Changing spark plugs......................

R

rgl1100

Member
Jun 21, 2010
146
Massachusetts
Boat Info
340 Sundancer 2003
Engines
Twin Merc 8.1S
Just wanted to drop a thread on changing out the spark plugs on my 2003 340 sundancer with 8.1HO V drives. As is mercruiser fashion I did all 16 plugs and was sore for a day. It's amazing how hard some of these things are to get to in this boat. I managed to do it and, compared to changing the water impellers, it seemed like a piece of cake but not the easiest job. I just ordered 2 spark plug wire sets from Rock Auto and will put those in once the boat is on land for the off season. However, if anyone is having fuel economy issues I'd advise to invest in changing out the plugs if they're over 3 seasons. I did and have had a real improvement in fuel economy and overall performance. The engines ran very well before but now they're truly outstanding. I decided to do the wires since they're original but, honestly, they do look fine. Two things are on the agenda for the off season. I'm going to redo both rudder stuffing boxes and change the hoses leading from the through hull engine intakes to the strainers. Both of those short hoses look a bit rough.
 
rgl1100 said:
Just wanted to drop a thread on changing out the spark plugs on my 2003 340 sundancer with 8.1HO V drives. As is mercruiser fashion I did all 16 plugs and was sore for a day. It's amazing how hard some of these things are to get to in this boat. I managed to do it and, compared to changing the water impellers, it seemed like a piece of cake but not the easiest job. I just ordered 2 spark plug wire sets from Rock Auto and will put those in once the boat is on land for the off season. However, if anyone is having fuel economy issues I'd advise to invest in changing out the plugs if they're over 3 seasons. I did and have had a real improvement in fuel economy and overall performance. The engines ran very well before but now they're truly outstanding. I decided to do the wires since they're original but, honestly, they do look fine. Two things are on the agenda for the off season. I'm going to redo both rudder stuffing boxes and change the hoses leading from the through hull engine intakes to the strainers. Both of those short hoses look a bit rough.
Click to expand...

Thanks for the info. I have the same engines. How was it changing your impellers? I was talking to the service techs at my dealer who I work with and they said part of my exhaust system will need to be removed for an impeller change on my boat. They charge about $350 per engine. I was going to have them done during the off season.

Spark plugs are also on my to-do list.
 
Ryan - I've done my own impellers on my (now sold) '05 340. The stbd one takes about 45 minutes, and I did the port one (without moving the muffler) in an hour and 15 minutes. And like rgl1100 I was sore for a day (pre-treat with Aleve!!!). The hardest part is getting the two hoses loose on the back of the pumps. Once you get the clamps off, work the pump up/down and back and forth and the entire pump will come loose. Hampton did a great write-up with pictures on the job.

Plugs are easy if you get a forked/u-shaped boot puller from AutoZone and a 30° wobble magnetic plug socket - about 30 minutes per engine with those tools. Bruce (Kreole Kid) switched from AC 41-983's to a Champion plug which he says lasts longer in the 8.1s.

Dealers will get $200 to $300 per engine for oil and filter changes. Buy the $150 Jabsco Oil Change Pump Bucket and you can do those in 15 minutes per engine/generator.

It's not easy, but it's not hard either if you can use a set of wrenches, screwdriver, and sockets. I am 66 (and I think I will donate my body to "science fiction"), and as I say - "working in my ER will either kill me or keep me young". It's not much better on my 410. Not dead yet!

My Dockmate just paid $3000 for a major service - the dealer used the wrong oil/wrong filters/put his used spare impellers in (by mistake) instead of new ones. To repair an inop rheostat on his dash lights he rewired them directly to the nav light fuse which now blows because of too much load (no dimming either!). It went on and on. He and I don't mind paying for service, but we don't want to get cheated either. His job was complete incompetence on the part of the dealer's mechanic. I look forward to hearing what they did to resolve the issues.
 
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carterchapman said:
Ryan - I've done my own impellers on my (now sold) '05 340. The stbd one takes about 45 minutes, and I did the port one (without moving the muffler) in an hour and 15 minutes. And like rgl1100 I was sore for a day (pre-treat with Aleve!!!). The hardest part is getting the two hoses loose on the back of the pumps. Once you get the clamps off, work the pump up/down and back and forth and the entire pump will come loose. Hampton did a great write-up with pictures on the job.

Plugs are easy if you get a forked/u-shaped boot puller from AutoZone and a 30° wobble magnetic plug socket - about 30 minutes per engine with those tools. Bruce (Kreole Kid) switched from AC 41-983's to a Champion plug which he says lasts longer in the 8.1s.

