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Exhaust hose reducers |
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Wilhelm Hertzog 
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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 Topic: Exhaust hose reducersPosted: December-15-2022 at 2:01am |
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My boat's exhaust risers are 3.5" OD, but the mufflers and exhaust tips are 3". There is about a foot of 3.5" hose running from the riser to a 3.5" to 3" stainless steel reducer to which the 3" hose then connects. There is a small water leak where the two hoses join at the reducer on the port side of the engine, which doesn't seem to go away even if I tighten the hose clamps thoroughly. The reducer has a small crack along a welded seam, and I suspect that may be the source of the leak. So I'm potentially looking at replacing the reducers, but have a few questions I'm hoping someone can help with:
1. I notice the commercially available reducers (from Centek) are all fiberglass. Any reason why fiberglass is the preferred material to use in this application and not stainless steel? 2. Is it feasible to DIY fabricate such a fiberglass reducer, or is it likely to be more tricky than it looks? I assume one needs a resin that can withstand reasonably high temperatures for long periods, but other than that it seems pretty straightforward? Thanks for any help! P.S. I wanted to post a picture, but am also getting the 'Not enough space on the disk' error. |
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: December-15-2022 at 8:33pm |
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I guess I'd wonder why you don't just get the SS reducer repaired. Maybe the picture that you can't post would explain that
 It's a lot easier to tighten the hose clamps on SS than on fiberglass which would deform/crack a lot easier
I think you'll find that all those marine fiberglass mufflers are made with fire/flame retardent fiberglass which makes them kinda expensive. Here on CCF people just seem to use regular resin for repair/patch jobs without burning things up. |
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Nautiquehunter
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Joined: December-31-2008 Location: Lake Lanier GA Status: Offline Points: 1010 |
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Posted: December-16-2022 at 11:44am |
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You can buy new SS exhaust reducers for automotive on line
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Wilhelm Hertzog
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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Posted: December-16-2022 at 2:16pm |
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I'm aware of the issues around crushing fiberglass exhaust system parts, which makes me wonder why the industry standard seems to be to use fiberglass and not stainless steel?
If there is no reason to use fiberglass over stainless steel I'll definitely look to get that reducer repaired. I did have an initial go at trying to get it out of the exhaust hose, but it looks like it's going to be a proper wrestling match... |
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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MourningWood
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Joined: June-13-2014 Location: NorCal Status: Offline Points: 918 |
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Posted: December-16-2022 at 5:43pm |
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So, I put some nice aluminum manifolds and risers on an '81....oops! 3.5" into 3" exhaust...what to do?
Cut a short piece of the old 3" (non-corrugated) hose, put it on the muffler, then ran the 3.5" right to and over it. Double clamped, no leak. The old 3" acted like a spacer. And if it did leak, it was already down in the bilge.
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1964 Dunphy X-55 "One 'N Dun"
'I measured twice, cut three times, and it's still too short!" |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: December-16-2022 at 6:32pm |
Back to your question about fiberglass vs. stainless steel I'd figure it's got to do with corrosion resistance in salt water as much as anything else and since you use your boat in fresh water, brackish water and salt water at different times, that's why I was wondering what your picture looked like. SS may be good in fresh water like most people on here are used to, but there's a reason monel is preferred in salt water cooling systems instead of SS of any kind. How long have your SS reducers lasted so far and what kind of condition are they in? If you're having a hard time getting the hose off the SS, it'll come off the fiberglass with about the same amount of wrestling and probably destroy the fiberglass while doing it. It's a lot easier prying on the SS than prying on the fiberglass till it falls apart.
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Wilhelm Hertzog
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Joined: June-14-2014 Location: Cape Town Status: Offline Points: 349 |
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Posted: December-17-2022 at 4:01pm |
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The reducers must be five to seven years old. Not sure how to judge their condition - other than the small crack I noticed in the one, the insides are pretty black from exhaust. I guess I'll have to pull them out to properly assess. But that will have to wait, as we're right in the middle of boating season here in the southern hemisphere, and the leak is small enough that I can live with it for now.
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1982 Ski Nautique PCM351W RR II Velvet Drive 10-17-003 1:1 II PerfectPass Stargazer
Do not go gentle into that good night. Rage, rage against the dying of the light. |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11155 |
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Posted: December-18-2022 at 7:59am |
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Sounds like a plan
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Wilhelm Hertzog wrote: