MerCruiser 7.4L Bluewater Exhaust

[mr300z87]

My wife and I are the new owners of a 1990 Sea Ray Sundancer 310 with a pair of 7.4L Bluewater inboards I do not have the serial #s but they are definitely 90 vintage Gen 4s. I know they need some exhaust work there is corrosion where the Manifold and elbow meet. I also know they are full closed cooled so the manifold have coolant in them only the elbow see raw/salty water and water jackets between them should be a block off. My question is what am in for? What usually needs replacing on these engines both elbows and manifolds or can I get lucky and only need gaskets and elbows? I know I wont know for sure until I tear it apart.

All my experience prior has been with raw cooled IOs I know that with them in salty water is all or engine failure. It's cold her in NJ this time a year except for the occasional Dec day at 65 like today, so nothing is going to happen with this for a while just trying see what I am up against this spring. The only good thing about having to replace the manifolds too, is getting to the raw pump for replacement will be easier. The 7.4L Bravo in my old 250 dancer was a dream to work on compared to this beast. I will get it figured out though.

As always any advice is great appreciated and have a great holiday season.

Mike

 

[alldodge]

Don't know any other way to check the elbows other then to remove. If the gasket is in good shape on the AF side then the mans should be fine.

As for getting to the pump, I feel your pain. I have to hang up side down to get at mine. The exhaust man gasket cost about $30 for a set. So for $15 just remove the man so you can get at it easier.

And two pieces of 3/8 all thread

 

[Bt Doctur]

Just be sure to drain the A/F side of the manifold first before removing the elbow bolts. You may have a SS blockoff plate, if so any 2 slot or 4 slot above and below the SS plate will work

 

[todhunter]

And two pieces of 3/8 all thread

This is priceless information!

 

[mr300z87]

Always good to hear from you AD. Thanks to all for the info. I am sure the elbows are shot, just hoping not to have to buy Manifolds also. I have old exhaust studs I use to support the manifolds during removal, I did an exhaust last year on out old boat's 7.4L. I would expect this gasket to be in between. GASKET (#27-8637251)
BT not sure what you mean by this " if so any 2 slot or 4 slot above and below the SS plate will work? I am assuming I can drain the AF off the manifolds only and not the whole system. I plan to use OE mercuriser parts and if my memory is correct there are a mix of elbow brands. The last time at the boat shrink was done but the access hatch was not installed yet so I could not get in the boat. Next time there I will look at things again.

Have a great weekend

 

[todhunter]

He's saying that if you have a stainless steel plate between the manifold / elbow, it doesn't matter which gaskets (either 2-hole or 4-hole) are used, as long as there is a gasket above and below the stainless steel plate.

 

[mr300z87]

So the block off plate I showed above requires a gasket on either side? I though the block was the gasket. I looked up the part number on ebay. it looks to be the same material i used on my raw cooled I/O. My elbows have 4 bolts per.

I do see some stainless blockoff plates from Barr advertised. Judging by the amount of corrosion at the joint I expect to find an aftermarket gasket. On my other boat I used all OE and did not show any signs of seepage. Is stainless really needed is the OE gasket good enough?

 

[alldodge]

Manual 16 list only one gasket per side

 

[mr300z87]

AD I agree, that what all the diagrams I saw show. As mentioned above I expect to find aftermarket junk for a gasket. I was going to head to the boat today to take some notes and photo but its gray and to cold out so I think I just going stay home and keep the fire going.

 

[mr300z87]

happy holidays to all

 

[mr300z87]

Hi all its been a while. Weather is looking up and marina needs me launched mid April. I am so not ready. Today we started removing the crusty old exhaust, started on starboard motor outer side all came apart with no problem. Center side did not go as well but all in all could be worse. Elbow came off no problem and 7 of the 8 manifold bolts are out. Number 8 bold which in the middle has a corroded away head and I can't even get a 1/2 in socket to bite its a 9/16. I can not see it at all but I think I can get in there with a small cut off wheel to cut the head off. Any recommendations, I am sure I'm not the first to experience this. Was thinking a small mirror would help if slid under the manifolds.

While I was down there after a bunch of badwords I was able to break loose 5 of 8 on port side center manifold. I figure I will mess with those after getting the other one off. The will give me tons more room.

Also while off I will tackle the raw water pump on the starboard engine, port was done late last season I have receipt from previous owner. Still can't even see it. Will it show it self with manifold off. Has anybody changed one on a inboard V drive sea ray?

Did not take any pics today worked to hard, now everything hurts. My plan is to use all mercruiser parts sourced locally.

Have a great night.

Mike

 

[Scott Danforth]

Cut the head off

Then use a vice grip to remove the bolt

 

[mr300z87]

Thanks Scott, yes that is the plan. I will update after I get to the boat. Stinks not having it in my yard like the 250 Dancer.

Question, on the 7.4L in my 250 I used stainless bolt for the manifold with no issues. Came right out after 5 years when I replaced the Manifolds. I thought I read some where that stainless bolts should not be used here?

Mike

 

[mr300z87]

Was going to try and use my dremel with the cut off wheel, but the are so fragil I was thinking of buying something better to use. Any recommendations? It is ver tight between the engines and I can not see the bolt head at all. I'm going to try and contort myself in there for better vantage point I may have other to do in the port engine.

 

[Scott Danforth]

dont use stainless on the exhaust.

Use a grade 8 bolt, Coat the threads with maalox and coat the head of the bolt with paint.

use a die grinder with a 2" cut-off wheel, or get the 4.5" cut-off wheels for a 4.5" angle grinder.

 

[alldodge]

If you have access to accelane heat works

 

[mr300z87]

I am think this is the ticket on my dremel.

 

[mr300z87]

no room to do anything arrow point to where I am working

 

[Bondo]

Ayuh,..... Those bolt heads don't look mangled, have you tried a 6 point socket, 'n a pipe on the ratchet,..??

A 1/2" drive, 'n breaker bar would be the best bet, 'n as long a pipe as necessary,.....

 

[mr300z87]

Thanks Bondo, but it's not the bolt you can see it's the one on the manifold to the head that you can not see. The elbow to manifold joint was leaking right at bolt the arrow is pointing to and ran down and corroded manifold bolt. I do not think the bolt is frozen in the threads as all others came out clean. Just can get a bite on the bolt head. I ordered some extracting sockets for stripped bolt heads they will be here later.

Headed there in a few minuets with an arsenal of tools, with any luck it will be off before lunch. I will post an update later.

Mike