Replacing Exhaust Manifold and Riser on 3.0L - Tips Needed

enginesilo

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The time has come to do some preventative maintenance and i'm planning on changing out the Exhaust Manifold and Riser on my 3.0L Mercruiser. The engine is a 2005 3.0L and an outer visual inspection the components look great, but I already know they rot from the inside out.

How difficult of a job is this on the 3.0L for a DIY type person? Anyone do it themselves recently? How long did it take from start to finish? The shop manual procedure seems straight forward. Anything to watch out for, or require anything more than what the manual states? I read a good tip that said to find some extra long headless bolts that you can put in place of the end bolts so the manifold is supported and doesn't go dropping off. Anything else to watch out for with the carburetor or anything?

I will be using OEM parts. Here is the parts diagram:
http://www.marinepartsplus.com/catal...860235A03_jump
-860235A03 Exhaust Manifold Assembly (Which supposedly comes with a lot of bolts and such)
-12076A2 Riser Elbow Assembly
Think buying these 2 part numbers will be all I need? I think so but i'm not fully sure. Should I be changing the exhaust shutter at this time or is it ok to reuse if it looks like its visually still functional?


All tips appreciated.

Here are the instructions from the shop manual:

Removal
1. Disconnect battery cables from battery.
2. Drain water from cylinder block, exhaust manifold and exhaust elbow.
3. Disconnect throttle cable at carburetor.
4. Disconnect exhaust hose and cooling hoses.
5. Disconnect fuel line at carburetor.
6. Disconnect crankcase ventilation hose at rocker arm cover.
7. Disconnect wires connected to electric choke.
8. Remove exhaust manifold fasteners; remove manifold assembly and discard gaskets.
9. Remove exhaust elbow.

Replacing Exhaust Manifold and Risers on 3.0L - Tips Needed


Installation
If exhaust manifold body requires replacement, transfer all parts (from old manifold) to new
manifold body.
1. Position new gasket on head and install manifold in position, making sure gasket is in
place.
2. Tighten fasteners evenly and torque to 23 lb-ft (33 Nm), starting in center and working
out toward ends.
IMPORTANT: After engine has been brought up to operating temperature, allow
engine to cool. Retorque manifold fasteners.
3. Install carburetor (if removed) and connect crankcase ventilation hose at rocker arm
cover.
4. Install exhaust elbow using new gasket. Torque to 25 lb-ft (34 Nm).
5. Install gasket as shown
6. Connect throttle cable to carburetor. Adjust as outlined in ?Removal, Installation and
Alignment.?
7. Connect fuel line and electric choke wires.
8. Reinstall exhaust and cooling hoses.
9. Reconnect battery cables to battery. Tighten securely.
10. Start engine, check for exhaust, water and fuel leaks and adjust carburetor idle speed
and mixture.
 
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TyeeMan

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I did this on a Volvo 4.3 V-6 a couple years ago, it was a pretty easy job. A 3.0 liter should be a breeze. The engine and original manifolds and risers were 1995, the reason I changed manifolds and risers was that I got water intrusion into the engine. I'm 97% sure the water intrusion came from a failed gasket between the manifold and riser, I just chose to replace manifolds and risers for good insurance. I did not buy OEM Volvo stuff just because of the cost. I went with an aftermarket with 2 year warranty I found on line. Here are a few thing that come to mind.

My manifolds came unpainted, , or had some kind of anti rust clear coat on. And they came with extra ports and such that needed to be plugged.
I plugged all extra ports I didn't need with pipe plugs, then painted everything except the mating surfaces with Rustoleum Engine Enamel. Man did that look nice!!! had the same texture and everything as OEM.
Scraping the old gasket off the block was a PIA!! To make it easier I removed the studs, , a lot of razor blades seemed to work better than a gasket scraper.
Oh, I also replaced the rubber tubes from the riser to the down tube.
I did not have exhaust shutters but if I did I certainly would replace them at this time.
Assembly tip - be it good or bad, and especially if you replace any rubber tubes, put a little smear of silicone/dielectric grease in the rubber tube, makes the riser (or whatever ) slip right into it with very little effort.
NOTE!!! After you have everything all assembled and your ready to put the garden hose on it and start it up, , , do a double check and make sure the joint between your manifold and riser is in fact tight.
I assumed everything was tight because when I torqued all the bolts everything torqued up just fine. I put the hose on it hit the key and I just happened to be watching the engine when it started and I saw a puff of exhaust gas come out between the manifold and riser. I quickly shut down the engine and turned the water off. Luckily the whole coolant system was drained so the manifolds never started to fill with water yet. Whew!!
The problem was that a couple of bolt holes in one manifold did not get tapped deep enough. I added a couple washers, retorqued and all was well. That's probably what I got for buying aftermarket stuff, but if that's the only problem I'll take that.

