Impeller service question

[Condor1970]

I have a Alpha One Gen 1 outdrive. So, I ordered and Alpha One Gen 1 kit off Amazon. I think it's a Sierra kit. Anyway, I'm dropping the lower today to swap the impeller, and noticed that the kit I bought came with a stainless orifice plate with 2 large holes for the suction, and some videos on YouTube and pics in my manual shows one small hole for the suction. Now, I don't know what plate mine is yet, but if it only has one hole in the plate, should I use the old plate? Or, swap it for the new one with 2 suction holes?

 

[Bt Doctur]

what is the kit number? This is Alpha type

Alpha GEN II type

 

[ktbarrentine]

What manual are you using? Mercruiser manual #6 ("the" manual) page 3B-8 shows the pump you have (like the top drawing above). Note also (off topic) that your sierra kit will have "extra" gaskets and o-rings that you wont need. (you probably got the 18-3217 kit?, or 18-3517?)

 

[Condor1970]

Ok, I think I have a strange issue then. I replaced the impeller, and noticed a couple things.

1. The drive shaft only had the one seal on top of the pump casing. In fact, there is a spot to put an O-ring on the shaft, but no O-ring. It only had the large collar type rubber seal. The other, is that my seal kit didn't even come with those seals, so I had to re-use the one I have.

2. It appears to be the pump in the diagram shown first drawing, because all the gaskets and orifice plate are the same. However, it has only the single seal, like the pump shown in the drawing below it. Makes me wonder.

The good news is, the old impeller and pump inner liner looked mint. The new impeller seemed to go in fairly well over the keyway, and the impeller itself seems to have sort of a double sealing surface in the rubber itself to help keep it from leaking out of the housing. I wonder if this is why it only has the one collar seal on the outside?

 

[ktbarrentine]

Yes.... there is no real "seal" in the top of the pump housing (more of a bushing). The large rubber "collar" ring (#41) is a slinger ring that fits down closely on top on the pump casing and slings leakage away horizontally.
The missing O-ring (#17)... I am assuming you are referring to the o-ring groove near the top of the vertical drive shaft, above the point where the upper half shaft seal rides. Most people (myself included) do not put an O-ring there anymore, because it did more harm than good, as it would interfere with that seal in the upper housing when reassembling the drive, and sometimes ruin it, making it useless (and that would let water up into the splined area of the vertical shaft where it enters the upper shaft). The later models did away with that O-ring groove (in addition, it added a weak spot to the vertical drive shaft and some folks had their shaft break there when they hit something hard in the water).
Your old impeller can look fantastic, but may have taken a curved "set" from living in the pump housing. That's why it is good to replace the impeller every two years no matter what the hours are on the boat. But what this does say is that your drive probably didnt have a recent overheat (loss of water) condition that can cause parts of the impeller to go missing in action.
Sounds like you are close to getting 'er back together, doing a pressure test, and pumping in some oil.

Never answered which brand manual you are using.

 

[Condor1970]

I have the Mercruiser Sterndrive Shop Manual, by Clymer. #B742 Alpha One and Bravo One 1986-1989.

I've thumbed through the whole bloody thing, and can't find a drawing of what pump I have. Got great instructions on rebuilding drives though. Heck, it practically has everything to rebuild a 3.0L engine. Including wiring diagrams in the back.

Oh, and yes, I agree, the impeller definitely has permanent curvature. This is normal. Especially when the guy said he had it done 4 years ago, and it sat for over a year without running. He said, "Don't worry it's fine." Well, I wasn't about to take the chance, even though it did appear to still work just fine.

 

[ktbarrentine]

Please get rid of the Clymer manual. It will cause more pain than good (as bad as, if not worse than SELOC). It does make a good knee-pad in the shop if you want to keep it, though.

Get the OEM manual. You can see it online here:

http://boatinfo.no/lib/mercruiser/manuals/mercruiser6.html#/0

This info is available in the "adults only" sticky at the top of this forum. There are also ways to download the manual free on here, but I dont have that link handy (maybe someone else can provide). I use the boatinfo site link (have it bookmarked) and print out the pages I need when I need them. Also has a great search feature.