Hole on inside of intake manifold

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MapleCub
Posts: 6
Joined: Tue Apr 28, 2020 10:55 am
First and Last Name: Ben Carlson
Location: St. Joseph, MN

Hole on inside of intake manifold

Post by MapleCub »

Howdy folks,
This weekend is below zero in MN, so I've been working on my K321 engine, replacing the head gasket and some other leaky gaskets. I completely rebuilt this engine with a new used block just three years ago, so I was kind of disappointed when the head gasket blew out this summer. Hopefully this time around it will last a little longer (I used a better quality gasket with copper coating just to be safe).

Anyways...while putting everything back together, I noticed that there is a small 1/8" dia hole on the inside of the intake manifold. I don't remember it being there before, but maybe I just missed it before. Looks like the threaded hole for the head bolt next to the intake valve poked through the side of the intake about an inch from the flange (see pictures).
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IMG_4859.JPG (83.56 KiB) Viewed 2606 times
It looks like the hole is blind otherwise (doesn't go all the way through the block), and is sealed (hypothetically) by the head bolt washer up top...so my question is: does this pose a problem with air leaking into the intake (causing a lean mixture), or should I not worry about it?

Has anyone else seen this happen in their engines? If it is a problem, what's the best way to fix it? (ie. welding, brazing, epoxy/JB Weld, longer head bolt, compensating for vacuum leak by setting the fuel mixture richer...)

Ben
1450, 149 (for parts)
44" deck, snowthrower, rear blade, #2 trailer, Cyclone spreader
Also 1947 & 1948 Farmall Cubs w/ sickle, cultivator, 2 plows & several larger Farmalls

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Tom Scott
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Re: Hole on inside of intake manifold

Post by Tom Scott »

I would absolutely seal the hole off, and JB Weld is perfect for that. Apply it from the inside, push a pea sized bit into the hole to give it some amount to grab from behind and stay put. and wipe it off flush with the inside so the bore is smooth.

It is never a good idea to try to band-aid a vacuum leak with jetting. Always fix the leak.

As far as head bolt lengths, I'd double check that you're using the correct length bolts in the correct locations. Do not vary from the factory bolt specification.
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mortten
Posts: 101
Joined: Mon May 02, 2011 2:41 pm
First and Last Name: Doug Anderson
Location: Peninsula, OH

Re: Hole on inside of intake manifold

Post by mortten »

Don’t forget to retorque the head gasket after you run it up to temperature.

MapleCub
Posts: 6
Joined: Tue Apr 28, 2020 10:55 am
First and Last Name: Ben Carlson
Location: St. Joseph, MN

Re: Hole on inside of intake manifold

Post by MapleCub »

Excellent... thanks for the advice
I was hoping that JB weld could solve my problems. I might put a bit of high-temp thread sealer like Indian Head on the head bolt just as insurance.

Also, I'm using all 1-1/2" head bolts, but just noticed that the online parts manual specifies one of the head bolts should be 1/4" longer than the others. Didn't see anything about this in the service manual though. Any idea where that would go?
1450, 149 (for parts)
44" deck, snowthrower, rear blade, #2 trailer, Cyclone spreader
Also 1947 & 1948 Farmall Cubs w/ sickle, cultivator, 2 plows & several larger Farmalls

mortten
Posts: 101
Joined: Mon May 02, 2011 2:41 pm
First and Last Name: Doug Anderson
Location: Peninsula, OH

Re: Hole on inside of intake manifold

Post by mortten »

If it has that l shaped lifting bracket on it maybe it goes there. Don’t put sealer on the bolts. Clean the bolts and the holes. Put some oil on the bolt threads and torque to proper torque in the proper sequence. Run the engine for half an hour or so under slight load. Let it cool all the way down. Retorque to proper torque again using the proper sequence.

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