Morris Minor Owners Club

yeah, I'm going to try taking its head off tomorrow.

I thought it would be too low for it to run, but it does. It is quite possible I messed it up, as I've never done a compression test before. The engine was hot and throttle was fully open so not sure what I could have done wrong.

Forgot to say, checked the valve gaps as well.They were all 12thou, which I believe is right? I've seen people say both 12 and 15thou on here, but 12 was what my workshop manual said.

As long as there IS a gap at this stage - that's good enough. But 12 inlet and 15 exhaust will be better when you have it running. The figures you list are ludicrously low - were ALL the spark plugs out?? But nevertheless - the ultra low reading (5psi!) indicates a burned out valve on that cylinder - or a burned out piston! Possible (but unlikely) head gasket failure - but not in to another cylinder.

Ahh, didn't realise that all the spark plugs had to be out, bloody online guides As i said, it was probably my fault.

Just done another (with all the plugs out this time) and got better, if not great, readings.


#1 - 60psi
#2 - 60psi
#3 - 15psi
#4 - 60psi

how would I tell if its the valve or the piston which is to blame? is it a simple case of looking?

Just in case the gauge instructions were really incomplete: with all plugs out, and the gauge screwed fairly firmly (hand only) into one cylinder. hold the throttle fully open and spin the engine over a dozen or so revolutions using the starter motor. If you gauge is the "stick" type, like a traditional tyre gauge, you should be able to unscrew it without disturbing the reading. Read, reset, repeat for all cylinders. Don't worry too much about whether the engine is hot or cold, but make a note which it was so if you want to compare the results in a year or ten you can do it under similar conditions.

To be certain where leakage is taking place, you'd need to do a leak-down test where you use an adapter to squirt compressed air into the cylinder to see where it emerges - exhaust, crancase breather, carburettor, etc.

Kevin

The results are still terrible - clearly something v bad going on in #3 cylinder....... Assuming you have set the valve gaps correctly before doing the test - off with it's head. The 'hot' test makes the engine much easier to spin over (thin oil) and ensure the battery is fully charged and doesn't start to 'flag' after the first couple of cylinders have been tested.....

Take the head off and look at everything - if it's your first time, don't be shy! You should be clearly able to see if something is amiss, but it depends on how mechanically minded you are etc.

Post up lots of photos and we will help you!

bmcecosse wrote:The results are still terrible - clearly something v bad going on in #3 cylinder

Absolutely. I thought I'd add the extra notes on compression testing in the (probably vain) hope that someone else might read the thread, now or when they search for "compression testing", and would not have to ask the same question. It's very easy to assume, when you've been doing compression tests since Lord Nuffield was alive, that it's obvious how to spin the engine over or that you have to carry on till the gauge reads a maximum.

Kevin

I took those readings straight after a short run, so it was a 'hot' reading (presuming i have terminology right this time )

Its a stick type and was turned it over about half a dozen times each. Did 1,2,3,4,4,3,2,1 pretty much same readings each way.

Didn't manage to get the head off today as I was called into work. It will be my first time (as you may have guessed by now, I don't have much experience) but hopefully I'll be able to tell... will post pictures.

It does sound like there's air escaping from around #3 when I turn it over by hand with the plugs in...

Whats so special about british condensers ( is the air inside somehow attuned to the UK climate ), unless defective parts or manufacture were common in the other sourced places.

Are you sure your readings are in PSI ?? Would make slightly better sense if they are Bars...... but still an obvious valve (or piston/ring) problem in #3.

got the head off today. Gasket was slightly buckled all round, and the layers had split near #3. Manifold gasket also snapped at the end.

couldn't see any problems with the cylinders or head themselves, so thats a good thing

Have you taken the valves out?
How do they look?

While you have the head off give it a decoke and either renew or clean the valves and lap them in. You will be pleased with the improvement in running.

If the gasket is ok - it must be the valves - or the piston/rings.

the gasket was worn and layers peeling at 3. But would you advise checking the valves anyway? and do I need to check all of them, or just those at 3? The idea of it sort of scares me, never done it before...

Just looked up how to decoke, seems easy enough. Should be able to manage it

I strongly advise removing all the valves for inspection/grinding/renewal....... A spare head is a useful thing - the car can be back on the road in an hour and then you can take your time checking out this head.

The valves should be taken out as part of the decoke - and don't waste money on a valve spring compressor if you have an old pillar drill to hand (don't run it of course!)

You will then be able to see if they are burnt out.

When cleaning up the valves DO NOT clean/abrade the shiny edge which comes into contact with the valve seat.

If you want more info and hints on decoking PM me, it really is easy but you can cock a doodle diddley it all up if you're not careful.

And the word c-o-c-k has somehow been censored and gained 'doodle diddely'.

I'll give it a shot :S don't have a pillar drill either :/
I'll get a spare one when funds allow, they aren't cheap, and I'm a student ;)


I love word filters...

Been there - done that - but keep your eyes open. Mini 998 engines/heads etc are sometimes given away FREE. Or for very little cost......