Morris Minor Owners Club

Just replaced the plugs for the first time on my Traveller. So thought I'd run a Compression test. From front to back in Bar:

1 - 8.5
2 - 13
3 - 11
4 - 9.5

Thats not good is it

I don't understand BAR so:

1 - 8.5 BAR 123 PSI
2 - 13. 188
3 - 11 159
4 - 9.5. 137

Are you sure these figures are correct? Take all of the spark plugs out at once so the engine can spin over freely and easily. Did you zero the tool and have the throttle wide open? Hold the accelerator pedal down with a brick. Disconnect the electrical connection at the top of the fuel pump. Take the IGN lead off the coil (white).

A couple of things stand out. 188 psi is rather high and the readings are very inconsistent between cylinders.

My suggestion would be to repeat the test before worrying and speculating.

You can also do a "wet" test by adding a teaspoon of oil in through the spark plug hole and repeating the test to get a set of dry (do this first) and wet compressions

Stephen

All plugs were out. Tool is Draper tester. Zeroed every time. Turned engine over for 10-15 seconds each time. Checkd #1 again after 4 and got same reading. No throttle

Maybe a daft question but why would throttle position make a difference?

Also tools been in the garage unused for at least 15 years! :-O

Wes wrote: ↑Thu Aug 13, 2026 1:32 pm Maybe a daft question but why would throttle position make a difference?

Also tools been in the garage unused for at least 15 years! :-O

The throttle disc “butterfly” restricts the air entering the engine when it is in the idle position, almost completely closed. Opening the throttle enables the engine to gulp in maximum air.

Stephen

Compression check should always be carried out at full throttle.
Crank until gauge stops rising on each cylinder.
10% Spread max to min on good engine no matter what scale psi or bar
Have you set valve clearances before carrying out the compression check?

Tappets done, but still sounds "tappety" which i put down to a worn rocker saft/rocker bearing surfaces as i can move rockers side to side quite a bit!

Original Engine & 'box which I'm sure its done more than the ~75,000 miles indicated!

My engine is the original from the factory, 1969. It had done 100,000 miles +. The compressions were still 150 psi across all cylinders prior to rebuild but at operating speeds it burnt loads of oil and drank fuel like a drunken sailor. So compressions are useful but sometimes misleading.

Stephen

svenedin wrote: ↑Thu Aug 13, 2026 3:42 pm So compressions are useful but sometimes misleading.

Stephen

yep but engine does feel a little tired. Ive been told it smokes a bit, uses oil, and there's a sound line a hard rubber ball rattling in a can which i suspect might be big end shells? not to mention the well worn rocker assembly. So whilst plugs were out i though id give it a test. Wish I hadn't now

What you dont know you dont worry about

Wes wrote: ↑Thu Aug 13, 2026 4:12 pm

svenedin wrote: ↑Thu Aug 13, 2026 3:42 pm So compressions are useful but sometimes misleading.

Stephen

yep but engine does feel a little tired. Ive been told it smokes a bit, uses oil, and there's a sound line a hard rubber ball rattling in a can which i suspect might be big end shells? not to mention the well worn rocker assembly. So whilst plugs were out i though id give it a test. Wish I hadn't now

What you dont know you dont worry about

True but it sounds like it has just confirmed what you already know. It feels tired, smokes a bit and drinks oil. Fine if you just bimble around and do few miles but if you want to go touring or whatever, it needs a rebuild

Stephen

I just bimble , if a journey is >30 miles i've got very lost!

So think i'll just put the blinkers back on and bimble until it goes bang

Wes wrote: ↑Thu Aug 13, 2026 4:40 pm I just bimble , if a journey is >30 miles i've got very lost!

So think i'll just put the blinkers back on and bimble until it goes bang

"Bimble until it goes bang" is a good philosophy for may aspects of life.

boingy wrote: ↑Fri Aug 14, 2026 6:07 am

Wes wrote: ↑Thu Aug 13, 2026 4:40 pm I just bimble , if a journey is >30 miles i've got very lost!

So think i'll just put the blinkers back on and bimble until it goes bang

"Bimble until it goes bang" is a good philosophy for may aspects of life.

I always think of the following comment and outcome to someone with blinkers:


“Smile and be happy”

So they smiled and they were happy….. and, lo and behold, things did get worse.

I also like the saying “If it ain’t broke, don’t fix it”. Just need to know when it is broke.

There are others (at least one) that might be appropriate for this thread….

[/quote]

I also like the saying “If it ain’t broke, don’t fix it”. Just need to know when it is broke.

There are others (at least one) that might be appropriate for this thread….
[/quote]

Having followed F1 for many years i did notice that when they introduced Parc Ferme rules after FP3 cars seem to get a lot more reliable ;-)

A great saying in the trade "let it develop" diagnostic is simpler at failure

I think when you own any old vehicle you need to allow it a few creaks and groans before being too quick to investigate. Otherwise it would never see daylight!

Don't sweat the small stuff, if its not safety related just drive and enjoy the experience. If you want quiet sanitised driving dont buy a classic car

Bill_qaz wrote: ↑Fri Aug 14, 2026 1:40 pm Don't sweat the small stuff, if its not safety related just drive and enjoy the experience. If you want quiet sanitised driving dont buy a classic car

Yeah, sometimes its 'Satanised' with these old cars!

boingy wrote: ↑Fri Aug 14, 2026 6:07 am

Wes wrote: ↑Thu Aug 13, 2026 4:40 pm I just bimble , if a journey is >30 miles i've got very lost!

So think i'll just put the blinkers back on and bimble until it goes bang

"Bimble until it goes bang" is a good philosophy for may aspects of life.

Fantastic! I bet the engine will carry on for a long time!

Stephen

myoldjalopy wrote: ↑Fri Aug 14, 2026 6:02 pm

Bill_qaz wrote: ↑Fri Aug 14, 2026 1:40 pm Don't sweat the small stuff, if its not safety related just drive and enjoy the experience. If you want quiet sanitised driving dont buy a classic car

Yeah, sometimes its 'Satanised' with these old cars!