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9.9 2 Stroke Lower Unit Pressure Test

N

NETim

New member
I rebuilt the water pump on the new to me 9.9 stroke (SN 0CXXXX). It will hold pressure at 10PSI for about 3 hours or so but overnight it will be down to zero. I have sprayed what I can with soapy water but can see no bubbles.

I re-assembled the bottom gaskets etc with no gasket sealant or RTV as the shop manual didn't call for any. I did notice that when I took it apart there was some black RTV on the plastic block,

I replaced all gaskets and seals with a kit, so I'm pretty sure they're good.

Should I pull it apart and put some RTV or Merc Perfect Seal on the lower gasket? Or is this sealing up "good enough?" I'm not sure what the spec is for maintaining pressure timewise. When searching the web, I see all kinds of opinions on just how long the lower unit should be able to maintain 10 PSI. 5 minutes to 24 hours!

Thanks!
 
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I have done some pressure testing as well.----Some time ago I realized that overnight the pressure would go to ZERO on some motors.-----After pulling my hair out I realized that air was leaking THROUGH the gasket material on shift rod cover.------Oil would seal that gasket material.
 
I assume you tested it dry, before adding any oil? Personally, I use a very thin amount of sealant on this gasket. I also operate anything that rotates or slides, once pressure is applied with my tester.
 
timguy said:
I assume you tested it dry, before adding any oil? Personally, I use a very thin amount of sealant on this gasket. I also operate anything that rotates or slides, once pressure is applied with my tester.
Click to expand...


I drained the LU for several days before undertaking this operation. I've been rotating the drive shaft and prop shart as well as operating the shift rod.
 
Did u spray soapy water on prop. Shaft seal ? Or your vent plug ( if pressure was at drain plug)
Also spray your pressure tester.
 
Mikey N.C. said:
Did u spray soapy water on prop. Shaft seal ? Or your vent plug ( if pressure was at drain plug)
Also spray your pressure tester.
Click to expand...

Oh definitely! The tester is an el cheapo eBay unit. First Time I've used it. It could well be that it is the leak. I should pinch off the line and let it sit to isolate the pump from the LU.

I have not been able to see any bubbles using the soapy water.
 
I'm into vacuum testing of these things. If they will hold a good vacuum, water stays out. If they leak a bit on pressure, some oil may get out, but there's plenty left (and very little is actually needed to maintain the gears and bearings). Inside the usual car/ truck trans is at least 60 to 70 percent (by volume) of air, right.

Jeff
 
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