Exhaust Manifolds and risers on 4.3L, how to tell when they need to be replaced?

[denhajm]

Hello, I have a 4.3L Mercruiser on with an Alpha out drive on a '90 SeaRay BR200. I've had the boat for three boating seasons and am wondering how to tell when the exhaust manifolds and risers are due for replacement? I have had the boat in salt water a few times exploring some near San Juan Islands on calm water days. But it is usually in fresh water when in use, then parked at the house (salt water rinsed out with muffs at home). Still, it is an old boat and I have no idea when they were last replaced, nor how corroded they may be in side. That be said, I'm toying with upgrading to a slight newer, slight more sea-worthy boat for the San Juan islands, so I'm not wanting to needlessly spend money. I've been quoted over $2,000 for the job, but I can buy parts for around $600, so I'm considering doing it myself. I just need to know how to determine when they are bad. Thanks!

 

[Bondo]

wondering how to tell when the exhaust manifolds and risers are due for replacement?

Ayuh,.... It's Good to hear ya got manifolds, 'n risers, rather than the one piece units that are time-bombs,....

If ya pull the risers off the manifolds, then Clean the gasket surfaces 'tween the passages,....
If those cast iron bridges that support the gasket ain't 'bout a 1/4" anymore,... ya need new ones,....

I suggest a flat file, 'n a careful hand to clean 'em back to clean cast iron,....

Then use the Merc carbon metallic gaskets, dry,...

 

[Scott Danforth]

agreed, do not use the Sierra green leaker gaskets.

 

[DaboatnutinWA]

I had the same question about the exhaust manifolds and risers on my 4.3L too since I really don't know how many hours are on them. Easy to take off and put back on and when i did, i inspected them closely and cleaned them out really good with a screwdriver. Also bought that Evapo-Rust stuff, filled all the cavities, let it sit for a while and rinsed thoroughly. Mine had tons and tons of this scale looking crap that had accumulated inside. At the same time I also removed the thermostat housing and cleaned that along with a new thermostat. Temp stayed in the 130-140 range which jives with the thermostat so I felt good about my hard work and diligence. I'd by the manifolds and do the job yourself and save some sheckels. Its not that tough of a job. JMHO.

 

[Soder99]

Bondo,

Can you clarify what you mean by one-piece time bombs? I have a 1997 Merc with manifolds that I haven't seen on any other engine. I'm afraid I'm driving with the bombs.

Ayuh,.... It's Good to hear ya got manifolds, 'n risers, rather than the one piece units that are time-bombs,....

If ya pull the risers off the manifolds, then Clean the gasket surfaces 'tween the passages,....
If those cast iron bridges that support the gasket ain't 'bout a 1/4" anymore,... ya need new ones,....

I suggest a flat file, 'n a careful hand to clean 'em back to clean cast iron,....

Then use the Merc carbon metallic gaskets, dry,...

Thanks!

 

[Bondo]

Bondo,

Can you clarify what you mean by one-piece time bombs?

Ayuh,.... Merc, 'n OMC used one piece exhaust manifolds for a couple of years, also known as "Batwings",....

Those things have been Destroyin' perfectly good motors, since the day they were intro'ed,...
Seems there was a major problem with "Core-shiftin" durin' the castin' process, which causes thick spots, 'n very thin spots,....

I've personally come across several motors lost to 'em,....
'ell, a Bud build an OMC 4.3l for his ole Chriscraft, ran it, blew the motor from hydro-lock, rebuilt the motor, then Begged me for a set of Merc manifolds I was scrappin',...
I told 'im, 'n told 'im, these too, will blow yer motor,....
His response, naw they look Great,... they look brand new,...
I told 'im, if ya take 'em, it's Without my blessin',...
He did, 'n promptly blew his motor to hydro-lock before our short season was over,....

I haven't had to do a conversion, but I hear you can get a Kit, that includes enough parts to reuse the y-pipe,.....
Manifolds, riser, 'n elbows,...

 

[Soder99]

When were they using these? How do I know if I have them?

 

[Bondo]

When were they using these? How do I know if I have them?

Ayuh,.... LOOK at 'em,...... If they're one single piece that look like wings, Ya got 'em,.....

 

[alldodge]

Here is a V6 but they also make them in V8

 

[Lou C]

I had 3 sets of these on my salt water boat and never had water in the engine. When I have replace em next time I want to adapt the Merc dry joint system to my engine. It can be done with a set of 4" to 3.5" adapters . The way they seal is much less leak prone than the older Merc design or the design Volvo still uses...

 

[Soder99]

Lou C,

Thanks for making me feel like disaster isn't waiting as soon as I go out next time. How did you know when to replace them?

I only boat in fresh water so I'm hoping that will help these doom-stricken risers last longer.

 

[Lou C]

You take them off and inspect them. If the riser water passages are getting clogged with rust, it means 2 things, one, you will start to get an overheated exhaust system from the clogging and two, that rust that's clogging used to be part of your manifold! So its getting thinner and eventually it can rust through putting water in a cylinder. Here in the salt pond we change em about every 7 years or so. I take mine off at year 5 and inspect, if they just have minor clogging I'll clean em out and fill em with acetone to check for leaks in the exhaust gas passages. If they look good I might use em about another 2 seasons, but not more than that.

 

[denhajm]

No Title

So after searching for the elusive Mercruiser gasket (Sierra seems to pop up everywhere) for my exhaust risers/elbows so that I can pull them off and evaluate their condition, I believe for my engine (OC861086) that the correct Mercruiser gasket is 41813, which has been superseded by 863724. See screen shots below taken from the Mercury Marine website.
The 863724 p/n leads me to this site that sells them: http://www.cpperformance.com/p-47463-gasket-mercruiser-27-863724.aspx Does this look like the carbon metalic gasket your recommend Bondo?

 

[Bondo]

Ayuh,... Carbonized paper on both sides, with a metal inter-liner,.... That's them,....

Install 'em dry, on perfectly cleaned surfaces,....

 

[denhajm]

Okay, thanks for the tip on getting good quality parts!

 

[Lou C]

And....if you are going to pull off the riser with the manifold still installed on the engine, drain them first because if there is any water or antifreeze in there it can leak into the center exhaust opening and run into a cylinder thru an open exhaust valve.

 

[denhajm]

Yep--good advice! I drained the manifolds last fall prior to cooler weather hitting.

 

[denhajm]

No Title

I pulled both risers off this past weekend. Put on some kroil and the bolts came out easily. Here are some pictures of the risers and exhaust mainfolds. I would appreciate the experts here giving me an evaluation of their condition as I'm not experienced with it. I do have the 1/4" thickness that Bondo mentioned above, but just the 1/4". Not sure what they would be if new. To my eyes, they look better than I expected. I haven not cleaned any surface yet--so the photos show what everything looks like right after separation.

 

[Bondo]

I haven not cleaned any surface yet--so

Ayuh,.... Ya can't evaluate the condition, til ya Clean 'em to Clean cast iron,.....

A large mill/ bastard flat file across the faces works pretty well, 'n keeps the faces flat,.....

This is the gasket surface faces I'm talkin' 'bout,..... it's All 'bout Flatness,....

 

[Lou C]

You need to get all the old gasket material off because in addition to the 1/4" width you are looking for pits in the sealing surface from corrosion. That can cause the gaskets to not seal well.