How far can I push a set of 7.4 heads???
 

I have a 2000 7.4 MPI with roughly 950 hours on it... always run and kept in salt... corrosion is heavy in entire bildge area.

Anyway... I had to pull the exhuast manifolds due to a small leak in the manifold itself. I had a hell of a time getting them out and thanks to some OSO members got the help I needed to deal with the frozen bolts. (for anyone who was watching that... a good bolt extracter kit from sears did the trick... along with some blood and a few broken tools but it worked)

My question now is if my heads are also toast... there was a lot of corrosion and even some pitting around the edges of the ports. I also have two bolts stuck in the head as they broke when I got tourque on the bolt head. I am sure I can drill those out but should I be replacing the heads as well?
I really dont feel like doing this work only to have to pull it all out again in another month or so.

Whats the usual rule about choosing to change up the heads? It looks like this will be another messed up wrestling match with rusted bolts... but not as bad.


ALSO... I was looking to purchase a set of Eddie Marine high performance manifolds but now I wonder if I should just go stock.

Any insite on this will be a great help....

Thanks in advance.

B

With 950 hours, my guess is you're going to end up with a complete rebuild before you're done. There are lots of little bits that have been wearing and deteriorating right along side of those heads and exhaust. I wouldn't be surprised to see cam chain wear, lobe wear, cylinder bore wear, etc.

Looks like exhaust has been leaking for a while. I think Chris is right rebuild or repower is in order. Shame is the leaking exhaust ruined it , anyone else reading this change your riser gaskets inspect internally your manifolds. This motor would have probably run longer if it didn't get water in it.

It will likely run a while if your just put it together. It just will be down on power. Do a compression or leak test and than make your decision.

So I have been told... I am really trying to avoid that this year and was only wondering if I could just install a new manifold and run with it... seems the worst that could happen at this point would be a leak at the connection between head and manifold. I guess at this point it's not going to hurt to try.

Thanks for taking time to answer Chris....

Brian

Thanks Mobil....

I have to say though... I have really been on top of risers and gaskets...and also changed the manifolds at about 400 hours... I take care of this engine really well and she runs strong. I have always had a really bad corrosion issue with this boat. Any new parts that go on are completely corroded in about one season. It sits on the water all year and gets used pretty heavy in the summer. I did have a bad case of water intrusion the winter before last due to bilge pump failure... bilge filled up with rain water and got into the cylinders. I cought it quickly and was able to get it all out... change oil a few times and had a good season last year.

The reason I am having to change manifolds was due to an actual small hole in the manifold itself. Initially sounded like a blown gasket but upon further inspection I was able to feel the exhaust air popping out of the side of the manifold.

I think I may just slap a new set of manifolds on and see what happens. I was going to upgrade but probably just gonna stay stock for now.

Thanks also for your reply.

B

Strip, You had stainless risers in the picture. I don't know why or who the genius was that put stainless on cast iron. It is old news it doesn't work. If anyone has stainless risers on there big block stock manifolds you better throw them away. They will inevitably leak and ruin your motor. In my opinion.

I can appreciate your sentiments. Nobody likes spending $$ to just stay where they are at- rebuilds suck. But looking at those head bolts leads me to think you may be popping the motor out just to work on it. You may be able to get away with just rebuilding or replacing the heads. That motor has a common and inexpensively available head on it. If it were me, I would look at replacing them- if your exhaust rotted, the heads may not be far behind. Why put guides, valves and machine work into shells? You'll probably spend more having those exhaust bolts machined out than a nice set of used heads anyway. Those head bolts look like they're going to bneed an abrasive disc to remove them.

You should also consider using salt neutralizer. It will greatly reduce the effects of salt water. You can use it when you flush the motors and if you keep some in a garden sprayer, you can hose your bilge out with it. Everything will last much longer.

Thanks for all guys.... Strip, that motor was really bad man... I thought I had it bad but I realize a lot of people have a similar problem. I am probably in for a similar problem with these head bolts.... YIKES!!!