Dealers will get $200 to $300 per engine for oil and filter changes. Buy the $150 Jabsco Oil Change Pump Bucket and you can do those in 15 minutes per engine/generator.

It's not easy, but it's not hard either if you can use a set of wrenches, screwdriver, and sockets. I am 66 (and I think I will donate my body to "science fiction"), and as I say - "working in my ER will either kill me or keep me young". It's not much better on my 410. Not dead yet!

My Dockmate just paid $3000 for a major service - the dealer used the wrong oil/wrong filters/put his used spare impellers in (by mistake) instead of new ones. To repair an inop rheostat on his dash lights he rewired them directly to the nav light fuse which now blows because of too much load (no dimming either!). It went on and on. He and I don't mind paying for service, but we don't want to get cheated either. His job was complete incompetence on the part of the dealer's mechanic. I look forward to hearing what they did to resolve the issues.
Click to expand...

Thanks for the thorough feedback. I've always had my dealer do our oil changes when they winterized. They package it together. They charge $490 per engine for labor and parts. That price also includes replacing the fuel filter and topping off fluids and fogging the engine compartment. With the generator and fresh water system, they end up charging me just over $1500. I feel like they do good work.

With that said, I'd like to start doing some maintenance myself. I have gotten very experienced with cleaning sea strainers, removing and cleaning out hoses, replacing the generator impeller (easy task) and fixing the AC pump from time to time. Also battery maintenance.

I think spark plugs would be an easy task. The issue with the impeller is removing the belt, which in my boat is tough. My engines face aft and the exhaust system is just inches from the belt.
 
Ryan,

On my 340, I could get aft of the engines and work around the mufflers using a 14mm and 16mm (if my memory serves me correctly) open end wrench, loosen the belt tensioner bolts and remove the serpentine belt. Do them one side at a time and you always have the other engine to look at to verify correct "routing" on re-installation. I could do this from the same position where I check the aft bilge pump, fire bottle pressure, and trim tab fluid level.

And you are right - that Kohler genny impeller is a 7 minute task.

I would order 5 gallons of Full synthetic oil and the tall HE oil filters from Merten Marine along with fuel filters and genny spares for about $200 for my fall oil changes - 9 Qts per engine and 1 1/2 qts for the genny. My Cats in the 410 each hold 6 1/2 gallons (the genny holds 1 gallon), so it will be a little more for oil on this one in November!

I would take my oil samples prior to the change as well.
 
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Carter, those Champion plugs are still going fine after a season running them. If my memory serves me right, I would have already been changing the A/C Delco's out right about now.
On another note, THE RED SOX ARE KICKING A$$ RIGHT NOW!!!!!:thumbsup:
 
Carter, I'm going to the the marina this evening and will report back to you later :thumbsup:
 
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Thanks Bruce,

Even though I'm not an 8.1 guy anymore, I had the same experience you did with the ACs and I would have switched next change as well...
 
Carter
Tell me more about the tools. Boot remover? Wobble magnetic plug socket? I think I have a bit more room to work than you did on the 340 but I'm sure it's still gonna be a task.

I ordered 16 from RockAuto and AC has a rebate program going now. $2 per plug, so they came out to about $2.50 per (minus the cost of a stamp).

Tough to find a gapping tool with the right dimension. I read it's best to use the wire type tool rather than the coin so you don't scrap the iridium off the end.

Note this one doesn't have .060". Had to order online. Pep Boys only had this one.

I've also heard that these engines are notorious for fouling plugs (?)

2ZPF9_AS01.JPG
 
This thread is timely... Noticing my port engine burning about 7-10% more fuel than my starboard. NO fuel in the exhaust that I can see but it sure does smell rich when I'm idling out in the channel.

Sounds like I'm going to have to contort my 6'2'' 250lbs in all sorts of ways. Someone needs to invent some sort of engine room harness to hang from the arch
 
Ron - Just Google "Spark plug wire puller tool". You'll come up with these:

Boot Puller.jpg
tool.gif

I like the second one better. I've had no luck with this type:
images.jpg

I used the coin type gapper. The AC plugs all came at .060 anyway, so it turns out all you are doing is "just checking". .060 is a wide gap due to the high energy ignition system that the 8.1s have.

Then Google "magnetic spark plug wobble socket" and get a set (or one) of these:
index.jpgindex1.jpg
they are worth the $40!

Zorba - those were the exact symptoms I had the first time mine needed changing - also I would get a minor surging at 2500 RPM. This was all on one engine, but that just means time to change them both. Good luck at 6'2"!

Guys, don't forget to remove that one manifold rubber hose to make your life easier.
 
Thanks Carter.
The plugs are 5/8" (not 13/16"), right?
 
Got a tube of that in my tool drawer all the time!
 
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