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Merc 7.5hp Blueband (1982) drive shatt o-ring help.

J

JimmyAt

New member
Hi all,

First timer here.

I have Blueband Merc 7.5hp outboard. Serial number is 6176604 which I think makes it a 1982.

I had some water flow issues that I worked out and she is pumping water fine now. But when reinstalling the lower leg it looks like there is meant to be an o-ring at the top of the driveshaft just below the spline. There wasn't an o-ring when I dropped the leg out (not sitting in housing anywhere either) but there is a groove there and it seems to make sense that there should be an o-ring at the top end of the spline. one video on Dr youtube showed a similar motor having an o-ring but wasn't the exact same model. Equally most Dr Youtube videos show an o-ring or rubber seal above the water pump housing that needs to be slid back up over the drive shaft before removing the impeller housing, there was not one on my motor.

Any help would be great to keep the old girl going smoothly.

Cheers
 
There needs to be one up top in the groove to seal the splines from water intrusion in the crank. The crank is probably all pitted from it not being there. The square O-ring on top of the pump is call a slinger just push it down to the pump seal after installing the housing. lightly grease the splines and upper oring sust prior to insalling the lower unit. Too much grease can cause a hydraulic effect putting pressure up on the crank and down on the driveshaft. A light coat of grease will protect the splines from rusting in the crank.
 
thanks mate. you would happen to know the part number for the o-ring would you?

there is plenty of oily crude in the housing/leg, might that be from not having the o-ring in place? or perhaps just a rich oil mixture and exhaust gases. I assume it should be pretty clean inside the housing/lower leg (I'm a little green on outboard motors).
 
You can find all the part numbers here using the serial number range. The dirty driveshaft housing is normal especially if doing alot of slow speed operation. Just get it running good and blow it out running at high speeds for extended periods. Get a can of seafoam spray and give it a good decarb also after a good tuneup.
 
Howdy, on older models the crankshaft was bare-ended and the O-ring on the driveshaft sealed against the I.D. of the machined surface of the crankshaft.

On newer models like yours, Merc went to a stainless seal carrier sleeve pressed onto the crankshaft end, with a rubber seal pressed onto the end of the sleeve.

The driveshaft had no groove, and passed thru the rubber seal, which rode against the smooth part of the driveshaft (below the splines), sealing in that manner.

Some possibilities: A previous owner may have replaced a bad lower unit with an older one that had the groove. Or, someone has had the powerhead off and the seal carrier and sleeve were removed.

I think the O-ring groove should be able to pass thru the rubber lips of the driveshaft seal without harming the seal, if it's there. You can verify by looking up the middle of the mid-section with a strong light, to get a view of the end of the crankshaft.

If the seal is there, it should be evident. Other possibilities are just the stainless sleeve with no seal on the end, or seal and sleeve gone, in which case you'd see the bare end of the crankshaft, with the crankshaft splines clearly visible.

It's very important to figure out what's going on, because water isn't supposed to get into the crankshaft splines. The crankshaft is steel so the splines will just rust away and that's a bad thing!

So that's my advice, FWIW; take a look up there and see what you have. For piece of mind, if anything else.

See the attached pics, the stainless seal carrier is #3 in the crankshaft diagram.

HTH, let us know what you find.........ed
 

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Do yourself a HUGE favor and leave it out. Just lube the splines thoroughly with a marine grease. Most Mercs never used that O-ring, and it makes getting these 'slanters' back together a pain in the *ss.

Trust me; I've do several dozen a year.

Jeff
 
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