Heads, core plugs, overheating etc. What's happening?

[dasadrew]

The white/blue Bavarian Stag has been completed, so to speak, since about a year but hasn't been totally trouble free. To be honest, it's not been all bad and the real taxing issues have been centred on the engine cooling. There were several incidents which could even merit their own thread but which have hopefully been sorted now:

- the first runs out were plagued by some pretty hefty overheating which I finally traced to the "new, refurbished" water pump which didn't seem to be doing anything. I then acquired an NOS BL pump and that cured the circulation issue. (The overhauled pump had an impellor fitted which, according to the part number, is a Dolomite one. Impellors are often sold as being suitable for TR7/Stag/Dolomite but experience has shown that there are dramatic dimension differences even if they look more or less the same)

- the next runs out still saw me losing some water and, when the filler neck on the "new refurbished" radiator came off in me hands I took the radiator to a specialist who also diagnosed microleaks from the entire matrix where waater had been escaping. A new 'outright' remanufactured rad went in and that sorted the gradual water loss.

- temperature was still on the high side in summer so fitted a Revotec and that did its job in queues in town at 30°C outside temperature. Then discovered that the take-off in the RH transfer housing for the capillary gauge runs about 5°C hotter than the original LH take off point so became less concerned about the needle being a bit on the "H" side of the "N"!

Now comes the Armageddon bit where I'd welcome all suggestions, comments, ideas or soothing words!......

Going out on a longer run in hot summer all hell breaks loose.... car enveloped in its own steam, overtemperature buzzer screeching .... Pulled in rather sharpish and eventually discovered that a core plug had popped out of the LH cylinder head!!! Let everything cool down, got a bucket of water from a local farm and limped home in very short soft bursts with continuous topping up and cooling off. Fortunately I was only a mile or so away from home.

Over the next week or so I managed to remove enough components to be able to get a new core plug in, reassembled all, and off we went again in very close circular routes around the house. All's well, temperature ok now that the hot summer had gone, no water loss and eveything hunky-dory tickety boo. (small carb flooding incident but unrelated to the above and quickly solved).

On one of these exploratory trips can you believe it? The second core plug popped out of the LH cylinder head. Fortunately this time I could more or less coast home to the garage.

The car is now in the freezing garage with heads, water pump etc. all off, stripped down, cleaned, inspected and all the rest. I have noticed that the alloy heads and attaching bits don't seem to be as forgiving as the old iron Pinto bits I'm more accustomed too with respect to gaskets (e.g. on water transfer housings) sitting and fitting 100% and I noticed that most bolts could have done with being nipped up a bit. I'm certainly going about this re-assembly a lot more meticuously than the first time round and being particularly sensitive when I see any alloy porosity on a sealing surface.

The bottom line is that I can't for the life of me work out why I lost two core plugs on one cylinder head. Albeit in iron engines, they've not exactly been the first core plugs I've fitted. I did use a smear of Hylomar which I could maybe suspect as having got overheated and started acting more like a lubricant than a sealant, but why suddenly just on the LH head? And what sort of pressure would be needed to blow out core plugs??!!!

I've inspected the Payen head gaskets and they both look perfect with no signs of leaking or blowing anywhere. Thermostat has been in a hot water bath and opens and closes as it should. Head and block surfaces look perfect and straight. A steel ruler check with my thinnest feeler gauge (5 thou) showed no warping. (The heads had been treated to a very light facing skim before assembly).

Any ideas folks??

Drew

[72BLUE]

I have no recent experience of fitting core plugs, but think that they would only 'pop' if they were a poor fit (ie under-size), incorrectly fitted or way too much internal water pressure that forces them out? What else could it be?

What about checking the diameters involved? Are the core plugs a tad undersized, another case of poorly made parts? I would also do some research about the use of Hylomar.

Cheers
Keith

[Motorsport Micky]

I fear the Hylomar prevented "metal on metall" compression which is what you need for holding back the water pump pressure, fit them dry and then a light smear of epoxy resin into the join just to prevent any weeping. After a short time the crap which always circulates in the water will seal it anyway.

Micky

[alan_thomas]

I agree they must be undersized. The rad cap would have let go at 18 or 20 psi and any core plug should laugh at the sort of pressure. I always refit core plugs with a smear of Hylomar as I believe it fills in any minor scoring on the plug or the hole, never had one pop out. Were they a good hammer fit in? They were all imperial sized? - Alan

[dasadrew]

I must admit that I also rather hope that it was a core plug fit problem. When the first one popped out, my first thought was "I've bodged the core plugs and not stuffed them in tight enough!. So I checked the second plug and it was certainly hammered in but, on reflection, the rim was almost flush with the cylinder head surface.

I also feared a size problem and ordered up different core plug sizes from different sources and also in metric to see if another size would fit, but no other size was "just a bit tighter".

Another factor is that there are two schools of thought on banging them in: a) with a mandrel in the plug which fits snugly but not so snugly that it will be trapped and b) a mandrel which sits on the rim of the plug, the idea being that method a) will cause the plug to decrease in diameter a bit as it sort of collapses on the mandrel.

So, I've now cleaned up the head holes so they're squeaky clean with no burrs etc., made mandrels which sit in the plug but which work by pressing on the rim, I've smeared them with Loctite 648 which is a sealant/adhesive for press fit cylindrical metal parts, and I've hammered them in so they are just a midge further in than the head surface.

Maybe I just didn't hammer them in far enough, or they got pinched up because I used a mandrel in the centre of the plug?

Thanks for the ideas and clues guys.

Drew

[mole42]

AFAIR core plugs are made with the centre domed. When you tap the plug in using an old socket of suitable size to push on the edges, the plug will seat on the hole bottom lip. You then tap the centre of the plug to push the dome in which expands the bottom edge into tighter contact with the hole.

