Boilermonkey Posted August 27, 2017 Report Share Posted August 27, 2017 During our annual we replaced or mags on our M20C. Once we got everything tougher we checked the timing using a tone box. Looked good. Started, did a run up test and there was a 300RPM drop on both sides. Turned it off and the plugs which had been cleaned were dirty. Cleaned them again, checked timing, and tried starting... Will not start. Ideas? Mechanic thinks the timing might be off and wants to pull the mags off to check the gear alignment. Or, a fuel supply issue. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted August 27, 2017 Report Share Posted August 27, 2017 (edited) If the points open at 20 or 25 BTDC then they are timed right. Verify TDC and also the marks you are using are actually 20 degrees or 25. What kind of mags and who rebuilt them? It could be running super rich. Try setting the throttle to 2000 RPM, then lean to peak RPM and try the mag check there Edited August 27, 2017 by jetdriven Quote Link to comment Share on other sites More sharing options...
Hank Posted August 27, 2017 Report Share Posted August 27, 2017 Well, in no particular order: Make sure there's not too much antiseize on the plugs, it'll run down and short them out. Put the timing box back on and make sure you are really at TDC when starting the timing process. Check the resistance of your plugs, should be 5000 ohms or less. Clean, gap and test your plugs. Make sure you put the correct model magneto back on the engine. Things have been known to get swapped / mixed up before . . . Make sure the caps on the magneto are correctly aligned. Ideally, they only go on one way. Did the springs under the cap go into the holes? What does your ignition harness look like? When I had my left magneto serviced, i discovered the wires had slipped between the battery box and doghouse and were badly worn. Now it's something to check every time I have the cowl open. 1 Quote Link to comment Share on other sites More sharing options...
PhilB Posted August 27, 2017 Report Share Posted August 27, 2017 New/overhauled mags have been known to fail out of the box. We've all seen that more times than we'd like.CHECK YOUR ENGINE DATA PLATE for the correct timing. Make sure you're timing the engine to the correct cylinder. I have had FNG's that work on Lycomings one day and Continentals the next try to time an engine to the wrong cylinder. (In their defense, they were on the correct side of the engine. I've even seen a mechanic time one on the exhaust stroke!You mentioned a 300 mag drop but didn't say what side. Pay double attention to the things that affect BOTH mags. Induction pipes. Fuel delivery. Fuel primer and it's lines. Mag switch.Double check any maintenance done during the annual on these items.Make sure fuel is making it past the gascolator!!! The gas selector has to be on a tank with fuel in it!I seriously doubt you have two bad mags. But I wouldn't bet $20 on it. Walk away. Get lunch. Relax and think about other things for a while. Then look at it again with a fresh perspective.Good luck Sherlock!Sent from my iPhone using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
Boilermonkey Posted August 30, 2017 Author Report Share Posted August 30, 2017 Got the plugs out again...no spark on any of them. Since the mags are new and they should send a spark even if miss timed....ideas? Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 30, 2017 Report Share Posted August 30, 2017 Check the internal timing, the points may not have been tightened and slipped. Is there a problem with your ignition switch? Quote Link to comment Share on other sites More sharing options...
Guest Posted August 30, 2017 Report Share Posted August 30, 2017 What type of magnetos are on your engine? Slick or Bendix? Even if mis timed to the engine, turning the engine over with the plugs removed should result in sparks jumping from the wire end when held close to the engine. If no sparks are present you'll be taking the mags off and checking them or having them checked again. Clarence Quote Link to comment Share on other sites More sharing options...
RLCarter Posted August 30, 2017 Report Share Posted August 30, 2017 No spark from either mag? Disconnect your "P" leads from both mags and recheck which eliminates the switch. If both mags are faulty buy a lotto ticket 1 1 Quote Link to comment Share on other sites More sharing options...
Boilermonkey Posted August 31, 2017 Author Report Share Posted August 31, 2017 Of course as luck would have it, I jammed my heal into the corner of a jack stand while working with the mechanic, brused the bone and ACL. So, I am in a walking boot for several weeks. I guess we have time to figure this out. ...well except the other two owners would like to fly. 1 Quote Link to comment Share on other sites More sharing options...
RLCarter Posted August 31, 2017 Report Share Posted August 31, 2017 10 minutes ago, Boilermonkey said: Of course as luck would have it, I jammed my heal into the corner of a jack stand while working with the mechanic, brused the bone and ACL. So, I am in a walking boot for several weeks. I guess we have time to figure this out. ...well except the other two owners would like to fly. That sucks, recovering from a broken toe myself 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.