Engine Doctor Posted March 26, 2021 Share Posted March 26, 2021 (edited) In the "Buyers Beware" thread the topic sort of steered towards diesel conversions. This sort of hijacked the OP so have started a separate thread for conversions . After seeing Michaels conversion of a OS Fx engine I thought I would have a go. My first diesel conversion of an old Magnum GP40 (clone of ans OS FP 40) Rather than use the "O" ring type contra piston I made a steel insert and contra piston . I'll try the "O"ring method next time on a smaller engine Could the mods transfer any relevant post onto here ? Edited March 26, 2021 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted March 26, 2021 Share Posted March 26, 2021 Nice one how does it run ? Over... Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted March 26, 2021 Share Posted March 26, 2021 Thats great ED I shall try to add my pennies worth . I know I have an FP 40 so will dig it out . On fuel consumption , the Irvine 20 I converted , I thought it was a little on the high side , but running has been very limited , so at present its just a "feeling " cheers Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted April 2, 2021 Share Posted April 2, 2021 well I "did" an OS 40 FP !! After the Irvine 20 , I thought this would be a doddle , and to be honest it was , till I came to turn the engine over when all was completed . the OS has a very long stroke ,and the inlet timing is very late so the suction in the cylinder is high !! Being an "O" ring type contra piston with in the region of 1/2 thou clearance it is a super smooth fit . Therefore as the piston goes down on its suction phase it is closely followed by the contra piston which is shorter that the engine stoke and it falls into the cylinder and jams the whole lot up ! Not really happy about making a "tight " fitting contra piston , cannot make it longer !! so a little head scratching is required ! Other wise excellent compression and would definately run ! cheers Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted April 4, 2021 Author Share Posted April 4, 2021 (edited) Hi Stuphedd. Can you not make a steel insert with an iron contraposition to fit in the head ? It looks as if you have enough height in the head. The head I made for the Magnum a much higher profile than needed and the insert is simply clamped into the cylinder by the head. The Magnum Is pretty much identical to the FP and doesn't have this problem. The Contrapistion is stiff/ firm to adjust and gives a nice click when it re-sets so shouldn't have issues with the comp screw comming loose during running. The down stroke should still be holding compression and that should keep CP in place ?. If it's sucking the CP out into the cylinder then ii must be loosing it's compression somewhere. Hi Rich .I still haven't run it for any length of time as have been busy with other stuff. It starts very easily on a prime . I intend to try converting some smaller engines later 10 or 15 size glows. Has anyone converted an older engine with a baffled piston like an Enya ? I thought if I made an aluminium grip to hold the piston I could turn the baffle off without damaging the piston. Failing that making a new iron piston. These older engines were generally lower reving and I think would suit vintage style models well. Edited April 4, 2021 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted April 5, 2021 Share Posted April 5, 2021 Has anyone converted an older engine with a baffled piston like an Enya ? One could always retain the baffle and peg the contra-piston as OS did many years ago http://sceptreflight.com/Model Engine Tests/OS Max 15D.html Of course, one would have to mill a matching slot into the contra-piston. The main problem that I have found converting glow engines to diesel is determining whether the con-rod and the crankpin are up to the task and if the piston/liner fit are sufficient to give the required compression seal (I have yet to encounter a model diesel engine that uses piston rings) Chris Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted April 5, 2021 Author Share Posted April 5, 2021 2 hours ago, Christopher Wolfe said: Has anyone converted an older engine with a baffled piston like an Enya ? One could always retain the baffle and peg the contra-piston as OS did many years ago http://sceptreflight.com/Model Engine Tests/OS Max 15D.html Of course, one would have to mill a matching slot into the contra-piston. The main problem that I have found converting glow engines to diesel is determining whether the con-rod and the crankpin are up to the task and if the piston/liner fit are sufficient to give the required compression seal (I have yet to encounter a model diesel engine that uses piston ring Hi Chris yes the pegged CP is an option but a comparatively difficult one to achieve considering the shape of the CP and maintaining compression due to the peg and slot So will stick with a flat top piston and adopt the kiss principle ? The bottom end of the engines do vary considerably in construction and therefore strength . I wouldn't consider any engine that has a made up crank is pressed in big end etc or cranks and Conrods made from cheap soft materials as they would not take the strain imposed by the higher compression needed in a diesel. Generally Enya, Fuji most OS and some British engines were over engineered so are candidates for conversion. Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted April 5, 2021 Share Posted April 5, 2021 Thanks for the advice ED , I shall make an "alternative" when I have time , but at present I am catching up on my flying , The OS has fantastic compression , and actually appears to be unrun !!I shall give it a run when I have mixed up a new batch of fuel ,which will be when the weather gets warm enough to allow the Castrol M/R to flow !! cheers Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted April 6, 2021 Share Posted April 6, 2021 The Cox Conquest .15 is a popular subject for conversion to a diesel here down under. It makes a decent engine for diesel team racing as it starts readily and has quite useful power. The 'Cossie' is a Cox Conquest with a Rossi .15 piston and liner (they go even harder) ? Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted April 6, 2021 Author Share Posted April 6, 2021 Hi Christopher I like the the look of the low profile head on the silver crank case Cox . Is it a "O" ring type Contra-piston ? Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted April 6, 2021 Share Posted April 6, 2021 I have a Cox 15 standard glow , which my fingers consider an "Evil" engine ,but powerful ! cheers Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted April 7, 2021 Share Posted April 7, 2021 15 hours ago, Engine Doctor said: Hi Christopher I like the the look of the low profile head on the silver crank case Cox . Is it a "O" ring type Contra-piston ? I shall ask the builder next time I see him at a comp. as it's a nice looking conversion and it ran very well. Most of my conversions are 'factory' ones mostly Enya's (SS 25BB DS, Ultra 11CX DS and a 41-4C diesel four stroke) Chris Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted April 7, 2021 Share Posted April 7, 2021 ran the OS40 today , very good , easy to start, well it went well till the silencer fell off! The engine even throttles . The silencer was not an original and a bit of a miss mass ! so needs a bit of modification , or a hunt through the junk box for a better one . so a bit more later !! and must check the prop balance ? cheers Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted April 9, 2021 Share Posted April 9, 2021 Ok managed to mix a drop of fuel and find a silencer that stops in one piece , plus a Tornado 10x6, so managed a short vid 1747315853_OS40vid_Trim_Trim.mp4 Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 20, 2021 Author Share Posted May 20, 2021 I have nearly finished a conversion on a Magnum 15 GP from glow to diesel . A much smaller engine so tried the "O" ring type contra piston. I have set it up using nitrile "O" Rings but have ordered some Vitol rings as they apparently last far longer. I will put some pics on later. The Magnum is a long shaft version so an anodised prop driver will stand out well. The issue is what colour anodising for the head and spinner ? . Blue or green me thinks ? Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted May 20, 2021 Share Posted May 20, 2021 3 hours ago, Engine Doctor said: The Magnum is a long shaft version so an anodised prop driver will stand out well. The issue is what colour anodising for the head and spinner ? . Blue or green me thinks ? E.D. Whatever colour makes you happy. It won't affect the revs too much. It's only a Magnum so don't go overboard. Black anodising is good for cooling but any colour that takes your fancy should work; For the Viton rings consider adding a lock to the comp screw as the 'feel' is very soft for a model diesel engine. Chris Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 20, 2021 Author Share Posted May 20, 2021 Hi Chris . Yes the O ring wasn't my preferred choice but wanted to try it as making the steel cylinder extension wit iron contra-piston as I did on the 40 is a lot more time consuming . I have opted for two rings and the adjustment feels quite stiff. Not as stiff as an iron CP but still quite stiff . I have left enough thread on the comp screw to allow for a locking arm . I was only joking about the anodising colour but I have to admit I do get a sense of satisfaction from making the job look good. Re "its only a Magnum " One thing I did find back in the day was that the Magnum engines(not the later ASP/ SC/Magnum clones) were/are every bit as good as an OS for much less money and the Magnum spares were used to repair the OS FP when the chrome started coming off. Just going out to take some pics . Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 20, 2021 Author Share Posted May 20, 2021 (edited) First a correction . I have earmarked two engines for diesel conversion The Magnum is a 10 GP not a 15 as I mentioned and can clearly be seen in the picture below .The next engine I intend to convert is an OS LA 15 hence the mix up. So here are some pics of the Magnum 10 so far . Here is the engine assembled before being dismantled for polishing for anodising . The engine was bought by me many years ago and had little use in a model called " The Answer ". Compression is excellent so should cope with diesel very well. Edited May 20, 2021 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 20, 2021 Author Share Posted May 20, 2021 (edited) The head is now removed and readied for buffing to get a good anodised finish . Anodising will not cover any imperfections in fact it emphasises them so a good finish is important , Edited May 20, 2021 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 20, 2021 Author Share Posted May 20, 2021 Parts all polished and ready for an anodising session . Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 20, 2021 Author Share Posted May 20, 2021 Here is the Contra piston with two O rings fitted.Two O rings gives a good tight fit that is unlikely to move in use but I may make another CP with a single O ring as the twin o rings are tricky to get into the head without damage. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 20, 2021 Author Share Posted May 20, 2021 The comp screw shown here is just a 4mm cap screw filed to shape then bent with the help of some heat to give that nice vintage look. Once bent to shape its cleaned then heated and quenched in some oil for a blued effect that also helps prevent rusting . 1 Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 25, 2021 Author Share Posted May 25, 2021 This is the completed engine all anodised . I wanted a green finish and mixed a blue and yellow dye that gave a really nice lime green colour to the head. When sealing the anodising the yellow immediately washed out left the blue colour , so blue it is . The colour take up of different alloys is evident by the difference with the head turned fro 6082 alloy to the prop driver made from chinese alloy unknown. 1 Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted May 25, 2021 Share Posted May 25, 2021 Brilliant job, looks as good as you get ! Have you run it yet ?? And/or planned the next one ? Once run mine go back in their boxes probably never to emerge again ! keep them coming cheers Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 25, 2021 Author Share Posted May 25, 2021 Hello Stuphedd Again only run on prime. Will wait until I can get them up the field as too much stuff in workshop to get splattered with oil etc. I intend to fly them at some time. I have a Ben Buckle 70 inch Taylor Craft kit waiting so the 40 is ideal for that one.Was planning a OS 15 LA conversion with Nice dark blue head. On stripping found the dreded plating falling off the liner ! I really don't know how OS got away with it. Just spent the afternoon re anodising some of my old diesel cylinder heads as some looked a bit tatty. Quote Link to comment Share on other sites More sharing options...
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