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MG Midget and Sprite Technical - loose oil hole plug

I need a little help from the machinists in the crowd to fix the last oil leak on my midget.

My 1967 1275 with a stock cast iron head (12G938) is leaking from the little plug in the cut-out section on the front face of the head, just left (toward the driver's side) of the thermostat housing.

Does anyone know how to fix this leak? The British Leyland manual notes a plug in the line drawing, but the text says nothing about whether it's pressed in, brazed, inserted with cement... anyone have experience refitting these plugs? I just had hardened seats put in, so I'm hoping this can be done without R&Ring the head again.

Thanks!
JM Young

The plug is just pressed (hammered!) in. It may be tapered to start with, but I never saw a new one. I cannot recall if there is a step which stops it going in any further. If so, you may be able to tighten it by smacking it with a punch, but that will certainly make it harder to remove, which will be necessary if it goes in too far or continues to leak. You may be able to drill and tap the plug for a small machine screw as a puller, since it is evidently loose. Otherwise, the usual procedure is to drill and tap for a threaded plug, with sealant.
You might contact somebody who modifies these heads, since they routinely extract the plugs for race prep. Try Peter Burgess or MGExperience> Motorsports BBS.
That oil feed has minimal pressure, assuming the rocker pillars are correctly fit with the drilled one in front, and the rocker shaft is assembled correctly.

FRM
FR Millmore

Thanks very much. I will try emailing Peter before trying your suggested method of removal. My only concern, I guess, is getting metal shavings in the hole while tapping it--though I suppose I could simply fire it up and let the oil pressure flush them onto a rag...?

Joel.
JM Young

Some years ago we had a leak on an MGB block - oil gallery bung - as FRM noted, I drilled through it (brass) - using a hand drill with drill bit in grease - changed the grease quite a few times and caught the swarf.

Then ran a tap in (again in grease) - used a bolt with a spacer socket/washer and used it as a puller to get the plug out.

Couldn't get the correct bung so machined up a soft brass bung with a very small taper (few thous) and drifted it in.

R.
richard boobier

it looks like (please note I only said "LOOKS") the Metro only has a big Pop-rivet in the hole I THINK you are talking about to blank it off.

I s'spect I have it all wrong though here :-)
Bill 1

Bill - yes, I believe the Metro head is different in that regard, if it uses a rivet. I've since checked the Moss website, and they do list the plug, so I ordered a handful.

I think at issue is merely: (a) how to get the existing plug out without damaging the orifice; and (b) if that's not possible, how to reseal the hole. Looks like the preferred method in the latter instance would be Mr. Millmore's standard suggestion of drilling and tapping for a threaded plug.

Now that I think about it, Richard's suggestion--slightly altered--would make sense in that regard. That is, if I wanted to avoid metal shavings getting into the oil passage without removing the head, I suppose I could inject some engine assembly lube into the hole. Then, drill and tap, place a rag and jar (or clear vinyl tubing leading to a jar) under the hole, and fire the engine briefly to flush the lube and shavings trapped therein.

Of course, what I'm hoping is that the existing plug--which sounds like it may be brass--comes out cleanly, and that I'll simply be able to drift the new one in.

That said: Richard and Mr. Millmore, does one use any sort of cement or non-hardening sealant on a tapered brass plug like this? (No reply as of yet from Peter B.)

P.S. - Thanks in part to the generous advice from members on this bulletin board over the past 2 years, my Midget is now a completely sorted, daily driver statewide around New Mexico:

- Original 12CC (high compression) engine with new seals and hardened exhaust seats, purportedly with 69K on the clock;
- pertronix pointless distributor and Lucas 'sports' coil;
- Custom aluminum cold air intake (channeled through the driver's side fender) utilizing K&N panel filter and MED Engineering aluminum billet stub stacks;
- Speedwell aluminum radiator w/thermo-controlled 11" Spal puller and 5" pusher blowing on manifold (original radiator for sale, great shape);
- Rivergate 5-speed conversion and late model 3.9:1 rear end (original ribcase for sale - shifts great);
- Disc wheel conversion with tapered wheel bearings up front, and 13x5" aluminum minators (original rear axle and wire wheels available for a song);
- Late model, dual circuit master cylinder and ventilated discs;
- Frontline tubular shocks fore and aft with shortened, stiffer springs up front (levers looking for a home, too);
- Late model alternator with junction strip supplanting old regulator box;
- Hella Vision Plus headlights on relays, dimmer switch moved to under-dash toggle for *dramatically* improved left leg room (I'm 6'3").
JM Young

Plug is brass.
With new plug in hand, you can see how long it is, and maybe not drill all the way through - no chips down the hole.
Tap and pull with machine screw. Use a long thread screw with a spacer, washer, nut. Turn the nut to pull.
If not, drill just to the end of the plug, remove chips. Drill through with greased drill as Richard said. Go JUST through. Tap, again JUST through with greased tap.
If you have to tap the hole, same deal; minimal depth with greased tap.
Starting the engine to flush is fine.
Then degrease,fit brass taper plug dry or with a wipe of Loctite; screwed p[lug with Loctite or Permatex #2. NO damned Silicone/RTV!

Underdash toggle sounds awful for dipper - hate moving my hands to dip! Hate it even more when opposing driver is slow at it!!

FRM (Fletcher)
Like to see your CAI arrangement.
FR Millmore

Fletcher,

Thanks. I called Moss, and they sent me what looks like a miniature freeze plug--kind of like those that fit inside the ends of the rocker shaft, only perhaps 10~11mm O.D. The plug I need appears to be half that size.

So: I'll remove the thing per your and Richard's suggestions, then check with the local machinist who did the hardened seats on my head. Perhaps he has a source for hard-to-find bits like these. Failing that, I'll have to turn one from brass rod as Richard did, or tap for a threaded plug. That might be more secure and, of course, easily resealed in the middle of nowhere (much of NM) some dark evening.

Thanks again for your help.

BTW - I have the CAI off (didn't put it back on after R&Ring the head, as I was too eager to try her out). I'm under the knife tomorrow, so this weekend's out. When I get her reinstalled, I'll start a thread with pictures called "Cold air intake for 1275 Midget."
JM Young

Yea verily, they is a bunch a idjuts!
Did they charge you?

As stated, there is near zero pressure behind that plug. The feed is intermittent from the cam, and there are lots of holes to let the pressure out at the rockers. You ARE getting oil at the rockers?

Should be near possible to seal with chewing gum.

For kicks, I went and found a head. The plug stands proud of the surface a bit, and was mashed over to an erratic 5/16" dia. Filed it flush, and the hole is .250". I center punched it and it moved in a bit.


OK, took out plug. Drill #29 for 8-32 tap/screw'
Plug is only .250 long, including what I filed off. Intersecting oil passage is only about .375 below head face, so be careful on depth. There is NOT a step/stop. Plug diameter appears to be .250 small end, .260 large end.
OR:
To install a threaded plug, tap for 5/16" allen setscrew, only about 4 threads deep, use sealant, sparingly and only on the screw so you do not get it in the oilway. (tap drill for 5/16-18 UNC is 1/4", so you do not need to drill)(you will need to use a bottoming tap for this short thread)

(If drilling in situ, note that the hole axis is horizontal but NOT parallel to the engine! Hole axis aligns to the midpoint between the two studs in #1 rocker pillar)

I will be out for my brew sometime!

FRM
FR Millmore

Add this:
I expect the reason for the leak is that they neglected to break the sharp edge of the hole before driving the plug in. This would tend to shave off the side of the plug. Break the edge with a pocketknife. You are looking for a 60-75 degree entry angle, but it does not need to be exact and only very small - the sharp edge.

FRM
FR Millmore

And (woke up on the middle of the night with this):
Use WD40 or similar, insert plastic pipe all the way to the back of the passage to flush chips out.
The passage from the block comes in at about a 45 from the bottom, and chips will certainly fall down this. After you clean the horizontal passage, start the engine and oil should flush the chips out of the up passage. This is pointed out the hole, so any chips ought to come out without reversing into the horizontal passage.

FRM
FR Millmore

Fletcher,

Yeah, they charged me, and the 'tech' department did not call me back when I left a message (guess we shade tree mechanics keep 'em busy). That said, the salesperson was very nice about apologizing for sending me what, for all the world, looks like a teensy freeze plug. If only I smoked, I could use them for tiny ashtrays or something..