Hey Mobil, I did not see any pics of stainless steal risers but gotta ask... Eddie Marine is trying to sell me a performance upgrade with a set of cast aluminum manifolds with stainless risers... supposedly adds like 30 horse or something. They say it is safe and should last longer than stock... is this not true?

Chris, I have been looking and I am finding some cheap heads for this engine and may just try that... and the salt nuetralizer??? Will I find this at the local marine supply? I will give it a shot... thanks.

Looks like I will be keeping dry for a while... sux but gotta do what we gotta do.

Thanks....

B

Im missing something? the engine in the thread was a 415mpi 1996 stock exhaust.

Thats what suprised me the engine looked better than norm on the inside, I guess my buddy should of taking better care of the outside.It would of not rusted as bad.

Yes the risers in that pic was of a stainless risers. There are still a bunch in service. and still leaking in to the motors. Merc stopped using them thankfully.

The problem with stainless and stock cast iron is the gasket is in a hopeless battle dealing with corrosion problems from dissimilar metals. different expansion rates, and narrow surfaces separating water and exhaust.

All the aluminum manifolds I have seen pass water around the gasket surface not thru it and don't have a water weep problem.

I see what your saying but this is the only pick of the manifold is see in my head bolt thread,Stainless risers?

Gotta admit I am missing something too... I did not see any stainless risers in those pics... maybe Mobil knows something we dont but they look stock to me. All of the stainless risers that I have seen are very distinct looking and in fact I argued with a guy trying to sell them to me that they would not fit in my boat... turns out they line right up to the stock 4" hose that goes to my captains choice exaust.

Anyway... I always knew this wasn't a poorman's hobby. If it were up to me I would be taking all the doe and putting down on the new 382 I want with the twin 700's. That one aughta be fun once chit starts to go south huh? Maybe next year...

Thanks again guys... really appreciate the help.

Brian

So does this mean I should be good with aluminum manifolds and stainless risers??? That's what Eddie Marine is trying to sell me... supposed to work well but I may not be willing to try them on these heads.

Thats what we put on this Scarab, he found a used set for 400,had to ad a angle plate to the riser to get it to line of with the transom.he only keep it 2 years after so I don't know they held up.I wouldn't think Eddie would be selling something that would be a potential prob? I dOnt have any experience with alum manifolds

Thanks Strip...

After a bunch of thinking on it today and some number crunching I have come to the conclusion that it is just time to repower this thing... I am looking at a nice 502 mag HO ready to go... a few tweaks here and there and she should be good as new. Probably not going to happen until next season but in the mean time I am going to find a cheap set of manifolds and see if I cant get a few more hours out of her this summer.

It will be fun to do the repower when the time comes though... thanks for the great post on the job you did on your friends boat... it helped a lot.

Peace.

Brian

Start a thread in the wanted section Ive seen some guys just give them manifolds, or atleast 200. but the freight will be close to the same:D

http://www.offshoreonly.com/forums/s...archid=2027144

Thanks man... I'm on it

That being ,Going back and looking at the head surface I still don't think its going to seal.It would be easy while the exhaust if off to swap heads, find a set of good take off for now.
I am thinking even if you took the heads off, they machined down the gasket surface,nope. But if ya try it get a gasket that has the metal in it, like a Felpro and get some Black high temp, maybe it will fill in the holes when ya put it together,Goodluck:ernaehrung004:

Yes, Just because it is black doesn't mean its not stainless. Put a magnet on it SS is non magnetic. The 4" risers with the short mount bolts are
SS. The ones with long bolts that reach to the top are cast iron.

The Aluminum manifolds usually have a hose that directs the water around the gasket. If the tailpiece gaskets only seal exhaust your good. If by chance you find a brand { I don't know of any} that the tailpiece gasket seals exhaust AND water I would stay away from it.

Confirmed, those are stainless risers. I currently have a real nice pair of used ones that have been collecting dust for about 6 years in my barn. On the side it reads:

Mercruiser
stainless steel

Believe that set came off of a 92' Baja....

Thanks again Strip...

I thought about adding some high temp also... it looks like I can get a seal. I just gotta get those dang bolts out of the head.... any suggestions....

Be well..

B