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Old 06-26-2021, 07:13 AM   #1
marty in Ohio
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Default Manifold milling

Two of my model A friends have a discussion going about milling the surface on the manifolds. One friend, who thinks anything can be fixed by throwing money at it, says that if you change one manifold or the other you must have a machine shop mill the surfaces. My other friend and I put together two manifolds and sighted them. They looked pretty good and we mounted them on the block with copper gaskets. No leaks. My take on it is that any small imperfections are are corrected with the gaskets. Isn't that what gaskets are for?
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Old 06-26-2021, 07:27 AM   #2
Werner
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Default Re: Manifold milling

Marty,

during the engine revision, I measured the assembled intake and exhaust group against each other. The difference between the inlet group and the outlet group was 1.2 millimeters.

The outlet group alone had a difference of 0.5 millimeters.

The seals can compensate a little bit. But the differences can cause the two elbows to crack and break!


I had that surface grinded in an assembled unit.
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Old 06-26-2021, 07:35 AM   #3
BRENT in 10-uh-C
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Default Re: Manifold milling

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Originally Posted by marty in Ohio View Post
Two of my model A friends have a discussion going about milling the surface on the manifolds. One friend, who thinks anything can be fixed by throwing money at it, says that if you change one manifold or the other you must have a machine shop mill the surfaces. My other friend and I put together two manifolds and sighted them. They looked pretty good and we mounted them on the block with copper gaskets. No leaks. My take on it is that any small imperfections are are corrected with the gaskets. Isn't that what gaskets are for?
Marty
Sure, just add a handful of gaskets to overcome any misalignments!


Actually, you probably can attribute your success to 'luck' as most times the two will not align that perfectly. Nothing wrong with having luck though.
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Old 06-26-2021, 08:05 AM   #4
Patrick L.
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Default Re: Manifold milling

Lay a straight edge across the manifolds and see how many thousands difference there is between them. Just eyeballing isn't enough. If its close to .010" take them to a good machine shop to be cut together.. I prefer to cut them if there is over .005"
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Old 06-26-2021, 08:35 AM   #5
Tacoma Bob
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Default Re: Manifold milling

Not having the two "mannies" milled together caused me to throw money at a new exhaust manifold. Lady Luck has rarely been in my world. LOL
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Old 06-26-2021, 09:15 PM   #6
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For $20 (in my town) I just have ‘em milled. No big deal. i’ve got 100x that in the rest of the engine.
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Old 06-26-2021, 11:01 PM   #7
old john
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Default Re: Manifold milling

I used a small slab of granite and a sum belt sander sand paper and sand away did not take long John
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Old 06-28-2021, 08:57 AM   #8
Bob Bidonde
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Default Re: Manifold milling

There are two 5/16-18x3/4 bolts that connect the intake & exhaust manifolds to make a hot spot warmer for the intake. If the manifolds are not flush to the cylinder block, then one or both 5/16 bolts will crack the intake manifold.
It is wise to have both 5/16 bolts out of the manifolds when mounting the manifolds to the cylinder block. Thus if there is any misalignment / gaps between manifolds, they can be detected and corrected before any damage occurs.
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Old 06-28-2021, 09:50 AM   #9
Patrick L.
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Default Re: Manifold milling

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There are two 5/16-18x3/4 bolts that connect the intake & exhaust manifolds to make a hot spot warmer for the intake. If the manifolds are not flush to the cylinder block, then one or both 5/16 bolts will crack the intake manifold.
It is wise to have both 5/16 bolts out of the manifolds when mounting the manifolds to the cylinder block. Thus if there is any misalignment / gaps between manifolds, they can be detected and corrected before any damage occurs.



I agree. I leave them loose/snug once mounted. I don't think they need to be tight.
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