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  1. #1
    Seaman Apprentice
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    Default Pressure Testing Mercruiser Outdrive (Tutorial In Progress)

    First let me explain I have read just about every "Adults only" article. I have downloaded what I think are the proper manuals... I have tried searching and just seem to be spinning my wheels...

    I have been reading the manauls but again I feel like I am spinning wheels tons of information but but seems like too much to comprehend at once!

    Is there an article or post on exactly how to pressure / vacuum test and outdrive for leaks? The one in the adults section talks about the apparatus but doesn't explain the procedure.... If I understand the procedure I can build and aparatus...

    Here is what I got:
    1992 Mercruiser 4.3 Alpha 1 with Thunderbolt IV
    Engine Serial #: OD823128
    Outdrive Serial #: OD760439

    A simple tutorial with procedure, tips tricks etc and what to look for.... Any help would be appreciated, thanks!

  2. #2
    Master Chief Petty Officer
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    Default Re: Pressure Testing Mercruiser Outdrive

    Did you see the pump ziggy put together in the "adults only" thread? if you did you just hook it to your drive and pump about 15psi into it and see if it will hold the air. It should not drop in pressure at all.

  3. #3
    Petty Officer 1st Class fuzzybob's Avatar
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    Default Re: Pressure Testing Mercruiser Outdrive

    You can pick up a ready made tester on E-bay for about $30 bucks or make one. To use, just drain the oil from the drive and put 15 pounds of air pressure on it through the drain hole. You can use a bike hand pump or compressor or what ever. Let it sit a couple hours or over nite and see if the pressure drops. If its OK then put vacume to it and do the same. A Myty- Vac works well, you can also apply the pressure with one also. Most Auto stores carry the Myty-vac or similar for bleeding brakes on cars bout $30 or so bucks.
    93 Larson 190 All American, 4.3 LX 4 brl Weber, Sn OF 073363, Alpha 1 gen 2 SN OF 723905, GR 1.94 R, transom SN OF 090473

  4. #4
    Seaman Apprentice
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    Default Re: Pressure Testing Mercruiser Outdrive

    ok so...
    1) Drain Oil from Outdrive (Procedure in Manual)
    2) Remove Outdrive (Procedure in Manual)
    3) Build or Buy Tester (Adults Only Section or Ebay)
    4) Pressure up to 15 PSI and Wait ( No drop in 24 hrs)
    5) Vacuum Test to -15 PSI and Wait (No Drop in 24 hrs)
    6) Reattach Outdrive or Repair Leaks and Reattach Outdrive

    Any tips or tricks? Do I have to clamp or plug and vents or lines?

  5. #5
    Petty Officer 1st Class fuzzybob's Avatar
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    Default Re: Pressure Testing Mercruiser Outdrive

    You don't have to remove the drive to test. The tester just scews into the drain hole. Nothing to plug or clamp. If the drive fails the test then remove and find the leak. Listen for the leak or use some soapy water. It's also a good time to service the drive. You can do the test with the drive off if you want.
    93 Larson 190 All American, 4.3 LX 4 brl Weber, Sn OF 073363, Alpha 1 gen 2 SN OF 723905, GR 1.94 R, transom SN OF 090473

  6. #6
    Admiral ziggy's Avatar
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    Default Re: Pressure Testing Mercruiser Outdrive

    ok so...
    1) Drain Oil from Outdrive (Procedure in Manual)
    2) Remove Outdrive (Procedure in Manual)
    3) Build or Buy Tester (Adults Only Section or Ebay)
    4) Pressure up to 15 PSI and Wait ( No drop in 24 hrs)
    5) Vacuum Test to -15 PSI and Wait (No Drop in 24 hrs)
    6) Reattach Outdrive or Repair Leaks and Reattach Outdrive
    looks good to me. but #5, the vac. test. i don't think you'll get it to hold 15hg. the way i understand it about 7hg is about all you can get before a leak occurs. apparently the seals will normally fail above 7hg. under normal operating i guess there's never more than around 7hg of vac. so if it holds that it'll be fine. i tested mine at 5hg & 12psi last year. might also turn the drive shaft while under pressure and vac. see if it leaks after parts have been moved in the drive. what you want to see is that gauge (vac or pressure) be exactly where it was when you left it...
    'Lime Time'
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    Mercruiser 165hp (chevy 250 L6), MC-1 drive

  7. #7
    Rear Admiral Fishermark's Avatar
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    Default Re: Pressure Testing Mercruiser Outdrive

    The only thing I would add is that you screw it into the vent hole - not the drain hole. I could be wrong, that's my understanding.

  8. #8
    Chief Petty Officer
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    Default Re: Pressure Testing Mercruiser Outdrive

    Jim Frye, Mercury west coast instructor's answer to vacume testing is " show me in any manual where we say to vacume test a lower unit or outdrive". He specifically said not to do it.

    Gen II Alpha and Bravo drives with resivior bottles should be removed prior to pressure testing.

    James

  9. #9
    Petty Officer 3rd Class
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    Default Re: Pressure Testing Mercruiser Outdrive

    What Ziggy said agrees with the thought that some oil seals are design to hold the lube in, but not keep the water out. This is true at the drive shaft seal. Don has stated many times to check the bellow for water, because it can leak past this seal and contaminate the lube.
    5inHg (inch of Mercury) = 2.45 psi

  10. #10
    Seaman Apprentice
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    Default Re: Pressure Testing Mercruiser Outdrive

    A) I was going on what I read and though I understood that you have to remove the drive to pressure test b/c with it attached it won't seal and lube will leak out.

    B) I just assummed that it needed vac testing based on reading and the fact the adults only section shows the apparatus with both pressure and vacc guage and both a pump and vaccuum pump...

    Here is an updated procedure I wish there was a step by step tutorial on here or anywhere that would make it very easy for us noobies!

    1) Drain Oil from Outdrive (Procedure in Manual)
    2) Remove Outdrive (Procedure in Manual) (*Optional on Alpha I Drives)
    3) Build or Buy Tester (Adults Only Section or Ebay)
    4) Attach tester to Vent Hole (Upper Plug on Drive)
    4) Pressure up to 15 PSI and Wait ( No drop in 24 hrs)
    5) Vacuum Test to 5 inHg (inch of Mercury) = 2.45 psi
    and Wait (No Drop in 24 hrs) (*Possibly not a good Idea??)
    6) Reattach Outdrive or Repair Leaks and Reattach Outdrive

    Additions or corrections... My plan at this point is to build the apparatus and do the procedure documenting the process and publishing an article or thread on here for all the noobies that follow after so input is appreciated!

  11. #11
    Chief Petty Officer
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    Default Re: Pressure Testing Mercruiser Outdrive (Tutorial In Progress)

    Vacume testing is called for in the OMC manuals. Acording to a very knowlegable merc factory instructor you should not vacume test Merc drives. Also it is not called for in the merc manual. Everyone here can do what they want. I was told by someone I trust not to do it on merc drives so I will not.

    James

  12. #12
    Seaman Apprentice
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    Default Re: Pressure Testing Mercruiser Outdrive (Tutorial In Progress)

    with the exception of the vaccuum test are we looking good? any more tips I am getting ready to start this project...

  13. #13
    Seaman
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    Default Re: Pressure Testing Mercruiser Outdrive (Tutorial In Progress)

    The actual pressure testing is easy, but the hard part may be finding the leak (if there is one).

    I'm losing pressure at a pretty good rate (it only takes a few minutes to go from 15 psi to 0 psi). I did the test with the drive removed and I have been unable to find the leak so far. The yoke and seal on the upper gear housing are brand new. It appears that neither the yoke seal nor the prop seal are leaking, so I'm in the process of addressing the other seals in the gear housing. Tomorrow I'm going to have a look at the shift shaft seal and the water pump seal.

    You may want to keep this in mind if you have similar results.

  14. #14
    Chief Petty Officer coastalcruiser's Avatar
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    Default Re: Pressure Testing Mercruiser Outdrive (Tutorial In Progress)

    This is the vac-pressure tester I made.

    Fuzybob
    Listen for the leak or use some soapy water
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  15. #15
    Seaman Apprentice rbthntr64's Avatar
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    Default Re: Pressure Testing Mercruiser Outdrive (Tutorial In Progress)

    Did you ever find the leak? If so what was it? and did it require a complete teardown to remedy?
    Freedom is not free. Some will perish to preserve it for the many.

  16. #16
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Pressure Testing Mercruiser Outdrive (Tutorial In Progress)

    Why did you ask this on a thread from 2009. The OP hasn't even been back since 2009.
    If you have a problem, start a new thread of your own, include your engine and drive info and what you have found. Just because someone fixes their leak doesn't mean you have the exact same leak.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

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