Merc 7.4 exahust manifold bolts?

[muskie hunter]

I took my boat in 2 weeks ago to have the manifolds replaced and they are not done yet! Im starting to get really ticked. The marine mechanic says the boat was run in salt water and he cant get the manifold bolts out. The boat has only 140 hrs on it. I am about ready to get the boat back and do it myself. I have a few questions are the manifolds held on by bolts, or studs and nuts? How far into the block do they usually extend. how many bolts hold the manufold on? 2 per cylinder or 1 per cylinder? Does anyone see any problems cutting the manifolds off with a sawzall or cutting disc so that the bolts or studs can be accessed, lubricated or heated. I know about the gas fumes and fire issues. but if I run a fan it should be ok.
I truly believe the mechanic is not wanting to do this job as we live in ohio and he problably hasnt worked on many motors that have been in saltwater. Any advice frome anyone that has faced similar problems would be great. I have a snow plow truck and have had to cut headers off of my smallblock, but a boat manifold is a little different.

Thanks steve.

 

[Haut Medoc]

Re: Merc 7.4 exahust manifold bolts?

I took my boat in 2 weeks ago to have the manifolds replaced and they are not done yet! Im starting to get really ticked. The marine mechanic says the boat was run in salt water and he cant get the manifold bolts out. The boat has only 140 hrs on it. I am about ready to get the boat back and do it myself. I have a few questions are the manifolds held on by bolts, or studs and nuts? How far into the block do they usually extend. how many bolts hold the manufold on? 2 per cylinder or 1 per cylinder? Does anyone see any problems cutting the manifolds off with a sawzall or cutting disc so that the bolts or studs can be accessed, lubricated or heated. I know about the gas fumes and fire issues. but if I run a fan it should be ok.
I truly believe the mechanic is not wanting to do this job as we live in ohio and he problably hasnt worked on many motors that have been in saltwater. Any advice frome anyone that has faced similar problems would be great. I have a snow plow truck and have had to cut headers off of my smallblock, but a boat manifold is a little different.

Thanks steve.

There should only be four bolts per side holding it to the block......
They only go in 1-1/4" or so.....
If you have the tools, I would give it a go myself.....
I'd try some heat on 'em & try to break the bolts loose before I did any cutting, as long as ya have some ventiation.....

 

[Bondo]

Re: Merc 7.4 exahust manifold bolts?

Does anyone see any problems cutting the manifolds off with a sawzall or cutting disc so that the bolts or studs can be accessed, lubricated or heated.

Ayuh,........

You'll find it Much Easier to just grab a BFHammer,+ Smash the old manifolds to Bits,......
Then Vise-Grips can be used to remove the Bolts/ Studs.......

 

[muskie hunter]

Re: Merc 7.4 exahust manifold bolts?

Ayuh,........

You'll find it Much Easier to just grab a BFHammer,+ Smash the old manifolds to Bits,......
Then Vise-Grips can be used to remove the Bolts/ Studs.......

Are you serious? I bet the bolts holding the manifolds to the heads will break, then you are really screwed!!

 

[Bondo]

Re: Merc 7.4 exahust manifold bolts?

I guess You've never done this before,.........

The Manifolds are Cast Iron,+ Very Brittle,.......
The Bolts/ Studs are Steel,.......

It's quite Esay to Smash the Manifolds out of the Way,+ Leave the Bolts/ Studs.........

 

[muskie hunter]

Re: Merc 7.4 exahust manifold bolts?

I guess You've never done this before,.........

The Manifolds are Cast Iron,+ Very Brittle,.......
The Bolts/ Studs are Steel,.......

It's quite Esay to Smash the Manifolds out of the Way,+ Leave the Bolts/ Studs.........

Anyone else ever tried this method without cracking the cast Iron head or fracturing the bolts. I would try it but I need a little more assurance. I know cast iron breaks easily but.........

 

[rodbolt]

Re: Merc 7.4 exahust manifold bolts?

big blocks use 8 bolts to hold the manifold to the heads, the heads of the bolts have a tendancy to rust away. if you have room simply sawzall the manifolds. if not cut or burn off the remmanants of the bolt heads.
I do several sets a year, sometimes it will take me 4 or 5 hours per manifold and occasionally engine removal is required for access.

 

[f_inscreenname]

Re: Merc 7.4 exahust manifold bolts?

Ya, they have 8 bolts per side. And with mine I can see a motor pull for access.
PS I have never done it even though I have cut off a few exhaust bolts before but Bond-o and his "BF Hammer" has never steered me wrong.

 

[Bt Doctur]

Re: Merc 7.4 exahust manifold bolts?

Have also used "The bondo hammer" .It does work in extreme cases.
oxy/acet to "wash" the heads away.
die grinder to grind the heads away
center punch and drill away the heads

 

[farmboy]

Re: Merc 7.4 exahust manifold bolts?

Doesn't matter how you have to go about it, the manis are easy to break (try dropping a new one onto a concrete floor sometime). However you do it, protect the other engine parts; drive pumps, tab pumps, wiring, pressure lines, ect. with padding and/or fireblankets if called for. If you have to torch the headers off, make certain the bilge area has no flammable material exposed in it. Safety glasses are the minimum; a full face shield is even better for your happy boating future. Don't forget the anti-sieze on those new threads so you never have to use the extreme method again.

 

[Mischief Managed]

Re: Merc 7.4 exahust manifold bolts?

If you have to torch the headers off, make certain the bilge area has no flammable material exposed in it. Safety glasses are the minimum; a full face shield is even better for your happy boating future.

Don't forget that fiberglass (or "fiberglass reinforced plastic", the real name for what most of our boats are made of) is quite flammable, so the bilge itself is flammable.

Any reason to not use SS bolts for the new manifolds?