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Mad Harold
United Kingdom
225 Posts |
 Posted - 27 Dec 2020 : 07:40:34
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Not necessary just yet as outboard is only just over a year old,but I have never replaced an impeller on an outboard,and I do know the theory(removing outboard from the boat or stern up a ramp) what worries me is the "through the prop exhaust (Tohatsu 8hp)Can't find any info on this specific engine.
Am worried that I will get it apart and not get it back together again.
Are there any particular difficulties with a through the prop exhaust?
Any comments welcome. |
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df
United Kingdom
5990 Posts |
Posted - 27 Dec 2020 : 09:04:07
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Through prop exaust makes no odds, there's rarely any gasket between leg and lower gearcase, most impellors will last years with no problem if never run dry.
NBAS--The communal colostomy bag of the boating community.
 Visit leomagill.co.uk |
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cliveshep
Thailand
1324 Posts |
Posted - 27 Dec 2020 : 10:08:10
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You got 3 or 4 nuts or set screws to undo plus disconnecting the gear rod and the lower unit should just pull off.
Then 2 or 3 screws to remove the impeller casing located around the drive shaft that will be sticking up. That allows the pump casing to be pulled off. Take note of which way the vanes are folded because if/when you replace the impeller that is the way the new ones should go. Get it wrong and as soon as you start then engine 2 things could happen, the first is you risk tearing off the vanes and the 2nd is it won't pump.
The exhaust is simply ejected down the leg and either comes out through the prop or, dependant on engine make. through an orifice (do you like that word?) angled out stern-wards over the top of the prop under the anti-cavitation plate so gases and cooling water get pushed away by the prop.
There are oil seals in the pump, and normally a gasket between the two halves. The bottom oil seals stop water entering the gear-case and oil escaping, generally there are two oil-seals on the bottom section fitted facing each other - one stops oil coming up and the other water going down.As they are dead easy to prise out and replace it makes sense to change the seals when you change the impeller.
Similarly and unconnected to the water pump there are a pair of opposed oil/water seals on the prop shaft behind the prop working in similar fashion to prevent water getting into the gear case and oil getting out.
Do check the oil in the gear-case, if it is creamy the seals have failed. Fishing line is a likely culprit on the prop-shaft seals and you should periodically take off the prop and inspect. On most motors you can dig out the prop-shaft seals and drive in new ones using a piece of tube to drive them home.
Finally Dave is right, so long as it never runs dry an impeller should last more than a season but if it gets tired and bits break off the engine will start to run hot and noisy and you'll lose the "tell-tale" water stream peeing out from the hole in the leg. If you are somewhere that might be dangerous to lose your engine you will be sorry you didn't change the impeller in your Winter recommissioning service.
Many folk do advocate changing the impeller annually and certainly do carry a spare one and the necessary tools with you on a cruise and make sure you actually know how to pull off the lower unit. You are lucky - a Tohatsu 8hp is a small and fairly manageable engine, get above 25hp and you need muscles to lift one off the transom.
Tip - before lifting it tie it off in case you drop it! Dead easy to put some cardboard on the cockpit floor and do it in comfort there. Bridges with railings are useful here to loop a rope round TWICE and down to the engine while crew (kids or wife) hold the other end, and take in the slack as you lift, one child's hand can hold a quite heavy engine as you have 2 turns around the railing the friction is sufficient.
Finally living the dream!
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philihun
United Kingdom
283 Posts |
Posted - 27 Dec 2020 : 10:28:18
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Go online , and just google changing the impeller on a Tohatsu. BTW Mercury and Mariner are the same set up,(same company) so they might come up rather than Tohatsu. Will probably come up on you tube. It costs nowt and explains all what Clive said.
pr hunt |
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Mad Harold
United Kingdom
225 Posts |
Posted - 27 Dec 2020 : 13:49:36
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Thanks for the replies Gents.
Very helpful. |
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df
United Kingdom
5990 Posts |
Posted - 27 Dec 2020 : 14:09:27
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As an add-on to Clives bit about seals, I think the other way, if a seal isn't leaking or showing signs of damage leave it alone, it's a chance to scratch the shaft that runs through it or gouge the housing it sits in and cause a leak you didn't have.
If it aint broke don't fix it.....But if you have to remove a seal replace it with new.
A new impellor fitted the wrong way will likely flip itself right first turn of the engine and pump fine, an old one will probably just rip the vanes off as it will be less flexible.
I think the impellor in my old yamaha 8hp was about 20 years old and worked fine.
NBAS--The communal colostomy bag of the boating community.
Visit leomagill.co.uk |
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Knighty
United Kingdom
654 Posts |
Posted - 28 Dec 2020 : 09:47:04
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| If outboard is only one year old be careful of falling foul of the warranty if doing own servicing, assuming you have 3 or 5 ears warranty. I had a new Mariner on my 20 a few years back. I was advised it would need servicing and stamped at yearly intervals by approved service agent whilst in warranty. |
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Mad Harold
United Kingdom
225 Posts |
Posted - 28 Dec 2020 : 15:48:30
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Thanks Knighty,but I have already lost the guarantee due to doing the first oil change.
The gear oil was blue and although the handbook specifies EP90 I contacted the people who supplied and fitted the engine to query the blue gear oil,and was given a bit of a bollocking and informed that my warrenty was invalid.
The engine was bought by my boat's previous owner,and the dealer is in Leicester and as I am in Huddersfield I am not keen on lugging an outboard to Leicester just for an oil change.
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df
United Kingdom
5990 Posts |
Posted - 28 Dec 2020 : 16:10:11
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Outboards are no different from cars, as long as the right parts are used and done to the right standard there is no legal requirement to use an official agent warranty wise, if the unit is proved to be faulty it's still covered, if you used the wrong oil then they may have the excuse but any make of the right spec still covers you.
My suzuki outboard is well out of warranty as I had to strip it and put it back together properly after a suzuki agent cocked it up with no concept of cam timing, I'm glad to say they went down the pan.(I have to admit it was me using avgas that originally caused the valve issue but they had no reason to split the crankcase.)
NBAS--The communal colostomy bag of the boating community.
Visit leomagill.co.uk |
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Topic |
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Replacing outboard lmpeller
