9.9 HP Impeller looks good to me

[Jerry_NJ]

I pulled the lower unit on my 1990 (est) 9.9 HP Yahama to check/change the impeller. When I tested it there was no "pee" stream coming out. The unit is very low hours in spite of it age.

The impeller looks excellent to me, soft/flexible and has a slight bend in the direction of rotation. The housing also appears like-new polished. Please click on the two pictures attached to get a good view of what I am talking about.

What could be the problem? I previously opened the engine cowling and blew through the hose connecting the coolant area to the "pee" hole. Air passed with no problem.

This engine takes water in from below the cavitation plate. There is nothing in that area that appears to be plugged. Not sure how to test, perhaps I can just put the lower unit in a tub of water and see if water come up into the impeller chamber - any ideas?

 

[robert graham]

Re: 9.9 HP Impeller looks good to me

Run a section of monofilament/weed eater string into the tell-tale to clear for possible spiders/bugs/wasp nests....they can and will plug them up!....

 

[CheckmateEnticer]

Re: 9.9 HP Impeller looks good to me

Did you pull it up to check the keyway?

 

[Jerry_NJ]

Re: 9.9 HP Impeller looks good to me

Thanks, before pulling the lower unit off I took the hose from the engine block to the "tell tale" and blew in it.. I could feel the air coming out.

The "picture" just doesn't look right. The previous owner (of the boat too) didn't use the 9.9 Yamaha using a 25 HP in its place. The engine appears from the model number to be a 1990, 23 years old, isn't that enough time for the rubber impeller to "dry" up and become stiff an brittle? This impeller looks new.

When I was negotiating the price I argued against the "like new" engine saying if it had just been sitting for 23 years the impeller must need to be replaced, I'll guess over $200 at an engine shop. They didn't argue the point or say they had it chanced a couple of year ago. The seller stuck me as a "regular" guy., not some "pssst" sale, I bought if from him at his home.

When reassembling I noticed the 4 bolt pattern looked like it could take the impeller housing in either of two possible directions. I looked up the engine housing and could see where the impeller output plugs into the cooling up-line to the block. I'm not sure it couldn't be put in backwards, but if it were there would be no water going to the block, and thus none to the "tell tale" output. Given there was no output when I test ran the engine, I wonder.

Looking up the drive shaft housing I wonder too how the exhaust gets to the center of the prop, or were the cooling discharge gets back to the lake.

I will try the string cutter line, I have some moderately heavy line, to see if I get a clean path from the intake on the bottom of the anticavitation plate to the impeller. I fished round with length of aluminum wire and it hung up in the bends, at least two 90 degree turns.

If the exhaust just flows in the hollow area of the drive shave housing (and place to which the lower unit bolts) one would expect to see a rather nasty dirty interior, it looked factory clean adding proof to the claim the engine has seen very little use.

On the pulling the impeller, no I didn't but it seemed (no direct check) rotate with the drive shaft. I tugged on it a bit with my hand but didn't try to pry the impeller off. Does the key play any roll beyond "locking" the impeller to the drives shaft

 

[Jerry_NJ]

Re: 9.9 HP Impeller looks good to me

I put the impeller back together, no replacement, and refilled the lower unit oil. I again checked the "tell tale" hole by blowing into the hose that connects to the engine block - air went through.

I put the boat in the lake yesterday and on the on the start I could see a steady stream of water coming out of the "TT" hole. It is my opinion that the stream is weaker than that from similar age Evinrude, but that may be a smaller hole on the Yamaha. I ran around the lake at various speeds and not sign of overheating.

This 1990 9.9 Yamaha is a very easy starting engine and smooth running, but seems to develop less speed than my Evinrude on a similar size boat (a 14' Grumman with V hull but bass boat like decking and equipment). The Discovery/Yamaha is 6" wider than my Grumman and may way upwards of 200 pounds - that could slow it down some. As I don't have a "speedometer" I am just estimating the speed. But it is clear that at full throttle the Yamaha wake remains a churn, not a "V" wake like the Evinrude develops at top speed.