How to change spark plugs 496

[jetboatmatt]

Hi guys I was just wandering how hard it is to change the spark plugs on my 496mag? I have changed plugs on motors that did not have coil packs.
It just looks tricky,any ideas?
Can I run into trouble by doing them myself?
What plugs do you guys use in yours? Any after market ones or just stick with Mercruiser?
Thanks for any info ou guys have!!!!!!!!!!!

 

[riverbrian]

I will be taking on the same project this winter. I just am afraid I will buy the wrong plugs.

 

[McRib]

How many hours do u guys have?? Replacing plugs is not a common thing under 300 hrs. I was lookin in my merc book and it says nothin about plugs before 300 hrs. When u do it id use what merc says. Call there 800 number or a reputable shop and buy them. Merc replacements are like 30 bucks each. Not a cheap project fo sho.

 

[riverbrian]

yea....I think i will wait, 160 ish hours.

 

[ghansen]

The plugs are platinum. They are pricey.

 

[HBCraig]

Order them in accordance with your serial number. There is a difference.

 

[Jet-Daytona]

How many hours do u guys have?? Replacing plugs is not a common thing under 300 hrs. I was lookin in my merc book and it says nothin about plugs before 300 hrs. When u do it id use what merc says. Call there 800 number or a reputable shop and buy them. Merc replacements are like 30 bucks each. Not a cheap project fo sho.

Merc. is a ripoff:thumbsdown

 

[jetboatmatt]

Not sure what's going on then!
I had a vibration so I took it in and they changed one spark plug.
It then ran perfect for about 45 hours.
Took it out the other day,started to do that vibration
then it cleared out.
I had no choice in havasu but to put 91
and i hear that will make those run dirty!!!
I just thought maybe I should change them all to new ones and go from there...
I know there kinda of exspensive but it wont hurt
to put new ones in. 200 hundred if I do it...who knows how much if someone else does...

 

[DaveC]

Probably same plugs in an 8.1 chevy. Go to napa and get them

its the heat range thats important

 

[Crazyhippy]

Not sure what's going on then!
I had a vibration so I took it in and they changed one spark plug.
It then ran perfect for about 45 hours.
Took it out the other day,started to do that vibration
then it cleared out.
I had no choice in havasu but to put 91
and i hear that will make those run dirty!!!
I just thought maybe I should change them all to new ones and go from there...
I know there kinda of exspensive but it wont hurt
to put new ones in. 200 hundred if I do it...who knows how much if someone else does...

Did 91 octane cure the vibration?

 

[McRib]

Fuel filter and screen is clean I assume?? Running any thing other than 87 will cause ur motor to "detune" itsself to burn the 91 as 87. This may have caused ur original prob unless ur a 87 runner all the time. Pullem and clean them first and run again. Check ur motor and drive alignment also. I had a vibration a while back and it turned out one of my port side motor mount bolts had came loose and put a few things out of whack. Had a proper alignment done and have not had the vib since.

 

[jetboatmatt]

Hippy it did not!! I always run the 87oct just one trip I put about 30 Gallons of 91 in. Then came home and ran it a month later on my local lake and it started to have a slite vibration as I got on the throttle it cleared out ran great the rest of the day!!!

Have any of you guys replaced the plugs before?
If so how hard and any tips for me???
Thanks guys!!

 

[Crazyhippy]

91 not curing it tells us that it's most likely not something simple like old fuel.

Changing the plugs shouldn't be to tough. There are still plug wires on the BBC's. It's just like the old motors, only it has 8 coils and no distributor. Might actually be easier, because you do not have to worry about mixing up wires any longer (just did a tune up on a dual plug Porsche 6... 12 plugs, 12 wires, and not layed out like you would think:bash

All in all, plugs are quick and easy (relatively). Some of my hot rod stuff I changed plugs every oil change (course plugs were a buck a piece).

 

[Boat Tech]

You could also pull out a spark plug and get the number off the spark plug itself, Then go to a GMC/Chevy dealership and buy the plugs there, You should save some $$$ doing it that way.

Do you have your engine serial number?

 

[icecreaman]

Let me start this by saying that I'm not experienced with Merc as a power plant, but do have some knowledge with GM products as a previous tech. Two things you may want to consider; 1) It's taboo to cleen platinum plugs (spraying off with carb cleen is ok, just don't bead blast them.) 2)Platinum plugs are designed to run for several hundred hours, thats why there like $15.00 a piece,they don't foul on their own for no reason. If in fact you are fouling spark plugs, you need to find out the reason why. Point is the spark plug isn't the cause of the of the problem, but the effect of the problem. Possibly either an ignition or a fuel problem, but I don't think it's as simple as 87 or 91 octane fuel. Someone needs to look a little deeper into this. Good luck.

 

[dribble]

I changed mine at 77 hours to cure a cold start misfire (it worked). They are very easy to change. Also don't buy them from the marine dealer. I bought the correct AC plugs at Autozone for about $24.00.

 

[Gelcoater]

Fuel filter and screen is clean I assume?? Running any thing other than 87 will cause ur motor to "detune" itsself to burn the 91 as 87. This may have caused ur original prob unless ur a 87 runner all the time. Pullem and clean them first and run again. Check ur motor and drive alignment also. I had a vibration a while back and it turned out one of my port side motor mount bolts had came loose and put a few things out of whack. Had a proper alignment done and have not had the vib since.

Im thinking there might be something to the first part of this post.If the engine is designed to run 87,the switch to 91 may have caused the computer to change the tune a little.Octain rating is an age old bench racing topic,higher the number the more resistance to burn.So if you start running 91 where 87 worked,it would seem you may be passing more unburned fuel past the plug,creating fouling,thats why when you had a plug changed it ran better. Now its back,so sounds like another fouled plug. IM thinking I would change em all,and stick with 87.
If by chance you change plugs,and run only 87 and the problem sticks around,I would take it in for a check up,Ignition.

 

[jetboatmatt]

Thanks guys! I was thinking the same,change plugs only put 87 and go from there.... There is no smoke or wierd noise or any soot on the back of the boat. When I am full throttle it gives me the full 4800 that the 496 is suposed to give. It does'nt miss a beat. I do understand what a few of you said about the plugs fouling. I hope it's not more sinister then just a good change of plugs and gas. I think I will put a new fuel filter and water separator just to cover that part.

The motor was put on the PC and it all looked good the first time.
I hope the alarms would go off if something major was going on!!
Only have 120 hours on the motor! Im sure it's fine!!
Thanks guys!!