Low Top End GT40 |
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Posted: July-06-2016 at 11:16am |
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After putting a new prop (ACME 422) on my boat and posting results in the sport prop thread , it was confirmed what I already knew. My GT40 is missing a few ponies.
I've decided to create a new thread to document my search rather then keep posting in the prop thread. I did a compression test before buying the boat and had a couple low cylinders. Below are the results. 1. 120 2. 100 3. 120 4. 110 5. 120 6. 110 7. 90 8. 120. My 95 Sport with GT40 current WOT RPM is 4500 and top speed is 43.5 with the ACME 422. I also feel like my gas economy isn't great but I don't really know how to confirm this, I just seem to be using more gas then I'd expect but this may be due to all the WOT runs to see if I've 'run the rough out'. I also have a loping idle when the boat is warm which for now I assume is a separate issue to the top end. I posted when originally looking at the boat and was told to run the boat for a while and it might correct itself. I've put about 30 hours on the boat since buying it and want to revisit the issue. I am going to redo the compression test myself and if I still have low compression I'll do the test with a teaspoon of oil and get a leak down test done by my Marina. I also plan on doing any recommended maintenance/tune up items that haven't been done yet. So far since owning the boat I have done the following - Oil and filter change - ATF changed - New FCC fuel filter - Cleaned flame arrestor. - New spark plugs. - Can of Fuel cleaner (BG44K). This weekend I plan to - Change the plug wires, cap and rotor. - If time permits I'll redo the compression test. I am new to all of this so any guidance or suggestions are welcome. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21171 |
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If you are in fact a little tired like you suspect, a shorter prop to ease the load and raise rpm to 4800ish would likely help performance. It would also increase fuel consumption.
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DayTony
Gold Member Joined: June-30-2013 Location: Salem MA Status: Offline Points: 832 |
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a leak down is going to tell you a lot more than another comp test. i wouldn't even bother with that. You can watch a few youtube videos i'm sure, and it'll tell you how to do a leak down and you can probably rent the fittings you need from autozone.
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1988 Barefoot nautique-454
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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I am just going to get the marina to do the leak down. I don't have an air compressor and renting one will cost about the same as getting a 'pro' to do the test. The reason I wanted to redo the compression is to see if there was a change since the last time (running the boat for a while) and because it was something that I could do myself. I'll leave it then and just get the leak down done. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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63 Skier
Grand Poobah Joined: October-06-2006 Location: Concord, NH Status: Offline Points: 4269 |
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Absolutely do the leakdown or another compresson test to see what you have now compared to those earlier numbers, but I'm not sure I'd get too concerned about one cylinder under 100 and overall pretty balanced numbers. I got 4,940 rpm at 45.4 mph in my '98 Sport with the 422, not sure of total hours but I'd guess in the 800-1,000 range. So you are looking for maybe 400 more rpm if the hulls are expected to perform the same, and after some really interesting threads on the Sport hulls I still don't know what to expect there.
Would be interesting to know, but not sure I'd do too much to a good running GT-40 if all I was lacking was WOT. Does it come out of the hole strong? I also have the loping idle when warm issue, only in neutral, only after idling for a while. Starting and stopping between ski runs it doesn't happen at all, and it really only is an issue after extended running when trying to dock, will surge in neutral and settle down once in gear. I've ignored it, really a non issue for me. |
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'63 American Skier - '98 Sport Nautique
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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I believe the NWZ is a little quicker then the TSC sport with a nice running engine I'd expect those 400 RPM. You are probably right this isn't worth chasing but it's more an learning exercise for me then anything else. $100 to do a compression test and verify the issues isn't something else would be worth it. Really I have no issues with how the boat runs, I guess the responses to my numbers in the prop thread got me thinking this is something I'd like to at least attempt to solve. Hoping the source of the power loss ends up being from something other than low compression.
Not sure, this is my second boat but my first was a very poorly running 1980's Ski Supreme that had lots of issues and didn't run nearly as well. Hoping the CT Mini happens and I can get somebody here to come for a ride and let me know what they think. I did a couple of WOT starts this weekend and the RPM climbed to 3200 pretty quickly (not instantly) before slowing down, which I believe is what we should see from a GT40.
I also have the issue only in Neutral but mostly notice it while pulling riders. Not a big deal for me at the moment but thought it was worth a mention. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21171 |
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There is no TSC sport... They are all NWZ based.
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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I am going to attempt to replace my distributor cap and rotor this weekend as well as wires.
I have done some reading and the process looks fairly simple as long as you get the wire back in the correct place and the distributor back on in the correct orientation . But I have a couple questions. 1. Do I need to disconnect the battery or anything else to prevent getting shocked? Most of what I have read doesn't mention this. 2. Is cylinder number 1 the one closest to the driver? I also plan to check the engine timing and think I understand how to do it but was wondering if the timing light works in sunlight? Can you still see the advance numbers? |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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JPASS
Grand Poobah Joined: June-17-2013 Location: Orlando Status: Offline Points: 2283 |
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you don't have to disconnect the battery to swap the cap and wires.
