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Thread: Terminology

  1. #1

    Terminology

    Took a little time this morning to read through some of the different topics and did some searches for various subjects/new words. I would like to know if there is a resource somewhere that breaks down all that I read about on here. Some of this terminology is very overwhelming. I have basic auto skills (engine assembly/rear end builds/cam degreeing/basic parts changing - modular mustangs don't laugh), but never really got into the 2-stroke mechanic thing as I was always just the rider (Dad and shop were my mechanics).

    Items and terms that are blowing my mind:

    Rave Vavles?
    Different engine/motor numbers
    wear ring
    carbon ring
    flame arrestor (I assume is just what it is on a mx bike - silencer)
    intake grate (I assume on the bottom of the boat)

    I'm sure there are more that I am not thinking of right now, but will surely come across and ask more questions than I need to. And that's why I'd like to see if there was an all inclusive resource. Thanks.
    hull numbers


  2. #2
    KrunchovXPL-GTX-RX's Avatar
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    Quote Originally Posted by Bhilton2v View Post
    Took a little time this morning to read through some of the different topics and did some searches for various subjects/new words. I would like to know if there is a resource somewhere that breaks down all that I read about on here. Some of this terminology is very overwhelming. I have basic auto skills (engine assembly/rear end builds/cam degreeing/basic parts changing - modular mustangs don't laugh), but never really got into the 2-stroke mechanic thing as I was always just the rider (Dad and shop were my mechanics).

    Items and terms that are blowing my mind:

    Rave Vavles? -Also known as a Power Valve. The RAVE is a paddle that slides down in a slot cut into the side of the cylinder just above the exhaust port. When all the way down (the normal position) the paddle projects into the exhaust port simulating (it does not touch the rings, so it is not a true seal, but close) a lower closing point for the top of the port. This produces better torque at low to mid range rpm. When the RAVE opens (either by bleed pressure-787, or on command through a solonoid-947) the paddle slides up and the true top of the exhaust port is then used allowing for better top end power.

    Different engine/motor numbers -Rotax makes engines for several different applications including aviation, marine, ATV, Snowmobile, ect. They used to (but seem to have stopped doing so) identify the engine type by giving it a certain last digit based on the application. SD engines were of course marine and the designated last digit was 7. Rotax would take the displacement of the engine and round down (generally) to the next 7. Thus the 718cc engine is known as a 717 (but also called a 720 by those who like to round up on their own). The big two-stroke has a displacement of 951cc, is officially a 947, and is commonly called a 951. 787s are probably the most confusing since they are known as a 785, 787, and 800 (though there may be a 785 that is different as well but the guys who mess with them would know better than I do, I am a 947 guy).

    wear ring -The wear ring is a plastic or stainless steel liner on the jet pump. This ring surrounds the impeller and its purpose is to, well, wear. The idea with the plastic ones is that they are softer than the prop and will take the wear/damage rather than the more expensive and more difficult to fix impeller. With a stainless wear ring you are strictly going for maximum performance and heaven help you if something gets into the pump.

    carbon ring The carbon ring is the seal for the drive shaft. It was used as of about '97. The ring is mounted in a rubber accordian boot that is clamped onto the hull and rides on a stainless steel collar that is held back against the tension of the boot by an o-ring (early models) or a clip (later models) that sits in a groove on the drive shaft. The carbon ring is not a perfect seal and will take on water if you doing a bunch 360s and stuff like that. With a good boot, though, it will not take on much. The advantage to is that there is hardly any maintenance to do on it (just keep it clean and check the boot), they last a long time, and there is very little drag on the drive line compared to a carrier bearing/lip seal design.

    flame arrestor (I assume is just what it is on a mx bike - silencer) -Not quite the same. It is a kind of air filter though not really filtering. The purpose is to catch a combusting backfire and keep it from burning outside the carburetors. The stock air box is like your bike in that it is a silencer as well as a flame catcher. Open flame arrestors (as most guys are talking about when they say flame arrestors) do not silence anything, nor do they filter, they just that, open, with a mesh screen to hopefully catch a backfire.

    intake grate (I assume on the bottom of the boat) Exactly. It is to keep bad stuff (rocks, sticks, 2X4s, ect) out of the jet pump. On some hulls the grate also helps with tracking and ride quality. You can get aftermarket grates that have foils on them to "Stuff" more water up into the pump. Depending on the setup, these can speed you up, or slow you down but as a general rule, they improve performance in rougher water. These suffer or "Loader" grates also improve tracking and steering on most hulls.

    I'm sure there are more that I am not thinking of right now, but will surely come across and ask more questions than I need to. And that's why I'd like to see if there was an all inclusive resource. Thanks.
    hull numbers

    Hope this helps.

  3. #3
    Thanks for the reply. Big help, but I'm sure it's just a start. BTW - I see your over in salisbury. You ride at Norman? I'm over in Mocksville. 20-30 minutes from you.

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    KrunchovXPL-GTX-RX's Avatar
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    Oops, I have to change my profile, I am in Aiken, SC now. Used to ride on High Rock Lake a lot but hit Norman a couple of times.

  5. #5
    How was High Rock? Where did you put in at? I use to ride down a the wild life way back when.

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    KrunchovXPL-GTX-RX's Avatar
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    We put in at that ramp off of Bringle Ferry Road. I liked riding it. There are some coves you run up into (one of them is blocked if the water is too high, you can not get under the RR bridge) if it is rough. We used to go to the islands just up from the dam and pull up to chill for a while. Last time we went the lake was so far up you would have to pull into the trees so that kind of sucked.

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