Home › Forum › Ask A Member › Mark 20 with bendix ign problem
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January 23, 2017 at 3:33 am #6172
Hello I am having some issues with my 1953 mark 20 I had it running but not running right, kept dropping cylinder pulled off the flywheel
found both coils cracked badly cked out rest of system every thing ok replaced both coils with preferred parts 399-125 rechecked points at .018.
On the coils I put the red wire to the point side and black wire to ground. Put it all back together had really nice blue spark. put it in test tank and it doesnt start not even a pop tryed starting fluid nothing. rechecked for spark still there. any help would be great. I have not touched anything else since coil replace. Thanks MarkJanuary 23, 2017 at 4:18 am #51538Are you sure the motor is getting fuel? What kind of tank are you using? If it’s a pressure tank, make sure it’s 100%. If it’s a single line and you have a fuel pump, are you sure it’s pumping fuel? Floats coming up?
January 23, 2017 at 4:24 am #51539yes I primed the carb and not even a pop or sputter
January 23, 2017 at 6:02 am #51540Plug wires switched to wrong cylinders?
January 23, 2017 at 6:03 am #51541No possibility of crossed plug wires ?
January 23, 2017 at 1:15 pm #51553Need to check to point resistance should be a close to ZERO ohms .
January 23, 2017 at 2:48 pm #51562How are you checking for spark? Open air tester or spark plug head against ground in open air? I have checked for spark with plugs and got good spark in open air but absolutely zero fire under compression with fuel / air in the cylinder. Are you using new spark plugs? My first thought was reversed spark plug wires as was previously mentioned, but I bad plugs is another possibility. If there’s no fire with directly primed cylinders I suspect no spark under compression.
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January 23, 2017 at 4:38 pm #51564try reversing the coil wires in the mag. it can give stronger spark if they are reversed
January 23, 2017 at 4:50 pm #51565These Scintilla systems can be very finicky. They are notorious for dropping a cylinder, but to have no restart, 😕 I would make sure that you don’t have the plug wires reversed. The point gap is critical, and the spec. of .018 is a Maximum gap. The better number is .015 as it gives the magnet a tad more time to charge the coil. The other important factor is the air gap between the magnet and the laminations. .008 if I remember correctly. A loose upper bearing can cause fluctuations in the point and air gap. Another factor is that the magneto plate is not moving evenly on the crankcase. There should be a split ring spacer under the crankcase for the fingers of the magneto to ride on. This prevents wear of the crankcase and also helps to keep a true plane for the magneto to rotate on. There are also two spring loaded friction screws on the base of the magneto that rub along the outer edge of the crankcase. These keep an even drag on the case, but if the case is worn out of round, it can cause the magneto to change the point and air gap as it rotates. As I said, these are often difficult systems to get to operate, but they are worth the effort. I prefer the earlier Scintilla systems as was OE on the KE-7 as these had a different rotor, and the flywheel had the point cam. Some folks have ended up converting their motors to the Phelon system, (and I have done a few myself), but the parts to do this are very hard to come by, so do everything you can do first before going in that direction. Adding an auxiliary ground wire from the magneto plate to the block is always a good idea. There has been extensive discussion on this topic over on Johnsoldmercurysite.com and there are a lot of folks over there who have taken on this battle. Some have suggested that the new coils do not have as many secondary windings as OE, so they produce less maximum voltage. I can’t confirm this, just repeating what others have posted. The one thing I keep going back to, is that these motors ran for a long time with these systems, they should be able to run this way again.
Steve
January 23, 2017 at 5:26 pm #51566Thanks mercman and everyone for the help I will go back a few reply’s start at top , Yea I have reversed the plug wires and got a loud pop and kick back. The next reply about the reversing the wires on the coil I didn’t get a wiring diagram with preferred parts coil so assumed the red wire went to the insulated side of points and the black went to ground. next reply I kinda thought that about no spark with compression and fuel I hooked up a spark tester and new plugs with spark plugs installed and it shows its firing. mercman I totally agree with everything you said and I have put a ground wire that connects mag plate to engine . I had a 1925 Johnson that I had to do that and ran fine after that. I will try to set points closer. This is so out there.
Mark
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