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  1. #71
    Sage18's Avatar
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    Quote Originally Posted by sdlvx View Post
    Another place of low hanging fruit to improve is the pump. The space between the impeller and the wear ring should be measured (it's in the service manual) and fixed. You can also match the parts of the pump if they are off or there's any big inconsistencies.

    I put a new wear ring and an impeller Impros went through on my superjet and it made a huge difference.
    I took the intake grate off tonight and measured the clearance of the impeller. .009Ē. The manual says .002-.008 is standard and service limit is .02. So looks decent? Here are some pictures. I didnít take the pump off yet. Stator looks good. Impeller has a couple small chips in it. Let me know your thoughts.
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  2. #72
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    I took the head off tonight just to take a look at the piston wash. Keep in mind it’s been running like this for 4-5 years. But infrequently. He said 10-20 hours a season. The cylinder walls looked great without any imperfections. Who knows what pistons these are? Can I just get rings or do I get a whole new set, right? The compression front to back was 115,110,112, cold
    Note the Mag piston has a different number.
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  3. #73
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Those are Wiseco pistons. So the top end has been replaced once already.

    Cen and PTO wash look great. Maybe, ever so slightly rich if you're trying to wring out every last bit of RPM from her. However, that is perfect for a reliable rec boat IMO.

    MAG is very rich. Need to pull some fuel out of it so it matches the other 2 cyls. (keep in mind its better to have too much fuel and pull it out, than to be lean and potentially do piston damage)

    Generally the consensus is to make the piston clearance bigger then what Wiesco recommends to prevent them from cold seizure. (Wiseco, AKA "seizeco", pistons would expand at a faster rate than the cylinder walls, thus causing a cold seizure. Tell tale signs of cold seizure is what they call a 4 corner seizure. 4 streaks evenly spaced around the piston. That is why SDLVX mentioned properly warming up your engine when using Wiseco pistons.

    I wonder how large of a piston clearance the installer used, as that might be why your compression is down some?

    The MM06970 part number on the piston dome tells you the exact size of the pistons you have. Those are 69.70mm (stock size pistons) so you know what rings to get if you do not replace the pistons.

    Personally I installed WSM (cast) pistons into my pro rebuild strictly because I used Wisecos once in another ski and had the cold seizure issue the first time I opened her up. (shuts down at WOT and then fires right back up) I want to say the newer Wiseco pistons look like they may have a bit more material on them now from older pistons I've seen. I suspect they may be trying to combat the cold seize problem they were known for, but that's just a wild guess on my end. I suppose we could find the weight of the old pistons VS. the newer made ones to find out, but I'm not going back down that road any time soon.

  4. #74
    Sage18's Avatar
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    Quote Originally Posted by xlint89 View Post
    Those are Wiseco pistons. So the top end has been replaced once already.

    Cen and PTO wash look great. Maybe, ever so slightly rich if you're trying to wring out every last bit of RPM from her. However, that is perfect for a reliable rec boat IMO.

    MAG is very rich. Need to pull some fuel out of it so it matches the other 2 cyls. (keep in mind its better to have too much fuel and pull it out, than to be lean and potentially do piston damage)

    Generally the consensus is to make the piston clearance bigger then what Wiesco recommends to prevent them from cold seizure. (Wiseco, AKA "seizeco", pistons would expand at a faster rate than the cylinder walls, thus causing a cold seizure. Tell tale signs of cold seizure is what they call a 4 corner seizure. 4 streaks evenly spaced around the piston. That is why SDLVX mentioned properly warming up your engine when using Wiseco pistons.

    I wonder how large of a piston clearance the installer used, as that might be why your compression is down some?
    .
    I can be on this forum all day. Thanks for all your knowledge. I measured the piston to cylinder gap and the closest I can measure is .009 if I try to center the piston. Just out of the limit. Where do you source WSM pistons from? WSM didnít show them on their website. The middle picture is the mag cylinder is that too rich? Or too lean? When I took the head off it seemed loose like it wasnít torqued down properly, Iím going to torque it down and retest compression just to see if there is a difference with the correct torque.

  5. #75

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    You need to measure the bores. You can open up nikasil with a hone and make the bore bigger. If someone opened up those bores for wiseco pistons and you put cast pistons in there, you might have a lot of clearance between the cast piston and the cylinder wall. Wiseco wants a lot of clearance for their pistons in watercraft. I forgot the exact number but it's quite a bit. IIRC it's like .045 or something.

    If those are wiseco pistons in there and the guy didn't open up the bores that is a cold seizure waiting to happen. I wouldn't even run it.

    I have had wisecos seize up on me, but if you stay in water above 55 degrees you're fine. They are really good pistons but you really have to be careful and you have to have the bores a little bigger. I also can get away with it because I have about a half a mile slow no wake to let it warm up. xlint rides on a big cold lake so he's always going to have a horrible time with them. I ride in a smaller lake that gets into the 80s in a good summer so it works out. If you're riding in cold water there is absolutely zero way I would recommend wisecos. When it's cold I just take out my superjet, because it's a lot easier and cheaper to fix.

