Compression test…

[sogatha]

Just taken set of readings off the 998 Mini.
Each cylinder is 100 psi. Feels a bit low to me but all four are within 5psi of each other and oil pressure is well up.
Any comments?!!!
Should I have a look at the valves…

[Exminiman]

Why did you do the test ?, were you suspecting you had an issue ?

[sogatha]

Ha!
Honest answer is just sheer interest.
I’ve only had the car a short while and while I was tinkering with the mixture I thought I’d have a look.
Car goes well so I’m not worried but felt 100 is just a little on the low side.

[Exminiman]

What process did you follow, ie oil down the bores, up to temperature etc…

If they are all the same, it may be that all is fine, just test method may not be recording a very high number….

[sogatha]

Warmed the engine up to temp.
Removed plugs one at a time - not the whole lot out, didn’t put oil down the bores.
Good idea - I’d forgotten about that.
I’ll have another go.

[Terence]

Compression test, will basically tell you very little other than there is compression.
You would be better off doing a leak down test, this will pin point the weakest components.
If you have an air compressor & buy low cost kit from eBay you will be further ahead.
https://www.ebay.co.uk/itm/393420043056 ... BMwOSS9b9h

[Old English White]

The figure may not be accurate? It does seem low on the face of it. However, I was always told that it is more important that the figures across each cylinder are similar than what the actual figure is - due to possible lack of accuracy of the reading for various reasons.

[Spider]

I don't place much faith in a 'Compression Pressure Test' to show the engines health, they don't remotely simulate what's going on when the engine's running.

[Ronnie]

And don't forget to depress the accelerator pedal while cranking

[Coolcat]

And, make sure your tester is good. Had to toss mine out when it read low. Borrowed another, just fine

[CooperTune]

I recently bought another mini only to find out it's a 1990 Mainstream Cooper. Another surprise was the amount of service info that came with the car. With the speedo showing only 34,000 KM being a German model. All indications are it is a very low mileage car. I warmed it up, removed all plugs, wedged the throttle plate open and ran a compression test. One though four 180, 150, 175, 180. No I did not add oil as I suspect when I leak test I will find exhaust valves on center cyls. If that's the case a valve job should set it right.
Reading I noticed Cooper offered a twin carb kit for these cars. Once compression is sorted I plan to add twin HS4s. Steve (CTR)

Edit: It is clear I'm dyslexic 1990 Cooper has 43,000 showing.