It’s been a few years since I last rebuilt an engine so my memory may be awry.

Richard

[dasadrew]

Not sure I understand that one Richard. The core plugs I've known in the past were indeed slightly domed, but you would need to be inside the engine block to be able to hit that dome to make it spread. Or do you mean they were domed outwards toward the outside of the block? In any case, all the core plugs I managed to gather for the Stag were absolutely flat, which was new to me.

Drew

[marshman]

AFAIR core plugs are made with the centre domed. When you tap the plug in using an old socket of suitable size to push on the edges, the plug will seat on the hole bottom lip. You then tap the centre of the plug to push the dome in which expands the bottom edge into tighter contact with the hole.

It’s been a few years since I last rebuilt an engine so my memory may be awry.

Richard

Richard you are correct BUT you are thinking of the domed type of core plug. The ones in the Stag cylinder heads are the cup type. I have mainly seen the domed type in older cast iron heads and blocks and as you say they rest against a lip and are inserted with the dome sticking outwards. When in place you knock the centre dome in which expands the circumference giving a tight fit. The cup ones do not expand and are essentially just a press fit ion the hole, I have seen these mostly in more modern (post 1960's) aluminium blocks and heads, though I have seen them in cast iron as well.

Back to Drews problem. Core plugs "popping" out is not unheard of on the Stag head. Several have posted on the issue over the years. I think some of the issue may be the fact the heads are old and will possibly have been rebuilt several times with the plugs being replaced at the same time. This can/will inevitably damage the soft"ish" aluminium of the head making the new core plug fit less tightly.

For what it is worth I think blue Hylomar is more likely to act as a lubricant and aid the exit of the plug. I prefer to use something that bonds and seals, such as an RTV instant gasket type sealant, most types actually bond to the metal surface. The Loctite sounds as if it will do the same job. I have always just gently tapped them in place with my trusty 1lb ball pein hammer, tapping evenly around the edge, keeping the plug level/square, until the edge is flush with the surface. ( I did replace the ones on my car in situ by pressing them in with a crowbar - there is a thread with pics somewhere).

Worth remembering the Stag cooling system can has a 20lb pressure cap so at approximately 1 inch area there can be up to 20lb pressing on the polug, coupled with a slightly worn hole and constant differential expansion between the steel plug and ali head it is not altogether surprising that the break free sometimes.

Roger

[Phil S]

I have always used a smear of hylomar as this was the ford way.
but the ford issue core plug tools bottom on the recess of the core plug and had a lip to give the correct depth of fit, like a small top hat. This allowed a fit, but caused no distortion on the outer sealing face.
Phil

[dasadrew]

Roger, you've ended my sleepless nights - thanks! It all sounds logical. Regarding the 20 psi, in the 70's there was a story going around from when a BAC Canberra was undergoing a cockpit pressure test in the hangar. After the test had finished, the mecahnic waited until the presuure had dropped so far on the scale that the needle was more or less on the stops, then drew the net back and cracked open the crew entry hatch. There must have been a small bit of residual pressure left, because the hatch (about 20" x 60" = 1200 square inches!!!) opened rather more quickly than the mechanic had thought it would!

I now kow what other core plugs were meant - I think the Stag has some of those curved discs in the gearbox area IIRC.

I've taken so much care now - much more than the first time round - and have discovered other nasties as well. The RH rear cylinder head area seems often to be cited as a weak link and I've seen some evidence of that too. Going in and up from the removed transfer housing area with a couple of dentist's tools, I extracted some primaeval goo with swarf in it. Also, there is a slot which drains down from the camshaft rear bearing area into the transfer housing chamber. It seems that this oval-ish slot is made by drilling holes and then filing them to make a slot. This was the case on the LH head but on the RH head only three drilled holes, not even deburred, so I think that was the source of the bits of swarf which seemed to have sat there since 1974. I fear I might have disturbed some of that crud during the resto as the rear two tappets have a few micro scores on their surface.

[DJT]

DSCF2815.JPGP1000293.JPG Whilst you are there, Drew, make sure the bleed holes in the inlet manifold and heads are clear. These are the ones that allow the system to be filled without getting an air lock. They are often blocked. I suspect you may have attended to this first time around, but worth checking whilst it is all apart.

[dasadrew]

Yep, I'm making sure everything is squeaky clean, but I can't have too many hints, tips and reminders! I'd never actually understood their purpose until now!

Cheers

Drew

[marshman]

I think that was the source of the bits of swarf which seemed to have sat there since 1974. I fear I might have disturbed some of that crud during the resto as the rear two tappets have a few micro scores on their surface.

You mention scores on the rear tappets possibly caused by some swarf debris. Just double check that some is not still embedded in the head itself. Although the head is "soft" aluminium steel can get embedded in the surface easily, this then wears the steel tappet/cam bucket surfaces - this can be a bit mystifying as you think how can the relatively soft aluminium wear the harder steel part.

Oh and one last thing, don't forget to check the core plug in the underside of the inlet manifold.


Enjoy your sleep tonight

Roger

[dasadrew]

Roger Roger!

[edd]

I always use loctite on core plugs and always installed by the means your now using on the exterior lip.
I had access to a hot wash whilst restoring my engine. It was like a dishwasher but for engines. People at the shop laughed at me washing the heads about 10 times at intervals of various stages blowing out every hole.
This heated wash really does shift stubborn debris much better than a parafin tank.
I also joined my rear transfer housing with a mod not proven but I liked the idea I also have two separate inline bleeding valves I have added partly due to me running a belt driven pump but they make bleeding so easy
I like to use REINZOSIL for fitting my inlet manifold
Good luck Drew
Edd