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  1. #1
    Click avatar for tech links/info K447's Avatar
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    Arrow Intake grate cracking at the tapered mounting bolt hole

    I recently noticed the R&D 750SL aftermarket intake grate was loose under the MSX 140. The bolt had backed out a turn or two and the grate was able to wiggle around by hand.

    I had sealed the grate to the hull in front and also sealed into the ride plate slow at the rear. The sealant was unable to prevent the intake grate from moving.

    Upon further inspection, the ride plate has a hairline crack right through the metal at the bolt hole.

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    If I had been in a hurry I might have just re tightened the bolt and gone riding

    Moral of the story, check everything. Especially if something seems unusual.

    Related note; make sure the top side of the intake grate is actually flat where it bolts to the hull. The replacement R&D 3-bar intake grate (OEM on Pro 785 machines) had a slight hump where the bolt hole was. When installed the grate might have been able to flex and wobble on the high spot, creating stress at the bolt hole.

    I used a file to flatten and even out the metal surface so it mates flat with the hull surface.


  2. #2
    Rasta Mon Condoms We Be Jammin!!!!! TxVirageTx's Avatar
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    my pro1200 did that,the area of the hull wasn't flat and was lower on one side.when i made the 700 style grate i custom filed it to fit into the recess and line up properly,best grate i ever ran on that ski.

  3. #3
    Click avatar for tech links/info K447's Avatar
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    Arrow Polaris watercraft intake grate fitment, check for poor fit or wobble

    Quote Originally Posted by TxPro1200 View Post
    My Pro1200 did that, the area of the hull wasn't flat and was lower on one side.

    When I made the 700 style grate I custom filed it to fit into the recess and line up properly. Best grate i ever ran on that ski.
    This is worth highlighting.

    The Polaris intake grate mounting design with a single center bolt at the front is susceptible to wobble if the mating surfaces of the grate front and the hull slope are not 100% in agreement.

    The sealant cannot fully resist the wobble unless you use something really hard. Regular marine silicone is going to flex where there is a hollow space between the grate and the hull surface.

    Where the intake grate slides into a slot at the rear, again there is some room for movement. The sealant in the slot does what it can to hold the grate in position but some motion is possible.

    When installing an intake grate, first mount it up 'dry' and evaluate whether there are going to be potential issues with wobble and poor fit.

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  5. #4
    Kosh's Avatar
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    I have the same grate with the same crack! the 3 bar I have installed atm had a better initial fit but they do need to be closely inspected upon assembly and modified for fit as you pointed out.

    Another issue is when the sealant is 'blown' out of where the grate locks into the ride plate it can flex! I have not tried it but it needs a packer in there or the grate tongue building up.

    On one MSX I installed a washer under the grate to take the wobble out, I used a strong sealant to back it up though.

  6. #5
    Moderator HiPeRcO's Avatar
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    The intake grate was missing on my MSX 150 when I bought it. Just a washer-like remnant under the bolt head was all that was left, lol.

  7. #6
    ripcuda's Avatar
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    Quote Originally Posted by HiPeRcO View Post
    The intake grate was missing on my MSX 150 when I bought it. Just a washer-like remnant under the bolt head was all that was left, lol.
    That remnant is the thin remains of the bolt hole bottom that commonly breaks out on the MSX stock intake grate. Happened on one for me... and the replacement I bought for it off ebay also had the bottom of the bolt hole broken out (got a refund thankfully). So yeah... pretty common.

    Cheers!

  8. #7
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by ripcuda View Post
    Quote Originally Posted by HiPeRcO View Post
    The intake grate was missing on my MSX 150 when I bought it. Just a washer-like remnant under the bolt head was all that was left, lol.
    That remnant is the thin remains of the bolt hole bottom that commonly breaks out on the MSX stock intake grate. Happened on one for me... and the replacement I bought for it off ebay also had the bottom of the bolt hole broken out (got a refund thankfully). So yeah... pretty common.

    Cheers!
    If you want to use a stock style intake grate on MSX you can use the non-MSX stock Polaris OEM intake grates on the MSX hull. The non-MSX version of the stock intake grate uses the tapered bolt rather that the MSX style flat bolt head.

    Going from memory the non-MSX intake grates mounted to the MSX hull required a 10 or 8 mm tapered head bolt. This is a larger bolt size than the other Polaris hulls use. I have posted elsewhere photos and the bolt specs including length.

  9. #8
    MSX 150 guy lives on Mr. GP1800's Avatar
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    Why were you running that big shovel of a grate?

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