will -0 Posted May 18, 2019 Share Posted May 18, 2019 ok, I'm surprised viton works with the nitro and methanol, that's all Link to comment Share on other sites More sharing options...
will -0 Posted May 18, 2019 Share Posted May 18, 2019 ok, I'm surprised viton works with the nitro and methanol, that's all Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted May 18, 2019 Share Posted May 18, 2019 "A trademark of DuPont, Viton fluoroelastomer in general has a high temperature tolerance and chemical resistance rating. It is a synthetic rubber that resists many hydrocarbons, biodiesel, and petro chemicals, but is NOT compatible with ketones. Do not use Viton with acetone, esters, amines, organic acids, acetic acid, MEK, ethyl acetate, highly polar chemicals, etc." We use it widely in oil and gas applications, but don't use it with titanium the flourides cause stress cracks in titanium. BTW the seals in my 1980s 61 and 75 are still the originals................ Edited By Frank Skilbeck on 18/05/2019 08:03:36 Link to comment Share on other sites More sharing options...
will -0 Posted May 18, 2019 Share Posted May 18, 2019 I should explain, all the compatibility charts i've ever looked at show "do not use" for viton for methanol and nitromethane. I appreciate you need something that will do the temperature, but I'm surprised that viton lasts in this application. If it does that's interesting, i guess the levels of exposure in the fuel/air mixture are low enough to be OK. Link to comment Share on other sites More sharing options...
Jon H Posted May 18, 2019 Author Share Posted May 18, 2019 The viton O rings are used to seal the carb and exhaust stubs to the cylinder head so fuel never actually flows over them. Abrasion damage from the bead blasted aluminium finish is the primary cause of O ring failure we see which is why the instructions say to oil/grease the rings before fitting the exhaust on a new engine, or a replacement exhaust on an old one. This prevents damage during fitting and gives a small amount of lubrication to smooth the small movements seen in normal operation. More often than not the O rings last a good long while and there are 1990's era engines still using their original rings. I suspect they might be a bit hard by now but that is another issue all together Link to comment Share on other sites More sharing options...
trebor Posted May 28, 2019 Share Posted May 28, 2019 On a Laser 70 how high could you install the carb center level above the center line of the fuel tank before it would cause problems ? Link to comment Share on other sites More sharing options...
Jon H Posted May 28, 2019 Author Share Posted May 28, 2019 Depends on the model. If its a super 60 or something like that then it will be fine probably an inch or two below. If its something more exuberant then the closer the better. I always aim for centre of carb to top of tank as the worst that can happen is that it will go a bit rich when inverted. Link to comment Share on other sites More sharing options...
trebor Posted May 28, 2019 Share Posted May 28, 2019 I keep looking at fitting it into this Flair Astrohog, only I don't want to cut the nose about. I would rather keep the vertical engine, the fuel tank is as high as its going to get so the centers look like 30mm apart with the engine mounted on paxilon. Link to comment Share on other sites More sharing options...
Don Fry Posted May 28, 2019 Share Posted May 28, 2019 Re 'o' rings, I have just replaced the original carb main needle ring on a well used 80, 2009 vintage. Cause of failure was abrasion damage, as its new home was a cowled machine where the needle comes out to remove the cowl and I did it dry. Quite a few times. Dunno what the new one is made of. Link to comment Share on other sites More sharing options...
Bob Cotsford Posted May 28, 2019 Share Posted May 28, 2019 Posted by trebor on 28/05/2019 14:33:35: I keep looking at fitting it into this Flair Astrohog, only I don't want to cut the nose about. I would rather keep the vertical engine, the fuel tank is as high as its going to get so the centers look like 30mm apart with the engine mounted on paxilon. I did once commit sacrilidge by drilling and tapping the exhaust to take a nipple in order to pressurise the tank. It helped even out the mixture variations through aerobatics. Link to comment Share on other sites More sharing options...
trebor Posted May 28, 2019 Share Posted May 28, 2019 Good idea Bob, plus I can do that easily when the engine is vertical later on. Link to comment Share on other sites More sharing options...
will -0 Posted May 28, 2019 Share Posted May 28, 2019 Hi, what is the correct size allen key for the tappet screws in older style engines please? Link to comment Share on other sites More sharing options...
