Yamaha 4.3L Exhaust Manifolds

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trentgarber

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Good morning,

I am just in the stages of replacing the 4.3L GM in a 93 Rinker I purchased. It has a Yamaha sterndrive setup which, until recently, I was unfamiliar. I now realize that parts are not easy to locate. I have a cracked exhaust manifold. Does anyone know where I can come up with an exhaust manifold for a Yamaha 4.3L set up or is there a reliable way to repair?

Thanks in advance.
Trent
 

Bondo

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Ayuh,.... Welcome Aboard,.... I believe yer only option is to adapt a set of Merc manifolds,....
 

trentgarber

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Thank you. Lots of good information here. Adapting over is what I was starting to think. I can't seem to find anything anywhere. I am planning to call Capt Ken tomorrow. Are there any Merc adapter kits you would recommend?
 

Bondo

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Ayuh,.... I doubt there's any "Kit",....

The motor side will be the same,....
You'll need to figure out which risers ya need to mate up to the Yamaha y-pipe though,....
Diameters, angles, 'n lengths are the variables,....
 

Scott Danforth

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There is no kit. You pretty much buy the merc manifolds and risers and gasjets and modify your y pipe as needed
 

Antax

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I've done the swap for the 5.0/5.7 and 77searay197 has done a 4.3. I even did a Youtube video to show the setup. You have to reuse your risers. I posted a write up on the things used with some part numbers for the 5.0/5.7.
 

Lou C

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Interesting, it appears that Yamaha wanted to have a 'warm manifold' system like Merc did on some of their models, the idea being that keeping the manifolds as warm as the block would evaporate any condensation in the exhaust and reduce the chance of water being sucked back in the exhaust at low speeds where the engine is running cool. Not sure if this would work but you may have been able to use Volvo manifolds with a Volvo thermostat housing which would have been simpler as far as the plumbing goes, not sure if they would mate up to the Yamaha Y pipe. VPs system is a cold manifold system though where the manifolds are usually cooler than the block by a considerable extent.
 

Fletch2018

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Well I am in the "same boat". I have a cracked yamaha exhaust manifold. I just found out from a Mercruiser expert that the exhaust manifold can be welded and fixed but you have to take it to a place that puts it in an oven and heats it until the metal is red and then it is welded while it is in the oven. It has to be heated so it does not crack, and this is a permanent fix. It is rather expensive though at ~ $200. Anyone else heard of this method? Just trying to share some information with you.
 

Lou C

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Too risky. I'd bite the bullet and upgrade the exhaust system to something that is available in the aftermarket.
I converted my old OMC one piece batwings on the V6 over to the Volvo style center riser that are easily available in the aftermarket. All I needed was the Volvo 90* adapter that connects the riser 4" hose to the Y pipe 3.5" hose, I used Volvo parts so it was expensive but it all fit perfect, and looks factory.
 
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Lou C

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Here is a pic, you can see the Volvo 90* adaptors, you should measure the diameter of your Y pipe hoses and start there.
 

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