The timing light will work in the sunlight, but do double check that you can clearly see the timing marks on the crank pulley. |
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'92 Correctcraft Ski Nautique
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hal2814
Groupie Joined: June-20-2016 Location: Bedford, TX Status: Offline Points: 76 |
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1. As mentioned above, no, but If you don't disconnect the battery make absolutely sure the key is out of the ignition.
2. Should be. The cylinder numbers are stamped on my intake. They may be on yours too. As far as timing,I put white out on my target timing and on 0. That makes it easy to see the target timing and easy to check the advance timing with my timing gun's advance knob. Without the white out I don't think I could clearly see my timing marks in direct sunlight but my gun is a Harbor Freight cheapie. Yours may be brighter. |
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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I replaced cap and rotor this weekend. Cap had some corrosion on the inside. I also confirmed the base timing was set to 5 degrees.
No change in performance. Boat still maxes out at 4500 rpm (43.5mph). I'm getting a leak down test done this week. Whatever the result I don't think it's in the budget to get it fixed this year but at least I'll know what the issue is (assuming it's a compression issue). |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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I bought my boat home this weekend in order to attend the Lake Zoar Mini and used it as an opportunity to do a leak down.
Overall the results were similar to the compression test. Most cylinders were leaking between 10% and 20% but 7 was around 30%. I only ever heard air leaking through the oil fill cap, nothing in the exhaust or throttle body. Guess this means the issue is with the bottom end. I was really hoping the it was going to be the values and all I'd need to work on the heads. So I need some help and advice on what my options are now. I bought this boat knowing that engine work may be in it's future and I'm okay with that. I'd like to try do as much of the work as I can but I am a newbie, but I am willing to learn. I'd also like to get one more season out of the boat before doing the work. My wife and I are saving up to by a house next year, so plan would be to get the work done over the winter next year. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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63 Skier
Grand Poobah Joined: October-06-2006 Location: Concord, NH Status: Offline Points: 4269 |
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Paul, I'm guessing you could get 5 more seasons out of it if you really wanted to! What you are describing, in my opinion, isn't something that will cause engine failure. It's some rings that aren't seating/sealing like they should, causing low compression in one cylinder. I'd expect you to be burning a bit of oil as well, but with those numbers could just be slight, and with the low amount of use boats get it could be less than a quart a season.
I also completely understand if you want to get it fixed, I'm the same way. Hopefully others with more rebuild knowledge will offer their opinion, if you are pulling the engine, dropping the pan, removing a piston, I don't know if it makes sense to just re-ring and hone that piston vs. doing a complete refresh of the engine. |
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'63 American Skier - '98 Sport Nautique
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Thanks David, It's good to know I can keep running the engine, without doing major damage. For what I use the engine for it runs great. I haven't noticed any excessive oil burning or any other issue besides low top end discussed above.
I would like to fix the engine at some point and learning about all this and how to do it is a big reason I bought the boat but knowing I can put it off until I am ready is great. I agree if I was going to do something I'd rather do it all then just try get the one piston done. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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63 Skier
Grand Poobah Joined: October-06-2006 Location: Concord, NH Status: Offline Points: 4269 |
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What do you see for oil pressure at idle and at speed? What oil are you running?
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'63 American Skier - '98 Sport Nautique
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Oil pressure is 60psi at both idle and speed.
I have VR1 20W-50 in there. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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gun-driver
Grand Poobah Joined: July-18-2008 Location: Pittsburgh, Pa Status: Offline Points: 4127 |
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Yes, I did confirm it was 5 degrees at all RMP with the spout removed.
Compression numbers are as important as the difference between the numbers but the compression is low on all cylinders. I am sure I'd see great improvement from a rebuild. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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Dreaming
Platinum Member Joined: May-21-2010 Location: Tacoma, WA Status: Offline Points: 1870 |
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rule of thumb is that you shouldn't have more than 10% difference between cylinders. I see your compression as an indicator of overall engine health, and that you need a set of rings and a hone or bore. Since it runs smoothly still, you may be able to run it for a while, but I would certainly plan on an engine rebuild... It seems to me that this is inevitable. Rusty cylinder walls may clean up if the rust is only on the surface, but if there is any pitting on your cylinder walls, the rings will eat themselves up, and you won't ever get compression to return. Loose or bad rings can wear the walls unevenly, or scar them and could cause the next rebuild bore to be larger to get the damage to come out.
