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exhaust manifold leak after gasket replaced |
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The Dude 
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 Topic: exhaust manifold leak after gasket replacedPosted: April-26-2025 at 2:00pm |
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The Dude
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Posted: April-26-2025 at 2:04pm |
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Well, that was a good post.
Hi guys, I haven't been here for a while, but I still love you all! My 95 Sport, 351 is leaking on the starboard side. I replaced the gasket. Replaced it again with RTV. still leaking...pretty badly. I'm running in brackish water, so this is especially not helpful to my engine block. What are next steps? I thought I'd prepared both surfaces very well with block sanding, making sure to keep everything straight/even, but it's apparently not good enough. Do I need to take it somewhere to have the manifold ground down a bit and leveled? Skied this morning anyway.
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KENO
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Posted: April-26-2025 at 7:52pm |
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You must be talking about the riser to manifold gasket leaking.
If it's leaking externally, it may be leaking internally too, but you can't see that happening. You could pull the plugs on that side and turn the engine over to see if any water comes out and also look for water on the plugs. A machine shop planing job on the manifold and riser would be the second best solution. First best but pricey
 Not knowing how many hours on run time you've had in brackish water, you might at least think a little bit about maybe getting new manifolds and risers depending on how ugly the internal water passages look |
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The Dude
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Posted: April-28-2025 at 9:12am |
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1350 hours. Replaced manifolds and risers 4 years ago. Manifold to block started leaking at gasket...manifold to riser connection (new gasket too) is fine.
There isn't any pitting on surfaces that meet. I thought I'd sanded surfaces evenly. I tightened manifold bolts from middle out in both directions.
OK...will pull plugs and see if water comes out...or wet. |
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KENO
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Posted: April-28-2025 at 9:19am |
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So you must be leaking exhaust gases from that joint (manifold to block) and not leaking any water?
At least I hope you're not leaking water there
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The Dude
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Posted: April-28-2025 at 10:53am |
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that's exactly where I'm leaking water....joint of manifold to block.
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KENO
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Posted: April-28-2025 at 4:29pm |
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If it's coming from one of the flanges with the red lines pointing at it, you've got problems. The only thing that's supposed to go through those joints is exhaust gases  Having a lot of water dripping could be a few things. Your manifolds are only 4 years old, so they're probably good and not leaking internally, but one could be bad That would leave some other choices like maybe a blown head gasket letting water into a cylinder or maybe a cracked head or block letting water into a cylinder.. I'd start with pulling the plugs like mentioned earlier in the thread and look for water on a plug or plugs, then crank the engine over with the plugs out and see if water comes shooting out of any spark plug holes. That should tell you something While the plugs are out, a compression test would give you some info also Pressurizing the engine cooling system with the hoses to the manifolds blocked off, to let you know if the engine has a leak or not is also relatively easy
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Fl Inboards
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Posted: April-28-2025 at 5:17pm |
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you have 3.5" risers? are they as new as your manifolds? PCM had a rash of 3.5" risers with internal leaking. and or units with thin inner castings that could potentially leak sooner than later. keep in mind that the 3.5 PCM risers are on back order right now and it does not look like they will be available earlier than June. if you suspect the Risers causing water intrusion you might want to make an inquiry here on CCF for a clean set of used ones. here is the part number for real deal PCM riser gaskets. www.nautiqueparts.com
RM0002 |
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Hobby Boats can be expensive when the hobbyist is limited on their own skill and expertise.
1993 Shamrock "fat" 20. 2008 Nautique 196 5.0 |
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The Dude
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Posted: April-29-2025 at 8:00pm |
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So Fl,
I haven't done anything yet except examine the manifold to riser gasket and all sides of the manifold. The water is almost certainly coming from the flanges as pictured above by Ken. I haven't pulled plugs yet, but am going to be really surprised if there is water in a cylinder. Boat runs great, doesn't get hot, and no excessive steam in exhaust. I'm guessing (hoping now) at this point that there is an inner casting that is has failed like you suggested and the water is escaping from the manifold gasket (connection to block). I realize it could be worse than this. My question is--knowing the history you do about the risers, is it more likely the failure is in the riser than in the manifold itself? |
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KENO
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Posted: April-29-2025 at 9:38pm |
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Okay Dude.....here's something for you to think about/check.
