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recapen(at)earthlink.net
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 Posted: Thu May 21, 2009 4:19 am Post subject: Adjusting spark plug gap |
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I have the tool to measure the gaps and make the gap smaller - what are you using to make the gap bigger? I don't want to risk damaging the center electrode or ceeramic.
I have some new plugs - fresh out of the box....their gaps are not consistent - some as low .015 and some as high as .025. I want to make them all the same.....
The plugs are UREM37BY and the outer electrodes go up then in (holding the plug in your hand with the working end up - kinda like car plugs), as opposed to in then up (which I've seen in pictures - not on my plane).
Thanks,
Ralph
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racerjerry
Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY
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| Posted: Tue Dec 15, 2009 5:31 pm Post subject: Re: Adjusting spark plug gap |
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Aircraft Spruce now sells a tool to increase the gap of aircraft massive electrode spark plugs, but I definitely would not recommend it. Years ago I made one in a lathe from 3/8 diameter 4130 rod by drilling a center hole (about 0.150) so that the center electrode would pass through and tapering the end about 30 degrees to a sharp point. The pointed tip was heated to red and immersed in oil to harden it.
I RARELY used this tool, because slight sideways pressure on the center electrode could easily crack the spark plug insulator, rendering the spark plug useless.
For Lycoming engines, Lycoming Service Instruction 1042Y (or later) governs approved spark plugs. In SI 1042Y, it also states that “Spark plug gage must be set at .016-.022 inch.” If your gaps are no tighter than .015, you have nothing to worry about and the gap will soon self correct with use.
At this point I am a whole lot more careful about squeezing the electrodes closed when using my gap adjuster tool (also homemade) and have not been tempted to use the gap enlarger tool in a very long time.
BTW, you gotta' measure the gap using a WIRE type feeler gauge. A flat feeler gauge will not work properly and will result in erroneously smaller readings. Could this be your problem?
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