Using a V-8 gimbal housing with a 470 (MR drive)

[NWVintage]

For reasons unimportant to this particular question, I'm going to be using an MR gimbal housing from a V-8 with my 470.

The question is: what do I do with those two extra exhaust ports? My original had the ports but they were dead-ends - the holes on the outside of the gimbal housing were drilled through to the main exhaust port. So there was a pressure release but it went from the main port. Do I just block them off and use an exhaust tube in place of the original bellows? Block them and drill through the main port? Block them and not worry about it? Anyone with any experience with this topic, I'd love to have your input.

 

[NWVintage]

Eureka! Drain plugs. I'm going to use a pipe tap to tap threads into them and then use brass drain plugs.

However, the question remains what to do with that extra back pressure...?

 

[Bondo]

The question is: what do I do with those two extra exhaust ports?

Ayuh,.... Which ports, Where,..??

If the idle relief ports, outside along side, leave 'em alone,...

 

[NWVintage]

Ayuh,.... Which ports, Where,..??

If the idle relief ports, outside along side, leave 'em alone,...

Yes, the idle relief ports. But I can't leave them alone. The 470 has the single port exhaust tube and the gimbal housing is for use with the Y-pipe.

exhaust tube:
http://www.ebay.com/itm/MERCRUISER-PRE-ALPHA-EXHAUST-TUBE-PIPE-CAST-53720-53113-/111063438576

y-pipe:
http://www.ebay.com/itm/like/111583001918?lpid=82&chn=ps

If I don't seal them up, it'll be like leaving the drain plug out. Times two!!

Anyway, I threaded them, used extra drain plugs that I had laying around and sealed them with 5200. I'm going to use an exhaust tube in place of the exhaust bellows - it'll provide more back-pressure relief than the idle relief ports anyway.

 

[thumpar]

My 120 had the relief valves. Maybe there is a different exhaust tube you could use.

 

[NWVintage]

Just to finish this topic...

My 120 had the relief valves. Maybe there is a different exhaust tube you could use.

My 470 originally had idle relief ports too. The problem is that they were drilled directly from the main exhaust port and did not use the separate holes that the V8 Y-pipe did.

My solution was to tap 1/2" FPT into the ports below the main exhaust port and put regular brass drain plugs in there. I used 5200 to seal them up. I installed an "exhaust tube" in place of the bellows and I think that should do the trick. I'll get back to you when I get the boat in the water...

 

[achris]

Why not drill from the outside up into the main exhaust chamber, just like the proper 470 gimbal. I assume you have the pipeplugs in from the inside, just below where the exhaust pipe goes.