You say the boat runs great, and to get water out the exhaust manifold to head gasket, you'd need to have 2 separate issues. That would be a leak into the exhaust from either the engine or the manifold/riser plus your gasketed joint would have to leak. As I think about it, it's probably not to likely to be the case. You didn't say what version of the 351 you have, but your diary entry says 310 or so HP, so I figure you have gt40 heads. One thing about those gt40 heads is that they tend to crack the water jacket right near the exhaust ports and leak externally which would make a leak like you're seeing. You should lay on the floor and get a good closeup look for cracks in the head. People have had this problem and you might say that JB Weld or whatever epoxy you might like just might be your best friend for a while maybe longer It might buy you years of extra time or at least this season so you can go skiing instead of making repairs now. Here's a link to some reading about the head cracks and another link to one thread in particular Not the best thing, but not the worst either. PS......I'm looking for a picture but not having any luck
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The Dude
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Posted: May-01-2025 at 12:35pm |
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Oh no. Reading those threads makes me think this is the issue. Just like a few of the others--when I get to a certain RPM the water shoots hard enough onto the engine cover that the carpet got wet. OK...I won't start looking at it until Saturday morning...will keep you posted. Thanks for your help!
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The Dude
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Posted: May-03-2025 at 2:17pm |
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Where do you suggest I buy a set of new heads? Really only need one, but might as well do both.
Definitely three cracks...just gonna replace. What else do I need? obvi gasket set...what else?
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Tomrupp
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Joined: October-14-2021 Location: MI Status: Online Points: 82 |
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Posted: May-03-2025 at 2:33pm |
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Do head gaskets, exhaust manifold gaskets too. Use the black gasket maker on your china walls. Throw out the cork. Pay close attention to your valve train. Line everything up in order. Let the gasket maker set up for a day before you launch. If you only wait 6 munutes, the gasket maker will leak. Ask me how I know…
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Tom
94 Ski Nautique Open Bow 351 with Carb 95 Double Decker Aqua Patio with 50hp Honda (3 carbs). |
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KENO
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Posted: May-03-2025 at 7:56pm |
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Well at least you found the problem
Is your engine a fuel injected gt40 or a carbureted high output 351?
You can get a marine top end gasket with Stainless Steel cored gaskets set from Felpro. There are 2 part numbers, one is 17260 which Felpro calls standard duty and the other is 17261 which they call heavy duty. I don't know what the difference is other than price. Summit Racing has good prices or you can shop around some Some places say the 17260 is for engines with stamped steel valve covers and the 17261 is for engines with cast aluminum valve covers. Only Mr Fel or Mr Pro knows for sure. I've been happy with the cheaper 17260 with stamped steel covers As far as heads go, you're better off finding a set of refurbished gt40P heads. They don't have the same tendency to crack like the gt40 heads. Places that come to mind are Clearwater Cylinder Head in Clearwater Florida, Bishop Engine in Dallas or do a search on gt49P cylinder heads. A couple things to keep in mind are that you want Brass freeze plugs in the heads and you want them drilled for the 351 head bolts because they were used on Automotive 302's.before becoming kinda popular for Marine 351's You'll probably have to make some phone calls to be sure that whatever place you pick will do the drilling and the plugs. You could do it yourself but there's not much room for error in the drilling....pay a little more and get the drilling and the plugs done or they may do it for free. |
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The Dude
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Posted: May-04-2025 at 9:22am |
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Super helpful Ken. Thanks.
My sport is a carbuerated HO. Is it right to assume that if the heads are drilled for the 351 head bolts and brass free plugs are installed, that the rest is pretty much plug and play (no valve adjustments or anything else)? Do these look right? http://https://www.bishopenginereplacementparts.com/Ford-GT40P-302-50L-4-Bar-Cylinder-Head-Assembly-Genuine-OEM-SET-Pair_p_2201.html |
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The Dude
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Posted: May-04-2025 at 9:30am |
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KENO
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Posted: May-04-2025 at 10:48am |
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I think these are the 2 places you sorta got linked. Good shopping by the way.  If so, both are good, just remember the drilling and brass plugs. link to gasket set from Felpro store on Amazon If you do a CCF search for "gt40 head replacement" you be able to read up on the installation and lifter preload checks when installing things. The head gaskets have to go on with the word FRONT in the Front. People screw that up sometimes because one gasket will look upside down. I'll add a link later to the FRONT issue |
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KENO
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Posted: May-04-2025 at 5:22pm |
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The Dude
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Posted: May-08-2025 at 10:14pm |
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Anyone know a part number for cylinder head bolt sleeves? I have two sleeves in the block on the port side, but the starboard head (the cracked one) pulled the sleeves out and they are in the bad head. I believe I need two of them.
