Can mercruiser exhaust manifolds be milled down?

[crusher19]

Hi guys, I have a 1983 sea ray seville 19cc, which I restored a few years ago, the boat is beautiful and looks brand new. it came with a 120 mercruiser which was way under powered. I have acquired a 3.8L 229ci mercruiser with the drive, gimbal housing, bell housing and all of the components for a very cheap price. My problem is that the width of my dog house is too tight over the width of the motor. I don't want to alter the dog house as it was just refinished. Is it possible to mill down the exhaust manifolds where they mate up to the cylinders without any ill effects? I would only have to take off between an 1/8 to 1/4" per manifold.

 

[Bondo]

Re: Can mercruiser exhaust manifolds be milled down?

Hi guys, I have a 1983 sea ray seville 19cc, which I restored a few years ago, the boat is beautiful and looks brand new. it came with a 120 mercruiser which was way under powered. I have acquired a 3.8L 229ci mercruiser with the drive, gimbal housing, bell housing and all of the components for a very cheap price. My problem is that the width of my dog house is too tight over the width of the motor. I don't want to alter the dog house as it was just refinished. Is it possible to mill down the exhaust manifolds where they mate up to the cylinders without any ill effects? I would only have to take off between an 1/8 to 1/4" per manifold.

Ayuh,.... Welcome Aboard,..... I doubt it'll work, but you could try it,...

I don't think the manifolds would clear the heads/ valve covers,....

Unless yer willin' to change the motorbox, yer pretty much limited to goin' with the 3.0l motor,...

 

[crusher19]

Re: Can mercruiser exhaust manifolds be milled down?

The 3.8 has about 1" of clearance between the exhaust manifold and the valve cover, so clearance is not an issue, just wondering if milling a 1/4" off of the manifold would affect engine performance such as compression or cooling?

 

[Pete104]

Re: Can mercruiser exhaust manifolds be milled down?

You can't! Milling them would change the center dimension hole to hole which would then be too narrow for the "bull horn".

 

[crusher19]

Re: Can mercruiser exhaust manifolds be milled down?

What do you mean by center dimension and bullhorn?, basically it is two flat surfaces between the manifold and cylinder that mate together, if anything i will just have to take a little off of the bolts too, I had a machinist look at it, he said no problem to mill it down, just wondering if it will affect engine performance?

 

[Pete104]

Re: Can mercruiser exhaust manifolds be milled down?

Do you plan on thru hull exhaust?

The "bullhorn" is the exhaust piece that routes exhaust down & out thru the gimbal housing.

 

[crusher19]

Re: Can mercruiser exhaust manifolds be milled down?

Thats a good point, maybe I'll get enough flex out of the rubber couplings

 

[crusher19]

Re: Can mercruiser exhaust manifolds be milled down?

Looks like the elbows can be turned slightly to line up to the y pipe after milling the manifolds

 

[Volphin]

Re: Can mercruiser exhaust manifolds be milled down?

I have done this on a 4.3L, however I was installing 3/8" spacers for taller valve covers. It shouldn't be a problem... I'd go with 1/8" and test fit. Use spray silicone inside the rubber exhaust tubes for easier fitment.

Why don't you post up some pics so we can see what kind of clearance there is now?

 

[crusher19]

Re: Can mercruiser exhaust manifolds be milled down?

I have already taken the manifolds off, there was an inch of clearance between the valve cover and manifold