07 Yamaha AR210. Need advice on finding some lost thrust.

[itsdgm]

So a little history. Boat is running great, rpm’s are normal. But over the past few seasons I’ve noticed that I’ve lost a few mph on the top end and that the boat takes a bit more time getting out of the hole. I’d guess that I’ve lost maybe 5-10% of thrust max.

I figured that this winter I’d tear down the propulsion system, rebuild the pumps, check impellers, wear rings and silicone on the intake end of things. This is the first time in the 13 years that I’ve owned the boat that I’ve looked at the thrust system. All I can say is wow. The pumps unbolted and slid out of the boat with ease. Things look and feel way better than I expected. The pump bearings are smooth as silk, no play at all. The impellers leading edges look clean as a whistle too. The intake looks pretty good, possibly a tiny bit of silicone that could be touched up here and there. The wear rings look evenly worn, with no real obvious signs of damage. But I’m not really sure what the impeller/wear ring gap should be. So I haven’t measured that out yet.

So what I’d like to know from you guys who have been down this road before. Where do you think my 5% loss of thrust could be? It has to be somewhere in the thrust system.

I’m planning on re-siliconing any missing gaps on the intake before putting it all back together. But my real dilemma is whether or not to replace the wear rings. They look pretty good to me. But I’ve never measured the gap on one or know what a normal gap should look like. I don’t mind buying new ones, but would hate to spend the $ (they aren’t cheap) if it didn’t help my issue.

Heres a few pics of the Port pump (both are in exact same condition). I appreciate any recommendations that come from real life experience.

Thanks in advance.

PS. If you do recommend wear rings. Would you go OEM or aftermarket? If aftermarket, which ones?


@swatski @Julian @CrankyGypsy @Bruce @Cobra Jet Steering LLC

 

[Cobra Jet Steering LLC]

check all your exhaust hoses and clamps exhaust in the hull will take away some of your top end so will a bad air filter or bad plugs

 

[itsdgm]

check all your exhaust hoses and clamps exhaust in the hull will take away some of your top end so will a bad air filter or bad plugs

Thanks Jeff. The engines feel like they’re performing as usual. Just a slight lack of thrust getting out of the hole. But, I’ll add those items to the list of things to check.

 

[Ronnie]

I’d clean the hull in addition to reworking the silicone. Also consider sending the impellers in to be refurbished. Lastly, paint the interior of the wear rings with epoxy like ceramic paint to see if that helps, if not look into inserts instead of replacement wear rings. Good luck.

 

[swatski]

Your impellers appear to be in pristine shape! And the wear ring(s) look good except for what looks like a touch of a cavitation burn. That could be a spot where air is being sucked from the bilge.

 

[itsdgm]

Thanks @Ronnie and @swatski for the advice.

 

[Seadeals]

I finally figured out that my gradual loss of 1 mph was due to two issues…loving beer and getting old at the same time, which tightened all the tolerances of my wardrobe. Kidding aside, things do look great and I would take a look at compressions, running a high quality fuel through the tank and (I am sure you have changed plugs) before changing wear rings. Piston rings wear too, so we do eventually get to a point where one or more cylinders start to lose their original efficiency/output. How many hours are you up to?

 

[itsdgm]

I finally figured out that my gradual loss of 1 mph was due to two issues…loving beer and getting old at the same time, which tightened all the tolerances of my wardrobe. Kidding aside, things do look great and I would take a look at compressions, running a high quality fuel through the tank and (I am sure you have changed plugs) before changing wear rings. Piston rings wear too, so we do eventually get to a point where one or more cylinders start to lose their original efficiency/output. How many hours are you up to?

Thanks for the post. This issue is for sure somehow pump related. Engines are running just fine.

 

[itsdgm]

I’m pretty sure that my fix will be found somewhere within replacing the wear rings, freshening up the silicone on the intakes and also rebuilding the cleanout plugs. So I’ll get those things done and report back after summer. ?

 

[Seadeals]

@itsdgm Good to hear. I just learned a hard lesson on my first boat (outboard). The engine got a little harder to start but I felt it ran great. I wasn’t at WOT a whole lot so not checking the top end. Come to find out I had lost all compression in one of the cylinders and it needed an overhaul. I was amazed it could sound so smooth and keep the boat moving as well as it did. I guess I wasn’t near as “in tune” back then either since it was my first boat and also feel like issues with our engines are usually easy to hear.