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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I definitely plan on rebuilding the engine but as stated above (unless I get a nice bonus from work) I'd rather wait until the end of next year to get this fixed. Hopefully I don't do anymore damage along the way. Maybe I pull the engine at the end of the season and bring it home and see what I can get done. Apart from the cost my second biggest issue is find a place to work on the engine. I don't have much room in my current garage and I'd really like to try do this as much of the rebuild myself. Ball park what would this cost for me to get somebody to fix this. I'd guess 2k to 3k does that sound about right? Edit: Just to clarify, when i say do it myself, I mean the take apart and put it back together parts, with a machine shop doing the difficult work. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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Dreaming
Platinum Member Joined: May-21-2010 Location: Tacoma, WA Status: Offline Points: 1870 |
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cost is dependent on your local area rates, and the work that needs to be done. you tackling the tear down and assembly will help your budget a good deal. My Machine shop quoted me 1500+ parts for this work, I assume that is a bit on the steep side as they are well known around here for performance builds, and they had an 8 week backlog. (translation, they didn't need my one off 351 build to keep them busy, especially with the racing season coming to an end in the next few weeks)
All in, I spent 2300 (including shipping and tax) on a roller long block, gt-40. While I was interested in doing the build work myself as well, time and cost were prohibitive to me, I figured I'd spend more than 800 in parts and tools to get this thing right in my garage, and many hours that I should be doing something else, so for me, experiencing the build didn't make sense. If it runs now, and you can get another season out of the motor, I don't see a lot of reason not too, I would venture that you'll probably purchase a long block if you're budget conscious on getting the new engine. |
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Ah yes, I was reading your post as your situation was similar to mine. Do you have the engine yet? Have you installed it? |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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Dreaming
Platinum Member Joined: May-21-2010 Location: Tacoma, WA Status: Offline Points: 1870 |
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Engine should arrive today or tomorrow. Since your on the right coast, you might check into Rapido Marine, it looked like they could do a marine 351 long block for about 1500+ shipping. Might be more with GT-40p heads, if they can do that. Michigan motors was another name that came up during my search, but I think they were more expensive.
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Are you paying somebody to do the install? What does that cost? |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Also, how do I go about deciding whether i need to fix what I've got (not even sure exactly what this would entail) or buy a new short block/long block and then move everything over .
Sounds like the easiest would be to buy a block and move thing over then sell my old block. Since as far as I can tell my heads seem fine, would a new short block do? |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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Dreaming
Platinum Member Joined: May-21-2010 Location: Tacoma, WA Status: Offline Points: 1870 |
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I am doing the install and swapping over the tin on my motor (intake, oil pan, timing cover and other external items) - One of the Spokane builders I checked with could do the whole motor assembly and rebuild for 2500 (including tin), but it would not have been a roller motor, so I am not sure of the straight $ comparison, but if you can wrench, the accessory mounting part is not too difficult as long as you have the tools and time.
- deciding on how to proceed is a process of counting costs, I figure if the bottom end needs work, you'll probably want to do a valve job on the heads, and make sure they are flat and not cracked... reworking heads is expensive (~3-400 is a guess) so I am not sure that you're money ahead to save them when you can get a long block for a similar price, and all the work is done. One good thing about a long block is that all the calculations are done, you wont have to worry about compression ratios, rocker heights, cam durations etc, its done. You may be able to run the heads as they are, but that decision is money based, and I don't know your situation. I too thought about the short block route, and the long block just made more sense to me. |
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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Kris,
Thanks for the help. I have a lot to learn before I make any moves but you've have really me understand some of the options, so thanks. Let us know how it goes putting it all back together. I'd really like to do the work myself because i want to learn how it all works. One more question, as I have a GT40 with EFI are there any additional considerations vs Carb when choosing an engine. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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Dreaming
Platinum Member Joined: May-21-2010 Location: Tacoma, WA Status: Offline Points: 1870 |
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your outside of my pay grade with the GT-40 questions, but I assume that the intake manifold is the biggest difference, and all the rest is just bolt on stuff and sensors.... Mine has a carb, so no personal experience.
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Blamey
Gold Member Joined: August-18-2015 Location: White Plains,NY Status: Offline Points: 631 |
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So I have been trying to read up as much as possible about what my leak down results mean and I need a bit of help to determine what my next steps should be.
For those that don't want to read the whole thread I have low compression in two cylinders. Results from when I bought the boat last year are as follows: 1. 120 2. 100 3. 120 4. 110 5. 120 6. 110 7. 90 8. 120. Low compression overall with 2 and 7 being particularly problematic. I did a leak down 2 weeks ago which confirmed the results. During the leak down I didn't hear any air escaping from the Exhaust or Throttle body. Which I believe points to either the rings or possibly the head gasket being bad. So I am looking for advice on what to do next and if there are any low cost options as I am not quite ready to pay for a short block or a rebuild. If there is anything I can do over the winter to the engine to either try improve performance or confirm that the issue is with the rings/block. I am new to working on engines but I am happy to try anything myself. So far I have determined the following as Options 1. Uses some snake oil and see if it helps. I purchased some Seafoam and some Restore and plan on adding the Restore to my oil and adding the Seafoam to the Gas and the running some through the Throttle Body. 2. Perform the compression test again, this time add some oil to the cylinder to confirm that the issue is with the rings. My thinking here is that is could still be a head gasket issue and this is the only way I can confirm this. Any other suggestions on thing for me to try other then a rebuild/re-power. |
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96 Super Sport
Previously: 95 Sport Nautique, 1980 Ski Supreme |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Paul,
The obvious cheap simple way is to try a "snake oil" I don't think you have much to lose however, if the problem is broken rings, the stuff won't weld them back together! Hey, even Autozone sells the Restore!!! |
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