MG Car Repair: Coolant Leak into #2 cylinder on 1275 MG midget, coolant leak, machining manufacturing

Question

Picture of 1275 head   A while ago, you were advising someone on how to find and fix a coolant leak on their MGB.  Youa sked if the coolant leak was between the #2 and #3 cylinder on the spark plug side.  That gentleman did not have that problem, but I do.  My #2 cylinder keeps filling with coolant as the car sits.  History:  I over heated a worn out head.  I pulled it off and put on a used, rebuilt head (that I bought off a guy who builds sprite motors in his spare time (has five of them in his garage).  Everything checked straight and I noted no discrepancies on the cylinder block or the head except for one.  On the head there are five  plugs in the head.  There are four brass plugs on the corners of the head plus one more on the spark plug side between #2 and #3 cylinder.  I can't tell the material for the #2 and #3 cylinder.  The four corner plugs are flush with the surface of the head.  Two of them are drilled out to let fluid pass from the head to the block.  The other two are solid.  Like I said, they are all flush and smooth to the head from the latest mill surfacing job.  BUT, the plug between #2 and #3 is not flush.  It is about 1/32" below the surface of the head.  When I pulled the head, there was coolant in that area and appeared to leave a small rust trail from there down the cylinder wall of #2.  Questions are:
1. Is that a plug leading to the coolant passages (a drill passage used in machining/manufacturing of the head?
2. Does the fact that it is not flush indicate that it is loose or has moved?  
3.  Does it have to be flush?
4. Do I fill it with something such as Silver Solder and machine it smooth (can do that at home) or take it in to have the plug drilled out and a new one put in, then have the head resurfaced?
5. Can I just have the machine shop remove another 1/32 material off the head?  I currently have no preignition problems and compression test show 105-115 dry and 115-120 wet so I might be able to accept the higher compression of taking more off the head.  

Thanks,
Jim

Answer
Hi Jim,

I would lay your head gasket on the head and note if the metal ring around the cylinder is close to this depression area. If it is just close but NOT over the depression, you could use a filler of some kind to fill the depression so that the gasket soft material has something to press against. Silver solder or something like Devcon would work but if the metal ring goes over the depression I doubt it will work as combustion temperature would melt silver solder.

Another problem. Your compression readings are too low, either you didn't open the throttle when running the tests or your gauge is faulty. I ran compression tests on many 1275 Austin engines in Midgets, Sprites, Mini-Coopers and I always expected to see from 135 to 165 PSI on the dry test. Are your pistons flat top or do they have a depression in the center?

If I were you and the cylinder metal ring on the head gasket came in contact with that depression, I would take the head to a auto machine shop a have them correct it with a plug of some kind. Don't forget to use a straight edge on the block near that area to be sure you don't have a warp in the block in that area due to the overheating.

If the depression is only in contact with the soft material of the head gasket and the metal ring is not in contact with the depression you could just use silver solder or Devcon to fill it in and surface it with a flat steel plate with sand paper or use a thick plate of glass with valve lapping compound to be sure it is flat surfaced.

It would probably be quicker and almost as cheap to just hand it to a machine shop and say "Fix It". A 32nd is almost to much to remove from a head mainly due to an up set in the geometry of the rockers.

Howard