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Core plug straps.


dazzer

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I seem to be doing several jobs at once at the moment and this maybe a long shot but has anyone fitted core plug straps to the early MK1 engines? These are the D shape welch plugs which you firmly hit with a flat drift to expand them into place.

Specifically the four core plugs behind the exhaust manifold on the block. I'm trying to gauge how deep I can safely drill and tap the block on the shoulder of the casting apertures.

Why? I hear you say...

Well two years ago before I had started the rebuild I gave the original engine a good working out on a track to see what it could do, fine, until on the way home, steam everywhere and the very centre core plug under the manifold dropped out.

So I replaced all four welch plugs. Once again out on the track, fine, until about a month later I noticed water on the garage floor, yes you've guessed it the front core plug was starting to move out of position!

I therefore had the engine rebuilt by a "specialist" and new core plugs were fitted. When it returned I also smeared some metaloy around the core plugs. On giving the car a workout last week, I've developed a water leak and its the centre core plug starting to move out of the block, metaloy and all!

Most people seem to have had no problem at all, although I picked up a number of threads where competition racers have lost the very same core plugs.

So would anyone know how much material is behind the shoulder of the casting holes before it hits a water jacket or similar.

I'm standing drill in hand ready to go.

Cheers

Darren


  

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Maybe your engines have the later cup shaped core plugs Tim?   I must admit I have never come accross that myself either though.  The only core plugs that I have sometimes struggled to seal are the dished penny type either side of the distributor on the Mk3 Spit.

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570 wrote:
I seem to be doing several jobs at once at the moment and this maybe a long shot but has anyone fitted core plug straps to the early MK1 engines? These are the D shape welch plugs which you firmly hit with a flat drift to expand them into place.


So which type of plugs are used on your engine? If it's an early Mk1, it would surely have the shallow saucer shaped plugs, rather than the dished ones I visualised from your description. Is it possible you have the wrong type of plugs for the application?

Cheers,
Bill.

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heraldcoupe wrote:


So which type of plugs are used on your engine? If it's an early Mk1, it would surely have the shallow saucer shaped plugs, rather than the dished ones I visualised from your description. Is it possible you have the wrong type of plugs for the application?

Cheers,
Bill.


Surely it is not possible to fit the wrong core plugs.
The shallow saucer ones go into a hole with a ridge to hammer against, the dished ones go into a plain hole with no ridge to stop it pushing through into the water jacket.

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Sounds like it could be typical behaviour on engines that are worked very hard - possible due to the block flexing slightly and causing the plugs to "walk" out due to their narrow line on contact with the block.

I don't like those old style core plugs - had one come out on my 1200 - the one on the back of the block, just above the bellhousing.  That filled the car up with hot water and steam almost instantly due to ill fitting tunnel cover.  Two bits of good news on that occasion were that my feet weren't scalded and I was only a mile from home (at end of 120 mile run!)

Is there enough depth in front of the plugs to allow a small hole to be drilled transversely into the core plug bore that could take a small roll pin or similar?

Nick

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Hi Guys

These are the D shaped washers (welch plugs) which you need to hit with a flat drift to expand them into position, not the later much more effective deep pan type core plugs which never seem to come out.

Interestingly i've discovered that a kit is offered for early Austin Healeys with these same type plugs, for racing applications. I'm sure it must be the block flexing or vibration that causes the problem.

Today I test drilled the block, much easier than I had anticipated, I then tapped the hole to M5. My initial drilling was approx 5mm deep (at its thinnest point the block on the shoulder of the casting hole is about 12mm deep before i'd puncture the water jacket). I'm going to go a little deeper tomorrow probably 8mm) maybe 7/8 turns on a M5 bolt.

I'll take pictures in case anybody else has the same problem in the future.

I'll seal the plug and threads with HD thread lock and a spring washer for a full belt and braces job.

Cheers

Darren

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570 wrote:
Specifically the four core plugs behind the exhaust manifold on the block. I'm trying to gauge how deep I can safely drill and tap the block on the shoulder of the casting apertures.


Dazzer,
If the plug has fallen out, you are already into the water jacket.   Easy to put your finger, or even a gauge, into the hole and measure the thickness of the block there.#

In the US, brass core plugs are common, rather than our routine steel ones.    This has a logical base as the coefficient of thermal epansion of brass is nearly twice that of iron.   So the hotter it gets the tighter the plug fits!
Might be worth a try?

JOhn

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Hi John

Thanks for the tip, I'll see if I can get hold of any brass core plugs. I gauged the 12mm thickness by doing as you describe, its quite undulating in there with the castings etc, but I feel fairly confident 8mm is safe.

Cheers

Darren

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Hi Alex

spookily I did contemplate exactly what you're suggesting, I was swayed to do individual ones because thats how the similar kits for Healeys are produced and I wasnt confident enough to reinvent the wheel so to speak.

PS I now think I've read somewhere that the MK1 heater will slide out from the side when the fans removed. It'll be tight and a bit sticky with the two seals(one base one on the bulkhead holding it back.) You can make new ones foam high density foam or similar and stick them in place with contact adhesive (evo stick)

Cheers

Darren

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Alex wrote:
I'd obviously wrongly assumed you were talking about one strap all the way across with intermitent fixings......any reason why you've done it this way?
Would what I'd invisaged not be viable?

Alex


If it were one long strap you'd have to remove the whole thing to replace one plug?

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The long strap would still need to be fixed to the block each side of the core plug, so the intervening strap would be redundant.
If you 'saw' a solid bar, fixed at each end, not rigid enough, unless massive, adding weight.
"How do you get your cars to win, Mr.[colin] Chapman?"
"Just add lightness"

John

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