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MG MGA - 1600 Engine Block Question

I have noticed for the first time that the two 1600 engine blocks I have both have a 1/2" plug with a slot for a flat screwdriver located in the 11 o'clock position of the front welch plug just in front of the top boss for the generator bracket. The 1500 block I have does not have this and don't see any mention of it in any of the books I have. Anybody know what it is ........?.....Tom
Thomas Koch

My 1600 block has the same thing in exactly the same position. When I saw it, I thought perhaps it was a factory repair of a small hole in a bad casting, but it probably is not?

Tore
Tore

Interesting,
I have two 1600 engines, neither one have the feature you describe. I'm curious. Can you post a picture?
Thanks,
Gerry
G T Foster

I was painting my 1600 block on the weekend and noticed this feature too. I will take a photo when I get home tonight and post it tomorrow morning Aussie time.

Steve
S HILL

This is a picture of a 1600 Engine in my 1961 (built in 1960)roadster. It is a no number tag motor.If you look to the 11 o'clock position of the welch plug you will see the 1/2 inch flat screw head. I will post again with the other block I have which show even more detail. I think it has to do with the casting process.


Thomas Koch

The block is upside down in this picture so the plug in question is now in the 5 o'clock position. You can see there is a 1/2 inch sloted screw head in the center of a very faint outline of a one and a half inch plug which is flush with the surface of the block. Sorry these pictures are kind of fuzzy but this is not the loch Ness monster it is there as you can see.....Tom


Thomas Koch

Probably part of the fixturing for holding the mold together when the block was originally cast. It's my understanding that the molds are generally made up of multiple sand cores, so the screw probably held one of them to whatever frame they were assembled in for casting.
Del Rawlins

Just looked at my 1800 engine. The screw head position you are referring to is where the alternator rear bracket hole is located.

Steve
Steve Gyles

Picture of the alternator bracket hole on the 1800 I was referring to.

Steve


Steve Gyles

If this all ties in then it is worth checking to see if there is another screw head imprint in the 7-o-clock position.

This then raises the question, was the 1600 prototype block originally cast and drilled for an alternator? Was a decision then made to stay with a generator mounting and the casting had the alternator lugs ground flat and the hole plugged?

Steve
Steve Gyles

Methinks you guys worry too much!!

What with global warming, international terrorists, religious conflicts all over the world, and you are worrying about a screw head on a casting!!!!

Let's just call it a casting mark, and get on with building cars?

CP
Colin Parkinson

Colin, point taken, but it's a lot less depressing to worry about marks on a MGA block than the rest of that stuff. ;-) It is in about the same position as the upper alternator bolt, but there is a boss for each bolt cast into the block and this one doesn't have a boss associated. It would be good to know if it went into the water jacket or was a blind hole. I'd think it isn't blind or I doubt if the factory would have installed an insert. The welch plug hole is really there to support the sand cores. We know that this design was used in other BMC applicatons, but it's just so unusual to have a hole into a water jacket that's not associated with a sensor position and no reinforcing boss around it like on the other bolts for brackets.
I can't tell from the photos, but are you really sure it's a screw? It does resemble the "clock" type casting marks I've seen on other engines that indicate the shift when the part was manufactured.
Bill Young

Even if they built in the provision for alternator mounting, they wouldn't cast it with a hole in there. There would cast a thicker area (aka a "boss") there and the hole would be drilled and tapped during the machining phase. I guarantee you guys that there is no plugged hole in the block, all you are seeing is the imprint of a screw head left by the casting process, which after thinking about it, had to have been an artifact from making the sand cores for the mold. If it was from a fastener holding the cores together for the iron pour, you would instead see the reverse image of a screw.
Del Rawlins

Colin

I side with Bill on this. My whole professional life has been and still is devoted to defending the peace. It's good to get a break from it all now and then and enjoy a good hobby. I spend plenty of time building/maintaining/driving the MGA. But part of the pleasure (for me) is also understanding the car's quirks and history. If we are not bothered with all these things we might just as well go and buy modern Euro boxes.

Steve
Steve Gyles

Hi guys, as promised here is a pic of my 1600 block with the screw head clearly visible.

Regards

Steven



S HILL

Come on guys, I'm growing impatient with this (rare for me). This is time for a lesson in sand casting. The thing that looks like a slotted plug is not a hole or plug. It is a copy in the casting surface of the impression left in the sand mold created by a screw that was part of the wood pattern used to create the sand mold before pouring the molten iron. I have exactly the same mark in my 1600 block. The long version follows.

"Pattern" is a wood block exactly the shape of the desired finished cast part. This pattern includes at least two extensions on top called sprue and riser that will form the holes in teh sand mold for pouring in molten metal and letting out air and steam.

The mold casing is a box in two pieces split down the center (generally speaking). These mold half shells shells are placed open side up.

The pattern is placed into one of the half shells with the center line (split line) of the pattern about even with the top of the mold shell. The shell is then filled with damp sand packed into place. The pattern is then carefully removed, leaving a cavity in the sand in the shape of half of the finished part. Then flip the pattern over and repeat the process with the second half shell to make a cavity in the shape of the other half of the part.

A "core" is then inserted into the sand mold. The core is a rigid hard packed sand piece exactly the shape of a void that is desired to be left inside the finished part. In this case the core represents the shape of the water jacket. The core will have multiple protrusions that will sit in notches along the split line of the half shell sand cavity to hold the core in proper position.

The second half shell is then carefully inverted and placed on top of the first one to close the mold. The mold is then positioned with the sprue and riser topside, and molten metal is poured into the mold to fill it. It must then be set aside for a while to allow cooling enough for the metal to solidify.

After cooling the mold is opened and the sand (now mostly dry) is allowed to fall away from the outside of the cast part. The part is then shaken considerably to get the sand from the core inside to fall out. End result is a raw casting with a hollow cavity inside and with holes in the sides where the legs of the core were sitting in the mold. When the casting is later being machined, these core holes are machined out to accept the round disc plugs called "core plugs". Please do not ever refer to these things as freeze plugs, because they do not reliable serve that function.

The screw that caused the impression in the casting was being used to hold together parts of the wood pattern. For small run castings, just to be neat, the pattern maker can cover up these "imperfections" in the surface of the pattern with bees wax to make a smooth surface on the finished casting. For mass produced parts like engine blocks these minor "imperfections" are commonly left unattended, resulting in said impression showing in the surface of all of the castings.

If you were wondering where the split line was on these castings, it was on top and bottom and front and back ends, all the way around the vertical center of the part. All of these surfaces are machined on the finished part, therefore removing all traces of the split line.

Now you might understand why "core shifting" causes variations in the wall thickness of the cylinder walls.
Barney Gaylord

So speaketh the guru.
Del Rawlins

Just a comment on this theme.

On my 1600 engine if you look at the 1600 where it is cast into the block you can see the shape of four small screw heads in each corner of a rectangle around the 1600 numbering.

So the pattern was made up and then the 1600 lettering screwed onto it, or they modified the 1500 pattern by screwing a 1600 onto it (and other internal changes I am sure).

Chris.
Chris CurrahWhitelock

Patterns are used over and over and are subject to wear and damage. Repairs are made to them as time goes on. It would then be probable that there would be more of this type of thing at the end of the life of the pattern that was evident in the beginning. When your block was cast would have a bearing on how many if any of these casting marks it may have.
Ed Bell

This thread was discussed between 15/11/2007 and 20/11/2007

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