Velvet Drive Knocking
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=2013
Printed Date: November-23-2024 at 12:13am
Topic: Velvet Drive Knocking
Posted By: Guests
Subject: Velvet Drive Knocking
Date Posted: July-06-2005 at 12:16am
My 79 Nauty is experencing a little knock coming from the transmition. I have the engine set at a low idle and when I put it in gear, forward mainly, there is a noticable knock or clatter from the tranny. The noise will disapear as soon as I give it more gas and the boat picks up speed.
Has anyone experienced this before?
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Replies:
Posted By: Guests
Date Posted: July-06-2005 at 2:14am
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the dampner plate between the motor and the velvet drive! The springs wear and or break which can cause some noise, and in my case they fly apart and get caught between the ring gear and housing leaving you in a tow situation
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Posted By: 80nauts
Date Posted: July-06-2005 at 4:38am
The plate will cost you a $100 and take a day to put out and in.
I am cheap enough to run it till it breaks. Just keep the Lake Sherrifs phone# handy for the tow.
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Posted By: skyhawkflyer
Date Posted: July-06-2005 at 10:17am
My 87 was doing exactly as you describe. I found that the prop shaft was every so slightly bend at the end (tip) although I never did understand why this would cause it to knock only at idle. It would vibrate bad enough at high speed to make the dash buzz. I changed the prop shaft, support bearing, and upgraded to an acme 540 prop. While I was at it I changed the transmission fluid. The knock went away. Maybe I got lucky, I don't know. No knock, no dash buzz, and lots of power out of the whole. The boat was used very little for a few years so maybe that had something to do with it (10 hours in 3 years)
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Posted By: Guests
Date Posted: July-06-2005 at 4:25pm
I would like to it out this weekend and inspect the situation. I've never taken the tranny from the engine, but it looks so easy to get to and that is what I'm afraid of. Usually these projects end up making me land locked for the summer.
What if I happen to run the vessel a few more times, and if it is indeed the damper plate, am I risking to break more parts within the tranny if the plate were to come all to pieces or is the plate isolated from other delicate parts?
I'm not ruling out the fact that it could be more servere than the plate, like another part of the tranny or like SKYHAWKFLYER suggested the prop saft(one which I will also inspect) but I am just trying to feel out what others have experienced.
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Posted By: skyhawkflyer
Date Posted: July-06-2005 at 4:41pm
79Monk
I taped a pencil (and a block of wood) to the prop guard on my trailer (the part that protects the prop) and pointed it toward the center tail portion of the prop shaft. As I turned my prop I could see the shaft wobble as it was being turned using the pencil as a reference point. You can use anything as long as it's a stationary point to reference to. Hope that helps.
(When I pulled the shaft I noticed that it also trashed the support bearing, causing movement of the entire shaft when under load in the water)
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Posted By: tommer12
Date Posted: July-12-2005 at 12:04am
I had the same issue with my 84 at one time. It was knocking and it turned out the damper plate was bad. It has a series of springs all around the plate on the outside. Most of the springs were broken off. Get it replaced ASAP. It will cause more damage as you shift in out of forward - neutral - reverse. Basically throwing direct force onto your gears in the velvet drive, rather than "dampening" the power and "sliding" it into gear.
cheers
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Posted By: David F
Date Posted: July-12-2005 at 12:36pm
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My engine/drivetrain will rattle a bit if the idle is set below 600 rpms, but goes away at about 650-700 rpms. You might try just turning your idle speed up a bit since you state that you have it set low. I believe the slightest roughness to idle quality and the low idle speeds cuase this noise even with a good damper plate.
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Posted By: skyhawkflyer
Date Posted: July-15-2005 at 10:59am
I might take a look at my damper plate just for kicks to check it out. If I back out the velvet drive bolts can I get down into the damper plate area with a small mirror to inspect (without pulling the whole transmission). The springs break? Would I also be looking for pieces of spring at the bottom of the transmission housing?
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Posted By: 75 Tique
Date Posted: July-15-2005 at 4:19pm
All of those mechanical reasons mentioned above may be the problem, but before you rip it apart or do anything drastic, change the fluid and try it. I had a knock at low rpm, smoothed out higher rpm. Changed the fluid and it ran like a champ.
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“So, how was your weekend?”
“Well, let me see…sun burn, stiff neck, screwed up back, assorted aches and pains….yup, my weekend was great, thanks for asking.”
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Posted By: 79Monk
Date Posted: July-18-2005 at 4:20pm
OK, last sat. I removed the tranny and damper plate. My particular damper plate is very hard to inspect because the springs are not exposed, they have covers pop rivited over them. Well the plate is pretty rusty and seems to be locked up so I ordered a new one today.
Since I was unable to justify the noise was coming from the damper plate, I bought a coupling to join the two hydraulic hoses while the tranny was on my work bench. Then I proceeded to attach my electric drill to the input shaft. I gradually increased the speed of the drill and never heard a noise. Even with my father holding the output shaft to add some resistance the velvet drive operated smooth as ever.
So this made me more comfortable in putting the blame on the damper plate. I will install the new plate this weekend and post (hopefully) some good news.
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Posted By: vectwar
Date Posted: July-19-2005 at 6:08pm
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I have an 84 2001, I have experienced the same knocking noise. How loud of a noise is it? Mine sounds like some one is hitting the engine with a hammer. Is that how loud it usually is?
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Posted By: tommer12
Date Posted: July-19-2005 at 6:56pm
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Same deal... Its usually only when you are in gear.. I had an 84 with the same problem I thought it was my whole transmission.. so I took it a dealer and they pulled it apart and found the plate was bad (all the springs rusted off) Total job for the dealer was $500.. $150 for the part (PCM plate) and the rest was labor. Have to take the whole tranny out, replace the plate and put the tranny back in
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Posted By: 79Monk
Date Posted: July-20-2005 at 1:31pm
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not quite like a hitting it with a hammer but more like two rats fighting for the hamster wheel
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Posted By: Guests
Date Posted: July-21-2005 at 8:28pm
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Was there any alcohol involved???
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Posted By: 79Monk
Date Posted: July-22-2005 at 1:18pm
I put the tranny back in yesterday with the new damper plate, new fluid and a fresh coat of paint. Once everything was ready I cranked her up without the prop-shaft connected and let it idle for a while, then I put her in drive and I could still hear the noise but it was much quieter and softer, could not hear it if the motor cover was down.
So now I believe it could be the pump inside the tranny or some gears that have a little bit of slop between them. But as I see right now, it will just be something I will have to live with until it becomes a problem.
Thanks to everyone for the comments and help!
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Posted By: 64 Skier
Date Posted: August-01-2005 at 11:28am
After a engine rebuild, new tranny and flex plate, and prior to final tuning my flex plate growled and made me think somnething was wrong internally to transmission. Woody at SECC told me that after the final tuning the noise would go away and he was 100% right. Are you sure the engine is not slightly out of tune? A quick timing check and maybe take a look at how steady the vacuum reading is could shed some light and allow you to sleep easier.
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64 Skier
66" HO VTX and 67" HO Triumph
http://www.correctcraftfan.com/diaries/details.asp?ID=1071&sort=&pagenum=3&yrstart=1971&yrend=1975 - 71CC
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Posted By: 79Monk
Date Posted: August-01-2005 at 4:05pm
Maybe your right, after the first day of putting the new damper plate in, I could still hear noise. But since then I have put a few hours on the boat and the noise has seemed to dissapear.
Thanks
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