Martin McIntosh Posted May 24, 2021 Share Posted May 24, 2021 I had to talk to Model Fixings because the rear bearing offered was certainly a different width according to three micrometers I used and they insisted that their dimensions were correct, but on receipt of it it proved to be the right one and agreed with the measurements I had taken. Probably due to imperial to metric conversion as stated above so fit them with confidence. Quote Link to comment Share on other sites More sharing options...
Andy J Posted May 25, 2021 Author Share Posted May 25, 2021 Got the MF rear bearing this morning and it looks good to me when compared with the old bearing Martin. Will run my micrometer over it to see if I get identical measurements. Really good service from Simply Bearings and Model Fixings. Gavin got back to me about a replacement ring for the Merco so will need to ascertain his contact details so that I can send him the piston. All I know at the moment that he operates out of Pitstone and appears just to make rings for a wide range of RC engines. Quote Link to comment Share on other sites More sharing options...
Andy J Posted May 25, 2021 Author Share Posted May 25, 2021 (edited) Just measured the rear bearing supplied by MF and it compares well with the bearing I removed +/- 0.01mm so will go ahead and fit it tomorrow. Sorry Martin didnt check the width but will do so tomorrow. Edited May 25, 2021 by Andy Joyce Quote Link to comment Share on other sites More sharing options...
Andy J Posted May 26, 2021 Author Share Posted May 26, 2021 Martin, both bearings went in without an issue (rear one needed a little persuasion from a rubber mallet) so certainly the MF rear bearing size seems to be ok. Shame I snapped the piston ring otherwise the engine could have been back together again today. Quote Link to comment Share on other sites More sharing options...
Andy J Posted June 18, 2021 Author Share Posted June 18, 2021 Am I correct in assuming the piston is orientated such that the holes in the piston wall are 180 degrees opposed to the exhaust port? Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 18, 2021 Share Posted June 18, 2021 (edited) did u see the exploded view of the merco 61 marine I posted, a single plug version ? its a loop scavenge type engine with a deflector type piston ? the deflector is off set, with the " small area" of the piston crown being opposite the exhaust port, the crown larger area next to the exhaust port. i will nip down the shed later to check on the cylinder, ports and piston for you... the exhaust port is slightly higher than the transfer port...these being set by the cylinder position in the c/case.. no idea why this post is underlined..... Edited June 18, 2021 by Rich Griff Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 18, 2021 Share Posted June 18, 2021 (edited) The 2 round holes in the piston skirt line up with the 2 round holes in the cylinder, that are just below the many square transfer port holes. The 4 square holes ( 2 pairs of 2 ) are the exhaust ports and are opposite the transfer ports... So, the 2 round holes in the piston skirt are transfer holes and are below the small piston crown area involved with the piston deflector..... The deflector forces the transfer "charge" upwards to form the "loop scavenge" gas flow system.. If the deflector was not there, most if not all of the transfer charge would go straight out of the exhaust port... The More modern schnerle porting scavenging gas flow system is different...... Any tell tale or witness marks/staining would also follow this evidence. Even when clean some witness marks remain... Edited June 18, 2021 by Rich Griff Quote Link to comment Share on other sites More sharing options...
Andy J Posted June 19, 2021 Author Share Posted June 19, 2021 Thanks Rich, do you have any recommendations as to the thickness of the cylinder head gasket? Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 19, 2021 Share Posted June 19, 2021 (edited) Hi Andy, the exploded view of the marine unit I have does not show a cylinder head gasket, but does show a paper gasket between c/case and water jacket, and a water jacket gasket, the jacket being a two piece affair. The cylinder liner is surrounded by the water jacket where the aero engine "fins" would be ? Will look in kk handbook which shows aero 61 twin plug black head motor, but that's for Sunday.... I can measure the " cylinder gasket (a)" but it has been compressed as it was on/in the engine.... The kk handbook did say the smaller aero engine c/cases needed to be returned to merco for conversion to marine, probably having the aero fins machined off to allow the water jacket to be fitted. Does your engine have a seperate aero fins bit ? That the cylinder sleeve slides into ? The 29 I have must have been a marine version, aero fins machined off by the looks, no prop driver part but a flywheel, taper drive and split taper fitting onto parrallel crank stub and nut. I made a prop driver, and if I have suitable off cut of alloy, can make some aero fins. I do not have a water jacket...so what ever application this engine is going to have I will have to make some parts...perhaps it's going into a boat as the 29 looks a bit heavy. The kk book says it was the bee's knees of the time, being developed for radio control. The book also says the 61 is an enlarged version, but has bearings, the 29 being bearing less, and ringless. Edited June 19, 2021 by Rich Griff Quote Link to comment Share on other sites More sharing options...
Andy J Posted June 20, 2021 Author Share Posted June 20, 2021 Made a couple of gaskets today but now stuck on how the carb should be assembled. Has anyone got a schematic? Think the assembly should be obvious other than which end of the barrel the thrust washer should go and should the spray bar hole be positioned. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted June 20, 2021 Share Posted June 20, 2021 The thrust washer goes down the tunnel, ready to put pressure on the barrel, from sliding in and out but free enough to rotate. Is the great picture above the pre-clean picture, If not, then clean that lot up before assembly as oxides and rot will spread again through the metals. Quote Link to comment Share on other sites More sharing options...
Andy J Posted June 21, 2021 Author Share Posted June 21, 2021 All items have now been cleaned up Denis. Assume oxidation was probably why the barrel was seized prior to the engine strip down. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted June 21, 2021 Share Posted June 21, 2021 You may remember in school science how dissimilar metals accelerate reactions between them. Oil is our friend, not 3 in 1, but a drop of motor oil, if nothing else to hand, as motor oil is designed around aluminium and dissimilar metals. Quote Link to comment Share on other sites More sharing options...
J D 8 Posted June 21, 2021 Share Posted June 21, 2021 Spray hole in venturi general rule. One hole only in spraybar should point down into engine. Two opposite holes in spraybar they should be positioned across the venturi. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 21, 2021 Share Posted June 21, 2021 Are those all the parts for the carb ? Seems some parts are missing, or are they just not in the picture... Quote Link to comment Share on other sites More sharing options...
Andy J Posted June 22, 2021 Author Share Posted June 22, 2021 Rich what do you think is missing? Do have the needle. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 22, 2021 Share Posted June 22, 2021 The carb on my 61 marine is still off so will post a picture... I assume your carb is a merco unit. Fuel pipe collar and nut, conical round spring, and possibly a few other bits, will post later... Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 22, 2021 Share Posted June 22, 2021 Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 22, 2021 Share Posted June 22, 2021 Admin, the allowed "edit time" is far toooooo short ! Anyways this is the merco 61 marine engine carb, being very similar to the carb on the 29 marine and 35 aero I have. On these carbs, the Venturi barrel is spring loaded by a small wire conical spring which wants to push the barrel out of the carb body. It is prevented from coming out via the small screw and nylon washer which located in a groove, which is inclined, so the barrel moves in and out as it is rotated. The larger black screw is the idle or low speed needle, which is consistantly presented to the main jet hole, for a reliable and consistantly idle etc.. Your carb seems to have some rounded corners and seems a different design ? The new paw 09 I have ( and the paw 19 ) have a very simple single jet RC carb, with the spray bar rotating with the Venturi barrel... Is your carb a merco one or has it been changed at some point. Also, are the "cylinder cooling fins" on your engine a seperate parts please ? A picture of them would be good if they are....please. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 22, 2021 Share Posted June 22, 2021 I have looked at your picture again, perhaps your carb is like the paw type in design, spray bar rotates with the Venturi barrel ? The carb stub will have an o ring between c/case and carb body... There are visible tell tale marks/stains on the parts which should indicate how/where they came from/position.... Quote Link to comment Share on other sites More sharing options...
RottenRow Posted June 22, 2021 Share Posted June 22, 2021 Rich, Andy, The earlier Merco had air bleed carbs similar to Rich’s description of the PAW type where the spraybar moves with the rotation of the throttle. Andy’s is one of these. The later Merco carbs were of the twin needle type (which is what Rich’s carb is) and the barrel moves in and out due to the helical cut in the barrel. The spraybar doesn’t turn on these. This link will take you to an old Peter Chinn article on the early version of the Merco 61. http://sceptreflight.com/Model Engine Tests/Merco 61 Mk1 RC (2).html The test article shows and describes the early type carb. I bought a couple of 61s back in the ‘80s from a stand at the Woodvale rally. There were boxes full of used ones at a few pounds per engine. Turned out that they were used in target practice drones and the guy used to go out in the evening recovering them! Hope that helps. Brian. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 22, 2021 Share Posted June 22, 2021 Wow, collecting downed targets with engines, different from golf balls eh ! Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 22, 2021 Share Posted June 22, 2021 Interesting article, so the fins are a seperate bit, maybe I will convert this marine unit to aero, will look in my offcut box for suitable alloy for fins and prop driver....the boat it came from, huntsman, is too heavy for me to carry to the lake, the big gate is locked, so will be a struggle with the "old pram transporter"... I have some smaller boats to play with....I prefer wind powered yachts and slow electric, Leander Vic Smeed searider and HMS romper etc... Anyone wanna sea rider x 1.5 scale, it fits in a bath....very stable and a dry boat....would make a good fishing "bait boat".... Sorry, this is an aeromodeling site not fishing or boating....doh ! Quote Link to comment Share on other sites More sharing options...
Andy J Posted June 22, 2021 Author Share Posted June 22, 2021 45 minutes ago, RottenRow said: Rich, Andy, The earlier Merco had air bleed carbs similar to Rich’s description of the PAW type where the spraybar moves with the rotation of the throttle. Andy’s is one of these. The later Merco carbs were of the twin needle type (which is what Rich’s carb is) and the barrel moves in and out due to the helical cut in the barrel. The spraybar doesn’t turn on these. This link will take you to an old Peter Chinn article on the early version of the Merco 61. http://sceptreflight.com/Model Engine Tests/Merco 61 Mk1 RC (2).html The test article shows and describes the early type carb. I bought a couple of 61s back in the ‘80s from a stand at the Woodvale rally. There were boxes full of used ones at a few pounds per engine. Turned out that they were used in target practice drones and the guy used to go out in the evening recovering them! Hope that helps. Brian. Well don't think my spray bar rotates, its only the barrel that moves. Quote Link to comment Share on other sites More sharing options...
Rich Griff Posted June 22, 2021 Share Posted June 22, 2021 Yes but is the spray bar nutted to the barrel, when tight it becomes part of the barrel, and therefore turns with it, just like a paw RC carb for Thier excellent diesels...? Quote Link to comment Share on other sites More sharing options...
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