Tips on changing manifold on 3.0L

[enginesilo]

I'm considering changing my exhaust manifold on my 3.0L Mercruiser. Engine is around a 2005 year, don't have the serial handy.

Since this is the 4 cylinder, it is not like the 6 and 8 cylinders where there is a manifold on each side. Instead it has 1 manifold, and has the carburetor mounted on the top,along with I think the alternator or some other component mounted off of it. Makes it a harder job on the 4 cylinder than the 6 or 8 with these extra components.

I've read people suggest using long bolts with the heads cut off to help get the old manifold off, and the new manifold on which makes a lot of sense so i'll be doing this as needed.

Any other tips on getting the carb off, carb linkage, if I should be using any gasket sealer with the gasket, tips on getting the surfaces clean, other component removal, etc?

 

[TurtleTamer]

Should just be cooling hose from T-stat housing, alternator bracket, carb, riser, and if still equipped, EZ Drain system bracket, and manifold drain (if still equipped with plastic fitting, do not remove if it's not leaking, or it will break). I believe from the factory it comes with two studs at the front (where the EZ drain bracket bolts to it) and one at the rear, so you shouldn't need any long bolts to convert to studs. You can move them around to suit your needs on reinstallation.

Use OEM gaskets. PM for a popular company NOT to order them from due to poor shipping packaging (not this site).

No sealer should be needed, unless one of the experts knows of a bulletin or you have lots of pitting on a mating surface. I used a wire wheel on a 4" grinder to clean mine up. A shop vac to pull all the resulting crap out of the ports.

It is not a difficult task. Good luck.

 

[fishrdan]

The manifold swap is easy peasy, clean up the head port mating surfaces spotless and use OEM style metallic gaskets (silver grey color). Take a bunch of pictures before removing anything and during disassembly. Use line wrenches - flare nut wrenches on the fuel line on the carb. No sealant is needed on the gaskets, but pipe plugs should use Permatex #3 - Aviation Sealant. I use a gasket scraper, then razor blades held at 90* to scrape the gasket surfaces clean.

If you're changing the manifold as a maintenance item, you should change the exhaust elbow (riser) also. Check the shutters in the exhaust pipe while the exhaust elbow is off, heck I'd just replace them after 15 years. Use a good quality manifold/riser, OEM Quicksilver or Barr/Osco, not the cheaper GLM/Sierra china stuff.

Re-torque manifold and riser bolts after first heat-cool cycle.

 

[tpenfield]

3.0 manifold . . . cake walk. If I were me, I'd remove bolts from the outer ends towards the middle and then install the new one starting with an inner/center-most bolt and work your way out. That way the manifold will be nearly balanced on the center bolt(s) and not hard to handle.

If you want a challenge, that would be a 454/7.4 manifold

 

[enginesilo]

Should just be cooling hose from T-stat housing, alternator bracket, carb, riser, and if still equipped, EZ Drain system bracket, and manifold drain (if still equipped with plastic fitting, do not remove if it's not leaking, or it will break). I believe from the factory it comes with two studs at the front (where the EZ drain bracket bolts to it) and one at the rear, so you shouldn't need any long bolts to convert to studs. You can move them around to suit your needs on reinstallation.

Use OEM gaskets. PM for a popular company NOT to order them from due to poor shipping packaging (not this site).

No sealer should be needed, unless one of the experts knows of a bulletin or you have lots of pitting on a mating surface. I used a wire wheel on a 4" grinder to clean mine up. A shop vac to pull all the resulting crap out of the ports.

It is not a difficult task. Good luck.

Thanks for the extra details, so with the alternator bracket does that just have screws that hold the bracket on and then the alternator comes off? Do I need to do anything with the belt tensioner and the belt itself or anything like that?

The manifold swap is easy peasy, clean up the head port mating surfaces spotless and use OEM style metallic gaskets (silver grey color). Take a bunch of pictures before removing anything and during disassembly. Use line wrenches - flare nut wrenches on the fuel line on the carb. No sealant is needed on the gaskets, but pipe plugs should use Permatex #3 - Aviation Sealant. I use a gasket scraper, then razor blades held at 90* to scrape the gasket surfaces clean.

If you're changing the manifold as a maintenance item, you should change the exhaust elbow (riser) also. Check the shutters in the exhaust pipe while the exhaust elbow is off, heck I'd just replace them after 15 years. Use a good quality manifold/riser, OEM Quicksilver or Barr/Osco, not the cheaper GLM/Sierra china stuff.

Re-torque manifold and riser bolts after first heat-cool cycle.

More great tips, i'll definitely use these as I get into the deep. Good reminder to take both pictures and video as I work.

3.0 manifold . . . cake walk. If I were me, I'd remove bolts from the outer ends towards the middle and then install the new one starting with an inner/center-most bolt and work your way out. That way the manifold will be nearly balanced on the center bolt(s) and not hard to handle.

If you want a challenge, that would be a 454/7.4 manifold

I ended up getting OEM Manifold and Riser. Last year I swapped out the riser and never had the time to get the manifold done. So i'm hoping to do the manifold this year and then I should be good to go for a while. The manifold looked half decent when I looked at it so I wasn't all that worried last year, but I already bought the manifold so I'm going to change it out as I can find the time.

I like your style, i'll use your strategy with the bolts and get the new ones in so I can get the old manifold off and the new one on easier. Glad I'm NOT doing a 454, the manifold on the 3.0L is a beast weight wise, I can't imagine what the 454's weigh!

Thanks again everyone, i'll post back if I have any other questions or issues as I'm going through the process.

 

[Scott Danforth]

personally, I prefer to remove the brackets, remove the elbow and remove the carb so I am dealing with only the 3.0 manifold

use a straight edge on the manifold and the head to make sure both are true. many times I have found I had to have the head or manifold cut to true up the surface.