Jon H Posted May 29, 2019 Author Share Posted May 29, 2019 If it were me, i would mount the engine upside down in the hog. Tank sits on the floor, nice neat nose, great cooling and easier exhaust management. There is a thread around here somewhere showing exactly that. If i ever build one, thats how it will be If not then you can either move the tank up a little and add a small bulge to the top of the tank hatch or just give it a go at it is as 30mm tank centre to carb centre is not too bad. If you use a radio active tank they are quite flat and this will minimise any mixture change due to tank level. It also depends how much you intend to thrash it about. In general i would not recommend trying to fit a pressure nipple as the exhausts are not designed to take them and it wont be long before the thread strips out and you need a new exhaust. Will, they should be 1/16 if memory serves. Modern ones have a screwdriver slot instead but i prefer the allen key if im honest. Edited By Jon - Laser Engines on 29/05/2019 08:36:18 Link to comment Share on other sites More sharing options...
will -0 Posted May 29, 2019 Share Posted May 29, 2019 Thanks I have a lot of 1.5mm allen keys Personally I hate small set screws with hex heads as the hex hole is a good approximation to a circle as it gets to sizes m3 and below and it's very hard to get good torque transmission, more so with poorly toleranced tools or after someone's used the wrong size key. That said this engine also has a slightly tool modified rocker cover screw (and that's a flat head) - any chance you know the size I'd need for a replacement? Edited By will -0 on 29/05/2019 08:44:05 Link to comment Share on other sites More sharing options...
Jon H Posted May 29, 2019 Author Share Posted May 29, 2019 Posted by will -0 on 29/05/2019 08:43:25: Thanks I have a lot of 1.5mm allen keys Personally I hate small set screws with hex heads as the hex hole is a good approximation to a circle as it gets to sizes m3 and below and it's very hard to get good torque transmission, more so with poorly toleranced tools or after someone's used the wrong size key. That said this engine also has a slightly tool modified rocker cover screw (and that's a flat head) - any chance you know the size I'd need for a replacement? Edited By will -0 on 29/05/2019 08:44:05 Good torque? its only a rocker adjustor But i take your point about a previous owner being ham fisted with the wrong size allen key. The rocker cover screws were (i think) 8ba? could have been 6ba. As i was about 5 years old at the time i wasnt really involved. Sticking a 2mm down it usually does the job. Does the rocker cover screw go into the tapped rear head bolt or is it on one of those pillar nuts? If you arent sure shoot me a photo Link to comment Share on other sites More sharing options...
will -0 Posted May 29, 2019 Share Posted May 29, 2019 Rocker cover screw goes into the rear head bolt. The good torque thing becomes more important when some of my good colleagues use m3 grubs to hold gears and pulleys onto motors. or in the case of the laser, the grubs holding the exhaust and carb in place. Happily at least I was able to lay my hands on by BA sized set of spaniards. Next question: with the back cover off, the drive pinion is somewhat floaty. Is this an issue to worry about or is it fine once constrained by the back plate? Link to comment Share on other sites More sharing options...
Jon H Posted May 29, 2019 Author Share Posted May 29, 2019 the bearing at the front end might a little tired. its not totally the end of the world as the bushing at the backk will help hold it but if you are concerned then swap the bearing. Just be sure to note the timing first as there are no marks to help you get it back together Link to comment Share on other sites More sharing options...
will -0 Posted May 30, 2019 Share Posted May 30, 2019 Thanks I'll probably run it as is for now. Someone enjoyed themselves designing this Link to comment Share on other sites More sharing options...
trebor Posted May 30, 2019 Share Posted May 30, 2019 Did it come off easy ? I had one which was a sod Link to comment Share on other sites More sharing options...
dave parnham Posted June 12, 2019 Share Posted June 12, 2019 Not a Tech Question at all.....Just a great big THANK YOU John My Laser 180 arrived Today Hoorah!!! Link to comment Share on other sites More sharing options...
Jon H Posted June 12, 2019 Author Share Posted June 12, 2019 No worries Dave. If you break it you are dead to me Link to comment Share on other sites More sharing options...
Chris Walby Posted June 12, 2019 Share Posted June 12, 2019 ...most important question...what's it going in...? Link to comment Share on other sites More sharing options...
dave parnham Posted June 13, 2019 Share Posted June 13, 2019 Balsa USA Fokker DV11 Link to comment Share on other sites More sharing options...
Chris Walby Posted June 13, 2019 Share Posted June 13, 2019 Now that looks a nice model and I am sure with the 180 in it the will sound just great...please please build thread Link to comment Share on other sites More sharing options...
Jon H Posted June 13, 2019 Author Share Posted June 13, 2019 Indeed Chris, it should be lovely when complete. I have a bunch of 1/4 pup's to build but am tempted by the BUSA 1/4 camel as well as the DVII. so many planes, so little space Link to comment Share on other sites More sharing options...
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