Morris Minor Owners Club

The cylinder head gasket has gone twice on my 1098cc in the last 6 months, which has left me puzzled...

The previous owner put a new head on to run it on unleaded, and that has done about 4,000 miles.

Firstly it went between pots 1 and 2, and then secondly between 3 and 4.

I've been told it might be running too rich?

Any suggestions would be appreciated so I'm not changing the gasket twice a year!

Also, been told to avoid 4 in 1 fuel saver fuel pipes from the pump to the carb, and it inevitably has one fitted! Anyone know much about these? And if it affects my gasket blowing?!

Cheers!


Below is the second gasket

And below is the gasket which was on when I bought the car

Well if you torqued the head up correctly then there is only one answer. Have the head and block skimmed I'm afraid. Sorry

Hmm - to have one head gasket fail after 6 months is unfortunate.
To have two fail in a year is more like a pattern...

If the head gasket had failed in the past, this might be why the previous owner had decided to change the head (recently fitted unleaded head??). In which case it could be 3 fails not just 2?
When facing curious problems, it never hurts to ask the previous owner in case there was some history...

It's pretty rare for an A-series block to deform but anything is possible.. A distorted head is more likely than a block issue but also not common.

If it was a problem with the block or head flatness I would expect the head gasket to fail at the same point - although that's not guaranteed. A decent engine machinist should be able to check the flatness of the head for you before you decide if it needs to be skimmed. Checking the block is a lot more work (engine out, studs out etc..).
If the engine had been run too long with a failed gasket it can damage the surfaces, but this would lead to a failure in the same spot.

Are you sure there are no other issues? Minor A-series engines are very tolerant to overheating / low coolant but these will reduce the reliability of the head gasket (e.g. having a fairly blocked-up radiator will cause more problems on long runs..) . Major timing errors (way too retarded or a bit too much advance) or running lean can cause extra heat stresses.

However always start with the most simple checks... Is your torque wrench accurate and did you re-torque the head nuts after a bit of running?

After cleaning off the gasket residue put a straight edge across the head/block where the gasket blows and see what feeler gauge thickness you can get between them at that point.

At this point I would get the head skimmed as a matter or course,not worth the risk again.

4 in 1 fuel saver fuel pipes

What are they? What do they look like and what is the construction?

I would definitely get the head skimmed, as a slight increase in compression ratio can only help the performance and fuel economy - probably rather more than a dubious 'fuel pipe saver' I think.

The block needs cleaning up very carefully to remove the carbon and other residue from the failed gasket. Once done then it is a matter of checking the flatness in the area between the cylinders.

Out of interest, what is the thickness of the head? The original thickness is 2.75", and any less will show if it has been skimmed before, and by how much.

A couple of other questions - do you keep the heater valve open all the time and is the by-pass hose in place? The heater valve allows a good flow of water around the back of the engine and the by-pass hose does the same for the front. Yes, BMC did remove the by-pass hose on the A+, but they did NOT remove the by-pass system, just did it differently!

Once everthing is back together do make sure that the mixture and the timing are set up properly, as in a previous post, a small amount of over-advance can cause internal overheating and gasket failure, as can an over-weak mixture. Over-rich can cause wear and poor fuel consumption, but not overheating.

I agree with rayofleamington you definitely need the studs out and check the block top, even cracktest with dye pen would help. Use a decent head gasket as well. Good luck in your endeavor.

Thanks for all the feedback!

The head is back on and is torqued up, once cold and once after running.


Philthehill - I've done the straight edge/feeler gauge check after a careful clean up and both the head and block were ok!

When I come to turn the engine off it tends to run over for a second or two once the key has turned, which I believe is a sign of it running too hot. Not too well up on plumbing problems, so any advice on this would be of great use!


IslipMinor - I will get a picture of the fuel saver, not sure on its construction as I've never taken one apart!
Also, not sure on the thickness of the head, I'll look into that too!
The majority of the time the heater valve is open, otherwise I see less and less out my windscreen!

I have spent a little time on the mixture, but aim to spend more on it and the timing this weekend.

Glad to hear that your head and block are OK. As regards running on after switching the ignition you are right in that the cylinder mixture is self combusting indicating a hot spot somewhere in the combustion chamber. To stop it running on all I can suggest is that you make sure the timing and mixture are set correctly. Flushing the cooling system to remove sludge/rust etc so that there is the maximum transfer of heat from the area of the combustion chamber would not be a bad thing either. The water flow around the two rear cylinders is not as good as it should be at the best of times. Having the coolant flow through the heater valve as suggested by Islipminor should help.

Running on can be a sign of retarded timing and/or rich mixture but not anything to do with head gasket problems. Torque to 44 ft lbf.

When I come to turn the engine off it tends to run over for a second or two

A standard engine should not run on when switched off. Likely to indicate over-advanced ignition and/or weak mixture. Needs to be sorted very quicky, as you could already be on the way to blown head gasket number 3!

Or something is burning hot in the cylinder - some debris or something - that ignites the remaining mixture but you'd expect to have seen that when the head was off..

Exactly - which happens with RICH mixture (carbon to glow red) and RETARDED timing which runs the engine hot....

Another possibility is that the tick-over is set too high.

Indeed - that doesn't help.