous threads on this forum. Personally, I've had similar problems which I've cured just by buying fresh fuel. I don't believe Brian's water contamination theory though, since the "problem" fuel was also fresh and worked fine in some engines (including an OS32 in a Shuttle!). Graeme Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 25, 2014 Author Share Posted January 25, 2014 OK guys, I put the 12 inch on 'cause I thought its inertia would make the engine easier to start. The Irvine manual lists 10 x 7, 10 x 8, 11 x 5, 11 x 6, 12 x 4 and 12 x 5 so I figured it would be fine. I have to say that regardless of the prop size, as I use my finger to start I'm not left with a lot of prop to get my finger on - another reason why I fitted the bigger prop! However, as I asked for advice I'll follow it and refit the 11 inch. The smaller prop will, I presume, allow the engine to rev faster. I thought the thick oily sludge being deposited over the airframe was un burnt fuel and oil. If, as you say, this indicates that the engine is not run in I'm amazed! How much fuel does it take to run this engine in? It's already had about a gallon of fuel! Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 25, 2014 Author Share Posted January 25, 2014 Regarding water in the fuel: yes, this is possible in the first batch as I'm embarrassed how old it was, but it worked! However, the fuel I'm now using is fresh - I've only had it a few days. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 25, 2014 Share Posted January 25, 2014 Posted by Colin Anderson on 25/01/2014 16:30:16: I thought the thick oily sludge being deposited over the airframe was un burnt fuel and oil. If, as you say, this indicates that the engine is not run in I'm amazed! How much fuel does it take to run this engine in? It's already had about a gallon of fuel! Is the exhaust manifold joint properly tightened? Even slight movement will produce fretting and black oily residue from the aluminium particles. P.S. Don't be embarrassed by using old fuel - stored reasonably in a closed container, it should last indefinitely. Water in it? How much water would be contained in the air inside even an empty container - the answer is considerably less than one drop... Edited By Martin Harris on 25/01/2014 18:40:34 Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 25, 2014 Author Share Posted January 25, 2014 The exhaust is very tight, as when first fitted it leaked around the flange; now it doesn't. I didn't really believe there was any water in the old fuel either, but if there was going to be any it would have been in this fuel rather than the fresh fuel. Incidentally can you enlighten me as to the difference between sport 5 and GN 5? Is it the nitro content? Quote Link to comment Share on other sites More sharing options...
crispin church Posted January 25, 2014 Share Posted January 25, 2014 how much fuel has this engine had did you run it in as per book a engine thats not run in yet will not run right on low revs the bigger the prop the more work the engine does to spin it round not good for it run it in on a stand even a 4x4" with a engine mount in a black and decker work mater will do just keep it wieghted down Quote Link to comment Share on other sites More sharing options...
Stefan Hafner Posted January 25, 2014 Share Posted January 25, 2014 Colin, when you put the engine back on the test did you use the same tank as in the plane? Could be a problem in the tank thats in the plane if you used a different one on the bench. I know i've had problems caused by the klunk line, where it had a small hole in the line, then when the fuel level in the tank dropped below the hole it started to draw air too and messed up the mixture. Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 25, 2014 Author Share Posted January 25, 2014 This engine has had about a gallon of fuel through it. It was run in exactly according to Irvine's manual. Following advice from previous posts I'll be refitting the smaller prop. I understand the principle - smaller prop, less work, higher revs; bigger prop, more work, less revs. As previously stated I tried a bigger prop on the grounds of inertia making starting easier, but to be honest there's little difference - other than I've got more prop to get my finger on! Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 25, 2014 Author Share Posted January 25, 2014 Stefan, this problem is now effectively resolved, thanks to John. He advocated flushing the main jet and clearing the exhaust nipple. This solution did the trick. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted January 25, 2014 Share Posted January 25, 2014 fit a good filter to fuel pump line Colin I don't have them in model myself, but you do your own thing Quote Link to comment Share on other sites More sharing options...
John Privett Posted January 25, 2014 Share Posted January 25, 2014 Posted by Colin Anderson on 25/01/2014 18:49:30: Incidentally can you enlighten me as to the difference between sport 5 and GN 5? Is it the nitro content? Colin, there's lots of info on Model Technics fuels on this page on their website. Essentially, your GN-5 (referred to at the bottom of the list on the page I linked to above as "Nitro Mix" ) is a "traditional" fuel mix containing 20% castor oil and 5% nitromethane. I'm not sure what your "sport 5 (Irvine blend) " fuel is, if it's a Model Technics fuel then it may be their "Formula Irvine" which contains 18% Klotz Techniplate as the oil. This is a modern synthetic oil, though it, itself, does have some castor oil in it. The '5' in 'sport 5' almost certainly refers to the percentage of nitromethane. Edited By John Privett on 25/01/2014 19:33:40 Quote Link to comment Share on other sites More sharing options...
gillyg1 Posted January 25, 2014 Share Posted January 25, 2014 Hi Colin, I've had both the Irvine 40 and 46 and can recommend a 10x6, both run fine and throttle ok on this size, as previously stated else where running with a bigger prop makes the engine work harder, which it can only sustain for a short length of time before dying, and fuel I use is model technics contest 10. Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 25, 2014 Author Share Posted January 25, 2014 Thanks guys! So essentially sport 5 (Irvine formula)and GN-5 are the same; only the oil is different. Regarding the prop I'm inclined to go back to the 11 inch that the engine was run in with and flown. The 10 inch isn't going to give my finger much prop blade to flick, as the Cub's front profile takes up an awful lot of the prop's disk! Would the 10 inch really be suitable for a trainer? Irvine's manual suggests that I could go up to 15% nitro, but I'm not sure of the pros and cons of this; would it make the engine easier to start? I'm guessing also that the engine would run hotter as a result of high nitro? Quote Link to comment Share on other sites More sharing options...
