Mercruiser 260 - What's the trick for changing plugs?

alwhite00

alwhite00

Active Member
May 31, 2010
1,809
Michigan
Boat Info
1997 250 Sundancer
Engines
5.7 EFI/ BIII
I Changed the plugs in my mercruiser 260 and it was a royal PITA - I'm going by feel as I can not see anything and my engine is under the floor. I managed to get them all in but think I might have cracked one. Ths spark plug socket hits the exhaust manifold severly and puts everything in a bind.

I ground down the socket to see if that would help but it was marginal if any different. Any tricks or suggestions to make this a smoother process next time?

LK
 
I always did it with the rubber insert removed from the spark plug socket.

It will give you a little more wiggle room.

Gary
 
mrpaper said:
I always did it with the rubber insert removed from the spark plug socket.

It will give you a little more wiggle room.

Gary
Click to expand...

My socket did not have that in it, Just seems really tight but I can not see down there so I am not sure what is the clearance siiue.

LK
 
Fun huh? :smt013

Maybe try a "knuckle"....universal joint next time on your ratchet.

Not looking forward to when I have to do mine on the 454.
 
You can buy at any auto parts a thin wall socket I used the one that came with a stihl chain saw they will clear the tight ones just make sure you get one you can use a short extension or swivel wrench on some only have a wrench head.
 
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Most times, a regular socket will do it. But, I do have a regular socket that I ground/thinned down quite a bit. With that, I've never had a problem with any engine. But, yes, there are plenty of times that you will do things "by feel" - that's pretty much normal.

Tip: To get the new ones started back in the hole again... Use a 6" piece of rubber hose that fits just a little snug (not tight) over the spark plug body. If you end up starting to crossthread the plug, the rubber will spin instead of actually crossthreading.
 
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It might be hard, but not impossible. Take your time, and it'll get done.
If you think your's is hard, try it with twins.
 
Lazy Daze said:
Tip: To get the new ones started back in the hole again... Use a 6" piece of rubber hose that fits just a little snug (not tight) over the park plug body. If you end up starting to crossthread the plug, the rubber will spin instead of actually crossthreading.
Click to expand...

Good tip I forgot that one back when I was racing Hemi's we used a t-handle pipe with rubber hose on the end to get the plugs started cross threaded head is expensive.
 
I did the hose trick & got them snug - The problem is getting them tightened up, That damn manifold is just so tight around the plug with the socket on it, I am going to look for something a little thinner for the next time.

LK
 
My last boat had that problem on one cylinder. I ended up using a dremel with a grinder attachment and carefully ground some of the cast iron off the manifold which made the job much easier.
 
Be sure to use the best Platinum plugs you can get with the correct heat range and they should last longer and prolong the changing agony.
 
I have also used a plain wrench, the round closed end when the spark plug socket won't fit.
 
I use a regular 3/8" drive spark plug socket with various extensions and a swivel if needed on my twin 5.7's and there is no interference problem. I have Merc manifolds. I start them with the plug in the socket on a short extension.
My grandfather taught me how to 'visualize' with my fingers to do work in blind areas. He was missing his thumb and index finger on his left hand and could use the stubs as well as most people use their fingers. He was rebuilding chain saw carbs into his late 90's when he was all but blind from macular degeneration. It always amazed me how he could 'see' with those fingers and deftly manipulated those tiny carb screws with those stumps. I always feel like I'm channeling him when I do the plugs on the boat as it's all by feel and usually with my non dominant hand.
 
Marc-FL said:
Check this out as well. Low profile spark plug socket used with a wrench:
https://www.boatingmag.com/boating-spark-plug-diy
Click to expand...

Have you actually used that in a tight space? I see it as being good for tight longitudinal access, but if the space is limited laterally (often the problem) because of the manifold, then you still need to get a wrench on it and I'm wondering if that's doable.
 
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