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Give advice on how to replace the spark plug in cylinder number four (the lowest cylinder) on a 2019 Mercury 115 FOURSTROKE engine.

Q1: is there a special special tool or a special procedure to replace the spark plug on cylinder number for (the lowest cylinder) on a 2109 Mercury 115-HP FOURSTROKE engine?

BACK STORY
I began to replace the spark plugs on my 2019 Mercury 115-HP FOURSTROKE engine. To replace the spark plugs on cylinders one, two, and three, took only ten minutes. To replace the spark plug on cylinder four then took me an hour--a very frustrating hour.

My hand would not fit into the available space. I could not see the spark plug without a mirror. I do not want to repeat this process.

Note, I have the following tools:

• regular ratchet [wrenches]
• small [ratchet wrenches]
• three-inch extention
• three-inch flexible extension

Neither extension helped

[To install the new spark plug into cylinder four on the 2019 Mercury 115 FOURSTROKE engine], I pushed [the spark plug] into the [the threaded boss on the engine, but I could not see what was happening]. After ten attempts, I got lucky: I felt [the spark plug] turn. I tightened the spark plug with my fingers. The a three-inch socket was put on the spark plug, and vice-grips were used [to turn the socket and] tighten [the spark plug].

A ratchet [wrench] was tried, but the [ratchet wrench] kept locking onto the spark plug. I had to [loosen the spark plug socket from the spark plug]. The vice-grips allowed me the pull off the socket [from the spark plug]. This whole process was one hour of frustration. There [must] be a better way.

Thank you for any advice.

I am not familiar specifically with the details of how to change the spark plug for cylinder four of a 2019 Mercury 115-HP FOURSTROKE outboard engines, but typically if the lower pan of the engine cowling obstructs access to components of an outboard engine engine, you need to remove the lower pan of the cowling to remove the obstruction and get better access.

Kend wrote:Q1: is there a special special tool or a special procedure to replace the spark plug on cylinder number for (the lowest cylinder) on a 2109 Mercury 115-HP FOURSTROKE engine?

For a spark plug that is particularly hard to access, you may need to get a special socket with a universal joint built into the socket. For example, here is a link to one available on-line:

https://www.amazon.com/WORKPRO-Magnetic ... DXM2/?th=1

If that link goes dead, just search for "spark plug socket with universal joint" and you should find many similar results. These special sockets should be available in the sizes needed for spark plugs.

Generally a spark plug should be tightened to a specific torque setting. If a universal joint is used, the amount of torque applied to the actual fastner via the universal coupling will not be exactly the same as indicated by the torque wrench. See

Tested: Do Universal Joints Affect Torque Applied to a Fastener?
https://www.youtube.com/watch?v=pl7O7r7Rab0

The results of this testing showed that the decrease in torque applied to the fastener compared to torque indicated on the torque wrench varies with the angle of the universal joint as follows:

00-degrees = 0.967
30-degrees = 0.881
45-degrees = 0.764
60-degrees = 0.576

The [socket with universal joint linked above] looks like it will work. I have one on order from Amazon. The size and angle are correct.

Thanks for replies,

This may be blasphemy to some but I have drilled holes to allow the standard spark plug socket to have straight access to the plug. The hole created can be covered nicely with a rubber plug, just drill the hole big enough to fit the socket and to match the correct size plug. This works for many tight areas where you are going to need to access a tight space in future for maintenance like changing spark plugs. Rubber plugs are available at places like NAPA or on Amazon in Canada.

[I have replaced the original URL which was pointing to Amazaon-Canada. As a result the price of the recommended item was reduced to $14 from $20.]

https://www.amazon.com/Firewall-Assortm ... B09ZLBCJZX

The price of the universal spark plug socket is less than the price of the assortment of rubber plugs. I would be very hesitant to drill a large hole in the cowling of an outboard engine. A replacement OEM cowling at today's prices will be perhaps $300 to maybe $1,000.

Acquiring more tools is the quintessential “guy” thing to do, and, as we know, the guy who dies with the most tools collected is the winner.

You have to [alludes to a character popular on Canadian television, named Red Green whose eponymously named television show was a parody of the do-it-yourself home improvement guy, but I do not think most American boaters would understand this reference ] it sometimes.

[More about THE RED GREEN SHOW at Wikipedia]

If women don’t find you handsome, they might find you handsome. [Something has been lost in translation on this sentence.]