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97 SN Rattle at low speed |
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70CC 
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Joined: June-12-2006 Location: United States Status: Offline Points: 338 |
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 Topic: 97 SN Rattle at low speedPosted: August-08-2011 at 1:30am |
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Last fall I hit a stump with my 97 SN and bent the original 4 blade prop. I replaced the prop with an ACME 1442. When I changed props, I checked the shaft run out and all seemed fine. However, now there is a rattle noise when I put the boat in gear (forward or reverse) at idle. If I increase the throttle just slightly, the noise goes away. There are no vibrations at any other speeds. The noise seems to come from the rear of the transmission.
Thanks! -Phil |
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8122pbrainard
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Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Posted: August-08-2011 at 9:18am |
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Phil,
It's interesting that the exact same issue popped up in another thread on props!! The result was thought to be a combination of the 1442 blade surface area and too low of an idle RPM causing the reverse gear planetary set to chatter. |
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BuffaloBFN
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Joined: June-24-2007 Location: Gainesville,GA Status: Offline Points: 6094 |
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Posted: August-08-2011 at 10:26am |
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My acme also does this. From a dead stop, I engage the throttle and things go normally until the boat reaches the speed it will make at that idle rpm. From there I have to bump the throttle up to shut the damper up.
This hasn't happened with a few OJ's I've tried; even @ 550 rpms. @ 650 rpms with the acme, I still have to bump it. If we only had some engineers on CCFan... Is the acme that much more efficient? Eric, what tears up a damper? Does this rattle at idle lead to problems, or is it just an irritant? |
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21186 |
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Posted: August-08-2011 at 12:16pm |
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I dont get damper knock with any of my Acmes, so Im not much help there... but Im curious Phil, how much hull clearance do you have with that 1442? With the decreased shaft angle that the TSC+ hulls have, plus the lack of channel/pocket (present on the TSC2-TSC3), I would think that 13.25" wheel would be pretty darn tight. Im also curious how it performs, obviously!
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mdvalant
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Joined: May-06-2009 Location: Bellevue, IA Status: Offline Points: 2059 |
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Posted: August-08-2011 at 12:38pm |
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Hey guys, I started this same topic a couple days ago something like "2 of us need dampner plate help"
Phil has the Ski, we have the Sport. |
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KRoundy
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Joined: August-23-2010 Location: Lake Stevens Status: Offline Points: 1702 |
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Posted: August-08-2011 at 1:33pm |
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I'm an engineer but I work on airplanes, not boats. However, the note above about clearance is initially concerning. Without the right amount of clearance the pressure build-up between the prop wash and the hull at slow speeds could easily be causing this "bump". The reason for the difference between props could simply be pressure differentials between the two edge designs. The problem likely goes away at higher speeds because you simply power through the problem. It still exists, but your engine has the power/torque to push past it.
Just one engineers musings. I could be way off. Anybody know an engineer at Nautique? |
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Previous: 1993 Electric Blue/Charcoal Ski Nautique
Current: 2016 Ski Nautique 200 Open Bow |
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BuffaloBFN
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Joined: June-24-2007 Location: Gainesville,GA Status: Offline Points: 6094 |
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Posted: August-08-2011 at 2:13pm |
We have a good friend here on the site who is. I think a good bit of aeronautics jives with boats(*nautics LOL). Maybe the acme is efficient enough to reach a static point until the bow is pushing back enough to load the prop? More 'drag'? |
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M3Fan
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Posted: August-08-2011 at 5:06pm |
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Can you borrow a 422 and see if the noise goes away?
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2000 SN GT40 w/99 Graphics/Gel
2016 SN 200 OB 5.3L DI https://forum.fifteenoff.com |
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mdvalant
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Posted: August-08-2011 at 5:07pm |
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I have a 422 AND a 654 that I haven't tried on our Sporty yet.
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70CC
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Joined: June-12-2006 Location: United States Status: Offline Points: 338 |
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Posted: August-10-2011 at 2:43am |
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Hi Tim, I'll check the clearance tomorrow if I get a chance. Should have given you a ride at Green Lake - I had the prop on at that time. Top speed indicated by the speedo is 46 did not change but I'd say it pulls a bit harder. One thing I noticed with the ACME is it seems to bite more when I pull the throttle back to slow down compared to the original prop.
Mike, sorry I missed your earlier post - let me know if the other prop helps. I'll see if I can find a stock prop to borrow too. Thanks, Phil |
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70CC
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Posted: August-11-2011 at 12:44am |
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There is 1 1/4 inch distance between the tip of the prop blade and the keel.
-Phil |
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KRoundy wrote: