Yamaha 6hp service / impeller change

[jbavvo]

Hi all, started my Yamaha 6hp up on the stand at the weekend and it's barely pumping water. It wasn't pumping great when I last took it out, so think it's time to change the impeller and give it a once over service too.

I've already swapped the plugs and just received the impeller/gearbox oil in the post. The question is, how easy is a DIY impeller change and does anyone have any advice?

It's a 2002 Yamaha 6hp 2-stroke short shaft. Having youtube'd some videos it looks like several bolts to the water pump housing, then remove clean out and replace. Does that sound right? Anything to look out for?

Also, other than the gearbox oil, is there anything else I should be checking/replacing? I've not got a service manual, and could only find the one for 8hp online (which I understand is the same, but unsure).

Thanks for help as always!

[steve66]

Hi,
What i always do now when swapping impellers is when you have released the gearbox you will see a water pick up pipe from the impeller housing to the powerhead. Get a new silicone sealer screw on applicator end put the thick end on to a garden hose and the thin end into the pick up pipe till you get a good seal. Turn on the water with as much pressure as you can holding the applicator on to the water pipe. This will help unblock any partial blockages you amy have inside the cooling system. Also check the old impeller to see if all the vanes are still intact and also the vents where the water enters the gearbox make sure no debris has collected inside. This if partially blocked can restrict the water flow around the engine

[jbavvo]

Originally Posted by steve66

Hi,
What i always do now when swapping impellers is when you have released the gearbox you will see a water pick up pipe from the impeller housing to the powerhead. Get a new silicone sealer screw on applicator end put the thick end on to a garden hose and the thin end into the pick up pipe till you get a good seal. Turn on the water with as much pressure as you can holding the applicator on to the water pipe. This will help unblock any partial blockages you amy have inside the cooling system. Also check the old impeller to see if all the vanes are still intact and also the vents where the water enters the gearbox make sure no debris has collected inside. This if partially blocked can restrict the water flow around the engine

I tackled the impeller yesterday evening and started by the removing the lower leg and taking the housing off. The housing has partially melted and bubbled on the outside, so has clearly overheated slightly in the past. To my surprise, the inside of the housing was absolutely fine with the impeller looking in near mint condition. I cleaned everything up and applied a little grease to some parts, then put it back together.

I plan to try your advice and see whether there's an issue of water pumping through the powerhead.

Will the bubbling on the outside of the housing be causing the issue? Because internally it looks fine, and I'm reluctant to spend £40 to find out it's not the cause.

[steve66]

The impeller housing needs to be sealed with the lower part of the water pump. If its melted make sure it jahs a good mating surface with the lower part, also make sure the water pick up pipe fits well into the housing .If you have a leak at the pipe/ housing joint you will lose water pressure circulating the engine block . A bit concerning that the impeller housing has got hot, its usually been encased in water. Im wondering if maybe in the past a onr of the housing bolts have been a bit tight and some heat has been applied to help free??

[jbavvo]

Originally Posted by steve66

The impeller housing needs to be sealed with the lower part of the water pump. If its melted make sure it jahs a good mating surface with the lower part, also make sure the water pick up pipe fits well into the housing .If you have a leak at the pipe/ housing joint you will lose water pressure circulating the engine block . A bit concerning that the impeller housing has got hot, its usually been encased in water. Im wondering if maybe in the past a onr of the housing bolts have been a bit tight and some heat has been applied to help free??

Thanks for your advice.

The impeller housing seems nicely sealed when tightened with the gasket forming a nice seal. It's only the upper of the housing that has bubbling around two of the bolts, plus the tube to the pick up pipe. I did notice that the rubber housing joint is missing the two prongs that fit in the holes - it appears these have melted off, however I've ensured it's got a snug fit.

I agree, it's strange about the housing. The lower intake is complete free of obstruction so it should have always been encased in water. Very possible that someone has applied heat in the past to free a bolt, but they came out very easily for me...

I'll try it in water later and see what happens.

I didn't bother replacing the impeller because the one in there was perfect.