Mecrury 200hp Optimax SportJet pump impeller inspection

Does anyone have experience with inspecting the impeller and wear ring on a 200 Optimax Sportjet jet pump? WOT is at 5800rpm and 37-38mph. Boat builder indicates that my boat (18' welded aluminum w/12.5 deg. deadrise) and motor combo should max out at +/-5400rpm and 50+ mph. Informed me that I should have dealer inspect impeller for damage and/or slippage. Local dealers (I bought the boat in Oregon, live in NW WA) do not have much experience with my set-up. New boat with less than 10hrs. I know I have not done any damage. Have not had known speed and rpm verified. Tach is new with boat factory installed Mercury product, speed is from my GPS - I guess accurate? Am also interested in info on tolerances and shimming.

Re: Mecrury 200hp Optimax SportJet pump impeller inspection

With your RPM's being high, it sounds like you have too much clearance between the impeller and the wear bowl. The impeller will not bite as hard with too much clearance, so the RPM's go up. I will look at my manual once I get home and try to post some more technical data for your unit. <br /><br />As a general rule, there should be about .020 clearance between the two. For the riverbank mechanic (like me) that is just a bit larger than the thickness of a matchbook cover. If the clearance is too much, remove a shim from the top of the impeller and move it to the bottom. Always keep the same number of shim washers, just move them around to raise or lower the impeller. Generally it is easier to take the entire lower unit off rather than trying to make the adjustments upside down. Not too big of a job. Be sure that if there are any nylon bushings inside the impeller that you keep them in place when moving it up or down. If this bushing is worn it will also cause the impeller to slip.

Re: Mecrury 200hp Optimax SportJet pump impeller inspection

With your RPM's being high, it sounds like you have too much clearance between the impeller and the wear bowl. The impeller will not bite as hard with too much clearance, so the RPM's go up. I will look at my manual once I get home and try to post some more technical data for your unit. <br /><br />As a general rule, there should be about .020 clearance between the two. For the riverbank mechanic (like me) that is just a bit larger than the thickness of a matchbook cover. If the clearance is too much, remove a shim from the top of the impeller and move it to the bottom. Always keep the same number of shim washers, just move them around to raise or lower the impeller. Generally it is easier to take the entire lower unit off rather than trying to make the adjustments upside down. Not too big of a job. Be sure that if there are any nylon bushings inside the impeller that you keep them in place when moving it up or down. If this bushing is worn it will also cause the impeller to slip.

Re: Mecrury 200hp Optimax SportJet pump impeller inspection

Sorry for the double post. My system likes hearing me talk more than I do.

Re: Mecrury 200hp Optimax SportJet pump impeller inspection

Kev_alaska, <br />Being an old shadetree mechanic myself, I do understand .020" clearance - it was just about the exact thickness of the little cardboard box that small engine points came in - remember points and condensers?, I guess you have to go to a mechanics' museum to find those things anymore! Any way, thanks for the info. If I get a break from salmon fishing this weekend (when the salmon are in the the river, the wife won't let me have a minutes rest -got to go fishing! What a woman!) I will try to check the clearance and adjust the shims accordingly. Any detailed info on this would be appreciated. I am new to jet boats - I have owned prop boats most of my life and have done quite a bit of repair work myself - but this jet thing with the 200Optimax is a horse of a totally different color! I know that somewhere under all those wires, tubes, boxes, shrouds, housings, pumps, controls, and other assorted gobblygook is a basic V-6 2cycle engine block with a jet pump thingy attached to the bottom! As for the double post, don't worry, I sometime need to read things two to three times before it all sinks in...<br />Thanks again for the reply & info, <br />Jim

When I make turns engine tends to cavitate is it due to impeller being worn out

Sorry williamrock, you need to create a new thread and provide much more information about your boat/motor combination, the problem, what it is, how you notice it, what you have tried. And then you should get responses that may help you get it working.

williamrock said:

When I make turns engine tends to cavitate is it due to impeller being worn out

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Welcome aboard.

Read the Help Tip on top of the page about starting a new topic. This one is from September 2003 and very, very stale. Please start a new topic following the advice CharlieB gave, We need more info to give you a hand. Thanks.

Closed for posterity.