    There's a special tool you can use to measure the bore. Or if you have two feeler gauges you could measure on opposite sides.

    Before you order pistons you should take the cylinders off and inspect them. It probably doesn't matter that much if you're just going to have them relined, but it's always good to check.

  6. #76
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    x2 from the guys comments above. I have WSM 750 pistons in my limited boat and they have run well, even at 8000+ rpm. I did have an issue with a piece of skirt breaking off but it luckily went right out the exhaust port without causing any damage. I'm not sure why exactly it did that as the clearance was within stock spec. I put another full season after replacing that piston and have not had any further issues.

    My superstock boat runs Wiseco pistons with 0.0055" clearance. They call out 0.0045" clearance on the box. They have slightly streaked the cylinder walls but no signs of actual seizure nor can I feel anything with my fingernail. If I do them again, I would probably open them up to 0.0060" or so.

    To measure the clearance, you definitely need a dial bore gauge and a micrometer. I know they say you can try using feeler gauges but that won't be nearly accurate enough when you're measuring such tight clearances. I got both of those off Amazon for relatively cheap.
    Last edited by hyoctane23; 11-30-2019 at 10:16 PM.

  7. #77
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    Quote Originally Posted by hyoctane23 View Post
    .

    My superstock boat runs Wiseco pistons with 0.0055" clearance. They call out 0.0045" clearance on the box. They have slightly streaked the cylinder walls but no signs of actual seizure nor can I feel anything with my fingernail. If I do them again, I would probably open them up to 0.0060" or so.

    To measure the clearance, you definitely need a dial bore gauge and a micrometer. I know they say you can try using feeler gauges but that won't be nearly accurate enough when you're measuring such tight clearances. I got both of those off Amazon for relatively cheap.
    Just ordered a bore gauge. How do I tell if it still
    has the Nikasil coating? Do you think the rings wore faster because of the nikasil? Iíll know more once I measure the bore of the cylinder. Cylinders all feel smooth as can be.

  8. #78

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    Quote Originally Posted by Sage18 View Post
    Just ordered a bore gauge. How do I tell if it still
    has the Nikasil coating? Do you think the rings wore faster because of the nikasil? I’ll know more once I measure the bore of the cylinder. Cylinders all feel smooth as can be.
    Underneath the nikasil is aluminum. You would know if you got through it. But there's a good amount on there, some can be removed and it's still ok.

  9. #79
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    Quote Originally Posted by hyoctane23 View Post
    x2 from the guys comments above. I have WSM 750 pistons in my limited boat and they have run well, even at 8000+ rpm. I did have an issue with a piece of skirt breaking off but it luckily went right out the exhaust port without causing any damage. I'm not sure why exactly it did that as the clearance was within stock spec. I put another full season after replacing that piston and have not had any further issues.

    My superstock boat runs Wiseco pistons with 0.0055" clearance. They call out 0.0045" clearance on the box. They have slightly streaked the cylinder walls but no signs of actual seizure nor can I feel anything with my fingernail. If I do them again, I would probably open them up to 0.0060" or so.

    To measure the clearance, you definitely need a dial bore gauge and a micrometer. I know they say you can try using feeler gauges but that won't be nearly accurate enough when you're measuring such tight clearances. I got both of those off Amazon for relatively cheap.
    I finally got around to measuring my bores on the 785. .00541Ē is the gap between the piston and cylinder walls. These as they sit currently have streaked the cylinder walls (pictures to follow) as well but I canít feel anything with my fingernail nor did the bore gauge pick up any variances. I think I am going to try just putting rings in the 785, lightly hone the cylinders, along with going through the entire fuel system and doing the cooling lines as stated previously. Think thatís the plan.

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    Can anyone tell from these pictures about the nikasil plating? I assume based upon the bore size that it is there? Just not sure what to look for.

    Also what is the difference between a limited boat and superstock. Novice here

  10. #80
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Your clearance sounds about right. If the cylinders looked like that before you got into it, the engine probably wasn't warmed up enough before dropping the hammer or was ridden in very cold water. You can use a Scotch-Brite pad to remove the shiny glazing on the cylinder walls. I've also used a Flex-Hone to remove heavy glazing but don't overdo it. The plating looks okay in the pictures...as long as it isn't peeling anywhere. You'll be able to easily see that if it was happening.

    As far as limited versus superstock..those terms relate to the various racing classes or tiers that these (an other similar boats) run in. As the name suggests, the limited class allows you to have "limited" modifications while the superstock is almost an "anything goes" class. The biggest difference lies in that the motor can be ported in the superstock class as well as aftermarket ignition systems while those items are prohibited in the limited class.


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