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Old 10 June 2018, 05:31   #1
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Aligning shaft splines - Mercury 4 stroke 4 hp

Hello I'm looking for some advice from anyone who's worked on outboards where you've had to disengage the drive shaft. I've replaced an impeller. Now I'm trying to return the lower unit to the leg. Got gear selector aligned. Drive shaft splines not engaging resulting in gap between lower unit and the leg. I've tried turning motor via engaging start cord and turning the drive shaft to align splines but without luck so far. But as I had no engine stand I disassembled and am attempting to reassemble on the floor with outboard horizontal. Does anyone know if this will make any difference? If not I'll persevere later. Any advice gratefully received.
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Old 10 June 2018, 06:03   #2
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Easier doing this job with the engine on a transom or makeshift outboard stand. Ensure engine is in neutral and gearbox too. Easy for dog clutch to be engaged when replacing impeller. Try getting the engine vertical (even mount on a sturdy fence). You may have to wiggle driveshaft to engage but it will. Grease lightly first. You can tap home with a rubber mallet if it plays hardball.
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Old 10 June 2018, 06:06   #3
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It can be stupidly fiddly... or just engage immediately.

I always make sure there are no burrs or defects on the spline ends from a previous ham fisted attempt... and file away if found. Grease the splines obviously. On some I find it easier to have in gear and move the prop to align.

In truth I end up doing most sub 8hp motors on the floor on their sides.
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Old 10 June 2018, 06:37   #4
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Thanks Spartacus and Fenlander. I may make a stand but it's good to know it should work reinstalling horizontally. I got it new in 2000/1 Fenlander so any damage to the splines will be down to me but, confession, it's the first time I've replaced the impeller. I know I should have before. Low hours but old one looked better than I was expecting.

I'll return to it later today and wiggle it some more, and try out of and in gear options. Thanks both for the advice I'll let you know if I succeed.
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Old 10 June 2018, 11:51   #5
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Wiggle the prop as you offer it up so the shaft is moving.

Getting splines to engage horizontally can be an utter PITA - I've just done some work on my RRC gearbox which required removing the torque converter. This has a couple of sets of splines to engage on the input shaft. The factory manual shows doing it horizontally. I have done it that way before but it took a loooong time & our cat learnt some new words. This time I hung the box up vertically with an engine crane & lowered the TC onto the shaft. Straight on no problem.
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Old 10 June 2018, 12:52   #6
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Did wiggle the prop, no joy so I did try with it hung on fence still no go. Now I have gone in reverse having dislodged gear linkage clamp. And I need to get very long nose pliers or will have to fabricate a tool to hold up to gear linkage so I can reclamp via service hole in the leg.
I'll tell myself it's all experience.
Something tells me I may be some time.
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Old 20 July 2018, 05:34   #7
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So I fabricated a (wobbly) stand and fangled something together with tea stirrer, elastic band and screwdriver to get the gear linkage connected again. I'm now back to where I more or less started before taking a holiday. The distance between the leg and lower unit with prop and gearbox is around 4.3 cm. Does anyone know if there is something near the motor unit spline and the shaft spline that I need to thread through? Or is it still a matter of faffing about turning motor and trying to get alignment? Many thanks for any advice recieved.
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Old 20 July 2018, 05:57   #8
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Oh and I also forgot to ask any tip on making sure the pipe carrying water from the pump to the motor is aligned. Just in case this is part of my problem?
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Old 20 July 2018, 08:47   #9
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The 4.3cm sounds... give or take... where the splines start to engage. Are you totally sure there is no bur on them so that first engagement is reluctant?

Usually the water pipe will feed on OK as you push it together... in my case it has only ever been the splines being a pig to start.
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Old 20 July 2018, 15:34   #10
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There is an oil seal in a housing under the powerhead in those engines. I guess the oil seal is no longer in the correct place and you cannot get drive shaft through it. Get a torch and have a look , you will see oil seal if has came out housing. Powerhead off job to repair.
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