1973 Yamaha 8hp suspect impeller

[ent]

I have a 1973 Yamaha 8 hp outboard where the water has stopped coming out of the tell-tale. I reckon the impeller is worn as it has not been replaced in a long time. Could some one please advise where to access the impeller on the lower unit? I removed 4 bolts on the section above the cavitation plate but nothing would budge. Is this where the impeller is located and if so would it be okay to use force to get the sections to separate or is there something else I should be undoing something else first? Is there a pipe to carry up water from the impeller to the head and if so, where could I access this to check for a blockage? Any advise and maybe a diagram would be greatly appreciated

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[WayneS]

I remember doing this to my engine a long time ago.

The reason that it may be stuck is that the drive shaft may have become bonded into the power head by heat and corrosion. I'm sure that you will do no harm by trying a little force to remove it but not too much. I think that in the end I used a big screwdriver that I inserted between to two sections (Where you have just removed the bolts) but that left some damage. Something that was the lesser of the two evils at the time.

The water is carried up to the power head in a tube that fits into a rubber sleeve. Reassembly is a bit of a task as you need to get the water tube, drive shaft and gearshift rod engaged. I managed it 3 or 4 times though.

Good luck

Cheers

Wayne




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[ent]

Hi Wayne,

so if I understand you correctly the drive shaft should drop down from the head and remain with the lower unit when I separate these sections. Should the gear be in any particular position (f/r/n) prior to doing this?

thanks
ent

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[WayneS]

That is correct. It is fixed at the bottom and has splines at the top which git into a hole on the powerhead.

I cannot remember about the gear selector but I would have thought that neutral is the place to start.

Please see my PM

Cheers

Wayne

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[steve28]

i have done several of these outboards and the thing to know is that taking the gearbox cover off is essential if you want to avoid damaging the end.
there is a small circlip on this end and when you are forcing the lowwer unit off the legg it will certainly pullthis shaft from the gearbox itself, you will in turn physically tear the impeller drive pin through the top of the impeller housing.
when you have done this the job is much easier, i think your problem is much more likley to be where the water tube goes into the power head so you will need to break the joint there too.
when it comes to putting it back together use some light oil on the threads, not copper slip otherwise it will react with the alloy.

i spent 46.00 on part that included a new inpeller, housing, pin and pwer head gasket.


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[ent]

Hi Steve28

Could you please let me know where exactly the gearbox cover, circlip is and where the water tube enters the head? thanks for all the help
ent





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[steve28]

gearbox cover is behind the propeller, two bolts normally, circlip is visible on the end of the drive shaft which comes down the main leg.
once you have freed the main legg you can undo the bolts around the main powerhead and pull it upwards this will then reveal the pipe and water galleries which are all blocked up.

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[ent]

Hi Steve,

In order to pull the powerhead up I removed approximately 10 bolts underneath the powerhead on the outside but all this seems to do is loosen the powerhead plastic housing. There is a large cogged wheel that sits on top of the engine (which the manual starter interlocks with when pull starting the engine) which has a 17mm bolt in the middle securing it. If I undo this will this allow me to access more bolts that would secure the powerhead? When I try to undo this bolt the wheel just spins around..is there a way this wheel can be locked in place in order to allow the bolt to be undone or am I going about the lifting of the powerhead totally incorrectly?
thanks for all the help so far
ent

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[andyball]

err, if you're serious about the "cogged wheel"....? I'd certainly obtain a how-to manual before you carry on, many libraries have a basic o/b repair manual that although covering many models, should help you.

anyway....that's the engine flywheel, the teeth are presumably for a (optional?) electric start & removing the flywheel is not necessary.

I don't know the engine well, but on some o/b's the gear linkage must be disconnected to drop the gearbox.

The powerhead may be very stiff to break free & require a few careful thumps....as I say- get a book.

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[pete]

Hi
I have done same job on my four horse Yamaha but before you go to far carefully slide a thin piece of wire up the tell tail hole as they often get blocked.
On its leg there is a rubber grommet on removing this there will be two rods connected with a clip (Gear change rods) from memory its a 10mm head just loosen this enough to let rods slide apart, I did not remove any circlip in the gear casing I had a job getting the drive shaft out as it was really stuck in to the crank shaft in the power head but after a bit of knocking with a rubber mallet and a bit of leavering I got them apart .
The gearbox then has the drive shaft and the gear rod sticking out and the water pump is fitted over the drive shaft, the water pipe stays with the leg
Because it was so hard to seperate I removed the power head to clean the splines where the drive leaves the head, there is a water seal in this hole it was all jammed up with what looked like alluminium oxide and took a lot of poking out when I re assembled everything I greased the shaft splines hopefully to make the job easier next time.
good luck

pete

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[ent]

Hi Pete,

I forgot to say that I had already found the rubber grommet and separated the upper linkage from the lower linkage. So basically you are saying that the once this is separated the drive shaft should drop down from the head with a little persuasion? where exactly did you apply the rubber mallet and the leverage? where and how does the watertube separate, at the head?
thanks

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[pete]

Hi
the rubber mallet was used on the gear casing below the joint to the leg when I got a bit of a gap I used wood wedges and a bit of wobbling but take it easy,
( I had had the leg to bits before so new it could only be stuck on the splines),
From memory if you remove the upper leg joint from the engine the water pipe stays with the upper leg not the engine, and the upper leg connects to the engine with a gasket you can see some of the water ways in the joint,
Hope this helps

Pete


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[ent]

Hi Pete,

So if i'm removing the lower leg only (with the drive shaft attached), I don't need to worry about the water tube?
thanks

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[pete]

Hi
Thats right the water pick-up pipe just slots into a rubber seal on top of the water pump casing.

Pete

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[ent]

thanks Pete,

I'll try and have another go this weekend and see how it goes

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[ent]

Hi Pete,

sorry, another question. There are two joints between the lower unit and the leg. One joint occurs just above the cavitation plate (4 bolts) and the other joint occurs about 80mm above the previous joint I have just described (4 bolts again). Which joint should I be dividing the lower unit from the leg at? I have been working on the one just aove the cavitation plate
thanks, ent

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[pete]

Hi
As both my Yamaha`s( 4hp and 15hp) are short shafts they do not have this extension piece but you are right with the joint just above the cavitation plate. (bottom joint)
Pete


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