Good luck!! Sounds like you have your plan and know what your doing.
 

wahlejim

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Jul 23, 2015
Messages
884
I just did this on my 5.0, it was as straight forward as the instructions. I second the making sure all bolts are seated and tight. I had to run out to the hardware store as the existing bolts for my end caps were too long for the manifold. Keep in mind that a new manifold does not come with end caps so if those need to be replaced, order those as well.

Other than that, the first time you run it, inspect thoroughly for leaks. Make sure to tighten every single hose clamp. Check hose clamps you don't touch as well. Just the moving and removal of my risers broke the seal of the rubber boot that the riser slid into where it met the y-pipe. Take pictures as you disassemble so you can reference them during re-assembly. and don't miss anything.
 

Bondo

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The engine is a 2005 3.0L and an outer visual inspection the components look great, but I already know they rot from the inside out.

Ayuh,.... Are ya a saltwater boater,..??

Pull the riser off, clean the gasket surfaces, 'n inspect how much cast iron is left,....
If it's still 'bout 1/4" wide, yer still good,...
 

achris

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Messages
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I would only remove the exhaust elbow and do an assessment at that point before buying any parts. Once the elbow is off you can see how the inside of the manifold is looking and what condition the shutter is in. Also the elbow itself. Anything that looks good can stay.

Chris.....
 

enginesilo

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Messages
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Thanks for all the knowledge everyone, you all shared some great tips. So the manifold/riser are original to the boat and I boat in salt water and it's been docked in the water for 4 months per year for the last 6+ years so I'm guessing I am on borrowed time from what I hear in the forums (Saying (5-7 years max). It is also raw water cooled so I'm thinking I'll pull off and inspect but also just change the parts while I'm already turning wrenches.


OEM vs. Aftermarket parts?
Any reason to consider Sierra/Barr aftermarket parts or are the OEM's the best of the bunch? I know OEM costs a lot more but I don't mind spending it as long as they aren't proven inferior. I'm mostly an OEM type of guy when it comes to parts.


Change before spring?or end of season?
Another question for you all is, would it be wise to change at the end of the season before winterizing the motor? Or is it best to do at the start of the season so I can run it and re-torque after a few hot cycles? I have more time end of season but I'll wait till the spring if you all think it's wiser.


Is sealant needed on the gaskets either on the manifold to the block, or the manifold to the riser? I'll be planning to use some type of anti-seize on the bolts for sure.


My biggest wonder at this point is will it be an easy straightforward job, or will rusted and stuck bolts make it a nightmare. Knowing salt water I predict lots of swearing and bloody knuckles in my future.
 
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alldodge

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I would recommend OEM parts, the others can work but there can also be issues. achris brought up a good document in one thread about a study in exhaust elbows. This just dealt with the elbows and reversion. The issue was that other manufactures didn't have the same internal casting lips which can keep down on reversions. Not saying this will happen to you, just was a very good read.

Changing before or after is just some time. I would do it when you have time, but doing it at the beginning will allow a fresh start, but if there are issues, also creates their own issues.

Don't use any sealant, the gaskets will be what is needed. Check flatness of matting surfaces prior to installing, make sure their flat, even more so with non-OEM parts.
 

enginesilo

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I would recommend OEM parts, the others can work but there can also be issues. achris brought up a good document in one thread about a study in exhaust elbows. This just dealt with the elbows and reversion. The issue was that other manufactures didn't have the same internal casting lips which can keep down on reversions. Not saying this will happen to you, just was a very good read.

Changing before or after is just some time. I would do it when you have time, but doing it at the beginning will allow a fresh start, but if there are issues, also creates their own issues.

Don't use any sealant, the gaskets will be what is needed. Check flatness of matting surfaces prior to installing, make sure their flat, even more so with non-OEM parts.
Thanks for the tips AllDodge. Enough good reasons not to stray from OEM, i'll stick to the original plan then with Mercruiser replacements. Thanks for the tips on the gaskets/sealant as well.

I also want to change out my bellows/gimbal/etc so i'll either be tackling one of the projects this fall and the other in the spring, or i'll save them both and do in the spring. I'll be sure to post if I need some help, this community is the very best!
 

Fishermark

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Be sure to get the grey / graphite type of gasket between the manifold and elbow. I have sometimes seen the green paper ones included with the manifold - even with Mercruiser stuff. That's one place where a good quality gasket is essential.
 

