470 / 3.7 riser questions

[Eric H]

Hi all. Can someone clarify thing for me here. I have a 3.7 exhaust riser that has a water separation tube in the outlet similar to item 41 below.<br /><br /> http://media.stemtostern.com/LSDATA/LSDATA_FULL/CRUISER/75471/14.GIF <br /><br />I also have a riser that does not have the tube. My risers look like item 17 below with the outlet being canted at 45 degrees as opposed to 90.<br /><br /> http://media.stemtostern.com/LSDATA/LSDATA_FULL/CRUISER/99958/15.GIF <br /><br />I’ve looked all the model years on that site and none of them show the separation tube installed into the 45 degree riser outlet - yet I have a manifold that does have one. I do not have the serial number handy but the motor is a 1988 (OB774252-and up).<br /><br />1) Does anybody have a better exploded view?<br />2) Can anyone explain its function?<br />3) Would it hurt to run without it? My boat obviously has been for an undeterminable amount of time.

 

[MrBill]

Re: 470 / 3.7 riser questions

Eric...here's the schematics and exploded views that I use. They're accessible at mercruiserparts.com. Here's the link, go to "Search With Pictures", then select sterndrive, engine (4cyl) and specific model - I/m sure you'll find it. You might be referencing the part 22-36305 which is only used for models w/o power steering and often not shown in exploded views. Also, you'll need to know if your riser is aluminum or cast iron. Hope this helps....<br /><br /> http://www.mercruiserparts.com/mercruiser_parts.asp

 

[Northern Eclipse]

Re: 470 / 3.7 riser questions

My fathers 1988 3.7 has the manifold riser combo and it looks like the one in item 17, this riser is self draining.

 

[Eric H]

Re: 470 / 3.7 riser questions

MrBill, thanks for the reply. Those views look about the same as the others I've seen. The part number you mention is an elbow which I assume is for the power steering cooler plumbing. (Assuming I looked it up right)<br /><br />The part I'm curious about looks like a piece of flanged exhaust pipe about 2 1/2 inches in diameter by 3 inches long that fits inside the riser outlet. I can find no reference to it being installed in a 45 degree style (item 17) riser. I guess I’ll have to head down to the Mercruiser Monday and see what they think.

 

[MrBill]

Re: 470 / 3.7 riser questions

Eric...sorry I could not be more help. I am told that the 3.7l and predeccesor 470 and 488 models had three basic exhaust/riser combinations that might explain some of the different components that you have. In the early 80's the 470 was used in I/O applications as well as inboard, a 3" and 6" extender was available and attached directly to a 90 degree riser. Later applications had two different exhaust combo's, now referred to as "old" style and "new" style. The old style was a one piece system with a rubber type joint connection, and the "new" style was a two piece system. I have seen 'extensions' to an exhaust, similar to what you describe as a result of how the 3.7L had to be mounted into a hull. Are you trying to choose which riser and exhaust style to use in your application?

 

[Eric H]

Re: 470 / 3.7 riser questions

MrBill, yes and no. <br /><br />I suspect I'm not being clear enough. The 90-degree and 45-degree descriptions are my own - for lack of better understanding. Check the 2 links I posted in my initial question and it becomes obvious.<br /><br />The tube in question fits completely inside the riser outlet and is not any part of the rest of the exhaust. On the 90-degree manifolds it is listed in the fiche with the nomenclature being "separation tube". See item 41 on the first link I posted. This tube, when installed, is flush with the riser outlet. I've seen this set up before on an 80's Glasply I/O.<br /><br />The problem I have is that my existing (good) 45-degree riser does not have the tube in question. Another 45-degree riser I have (spare) does have the tube. The 45-degree style of riser is illustrated as item 17 in the second link I posted.<br /><br />The disparity between the parts got me to thinking my good riser might be missing this tube. After looking through all the riser fiche I can find, I never see a reference to the tube being installed in the 45-degree style manifold. <br /><br />This got me to wondering which manifold is correct and does the tube even have a purpose.

 

[MrBill]

Re: 470 / 3.7 riser questions

Eric...I have never seen a 45 degree riser with the separation tube, so I'm stump on this one. I can only say that my application and others that I've seen are exactly the way the schematics indicate. Wish I could be more help...