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Author Topic:   Testing Gear Case

windblown posted 01-30-2009 05:33 PM ET (US)
I've located a possible replacement gear case for my late 1980's Mercury 90-HP motor for my 17-foot Boston Whaler. The seller claims the gear case was in good shape and the power head failed, so he has removed the gear case and is selling it alone. What sort of test can I do to a gear to get a feel of its internal condition without tearing it apart?
Thanks.
high sierra posted 01-30-2009 06:40 PM ET (US)
Do a pressure test on [the gear case]. You can buy the gauge for $30 to $40, or borrow one. This tests the seals. Look for milky oil in the gear case which is a sign of water intrusion. Or take it to a dealer. high sierra
windblown posted 01-30-2009 07:51 PM ET (US)
Thanks for your suggestions.
jimh posted 01-31-2009 04:47 PM ET (US)
If you perform a pressure test, be sure to check the specifications for the maximum pressure to be used. Generally the pressure used in testing is quite low. You need a gauge which can read accurately at a low pressure, and also some way of creating the pressure. The recommended procedure may also call for both positive and negative pressure tests on the gear case.
Ask the seller if he has changed the lubricant in the gear case. If he has, there is not much point in checking it for water intrusion since the gear case probably has not been run in the water since the lubricant was changed. When the gear case lubricant is contaminated with water it normally takes on a milky color due to emulsification of the water into the oil.
high sierra posted 01-31-2009 05:05 PM ET (US)
The gauge comes with a bulb to do the pressurizing. Also comes with instructions. I guess Jimh has never seen one. high sierre
jimh posted 01-31-2009 11:52 PM ET (US)
The service manual comes with instructions on how to perform a pressure test on the motor's gear case. I guess high sierra has never seen one.
DeeVee posted 02-01-2009 11:48 AM ET (US)
If I remember correctly, a pressure test and a vacuum test is required to determine that the gearcase seals are serviceable.
Doug

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Author	Topic: Testing Gear Case
windblown	posted 01-30-2009 05:33 PM ET (US) I've located a possible replacement gear case for my late 1980's Mercury 90-HP motor for my 17-foot Boston Whaler. The seller claims the gear case was in good shape and the power head failed, so he has removed the gear case and is selling it alone. What sort of test can I do to a gear to get a feel of its internal condition without tearing it apart? Thanks.
high sierra	posted 01-30-2009 06:40 PM ET (US) Do a pressure test on [the gear case]. You can buy the gauge for $30 to $40, or borrow one. This tests the seals. Look for milky oil in the gear case which is a sign of water intrusion. Or take it to a dealer. high sierra
windblown	posted 01-30-2009 07:51 PM ET (US) Thanks for your suggestions.
jimh	posted 01-31-2009 04:47 PM ET (US) If you perform a pressure test, be sure to check the specifications for the maximum pressure to be used. Generally the pressure used in testing is quite low. You need a gauge which can read accurately at a low pressure, and also some way of creating the pressure. The recommended procedure may also call for both positive and negative pressure tests on the gear case. Ask the seller if he has changed the lubricant in the gear case. If he has, there is not much point in checking it for water intrusion since the gear case probably has not been run in the water since the lubricant was changed. When the gear case lubricant is contaminated with water it normally takes on a milky color due to emulsification of the water into the oil.
high sierra	posted 01-31-2009 05:05 PM ET (US) The gauge comes with a bulb to do the pressurizing. Also comes with instructions. I guess Jimh has never seen one. high sierre
jimh	posted 01-31-2009 11:52 PM ET (US) The service manual comes with instructions on how to perform a pressure test on the motor's gear case. I guess high sierra has never seen one.
DeeVee	posted 02-01-2009 11:48 AM ET (US) If I remember correctly, a pressure test and a vacuum test is required to determine that the gearcase seals are serviceable. Doug