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MG MGA - Head Gasket or ??????

Hello All,
While driving at about 67 mph in hot weather on the freeway. I noticed hot oil fumes coming into the cockpit. Looking back in the mirror we couldn't see any smoke. The oil pressure was good showing about 60 lbs, RPM was about 4 K, with the temperature gauge showing about 205F.
My buddies behind me said the smoke was coming from under the car and the engine area, not from the tailpipe. When I popped the hood I could see the oil was coming from the breather cap and and running down the back of the engine. I also noticed the breather pipe leading from the tappet inspection plate was also venting a lot of crankcase pressure. Resulting in pushing oil out of the crankcase and getting on the exhaust system, causing all the smoke.
When I got home I pulled the spark plugs and noticed number 1 spark plug was pretty clean. The ground electrode was somewhat white as it has been in the past. Number 2 showed a little black soot. Number 3 and 4 showed were very black. The black soot on 2, 3 and 4 plugs looked to be caused from a rich gasoline mixture, not from oil consumption.
I further checked the compression. Number one cylinder was about 61 psi, the other four were between 155 and 165 psi.

I am hoping it is blown head gasket on number one, pressurizing the oil drain passage in the head AND not a broken compression ring in number one.

What are your thoughts?

Ray
Ray Ammeter

Ray,
I think that if you had a broken compression ring, you would have a black (oily black) plug on cylinder #1. It does sound as if you might have a blown head gasket. If you would like to check without pulling the head, you can use air pressure as follows:
1. Remove the radiator cap.
2. Screw a fitting into the #1 spark plug hole, and apply air from an air compressor into the cylinder.
3. see if you have bubbles or water flowing out of the radiator, or whether you have air hissing from the crankcase oil fill.
NOte that you probably will have some air hissing from the oil fill regardless of the problem, but you should not have anything going on from the radiator end if your head gasket is good.

Good luck.
mike parker

Ray. Just to confuse things, I think the head gasket would not cause such a problem by itself. Normal mode of head gasket failure is between cylinders and is demonstrated by a compression test showing low pressure in two, adjacent cylinders. Secondary failure mode is from one or more cylinders and into the cooling passages of the head which would pressurize the coolant as Mike mentions. This produces rapid loss of coolant, overheating and blowing of coolant out the radiator overflow vent due to excess system pressure. When the coolant does make it into the exhaust, it looks like a cloud of white steam--because it mostly is.

Head gasket problems seldom show up as excessive crankcase pressurization, which is what you describe. The pressurized crankcase commonly comes from bad rings, bad pistons, bad bores or a combination of the three.

So, run a compression test. Run a leakdown test if you desire. But, you will have to pull the cylinder head, and probably the entire engine, to really find out what is causing you to blow out the oil which is being sprayed around the underside of the engine and burning off where it hits the exhaust manifold/head pipes. (The other areas it is dripping down rather than burning and little smoke is produced except where there is burning.)

A compression check would be the first place to start to see what it tells you. A good cleaning of the engine is another thing to do to try to determine exactly how bad the problem is (rate of loss of oil would be a clue as to how bad the problem is). Then, you need to decide how bad the problem is and what you need to do about it.

Les
Les Bengtson

I wouldn't pull the engine out at this stage. Remove the head to check the head gasket and for any head cracks. Then examine the cylinder bore and piston crown.
Then remove the sump (oil pan) to release the conrod bolts and the piston. Check rings and piston.
All this can be done quickly without removing the engine. Front sump bolts cause a bit of cursing. I don't know why pushrod MGA's didn't have the five holes in the front crossmember like the Twin Cam. A good modification whenever you have the engine out.

Mick
Mick Anderson

Take the head off an have a look. That's going to be required whatever the problem is. Compression that low is going to be cased by something easy to spot.

Crossed fingers that it's only the head gasket.
dominic clancy

Thanks Gentlemen for all your thoughts. I just went out and filled the radiator up so I could see if any bubbles were escaping from the radiator. I saw none.

It is running somewhat rough as should be expected,with one cylinder down about 100 psi from the rest. When I removed the filler/vent cap on the valve cover the vapor comes as a puff.
I think I can hear a tiny metallic clang when I let off the throttle a little,such as coming down from 1500 rpms back to idle.
As I know, the head needs to come off. This won't be soon as other house projects are ahead of that on the list. I will keep you posted when this happens.

Maybe this is the time for that 5 speed tranny and have the head redone also.


Ray
Ray Ammeter

My prior comment got sent before I intended.

I think it is a bad/broken ring and most likely will require the entire engine to be pulled out AFTER the head comes off and see what that reveals.

When I said in my prior post to have the head redone, I would take it to a shop and have the valve seats to run on unleaded and replaced with 3 angle cut and whatever else can be done within reason.
If the engines comes out, then I am looking at getting a five speed tranny. My old tranny is from a early 1500 and it needs to be rebuild. Synchros are good but it gets hard to shift when it warms up.

You folks have a great summer and for the ones "down under" have a great winter.

Ray
Ray Ammeter

It may yet be the head gasket. When mine went a few years ago, I had the crankcase being pressurised as it has gone by the oil way. This is at the back of the engine (by number four cylinder). It could also have gone by the pushrods.

As has been said, you'll only find out when you have a look. This may also be disguised by a wet compression test.

dan
Dan Smithers

This thread was discussed between 02/07/2005 and 04/07/2005

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