I just discovered an empty threaded hole on my engine block. It is on the surface of the block where the driver's side head mounts, at the rear of the engine by the upper right corner of the head (by the crankcase vent tube). The hole is partially obscured by the head when the head is installed. It is larger than a 1/2" pipe thread by a bit, and appears to have a finer thread. In an earlier thread I learned it was an oil galley passage way down to the rear cam bearing oil hole. I can't imagine the utility of this passage way, but that is neither here nor there. Two questions: (1) Is it possible this was never plugged? I honestly can't remember ever removing a plug (or seeing one) during disassembly. (2) Any idea what size pulg fits back there? The hole is larger than all my taps. Thanks, as always.
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Re: '64 block oil galley plug
Mark-----
The plug that you refer to is an oil gallery plug. The purpose of it is to plug a hole that the engine plant needed to drill in order to complete the engine's internal oil passages. On small blocks that I'm familiar with, this plug is 1/4" NPT plug with an indented, square head. It's possible that earlier small blocks used something different, but I'm not aware of it.
This plug is installed in the engine at the engine plant and is usually never removed at rebuild time. That's because it doesn't really need to be removed and it's VERY, VERY difficult to remove. Usually, impossible.
A 1/2 pipe tap is WAY larger than even the boss that this hole is drilled into, unless earlier engines used a way larger boss.In Appreciation of John Hinckley -
Re: '64 block oil galley plug
I checked my November 63 cast block and it has the 1/2 inch hole which appears to be plugged. I say it's a plug because it is flat and flush with the deck of the block. It is in the exact location that you described. I never noticed it until you brought it up. I had the engine built, so I don't know if the builder removed and replaced it. It definetly doesn't appear to be screwed in. It looks like it may be a small cup shaped plug placed cup side down. I'm sure that someone on this board knows exactly what it is. It is definetly plugged.
PhilComment
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Re: '64 block oil galley plug
Phil----
From your decription, it appears that the earlier blocks used a soft plug instead of a threaded plug. The plug on later blocks is 1/4" NPT which is about 3/8" OD. The thing that puzzled me about Mark's information was that he indicated that a 1/2" pipe tap wouldn't fit the hole. A 1/2" pipe tap is about 5/8" OD.
Anyway, I don't know if there will be a NPT size that one could use for this. Perhaps, though, the hole could be drilled and tapped for a 3/8" NPT which is about 1/2" OD. Otherwise, I'd just recommend that Mark re-install an original size soft plug. These are easy to obtain in any auto parts store and, if the hole is actually 1/2" OD, then a 1/2" soft plug will be required. Drive it in with a punch that has about the same diameter as the base of the soft plug with the cupped side up. Then, stake the top of the block with a chisel to insure that the plug can't come out.In Appreciation of John HinckleyComment
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Re: '64 block oil galley plug
My mistake on the tap and plug - I am mixing my bolt thread sizes and pipe thread sizes. The hole is larger than (a) a 1/2 x 20 bolt thread tap and (b) a 1/4 npt plug. Sounds like I need to try the 3/8 npt or use a soft plug. Since the hole is tapped, I'd rather use the appropriate sized pipe plug if I can find it.Comment
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Re: '64 block oil galley plug
Mark From Phillip's description he may have a pipe plug with an internal hex or square hole for installing it and then it would look flush. When I worked on the engine build up line this style plug was removed from intake ports to install fittings. LyleLyle
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Re: '64 block oil galley plug
Mark - you may want to check the hole with a thread pitch guage to verify the thread count and compare to a presumed correct plug before cranking it in....CraigComment
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The answer
is - the hole is threaded with a 9/16x18 bolt thread. I made a plug and should be good to go w/a little thread sealer. Thanks to all for your advice.
MarkComment
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that bolt will never seal the oil pressure
that size is close to 1/4" NTP plug size. straight bolt thread will not seal.Comment
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Re: that bolt will never seal the oil pressure
Clem----
I totally agree. It's virtually incomprehensible to me that GM would ever have used an NF thread size for such a plug. If that's truly how it is in this case, then "someone must have been there before" with a drill and tap and that "someone" was a neophyte. If so, though, then this should have been leaking before engine teardown because, as you say, there's no way that straight thread would seal against the oil pressure.In Appreciation of John HinckleyComment
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Re: that bolt will never seal the oil pressure
dispair is turning to dismay. What is the solution? 1/4 ntp is too small - it falls right in the hole. I don't want to drill and tap it out because that will put metal bits down the hole. Find a "plug" (the drive in and stake variety) of the right size (if there even is one) and install with some kind of sealer? Or am I totally screwed and destined to start this job over, tearing down to the bare block, drilling out and tapping the hole, removing all the galley plugs, etc, and cleaning from scratch, new cam bearings and so on?Comment
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Re: that bolt will never seal the oil pressure
Mark,
I took a picture of the plug in the deck of my 64 block (cylinder case). Send me your email address and I'll send you the jpeg. I think that you'll agree that it is a plug. I think you should visit an engine builder and see if they have an 870 casting 327 block laying around and ask thier oppinion. It looks like something that they might typically remove if they were going to hot tank the block. Even if they don't have a block on hand, they will probably know what's going on. I looked in the Chevrolet parts catalog at the typical V-8 illustration, and it's not like the 870 block, so it doesn't show the hole or plug.
Also, be advised that there was a Tonawanda cast block in late 64. It is not the same as the 870, so comparison to my engine wouldn't be accurate.
PhilComment
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you could try the bolt and a good epoxy
make sure the threads are clean and if you are on a engine stand turn the block upside down to make sure the epoxy stay where you put it. you can turn the block with the oil passage facing down,use a machine reamer to remove the threads and install a drive in cup type expansion plug. with the opening facing downward no chips should get into the passage. how far down does the threads go maybe you could just drive the expansion plug down to below the threads and that way you would not have to do any machining.if you use the expansion plug i would still use epoxy on top of it to help prevent a leak. remember the surface above the plug must be flat because ther corner of the head will cover it.Comment
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PS
instead of a bolt use a allen wrench type set screw with the epoxy.Comment
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Re: that bolt will never seal the oil pressure
Thanks, you have mail. Also, I have the proper block so we should be talking apples to apples.
MarkComment
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