Plumbing Mercruiser manifolds on a Yamaha

[Antax]

I didnt really know where this needed to be. It's a Yamaha engine setup but I'm using Mercruiser manifolds.

A little background. Its a 1992 Glasstream 190 SE with a Yamaha 5.0 setup. The previous owner didnt winterize the boat quick enough and the bloke and manifolds cracked so I'm doing a 5.0 to 5.7 swap. I tried having the old Yamahas welded and one of the turned out great. It even cleaned up on the inside better. The other cracked on the inside so I scrapped them. Probably should have done that anyway but I wanting to try to get a litle use out of the boat first. I ended getting a set of Mercruiser MC-1-87114 Manifolds and MC-20-44354 Risers. They have the mounting holes and bosses close engouh to the Yamahas that I can fabricate something to get my other accessories to mount onto them.

Anyway heres the questions. The Yamaha had a 3 hose, warm manifold setup with a Crusader water neck and a extra circulation plate under the water neck to circulate engine water through the manifolds. With the Mercruisers I have 2 choices 1: remove/block off the circulation plate (if I block it off then I would have to drill a very large hole through it so the water can flow through so if I do this then theres no going back), plug off all the holes in the Mercruiser manifolds and run the outlet hose to the bottom of the manifolds and have a cold manifolds setup or 2: try this...



I dont know how the riser will do being plumbed like this. The only water they will get will be the exit water and I'm not sure that will be enough. Would I be better going to a cold manifold setup and plumb the outlet straight to the bottom of the manifold?

 

[Bt Doctur]

I would remove everything Yamaha and go with the merc cooling system.

 

[Antax]

Not an option $$$
Besides I like the challenge

 

[Antax]

For comparison here is a shot of the Yamaha manifolds...

 

[thumpar]

I think you should have used the Merc manifolds that feed from the bottom. That is how mine are. There is only one hose so you would need to either plug up or connect together the other hoses depending on how that Yamaha setup works.

 

[NHGuy]

That Mercruiser exhaust should have slotted riser gaskets with water constantly feeding the exhaust manifolds. if your engine has a hot water exit from the block that can go to the risers. You don't block off the riser/manifold joint unless you are using closed cooling.
Doc is right, you can have Mercruiser cooling by just using their thermostat housing, as long as there's adequate cooling water.

 

[Antax]

Thanks guys

Your right Thumper, that was my option one. The Mercruisers have an inlet in the bottom that I would use. They also have 2 in the top of the manifold and one in the back of the riser. If I did that then it would be a cold manifold setup and this may be the best way to go. But I was under the impression that the warm manifold was better. Something about condensation maybe?

This is a very bad drawing of a cross section of the circulation block between the Crusader water neck and the engine block. I didnt draw in the Crusader water neck details but hopefully you get the idea.

BTW Its very good possibility I have the divider backwards. It might be the other way \

NHGuy the Mercruisers didnt come with a block off gasket. They had the 2 slots and 2 small holes. To make it act exactly like the Yamaha I would have to add a full block off gasket/plate to separate the 2 like the split cavities in the Yamaha riser. I actually did look at the Mercruiser water neck but I think my alternator and power steering pump are in the way.

 

[Antax]

Ok so this is what I ended up with. Yes that is a Yamaha riser bolted to Mercruiser manifold. BTW anybody want to buy a set of brand new Barr Marine Mercruiser risers? I'll make you a great deal lol

 

[dangerdj]

I have a 92 yamaha in need of a new block as well. Did this setup end up working for you in the long run? Any further advice? I noticed you plugged the holes on the top of the exhaust manifold, did that end up working? Thanks

 

[southkogs]

Welcome aboard dangerdj. Please take a few to read the forum rules.

This topic has been snoozing for five years. Why wake it up?