Tonight's task was to start the engine (Mosler 1/2VW, Slick mag with impulse), let it warm up, and change the oil. I ran the engine once before a few months ago, had a very hard time getting it started, but once started it ran fine. Tonight was no different.
First I wanted to check the compression to get a baseline. LH cylinder was 120, not bad, but the RH cylinder was only 60. I wasn't too worried about this, as it hadn't been run in a couple months so the cylinders could be dry so I put in the new plugs (NGK BPR5ES, which is a resistor plug) in and started swinging the prop. Using the routine given by the builder (mag off, choke on for a couple of pulls, choke off and mag on, should start by the second pull)... nothing. Kept it up for a long time, nothing. Couple of times it seemed like it almost wanted to run, fired once. Tried ether, still wouldn't start. At this point I noticed the RH exhaust was warm but the LH one wasn't. Pulled the plug and laid it on the engine, it sparked but looked a little weak. Didn't look wet like it was flooded. Tried the old plug (Champion N11YC, which is not a resistor plug) and spark looked much better. Both plugs were properly gapped. Put the old plug in the engine (leaving the new NGK on the RH side) and it seemed like it was trying harder to start, another try with the ether and it finally started.
I had installed a new oil temperature gauge (there wasn't one before, just a CHT) and though I ran it for a while, the gauge didn't move off the stop (100°F). Probably a bad gauge as it was certainly warmer than that. Didn't go full throttle as by this time it was getting late and I was working in my front yard, didn't want to annoy the neighbors. Shut it down and then had no trouble restarting it, and by feel (didn't check it again with the tester) the compression seemed good on both sides.
I did not check the ignition timing but seems unlikely it would have changed from when the previous owner was flying it.
So:
Is there an issue with resistor plugs (like the NGK I used) with these engines, or with the Slick mag?
Any other thoughts why it would be so reluctant to start, but then run OK?
The CHT gauge on the plane was broken and missing the ring terminal that goes under the spark plug. I made a new one of brass, but the recess for the spark plug is so tight it would deform and probably prevent the plug from seating, so I left it off. I'm thinking of using a smaller ring terminal and putting it on one of the cylinder studs (one of them extends far enough past the nut that I could get the terminal and another nut on it, without disturbing the existing nut and thus the head torquing)... thoughts?
More confusion: The engine manual I got with the plane specifies a .028" plug gap, but the copy I downloaded from somewhere online says .016". Similarly, my copy of the manual says .006 valve clearance, but the downloaded copy says .006 for exhaust but .004 for intake. So which is correct? Enough to matter?
Dana
First I wanted to check the compression to get a baseline. LH cylinder was 120, not bad, but the RH cylinder was only 60. I wasn't too worried about this, as it hadn't been run in a couple months so the cylinders could be dry so I put in the new plugs (NGK BPR5ES, which is a resistor plug) in and started swinging the prop. Using the routine given by the builder (mag off, choke on for a couple of pulls, choke off and mag on, should start by the second pull)... nothing. Kept it up for a long time, nothing. Couple of times it seemed like it almost wanted to run, fired once. Tried ether, still wouldn't start. At this point I noticed the RH exhaust was warm but the LH one wasn't. Pulled the plug and laid it on the engine, it sparked but looked a little weak. Didn't look wet like it was flooded. Tried the old plug (Champion N11YC, which is not a resistor plug) and spark looked much better. Both plugs were properly gapped. Put the old plug in the engine (leaving the new NGK on the RH side) and it seemed like it was trying harder to start, another try with the ether and it finally started.
I had installed a new oil temperature gauge (there wasn't one before, just a CHT) and though I ran it for a while, the gauge didn't move off the stop (100°F). Probably a bad gauge as it was certainly warmer than that. Didn't go full throttle as by this time it was getting late and I was working in my front yard, didn't want to annoy the neighbors. Shut it down and then had no trouble restarting it, and by feel (didn't check it again with the tester) the compression seemed good on both sides.
I did not check the ignition timing but seems unlikely it would have changed from when the previous owner was flying it.
So:
Is there an issue with resistor plugs (like the NGK I used) with these engines, or with the Slick mag?
Any other thoughts why it would be so reluctant to start, but then run OK?
The CHT gauge on the plane was broken and missing the ring terminal that goes under the spark plug. I made a new one of brass, but the recess for the spark plug is so tight it would deform and probably prevent the plug from seating, so I left it off. I'm thinking of using a smaller ring terminal and putting it on one of the cylinder studs (one of them extends far enough past the nut that I could get the terminal and another nut on it, without disturbing the existing nut and thus the head torquing)... thoughts?
More confusion: The engine manual I got with the plane specifies a .028" plug gap, but the copy I downloaded from somewhere online says .016". Similarly, my copy of the manual says .006 valve clearance, but the downloaded copy says .006 for exhaust but .004 for intake. So which is correct? Enough to matter?
Dana
