Should I gap my plug?


I own an FA50 (1984) and I just got a new spark plug. I've bought several already and used them. They are still okay to use, I just like to change them once a year, because they are cheap.

I never gaped them because I don't how and more importantly I don't have the tools. I know it probably is not necessary to do this (because I never have done it and I have had no problems), but I was wondering what the benefits of gaping a plug are?

Also, what dimension should the gap be, and where can I get it done (what price should I expect)?

Thanks again for the help

Re: Should I gap my plug?

Steamboat Aka J. R. Stevens /

Hey Nick, engineers determine the gap settings for each engine based on such things as compression and voltage available from the ignition coil. Check your owners manual. A tool to set spark plug gap may be purchased from most auto parts store for less than $5. Jim.

Re: Should I gap my plug?

A higher voltage is required for a spark to jump a wide gap than a small gap. If the plug is dirty, even more voltage could be required. The ignition's generated voltage will keep rising and rising until it arcs somewhere.. that somewhere is the point of least resistance.

So, forcing your ignition pump up to a higher voltage in order to jump a too-wide plug gap can be detrimental to the ignition (very high voltage may "arc" somewhere other than across the spark plug's electrodes).

If the arc is elsewhere than the spark plug, you get a misfire.. (perhaps the arc is inside the HT coil itself, destroying some wire insulation?) and that spot can be burned by repeated arcs.. eventually causing total ignition failure.

but a too-small gap is more prone to being fouled by a little drop of fuel or oil or water..

Gap all plugs at what the manufacturer recommends.. Spark plug gap tools are a dollar or two, available at any autoparts store. Ask them how to use it.

Re: Should I gap my plug?

just to be sure, when you mention a tool to set the gap, you just mean a gap gauge to measure your gap, right? i can't imagine spending money on something just to push in the end of the plug. haha.

Re: Should I gap my plug?

Gapping a spark plug is important to get the best performance from your 'ped. Gapping is ultra easy to do and takes 30 seconds.

You'll need a spark plug gapping tool, available at any auto parts store for $5. It looks like a deck of skinny metal cards all riveted together in one corner. Each metal card is thin and a specific thickness, which will be written on the card.

Read your owner's manual and find out what spark plug gap you need for your 'ped. Let's say for example that the manual says your gap should be 0.6 - 0.7 mm (0.024 - 0.028"). Open up your gapping tool and go find a metal card that is between these numbers, say a 0.610mm card. Grab your spark plug by the white ceramic end, spark plug threads and electrode side pointing up. Shove the 0.610mm metal card in the gap between the curved metal and flat metal parts. This is where the spark from "spark plug" happens.

If it can't fit then use pliers and carefully make the gap a little bigger. Try other metal cards such as 0.635 and 0.66mm. They should all fit. Then try a 0.711mm, which is too large for your optimum gap. If this metal card fits then your gap is too wide. Use pliers and carefully make the gap smaller, or push it against something to bend it so it's smaller. Recheck with your metal cards. When your gap is within your manual's specifications you're done.

Re: Should I gap my plug?

I knew about those little metal cards because I saw them in highschool (a few yrs back) and I knew that you used them to measure the gaps. I never knew you had to bend the metal hook thingy yourself though, if it was that simple I would have done it way back. I knew it was possible really, I just thought the pros might have a tool to do this precisely, instead of bending measuring bending measuring type of process. Thanks for the help thus far.

All I need to know now is:

What gap does the manual suggest (I don't own a manual)?

Does anyone know what the gap size should be? I heard .6 - .8 but that isn't very specific.

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