Mercruiser 3.0 Exhaust Riser Leak / Compatibility?

[JimEd B]

Hello again,

Got my notor running, but have an exhaust leak issue. Have Sierra 18-1966-1 manifold, and sierra 18-1971 riser.

This is a 3.0 LX motor, with a MC1 outdrive. Previous owner used the newer riser, and some cast iron sewer pipe to get down to the exhaust out on transom plate (j pipe, y pipe, proper nomenclature?)

Anyway, I have a leak out the stern side where riser and manifold mate. There are only two bolt holes in manifold, and four in riser. Previous riser had two bolts and sealed fine.

Do I need a different manifold?

 

[JimEd B]

Just bumping this post.

Guessing the number of folks working with an MC1 - 3.0LX combo is small, but here's hoping someone has some wisdom on the matter.

 

[Lou C]

why is there no stud or bolt in the recess where it should be?
I can't see how that would ever seal with only 2 bolts/studs & nuts

 

[dubs283]

why is there no stud or bolt in the recess where it should be?
I can't see how that would ever seal with only 2 bolts/studs & nuts

Didn't even notice that at first glance. Fwd fastener appears loose too

OP, you need to get the riser/elbow installed correctly with the proper gasket before further diagnosis.

That boot does not look familiar but some oem exhaust boots have a similar appearance. Don't know if that one is correct or like you say a plumbing part. Either way it appears to be cobbled together and no surprise it's leaking

 

[JimEd B]

Thanks fellas!

1. That is the stock boot for the old style exhaust riser. Plumbing parts were removed, and not pictured. That bit is not cobbled, and it's not leaking either.

2. To my knowledge I used the proper gasket, do you have part number? This is more what I was wondering.

3. The newer style risers all seal with two bolts, but this one does not. There are only two holes in the manifold, but four in the riser. New risers have only 2 holes. So yeah, that was the basis of my question.

Let me rephrase: Is there an off the shelf 3.0 manifold for the 2 barrel Mercarb with 4 tapped holes for old style riser?

Thanks!

 

[Bt Doctur]

If you only have two threaded holes in the manifold you need a riser for the 3.0 LX It uses two bolts only

 

[achris]

You bought the wrong manifold. You bought a late model manifold for a 1 piece elbow (not "riser") when you should have bought an early style manifold...

 

[JimEd B]

You bought the wrong manifold. You bought a late model manifold for a 1 piece elbow (not "riser") when you should have bought an early style manifold...

Yep. I bought the LX manifold. This was last year, before I understood this exhaust system. The previous owner had plumbed the exhaust with a newer offset elbow (thanks for the correction), and what I thought was sewer pipe. I just matched his part number.

Took a grinder to the "sewer pipe", and it's in fact another couple exhaust parts for a merc. V8 (from what I've found so far) connected by rigid exhaust tube. This setup did work, and is made from marine grade materials, but it's not ideal.

This setup had the unfortunate effect of putting cast iron into electrical contact with the aluminum pipe exiting the transom (j pipe y pipe? Anyone?), and created a bit if galvanic corrosion.

For anyone reading this far, I got an answer courtesy of Matt Speyer at NLA Marine. Really reccomend anyone needing older parts to check out his business: https://www.nlamarine.com/. Excellent company, and a real helpful guy.

Part# 42673 Manifolds are set up for 3.0 motors with Mercarb and a 4 bolt exhaust elbow (which i have previously and incorrectly referred to above as a "riser.")

This is different from the 42673-C1 manifolds, which only have two bolts for the elbow.

I appreciate all the help here, hope this contribution helps someone else.

 

[achris]

the aluminum pipe exiting the transom (j pipe y pipe? Anyone?),

'Exhaust tube'... (#1 in the drawing below)

 

[JimEd B]

Thanks man!

 

[JimEd B]

You bought the wrong manifold. You bought a late model manifold for a 1 piece elbow (not "riser") when you should have bought an early style manifold...

Actually, in hindsight, I think I was talking about the riser not the elbow? (EDIT: INCORRECT, again, see below.)

Also, looking up the parts numbers, I see a C1 stamped 42673 with 4 riser studs.

So... still not certain that's what I think it is, but should know shortly and will update this post at that time.

 

[achris]

Actually, in hindsight, I think I was talking about the riser not the elbow.

Also, looking up the parts numbers, I see a C1 stamped 42673 with 4 riser studs.

So... still not certain that's what I think it is, but should know shortly and will update this post at that time.

Looking at your photos, you do not have a 'riser' on that engine...

Although this diagram is specifically a V-engine, the parts names remain the same...

 

[JimEd B]

Thanks, this helps quite a bit. I was getting confused by all of the names different websites are using for these parts, I'd say the manual wins.

Seems Iboats is calling it an "elbow riser," lol.

Sierra - 18-1975-1 Exhaust Manifold Elbow Riser for Mercruiser replaces 95864A2, 12076A1, 12076A2

Additional Details:Fits: Late model Mercruiser 4 cylinder enginesFits: MCM 2.5L & 3.0L/LX (1982 & newer)Use With:18-1901: Manifold18-1954-1: Manifold18-1955-1: Manifold18-2748: Exhaust Boot18-2833: Gasket, Exhaust Elbow18-8551: Hardware Kit [Exhaust Elbow Bolts]18-2819-1: Gasket, Exhaust...

www.iboats.com

 

[JimEd B]

Ahhh, and this one is just an elbow:

Is this a learning moment? Is there a technical difference in these parts, or just nominal difference?

Sierra 18-1971 Exhaust Manifold Elbow

Key Features:3" Outlet90 degree down angleAdditional Details:Fits: MCM 140 (1966-1982), 470 (1976-1977), 165 & 200 in-line 6 cyl.Fits: MCM Ford V-8 engines & MCM GM V-8 (305 & 350 cid) engines (1982 & older)Use With:18-1950-1: Manifold18-1951-1: Manifold18-1954-1: Manifold18-1955-1...

www.iboats.com

 

[achris]

Thanks, this helps quite a bit. I was getting confused by all of the names different websites are using for these parts, I'd say the manual wins.

I'd say the company that made the parts in the first place have last say on any naming...

Seems Iboats is calling it an "elbow riser," lol.

Hedging their bets?

Chris.....

 

[achris]

Ahhh, and this one is just an elbow:

Is this a learning moment? Is there a technical difference in these parts, or just nominal difference?

I'd venture that 'someone' called it the wrong thing and it's become widely accepted by that name. That still doesn't make it right, just a lot of people calling things by the wrong name... Bit like 'replica'... Go find out what that ACTUALLY means... You'll be surprised (and you'll almost never call anything a replica again).

Chris..

 

[JimEd B]

I'm with you. Precise language matters. Especially in a forum like this where specific words refer to specific parts, which other users may very well go out and purchase.

As I know from spending a couple days worth of paycheck on the wrong manifold, buying the wrong part sucks (though that was entirely my fault). Missing days of fishing waiting for UPS sucks even worse.

Thanks for the help!