Man... you SHOULD come out for a brew. For all the work you did, I'll have the wife cook up a pot of green chili chicken stew, to boot. You might combine the trip with the international balloon fiesta. Goggle that phrase w/Albuquerque. A nice alternative would be cruising the Midget down to the Bosque del Apache to see the wintering cranes and Canada geese. We've gotta get the U.S. Midget drivers to do a Route 66, Rio Grande run.

Anyway, I wish I'd have read your last three posts before now, though it's possible I haven't hurt anything. Thinking I should try one last thing this morning before yanking the plug, I took a 1/4" drift and gave the thing a light, crisp rap. What happened precisely jibes with your excellent workup. The thing moved in slightly, so (not thinking about the possibility of a passage that bloody close to the orifice) I tapped it again. A little fringed ring formed around the circumference, and when I tapped a third time, the ring fell cleanly off.

Obviously, the sharp edge you've talked about sliced off the final few thousands of the broad end of the taper, forming a little doughnut. The outer end of the plug is *just* below the surface, so given your measurements, I should have .125" of clearance before the passage. At any rate, I put her in the wind and drove ~ 20 miles at 75-80 mph (5 speed, so 4,000 rpm). Nary a drop. The girl is finally oil tight!

So - last question. To tell whether I pinched off that passage, do I just lift the valve cover and see if things are still nice and oily? When I was a kid, I remember watching a mechanic adjust some sort of straight 8 or 6 with the valve cover off--running, I mean--and the oil just kind of gurgled out. Will a Midget squirt all over the place?

Joel.
JM Young

Joel-
Glad you are fixed.
Rocker feed should be OK, You can check with cover off, should drip off rockers at idle, but cover windscreen, as the fan blows oil mist back and ruins your wiper blades! Not much oil and it wipes off everything else.
They used to sell "oil deflectors" which clipped onto the rockers for running valve adjustments (still had to cover WS); standard kit of any 6cyl Chev mechanic.

Have a friend in High Rolls, and asst. relatives I haven't seen in 50 years from there to LA.

Q is, what are Moss selling that isn't right and doesn't fit too? I can understand parts that don't work, don't fit correct;y etc., but parts that have nothing to do with the car are puzzlements.

FRM
FR Millmore

Fletcher,

I'll just take off the yeller plastic fan while I try the dribbling idle rocker test. Sounds like it'll just take a glance, and I should be done before the Spal kicks on.

Whenever I find the little baggie with the so-called oil gallery plugs, I'll see if I can figure out how to shrink down a .jpeg enough to get a shot of one of the elfin things posted on this string.

High Rolls... even with my far-flung, cop-defending excursions around the state, I have never stopped there. Haven't been to L.A. since I bought a 1973 XJ6 (one owner) for $2,500 bucks and drove it back a decade ago. Should never have sold that thing. Yup, I can feel some sort of Midget convoy starting to take shape...
JM Young

J-
Should be obvious just by taking the oil cap off whilst running.
You sure those plugs are not in fact the ones for the rocker shaft?

FRM
FR Millmore

Fletcher,

Good idea; I'll just give a look this evening when I get home.

As to what I received versus what I need, Moss DID call me back just five minutes ago(feeling belatedly sorry for bad-mouthing them), and explained that the on-line diagram is all buggered up. What I received is (I am now told) a smallish freeze plug that goes in the back of the head. What I need is *not* listed on the cylinder head diagram at all, but rather appears on the cylinder block's page: 114-000 is a 1/4" brass plug, said the tech gent who called me back. I ordered two of the five they have in stock, together with a couple of upgraded thermo gaskets (you can't order < $10). These will go into my in-trunk took kit, along with a 1/4" drift and pocket knife to break the edges of the hole.

I don't know if they'll update their website, however, so 1275 Midget owners with a 12G938 head, be advised! I'll post again only if the thing *still* turns out to be wrong. Silence will mean that this part no. is good!

JMY
JM Young

This thread was discussed between 29/10/2011 and 07/11/2011

MG Midget and Sprite Technical index

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