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Thread: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head removal??

  1. #1

    Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head removal??

    Hi guys,

    I have an 04 Merc 2 stroke 3 cylinder which has been great for the past 5 years since I bought it second hand.

    Talking with my Outboard Mechanic he says it now needs a Major Service which involves removing the PowerHead to replace all of the gearbox gaskets and other gaskets below to ensure the Outboard stays A ok.

    I was surprised to hear this as its a big job and would/could cost lots especially if he struck issues removing it so I went to a local outboard mechanic and asked their opinion and they said this is not required. Their opinion was that at such major service interval something that 'does' need doing is that you check all the internal anodes. They said you may have to take off exhaust plate to check these internal anodes. Check for Corrosion around the cylinder and head exhaust plate and replace if required.

    So if there are any people experienced in major services on 2 stroke engines (Merc's in particular) I'd like to hear from you as to what 'your opinion is' as my regular guy thinks removing the Powerhead after so long is a must. He said that if its never been removed before (which I'd say would be true) it really needs to happen.

    Thanks for your thoughts and input.

  2. #2

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    That depends if u do have one or more anodes inside of your powerhead exhaust plate there may be inly one option that is to remove the powerhead so the mechanic can undo the exhaust plate bolts its a bit of a nad design if this is the case as anodes will be placed strategiclly to stop corossion however they need to be easily removed for replacement too

  3. #3

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    It will be for the bottom crank seal

  4. #4

    Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head removal??

    I don’t know where you are based but I would ring Mal at Creek marine 3354 1475 and ask some questions, he knows mercs and is based at Alderly . Matt
    A bad days fishing has got to be better than any day at work......


  5. #5

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    I'd get a third opinion from a long standing Mercury Dealer, where are you?

  6. #6

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    Quote Originally Posted by spud477 View Post
    It will be for the bottom crank seal


    This. Many a Merc has died from the leaking bottom crank seal.

    DoNotFeedTheTrollsAandBelligerent

  7. #7

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    I called Holt Marine today (long term Merc Dealer on the Northside as I am on the Northside of Brissy) and they say removing the Powerhead is not necessary and can open a can of worms possibly. I will call another one or two to confirm but that's there opinion anyway for an 04 model.

  8. #8

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    Holt Marine Merc Dealer just told me that there is none inside so that other outboard mechanic head man (from a very well known major Brisbane based boating and outboards outlet) was incorrect. So much miss-information out there its very frustrating.

  9. #9

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    Quote Originally Posted by Steeler View Post
    This. Many a Merc has died from the leaking bottom crank seal.
    Hopefully not mine though and hence trying to find out if this model 'really' needs this done. Not actually according to Holt Marine

  10. #10

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    They normally idle very badly on the muffs if the bottom seal is leaking.

    Assuming the leg will come off at some point to replace the water pump impeller they will be able to check for wear & rust around the top of the drive shaft, that should give a fair indication if the bottom seal is leaking.

    The best thing you can do for that motor is test it every time you go out, make sure it's idling normally, has normal power through out the range & most importantly make sure you achieve your normal WOT RPM.
    Even a couple of hundred RPM down on normal is cause to investigate further if it can't be explained by increased weight or different weather/water conditions.
    It sounds like a lot of mucking around but really it's nothing, just make sure it's running OK and give it a WOT blast, you will know if it's all OK.

    Exhaust plate can be a worry but it will show up in your performance tests above.

  11. #11

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    I found when i worked on my Merc 25 4 banger the local Merc dealer had no clue about this engine none at all i than went to another dealer to order my crank and rod bearings and they had to look it all up, they however know 2 strokes pretty well

    if i were u with all this conflicting information from the dealers i would go to the Merc web site and look to see if they have a owners manual u can download i know Yamaha do, this manual might tell u what is to be done at X hours

    removing the powerhead by a professional mechanic can be time consuming and costly however if u were to do it your self u could just lift the complete powerhead off in one go with everything attached minus a few minor things like manual choke rods and kill switch etc... but on a 04 model u may find the powerhead to mid section bolts seized

  12. #12

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    Quote Originally Posted by gazza2006au View Post
    I found when i worked on my Merc 25 4 banger the local Merc dealer had no clue about this engine none at all i than went to another dealer to order my crank and rod bearings and they had to look it all up, they however know 2 strokes pretty well

    if i were u with all this conflicting information from the dealers i would go to the Merc web site and look to see if they have a owners manual u can download i know Yamaha do, this manual might tell u what is to be done at X hours

    removing the powerhead by a professional mechanic can be time consuming and costly however if u were to do it your self u could just lift the complete powerhead off in one go with everything attached minus a few minor things like manual choke rods and kill switch etc... but on a 04 model u may find the powerhead to mid section bolts seized
    All good but way beyond me Gazza so it will only be done by a Merc mechanic who knows exactly what they are doing as I have no clue and last time someone (an outboard mechanic) pulled my engine apart it all went pear shaped so not wanting a repeat of that performance that's for sure!

  13. #13

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    Good idea a lot of mechanics won't touch a basket case

  14. #14

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    It's important to replace the powerhead gasket (some say after 10 years) and do other maintenance such as cleaning out the galleries of salt build up:

    http://ezinearticles.com/?The-Import...ets&id=4683563

  15. #15

    Re: Major Service on a Merc 90 3 cylinder 2 stroke - what's needed? Power Head remova

    Regular inspection of your plugs will also show signs of water ingress.
    On the older ones there were pry points to separate the crankcase cover from the crankcase itself so you really only needed to lift the powerhead up far enough from the mid section to gain access to the seals. We use to place three seals back in there for good measure

    DoNotFeedTheTrollsAandBelligerent

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