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KENO
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Posted: May-09-2025 at 7:56am |
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Pioneer S-1112 is a part number that'll work or here's a link to some others on Amazon
The old ones will come out, but they may be kinda beat up when you're done.. Vise grips work pretty good to get them out and maybe beat them up too. Slide a bolt in so when you squeeze and twist with the vise grips, it doesn't deform. Or just replace, like you're planning
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The Dude
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Posted: May-09-2025 at 9:29pm |
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Thanks a million Ken. I'm gonna owe you. Got the cylinder sleeves via amazon tonight. Bought these head bolts. My buddy says do NOT soak them in oil. What say you? I also assume I do not need the washers. Any tricks to cleaning out head bolt threads? Several threads suggest RTV (red) for heads (small amount) and generous amount for intake manifold. Your suggestions? I've been watching vids on pre-load of rockers/pushrods...think we've got that. Hopefully....ready to go.
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KENO
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Posted: May-10-2025 at 8:24am |
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Sequence in the link below The link for the bolts doesn't work but I'd follow the manufacturers instructions as far as washers, bolt torque, whether to oil the threads etc. You'll see various specs for 351W head bolts with the final number generally in the 100 to 112 ft lb range with the bolts lightly oiled Cleaning bolt hole threads.....it's easy to say spray lots of brake cleaner, use a wire brush and blow them out with air after you clean the threads with a thread chaser or a tap. That works good when the engine is all disassembled and on a stand. In the boat, you do what you can to cover openings and clean them without spraying and blowing junk all over the open parts of the engine. A shop vac comes in pretty handy instead of compressed air. The head gaskets go on dry, no sealer needed The intake gaskets can use some RTV around the water ports on both sides. Felpro doesn't say that but most people do it for a little extra insurance that you don't have a water leak into the engine |
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The Dude
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Posted: May-14-2025 at 9:06pm |
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Back together. Started in driveway. Everything seems good except RPM gauge is bouncing a bit. Water test soon.
Sooooooooo thankful for your help Ken.
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Deeski
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Posted: August-12-2025 at 2:11pm |
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This has been a very educational thread, although it's unfortunate that I need to become educated on this topic. I have a '90 Ski Nautique, almost 1,200 hours, stock carbureted 351 with 240hp to my knowledge, and recently noticed a small crack in the drivers side head. It's not spraying, only a slight drip, so the JB Weld approach should be able to keep me on the water for a while. That being said, I read in one of the other strings that Ken posted above as a reference that a user replaced his existing heads with GT-40P's and went from 240hp to 310hp. If that scenario is possible for me, I'd be motivated to install new heads sooner rather than later. So 1) does anyone know how can I determine what the replacement options are for my heads, i.e. will GT-40P's fit my engine, and 2) if I did this, should it really result in such a significant performance increase?
Dude, how did your water test go? Thanks to everyone for such great insight.
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KENO
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Posted: August-12-2025 at 8:10pm |
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I guess maybe you should get motivated, but the heads alone won't get you that 300 plus HP
A lot of the time people do heads, cam and intake to get to around 300 ish depending on the cam and intake. The gt40P heads are a bolt on, but wherever you get them from, you need to ask them to drill the head bolt holes to 351 size and put brass freeze,core,casting or whatever you want to call them plugs in place of the steel automotive ones they have for automotive applications. Plenty of CCF reading about what people used for intakes and cams. If you're doing the heads, I'd at least do an aluminum Edelbrock or Weiand intake to make it easy on your muscles lowering it into place on the heads You'll notice the difference in power mostly in acceleration and not so much in top speed because there's a lot of hull drag on the boat. Some people with their amazing increases started with a pretty sick motor before doing the changes, so the difference was bigger. Just a little warning.......Before you're done you'll be thinking about a new prop and a new distributor and a new carburetor when you get reading through the various threads on the gt40P heads.
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Deeski
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Posted: August-19-2025 at 12:44pm |
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Thanks Ken, great insight as always. I'll take this project on over the winter using the feedback here, hopefully we won't run into any surprises.
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William777 wrote:
