88 5.7 Mercruiser Spark plug change

[NHGuy]

I am in my 2nd year with this boat and hadn't changed my plugs yet. So I got up early today and went out to the yard thinking I'd pull a plug & look at them. I had bought a set of plugs but I was going to see how the old ones looked first. To my surprise I could not get a plug socket on the 3 plugs I tried. Am I missing something, or do I pull the exhaust to get my spark plugs out?

 

[Don S]

Re: 88 5.7 Mercruiser Spark plug change

I took a regular spark plug socket and ground it down as shown. Now it clears those older manifolds with no problem.

 

[NHGuy]

Re: 88 5.7 Mercruiser Spark plug change

Thanks, you just saved me beacoup time. I love having experts to share their knowledge. Really appreciate the tip.

 

[TilliamWe]

Re: 88 5.7 Mercruiser Spark plug change

If you get really lucky like I did, you'll find a deep well socket that has thinner walls and you don't need to grind it down. So if you don't feel like grinding yours down, take it to the tool store and compare it to others. If you find one with a smaller outside diameter, it might work, without modifying it. Good luck.

 

[NHGuy]

Re: 88 5.7 Mercruiser Spark plug change

You are right about thinwall sockets, in fact I run a tire & repair shop and most of our guys have thinwall car sized sockets in their boxes.
Any way I already "improved" the socket that came in my first tool set, it's the oldest of the 4 spark plug sockets I have in my box.
I kinda hope the plugs are necessary. I'm not getting the top end I expected with this boat. After the plugs and timing check I'm done with basic tune-up. The only things original to me are the distributor sensor and some excellent looking OE Mercruiser ignition cables. Do Boat techs do the mist test on ignition wires, ie. spray em with a water mist while running to check for arc's?

I have a set of new aftermarket wires, but I'm not putting them on at the same time as the plugs unless I find a reason to dump the existing wires. I want to change them by themselves so I will know what difference they might have made.
The reason for all these steps is I want to know what each thing does. And there is a reason for that too. I did a Chinese cap & rotor this spring to replace a corroded cap and good rotor. Motor lost 150 idle RPM. So I put the Mercruiser rotor back on, that's the next test. I should have just sprung for OE, I know better...sometimes I'm a cheapskate dope.

 

[JustJason]

Re: 88 5.7 Mercruiser Spark plug change

Do Boat techs do the mist test on ignition wires, ie. spray em with a water mist while running to check for arc's?

Nope.

But what I do to check for leaking high tension wires is grab a cheap test light, ground the ground end, then start running the probe end up and down the wires. On a V8, you typically won't hear it stumble, so look to see if the light starts to flicker.

BTW, plug wires are a normal maintenece item and should be replaced according to a time schedule (usually 3 to 5 years). If you don't replace them, caps, rotors, and coils will all fail prematurely.

What tire shop to you run? I may have a business prop for ya. Pm me.