Shaunie Posted January 25, 2014 Share Posted January 25, 2014 Glad you got it sorted. My money was on it being over-propped. You didn't go to a smaller prop when you washed the carb and lines out by any chance? Shaunie. Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 25, 2014 Author Share Posted January 25, 2014 The problems started after the first flight. Previously there had been no problems; it was run in and flew on an 11 inch prop. It was only after I got the problems that I fitted the bigger prop. However, as your all telling me I'm a bad boy for going up a size and going to be good (honest) and go back to the 11 inch prop! i might just fit a filter in the fuel filler line and hopefully this won't effect the running. I've noticed that occasionally some of that black gunk that is coating my airframe finds its way down from the exhaust nipple and into the tank; perhaps it was this that eventually caused the problem. Quote Link to comment Share on other sites More sharing options...
crispin church Posted January 26, 2014 Share Posted January 26, 2014 filter fuel before it gets to your plane dont fit inline something to go wrong Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 26, 2014 Author Share Posted January 26, 2014 I'm inclined to agree with you. However, I think it's worth trying, as I can always remove it should it creat problems. My feeling is that it was probably the main jet that was getting blocked, rather than the exhaust nipple (as I cleared both I'm unclear which it was); as some residue does occasionally travel down the pressure line and into the tank then some of that will eventually reach the jet. If a filter stops that then it's worth fitting. Quote Link to comment Share on other sites More sharing options...
graeme jones Posted January 26, 2014 Share Posted January 26, 2014 Colin - that's another reason that Brian Winch claims exhaust pressure feed is a bad idea, since all combustion products can in theory contaminate the fuel in the tank. In practice I always use it without problems, and OS motor instructions say you MUST use it as their carbs are set up for it. I've used a filter between the tank and carb for 50 years without problem. I've also used Irvine 40's on large props (up to 12X6) to reduce noise. All of the running problems I've had in the last couple of years have been traced to one of two things. Bad fuel and/or worn out plugs. Some of the fuel has been fresh but causes problems with some motors and not others. Plugs these days only seem to last for a few hours running, again more so in some motors. My set up for Irvine 40 is straight fuel (it has a high enough compression ratio not to need nitro unless you need more power) Taylor standard plug (or OS equivalent) 11X6 Master prop. Good enough to fly a Wot4 like a rat up a drainpipe. Graeme Quote Link to comment Share on other sites More sharing options...
crispin church Posted January 26, 2014 Share Posted January 26, 2014 to check the pressure feed just take it off and rich the high needle sometime a engine will run better with it disconnected but dont block it off must be left open Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 26, 2014 Author Share Posted January 26, 2014 Graeme, The Irvine 40 is the same. It's designed to run off exhaust pressure. However, when I ran it on the test bench I had the centre line of the tank level with the main jet and it ran just fine; there was no pressure feed as, at the time I ran it without the silencer - until I took pity on my neighbours! However, it is not possible to fit the tank high enough in the Cub. I ran the engine in and flew the Cub on an 11 inch prop which I replaced with a 12 inch. I've noticed with the bigger prop that the revs do not increase above half throttle on the stick, so I'm going to refit the 11 inch. I first ran the Irvine on GN 5 that was embarrassingly old; the fuel I'm using now is fresh sport 5, which is apparently the same, but with a synthetic oil. How do you tell if a glow plug is bad? I thought they either worked or they didn't. I've noticed that you refer to Brian Winch on more than one of occasion. I'm embarrassed to ask, but who is he? Quote Link to comment Share on other sites More sharing options...
graeme jones Posted January 26, 2014 Share Posted January 26, 2014 Colin - glow plugs work as a catalyst, or rather the platinum in them does. As they age the coil can change from bright and shiny to a dull white (you'll need a good magnifier) at which point they can give the symptoms you describe (once the battery is removed). I'm not sure why but they don't seem to last as long these days as they used to. Less platinum (expensive stuff) synthetic oils and higher engine outputs (therefore higher temps) are all possible reasons. Brian Winch writes a regular column for RCM&E and is their engine expert, but I don't always agree with him! Graeme Edited By graeme jones on 26/01/2014 20:22:02 Quote Link to comment Share on other sites More sharing options...
cymaz Posted January 26, 2014 Share Posted January 26, 2014 I found, only by experience, that if the engine suddenly goes out of tune at WOT and everything is the same then it is usually the plug. Those little things don't have an easy time of it. I Change the plug first as it is easy to do and easy to get to. Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 26, 2014 Author Share Posted January 26, 2014 Thanks guys. If I understand you both correctly you're saying that plugs glow less efficiently as they age. I can see the sense of this now it's been explained, so I'll fit a new plug and see if there's any noticeable difference. Quote Link to comment Share on other sites More sharing options...
cymaz Posted January 26, 2014 Share Posted January 26, 2014 Don't forget to put an Irvine recommended prop size on as well. Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted January 26, 2014 Author Share Posted January 26, 2014 Interesting that! As posted earlier, Irvine recommend props from 10 inch ~ 12 inch for this engine! Yet most of the posts on here are sugesting this is "over proped"! I'll be sticking with the middle ground an 11 inch prop. Quote Link to comment Share on other sites More sharing options...
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