340 head gasket questions

dibbons · Nov 17, 2017

#1 My 340 bare block is back from hot tank and deck surfacing. There are two very small holes in the decks on both sides located between the two center cylinders. The Felpro head gaskets (260 1121) have two tiny holes that correspond to the holes in the freshly milled block surface. However, the holes (in my case) seem to not be freely open all the way to the coolant passage area. I can stick a wire in the hole, but it stops almost right away (1/8"?). Do you think rust has plugged up the holes and I need to break thru? If so, do the holes reach all the way to the bottom of the cylinder?

#2 This is probably obvious, but the gasket package does not state which side faces "up" for the cylinder head or intake gaskets. I assume the "up" side is the side that has some kind of diagonal blue stripes. Is that right? Thank you.

One more thing, there are also the same small holes centered at the very REAR of the block deck surface but I don't see the same two small corresponding holes at the FRONT. It looked like a picture of a 340 block on the internet had these holes both front and rear (block has a 1971 casting date).

small center holes (is the right side one completely plugged up?):

dibbons · Nov 17, 2017

small extreme rear center hole located about an inch above the hole for the locating dowel (looks like it may be plugged with rust?):

small front center hole (missing, but I see a "shadow" which may mean there is no hole there at all, or the hole is plugged with rust?):

toolmanmike · Nov 17, 2017

Looks like the holes for the locating pins. The deck looks surfaced. Those would have to be removed.

dibbons · Nov 17, 2017

small rear center hole-half way between the bolt holes on the right side of the foto (opposite bank):

small front center hole-half way between the bolt holes (opposite bank, it is either "missing" meaning never machined/used/not needed at the factory or it is plugged with rust and invisible because of the recent/shiny machined deck surface). What I am saying is there is no sign of the small hole in this location:

toolmanmike · Nov 17, 2017

See above, I can't remember where the locating pins right off hand. Let me look.

dibbons · Nov 17, 2017

Disregard this post, sorry.

toolmanmike · Nov 17, 2017

Locating pin holes as marked

toolmanmike · Nov 17, 2017

The mark opposite of the hole is probably from the head gasket in your first photo. They punch holes in both sides and both ends so they can be installed any side. As long as the gasket doesn't say "front" or "up" and there is a corresponding hole in the head to line up with the locating pin you should be good.

dibbons · Nov 17, 2017

The locating pins are very close to the bolt holes, not even close to where I am talking about.

dibbons · Nov 17, 2017

toolmanmike said:
The mark opposite of the hole is probably from the head gasket in your first photo.

Compare my first foto (center/middle of the deck surface) with the foto of the block pictured in post #7. The #7 foto of the deck surface in the middle appears to have two small holes that go clear through to the water jacket, not one hole and the shadow of a rusty hole like mine.

On the other hand, in the #7 foto I see the small water jacket holes in the rear center of the deck surface, but no indication of corresponding holes in the front center of the deck surface.

toolmanmike · Nov 17, 2017

Sorry, not following the holes you are questioning.

toolmanmike · Nov 17, 2017

dibbons said:
Compare my first foto (center/middle of the deck surface) with the foto of the block pictured in post #7. The #7 foto of the deck surface in the middle appears to have two small holes that go clear through to the water jacket, not one hole and the shadow of a rusty hole like mine.

On the other hand, in the #7 foto I see the small water jacket holes in the rear center of the deck surface, but no indication of corresponding holes in the front center of the deck surface.

Between the second and third cylinder on #7?

dibbons · Nov 17, 2017

The holes I am talking about are the very "smallest, tiniest" holes in the block surface, about the same size as for the locating dowels. There are evidently two between the two center cylinders, which I believe are supposed to penetrate the water jacket (I think mine may be plugged up).

There are two more tiny holes in the middle deck at the very rear, halfway between the two bolt holes that I believe penetrate the water jacket.

Then there may or may not be the same tiny holes (as above) in the front of the deck surface, halfway between the front head bolt holes. One of my fotos shows a kind of a "shadow" or perhaps "false" hole there (refer to post #2, the second/lower foto).

dibbons · Nov 17, 2017

toolmanmike said:
Between the second and third cylinder on #7?

If we are talking about the passenger bank, they would be numbered #4 and #6, looking at the foto they are alongside one another.

toolmanmike · Nov 17, 2017

Sorry I can't be of more help. Hopefully someone with a 71 340 block handy can answer your question. I do know there were casting changes in blocks and heads between the years.

furrystump · Nov 17, 2017

78 block between 3 and 5 both holes go to water

furrystump · Nov 17, 2017

Corresponding holes in head

furrystump · Nov 17, 2017

Thats a 68 x head

nm9stheham · Nov 17, 2017

The really important coolant holes are the ones in the rear. The coolant flow should be front-to-back through the block, up into the heads and then rear-to-front through the heads. The other holes are likely there just to get the casting sand out. The ones that are plugged may just have casting trash in them and are not really important for the main cooling flow. Too much open area up front is actually a problem.

sireland67 · Nov 17, 2017

I actually have a 71 block that has a head off, I can take a photo tomorrow.

Jadaharabi · Nov 20, 2017

Those two little holes in the center of the head are at the hottest part of the head when the motor is running. Because you have two exhaust valves one on each side of them.
The two holes in the block that are plugged by rust can be cleaned out by hand with a drill bit locked into a pair of vice grips and you just gently clean the hole out.
My question to you, was that block baked or hot tanked? Were the freeze plugs removed and the passages cleaned out?
I know in your first sentence it says you just got it back from being hot tanked. But in the pictures it does not look to me like that block has been hot tanked that's why I asked if the freeze plugs were removed and it was actually tanked.

dibbons · Nov 20, 2017

The block was hot tanked with the freeze plugs removed, but it looks like there is still rust around the cylinders in the lower areas. To give you some idea of the rust that developed while this motor was in storage, check out the hole in the timing cover behind the water pump (see foto):

Jadaharabi · Nov 20, 2017

furrystump said:
Thats a 68 x head

Don't hold that against it. It's just as good as a j head with a 202 intake valve.

Jadaharabi · Nov 20, 2017

Got a picture of it now that it has been hot tanked, a side view?
Remember rust holds heat.
So the best time to get rid of it is now before you assemble it.

dibbons · Nov 20, 2017

I take some fotos tomorrow looking thru the freeze plug holes.

340 head gasket questions

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