Starboard Side Exhaust Manifold Cracked - '82 Mercruiser 260 - Ser 620xxxx

[andohh]

I recently bought an older deck boat with a Merc 260, (GM V8 350), the starboard side exhaust manifold has a crack that seems to be cracking under high load and then rusting shut again. When it is leaking, it's a slow drop or at least that's the worst I've ever seen.

My initial plan was to JB Weld it. After some research I found another topic discussing this on a Ford and it was brought up that this could somehow ruin the engine if the entire manifold isn't replaced?

My question is; how likely is that to actually happen? The crack appears to be on the outside of the Manifold, how could this cause engine damage?

On my engine, how could the water end up back into the engine block? How common is that?

Any opinions on good fix? JB Weld/Weld/Replace Manifold?

Right now, it's running great. It was running sketchy so I pulled the distributor and the points were burnt up. Replaced with Pertronix Ignitor II electronic ignition and Flame Thrower II coil 45,000 V 0.6 ohm. Replaced plug wires with premium Sierra MagForce and plugs with NGK BR6FS gapped just over 0.35. Set timing and settled on 9.5 BTDC. It's running great.

 

[500dollar744ti]

JB weld usually won't stick to rust, you could try it.

I bought my boat with the same problem, both sides were cracked and leaking water.

While it won't directly damage the engine, the condition of the manifold and riser could cause the exhaust water flow to get stopped up (from rust build up) creating a condition where the engine can severely overheat and start melting the exhaust elbows.

How likely is this to happen? I would say sooner or later it will. Mine plugged up while I was on plane at WOT, the only indicator I had was the high temp alarm buzzer went off just as the exhaust elbows started to pour out smoke and make me think something was on fire. My engine got hot but didn't overheat because I reacted quickly enough.

I rowed the boat to a nearby dock and took the riser apart to try and unclog it. I got it unclogged but it clogged up soon again. I was watching my temp gauge like a hawk after that.

Risers and manifolds have a limited lifespan and need to be replaced when they rust out. If yours are original, it's probably time to replace them.

Don't do just the one side that's leaking, replace both manifolds and both risers.

 

[andohh]

Thanks for the advise 500dollar744ti I still may go with the JB for now but taking into consideration what you said.

I was planning on doing some light removal with my Dremel to provide a good and strong surface for the JB.

That said, if the water flow is any indication I have very good flow now out the back right now especially when throttling up. Of course, I'm sure when things start clogging they may go quick. I did have serious overheating issues when I got it. It turned out the impeller base was toast and last time it looks like they just did the impeller but it was pushed down and from what I can tell the blades stuck in place while the keyed shaft acked out the inside of the impeller. I replaced the whole impeller/base assembly and also the thermostat with the recommended 145deg. Figured It was probably due. It actually runs cold now. Which is another concern but I'm assuming it's okay. Before it was going hot how it's cold and the thermostat usually won't even move. I touch the thermostat mount and it is just warm. The exhaust get's hot but that's to be expected I suppose.

Again, thanks for the advise. I will consider replacing the manifolds when I get more done on it. The thing needs a ton of work still.

 

[500dollar744ti]

It's okay to run cold (130-140*) with the old raw water cooling system and 140* thermostat. Mine is the same way, depending on sea water temperature.

I wouldn't try to chisel away at the rust hole, it's just going to make it leak more. If you want to JB weld, use a crap ton of it so it goes over the leaky part but spreads to a clean area where it will stick.

Be sure your bilge pump works, and works well. If that thing decides to open up one day you are going to have a lot of water to drain. Technically your boat is sinking if your exhaust is pumping water into the bilge. I couldn't afford to fix mine until it clogged up, then I had no choice.

 

[HT32BSX115]

Again, thanks for the advise. I will consider replacing the manifolds when I get more done on it. The thing needs a ton of work still.

You really should replace the manifolds............... if they're rusty and cracked and they are not leaking into the exhaust now, they could at any time.

If they do start leaking into the exhaust and on into an open exhaust valve after shutdown, you'll be replacing the engine too.

 

[andohh]

Yep, you guys are right. I got the idea to drain the manifolds, disconnect the coil, and have someone turn it over while I hold my finger over the drain hole to feel for pressure.... sure enough there is definite pressure coming from the drain plug. Not a lot but its there... $700 and change later and I have the starboard and port manifolds being overnighted from gander mountain... looks like gander and overtons has the same inventory and shipping? Same company or whole seller? Regardless had a lake weekend planned so I'm going to get everything tore apart and ready to slap the new manifolds on Thurs. Any tips would be appreciated... first timer here. Also a little worried about the flappers... the boats an '82... I assume they are original if they are still there...

 

[andohh]

Evident ally 0v3rt0ns is a bad word?

 

[500dollar744ti]

You are replacing both manifolds and both risers correct? If you have any stuck bolts, I figured out a way to get some of them out. It's tedious but you don't have to pull the engine.

I would work on getting the bolts free before you get the manifolds so if there's any trouble you can take care of it now. Then when you get the manifolds, they will be ready to slap on and go.

 

[andohh]

I don't have risers. Just the manifolds and then elbows. This is basically my setup:
http://www.jamestowndistributors.com/userportal/show_product.do?pid=69316

I didn't order replacement elbows yet. I figured I could replace them easy enough if needed after the fact. I plan on inspecting them very well and will also repeating my test checking for exhaust pressure from the drain plug hole. Externally, the only component with external issues is the starboard manifold. That said, I ordered and am replacing both.

What's your trick for freeing stuck bolts? That's actually my biggest time concern right now.

I've had an extended lake weekend (This Weekend) scheduled for some time and my goal is to have my work done by Thurs night. If need be I may delay replacing port manifold until next week. Visually there are no cracks and I also haven't been able to feel any pressure from the drain plug hole while the motor is turned over.

I'm also interesting in what I may find in regards to any water damage so far. The engine sounds very good when running but I'm a little anxious about the identified issue. I would like to hold onto this boat for a while so I want to resolve everything that is reasonable. That said, there's a point where I can only go so far. I mean ideally with unlimited time and money, it could be said that an entire tear down and rebuild would be best. This would not be realistic for me. That said, I am interested in what further steps would be realistically recommended to prevent any further damage from occurring.

 

[andohh]

Looks like I couldn't link to image... uploaded instead. This is my setup.

 

[500dollar744ti]

Yes, number 10 is the riser, at least that's what it looks like. What you are referring to as 'elbows' are the risers, they bolt directly to the manifold with 4 bolts. You should replace them, but if you want to wait, that's up to you. If your engine runs fine, there won't be any damage from the bad manifolds.

Try to break the bolts loose and report if any are stuck, looking at your manifold, yours is the old style rear riser, not sure if my bolt removal method will work. You would be surprised, I had only 1 get stuck and it was only because the head of the bolt had rusted down to the point I couldn't get a socket on it.

Post a picture of your engine compartment, there may be a better way for you to get any stuck bolts depending how much space you have.

 

[andohh]

I had one stuck bolt but I managed to break it loose after going after it with my impact driver for a while, then tried breaking it loose with a hammer and wrench, then just broke it lose by hand.

That said I am getting ready to install the new manifold and ran into a dilemma. There seems to be a restrictor between the manifold and elbow. The problem is I can't seem to find anything on this in my manual and the restrictor plate seems somewhat excessive to me. Any thoughts on this. See attached:

 

[andohh]

hard to tell in pic but the only actual opening is that tiny circular hole