Mercruiser 470 exhaust manifold

[IPtraffik]

I have an 85 Mercruiser 470 3.7l 190hp and am attempting to remove the exhaust manifold. *I have removed 1 of 2 studs and 4 of 5 bolts. *The remaining stud is really rusted in. *The remaining bolt head snapped off. *

My question is this: *Without removing the remaining bolt and stud I should be able to take off the exhaust manifold, correct? *

I have tried to yank and pull and pry and whack with a rubber mallet but I'm not seeing any movement. *Is there a bolt I'm missing or is it likely just baked to the head.

Any advice is on how to get this exhaust manifold off is appreciated.

-Eric

 

[nola mike]

Re: Mercruiser 470 exhaust manifold

Can't remember how many bolts there are off hand, but none of them are hidden. Sounds like you should be able to remove that manifold.

 

[vincechig1975]

Re: Mercruiser 470 exhaust manifold

I have a 470 and it might be that there is some corrosion preventing it from being removed easily, if it were mw I would hit it with some penetrant and wait then hit it woth some more and then some heat only on the manifold in the affected areas. Just a suggestion......

 

[ImperialV184]

Re: Mercruiser 470 exhaust manifold

Do you have the aluminum manifold or cast, mine was very badly corroded as well, it came off very easily, mine is an aluminum manifold, I would not hit on it too hard, there are three studs which can remain in the head when you remove the manifold, the bolts should've real obvious and I think there are two bolts or studs per exhaust port, except for one port, which I always thought was strange. If you do hit it to break it free, use a wood block, these can be expensive to replace especially if you have an aluminum one. Got any pictures

 

[IPtraffik]

Re: Mercruiser 470 exhaust manifold

I have sprayed some PB blaster where the manifold mates up with the head to problem is that the thick gasket there just kinda soaks it up so I'm not sure it's helping much.

Imperial - I have the cast iron version on mine. Mine only has two studs, one of which I removed. The other is so well rusted in I'm going to attempt to remove it AFTER I get the manifold off. Also, you stated "three studs which can remain in the head when you remove the manifold, the bolts should've real obvious"

Can I remove the manifold with a bolt still in, granted I snapped the head of the bolt off trying to get it free? Also, I was using a short 2x4 section try and knock it away from the head...it's not moving at all which is why I thought I had to be missing something somewhere...

I'll snap some pics if I make it out there today.

 

[ImperialV184]

Re: Mercruiser 470 exhaust manifold

You should be able to remove it if the head has snapped off. My studs absolutely could not be removed until I got the manifold off, I tried the two bolt method to no avail. Sounds to me like if you see a lot of rust that the stud could be rusted to the manifold, the gasket on mine was pretty sticky but not nearly enough to require a lot of force to remove. I Just tapped mine a few times and it broke free. May need to apply some heat near the stud, would also focus the penetrating oil on the rusted stud, wipe it off before the heat is applied of course, don't want any fires. Is the engine in the boat or out?

 

[Scott Danforth]

Re: Mercruiser 470 exhaust manifold

I have an 85 Mercruiser 470 3.7l 190hp and am attempting to remove the exhaust manifold. *.....................................................................Any advice is on how to get this exhaust manifold off is appreciated.

-Eric

det chord will remove it, so would a sawz-all. now if you want to keep the manifold, you may need to heat the area around the bolt/stud. the cyclical heating/cooling with penetrating oil will be needed to break the rust bond.

 

[IPtraffik]

Re: Mercruiser 470 exhaust manifold

The engine is still in the boat. I went out there today with a MAPP torch and a prybar about the length of my arm. The manifold is still very much stuck to the head.

Here's a picture of the side of the manifold.



You'll notice there are 7 holes total. One stud still remaining (hole 4) and two bolts with the heads snapped off (holes 5 and 6). I verified the inside of the holes on the manifold itself are not threaded, I can easily slide the bolts that have been removed in and out of the holes that there is nothing in.

I tried heating up the holes around the snapped bolts and the stud and then prying off the manifold with a long prybar using the engine block as a backer. I felt like I was gonna break the motor mounts before the manifold moved at all.

I'm missing all this perfect boating weather we've been having here in NW Ohio and the perch are near. Help!

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 470 exhaust manifold

It may not be the manifold stuck to the head.... but the bolt itself.

When the bolt snapped there may be a burr that extends beyond the body of the bolt which is preventing the EM from siding off. I think I would get a center punch and mark the center of the two snapped bolts.

Then drill some of the bolt to a point it is recessed below the EM, maybe 3/8"-1/2". Start small and work up to the largest drill bit that will fit in one of the other open holes in the manifold. That should remove any burrs and allow the EM to be removed.

Or better/more heat on the heads of those snapped off bolts get them hot and get them soft. Then try and pry again. Gonna need an oxy/ace torch for it to make it hot enough.

Just some ideas to try.

 

[Scott Danforth]

Re: Mercruiser 470 exhaust manifold

a MAPP torch is not enough heat anything other than a solder joint. you need to get your hands on an Oxy-acetylene torch.

also take a piece of 2x4 and a large hammer. the wood is to soften the blow of the hammer to prevent your exhaust manifold from cracking when you smack it.. you will want to have your major blows going toward the engine, and maybe a softer blow going vertically. this will help loosten things.

you are fighting the gasket material that is adhered along with the bolt and stud that are broken off and stuck in the bolt holes.

 

[fmalott]

Re: Mercruiser 470 exhaust manifold

when i rebuilt my 470 same problem it was a ***** taking the exhaust maniold off the head. i did the same thing snapped the heads off the bolts keep try to put penetrating oil down the bolt holes and see if you can keep prying off i was not succesful and i cracked the exhaust manifold so i had to buy a used one so just be patient and slowly try to bang it off it will come i just had bad luck. when i realized i cracked the manifold i realized the manifold was about an inch off the head so i hacked sawed the bolts and took the head to the machine shop and he was successful on taking the remaining studs out GOODLUCK!

 

[ImperialV184]

Re: Mercruiser 470 exhaust manifold

Yea, I second that, looking at the picture it seams there might be a burr or lipp on the broken bolts, would try to drill in a bit. Start with a small bit and work up, make sure to use oil or you will toast the bits fast, I think cobalt bits are what you need. You are doing all the right things, wood block at all different angles should get it.

 

[ImperialV184]

Re: Mercruiser 470 exhaust manifold

Out of curiosity, why are you neededing to remove the manifold?