Core Plugs

[jesprit]

We are currently having a debate on an external Esprit forum about the intended purpose of core plugs. I have searched google and it seams to be a world-wide debate!

Well not quite, but nobody seems to agree. The general consensus is that they are a manufacturing byproduct and are there to block the holes left by the casting process. That makes sense. But then it is some peoples theory that the core plug is used to stop the block cracking or becoming damaged under high pressures or freezing coolant as they are designed to be the 1st things to five. On some sites this is really disputed.

Any PH'ers have any comments?

Thanks,

Jason.

[omitchell]

in old tractors they used to be used for when coolant was just water so if it froze, the theory went it pushed the plugs out to stop the blocks from cracking so they may be just a failsafe now incase a numpty just uses water for coolant

[GreenV8S]

I believe the holes are created as a by-product of the sand casting method - the inner and outer moulds are connected together by plugs which leave these holes when the moulds are removed.

They do form a weak point. I don't know whether they are sufficient to prevent the block from cracking when the coolant freezes - given the complicated shape of the water jacket I doubt it. They certainly shouldn't push out under the sort of pressure the cooling system will reach - the hoses will split and the radiator burst long before a properly fitted core plug will move. My feeling is the plugs are there because the manufacturing method leaves the holes which then have to be plugged, any other benefit from having this wek spot is incidental.

[RichB]

I certainly had a core plug come out of the block on my old 1955 MG Magnette which ran a 1498 cc BMC B Series engine. There were 3 spaced along one side of the block and another at the rear. I simply bought another and hammered it in with the ball end of a suitable hammer. Rich...

[love machine]

I thought that the cores were held in place by bits of steel, hence in a cast block, overboring can strike a shiny bit of metal. I'll tell you what they ARE for. Getting the sand out of the core afterwards and cleaning. In lost wax and foam, there is still sand residue which needs to be got rid of. You need to seal them and they need to be big, hence purposefully made holes.

There ya go. Stu

>> Edited by love machine on Tuesday 25th January 15:11

[Boosted LS1]

When you cast cooling passages in the block or heads you insert solid cores made of sand & resin. These rods project out of the side of the block. Then you pour in the iron around them and let the block set and cool. You need to get the sand out so it comes out the block where the plugs are later installed. Also, take a look at some blocks near the tops of the liners. Often there are holes around the liners. Again, these let sand out of the block. They are nothing to do with cooling and should be covered by the gasket.

So, I submit that core plugs are there to let the sand out and a spin off is that they can save your engine if the water freezes and expands.

Boosted.

[steve_D]

Boosted LS1 said:

......So, I submit that core plugs are there to let the sand out and a spin off is that they can save your engine if the water freezes and expands. Boosted.

That's the way i've always known it.

Steve

[andy_ash]

Aren't core plugs that central cache of 13A fused thingys that everybody seems to have under their kitchen sink?

[bga]

[quote=GreenV8S

They do form a weak point. I don't know whether they are sufficient to prevent the block from cracking when the coolant freezes - given the complicated shape of the water jacket I doubt it. They certainly shouldn't push out under the sort of pressure the cooling system will reach - the hoses will split and the radiator burst long before a properly fitted core plug will move.
[/quote]

A numpty mate of mine forgot to add antifreeze to the coolant in his Astra. Core plug came out. Garage said that's what they are there for - something to do with there beign a greater volume of water at that point and therefore greater expansion on freezing than in rad or pipes.

[sheepy]

[redacted]

[chris1roll]

Theres a core plug in the end of the aluminium inlet manifold on the 480, so thats not there to prevent it cracking. I think its just a necessity of the csting process.

[wheeljack888]

I apologise for getting all techie again, but I was one of three designers who have recently designed a brand new volume 'clean sheet' cylinder block.

Very simply the core plugs are there to plug the casting holes. The casting holes are there because the internal cores like the water jacket don't touch the floor, but they still need supporting in the casting box. Those support legs grown from these internal cores fit together with the external cores when the box is built up, leaving holes in the casting.

We tried to minimise the amount of core plugs because they are a failure mode, they are extra machining and they are an extra assembly process. One can try a reduce them to the number of plugs to a minimum by trying to make those support legs part of the casting feature, for example a coolant inlet passage to the coolant pump.

As boosted said you do need to get the sand out aswell, but those passages to the water jacket on the flamedeck of the cyl block can also provide coolant to the cylinder heads.

[Boosted LS1]

wheeljack888 said:

As boosted said you do need to get the sand out aswell, but those passages to the water jacket on the flamedeck of the cyl block can also provide coolant to the cylinder heads.

But you don't really want coolant flowing up from the cylinders otherwise the fronts would run cool and the rears very hot. Coolant should flow to the rear of the block and then go up to the heads to travel forwards again. I notice that a lot of gaskets obstruct the passages around the cylinders. Mind you, I suppose they offer an option for tuning if need be

Boosted

[wheeljack888]

The gasket will block most of the holes off but if the water jacket in the block is fed from the front then the largest holes in the gasket will be at the rear to make sure that the rear cylinder get their fair share of coolant flow. When I designed the gasket we did a 3D Computational Fluid Dynamics of the water jackets in the block and head and tuned the hole sizes to provide the distribution and correct flow rate at all points. Can't have stagnation because it will boil and can't have too faster flow otherwise you may start eroding the passages (esp in aluminium) The most critical (or hottest) points to cool are the top ring-reversal and around the exhaust port.

[bga]

wheeljack888 said:

Very simply the core plugs are there to plug the casting holes.

My mate will be pleased to know they were talking rubbish then.

[Boosted LS1]

wheeljack888 said:

The gasket will block most of the holes off but if the water jacket in the block is fed from the front then the largest holes in the gasket will be at the rear to make sure that the rear cylinder get their fair share of coolant flow. When I designed the gasket we did a 3D Computational Fluid Dynamics of the water jackets in the block and head and tuned the hole sizes to provide the distribution and correct flow rate at all points. Can't have stagnation because it will boil and can't have too faster flow otherwise you may start eroding the passages (esp in aluminium) The most critical (or hottest) points to cool are the top ring-reversal and around the exhaust port.

Sounds good to me

Boosted.

[jesprit]

Thanks Gentlemen. The conclusion here ties in beautifully with a letter from Lotus on this matter. That is that they are there to fill the holes left from the casting process. They made no mention of the coolant expansion situation.

They did however say that too strong engine coolant is just as bad a too weak as far as corrosion is concerned. Something I was not aware of.

Thank you to everybody that replied.

Jason.