Bondo

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Check flatness of matting surfaces prior to installing, make sure their flat, even more so with non-OEM parts.
Be sure to get the grey / graphite type of gasket between the manifold and elbow. I have sometimes seen the green paper ones

Ayuh,.... Great points,.... Clean the paint off the new ones with a flat file,... You'll see any highs or lows quickly,....

'n ditto the graphite Merc gaskets,... the green paper ones suck,....
 

enginesilo

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Ayuh,.... Great points,.... Clean the paint off the new ones with a flat file,... You'll see any highs or lows quickly,....

'n ditto the graphite Merc gaskets,... the green paper ones suck,....
Thanks for the great tips guys! So doing the Exhaust Manifold/Riser in the fall right before I winterize the boat is fine? I always think of doing the work then a winterization gone wrong and potentially needing to do it again in the spring. Maybe i'll do this job in the fall, and then bellows in the spring. Lots to do either way in my future.
 

alldodge

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If you do it early enough in the fall you will know if you have a problem. If you do it and do not run it, then same thing as doing in spring. So if your going to do it and winterize at the same time, just do it in the spring
 

enginesilo

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So many great details shared in this original thread, I'm bringing it back to life since I ended up not completing this project in the fall and am planning to start soon.

QUESTIONS:
I saw someone suggested buying long headless bolts to help guide the manifold on and off since its so heavy. Anyone know what thread the exhaust manifold bolts are, and does Home Depot sell a machine screw of some sort with the same thread? Or can I just use the headless bolts that are used to hold the Exhaust manifold on that get the nut screwed on later? Couldn't tell if people suggest buying longer bolts, or if they are using the ones that you use for the actual install.

Another question, should I be scraping the paint off the flat mating surface where the Riser meets the Exhaust manifold where the gasket sits, or just leave as is? I've seen people mention filing it to get any high spots off, and some say to scrap to metal. Seems like in salt water conditions that may just leave a spot for rust to start from the outside in.

All tips appreciated. image_263775.jpg
 
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Bondo

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Anyone know what thread the exhaust manifold bolts are,

Ayuh,.... 3/8" - 16,.... A length of all-thread/ redi-rod will work,...
Ya need 'bout an inch or more, longer than the bolts, so's ya can get 'em out after ya start a couple of the real bolts,...
I just use some old bolts I salvaged, 'n cut the heads off,... I think they were originally long riser bolts,....
I've seen people mention filing it to get any high spots off,

Yep,... Clean 'em off,.... If yer worried 'bout 'em rustin',...
Paint the bare metal with Quick-sliver Perfect Seal, which is exactly the same as Form-a-Gasket, #3,....
 

fhhuber

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An issue that comes up in some boats....

Access to the bolts and to be able to remove/replace the parts.

The engine (as an assembly) is often installed before the upper deck is joined to the hull. That can create severe issues in getting at the engine to work on it.
 

enginesilo

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Ayuh,.... 3/8" - 16,.... A length of all-thread/ redi-rod will work,...
Ya need 'bout an inch or more, longer than the bolts, so's ya can get 'em out after ya start a couple of the real bolts,...
I just use some old bolts I salvaged, 'n cut the heads off,... I think they were originally long riser bolts,....


Yep,... Clean 'em off,.... If yer worried 'bout 'em rustin',...
Paint the bare metal with Quick-sliver Perfect Seal, which is exactly the same as Form-a-Gasket, #3,....

Thanks for the specifics Bondo, I'm off to Home Depot to find some of that thread rod!

Have another question, the engine is winterized right now with some anti-freeze poured into the block and everywhere else. Should I just drain the block from the port at the back of the riser, or should I be draining even more? Will there be any gas coming out of the fuel line and should I expect that to be full or does it fill when cranked? My kit came with a new fuel line so I'll be installing that too. Any tips on the liquids I should expect will be helpful since it's an in-boat install. I may video tape the install so I can share it on YouTube with others, I'll probably need to do some editing of my language though:)

An issue that comes up in some boats....

Access to the bolts and to be able to remove/replace the parts.

The engine (as an assembly) is often installed before the upper deck is joined to the hull. That can create severe issues in getting at the engine to work on it.

Sure hope mine isn't one of those, I'm definitely working in very cramped space but I'm guessing I can pull it off if I remove some sectional pieces back there.
 

fishrdan

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I saw someone suggested buying long headless bolts to help guide the manifold on and off since its so heavy.

Don't need em', you all ready got em'. They are the stock OEM studs #14 in the pic you posted.

The studs should stay in the head when you remove all the manifold fasteners. If the studs come out with the nuts still attached (shouldn't) just put them back in the head with some lock-tite or Permatex Avation sealant before installing the manifold.
 
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