Morris Mini Cooper Cylinder Compression Test

In this video I use a ToolPro compression gauge purchased from Super Cheap Auto to test the cylinder compression on a Morris Mini. I did not build the engine so I have no idea what the compression ratio is, however, the gauge reads 125 psi (9 bar) on each cylinder.

[@jackmorris2758]

two points - you are suppose to crank it for 5 seconds and remove the other spark plugs as this will add extra resistance.

[@CafeRacerLab]

Thanks I will try again and see if it makes a difference.

[@jackmorris2758]

@@CafeRacerLab awesome let me know

[@demetrispatrikarakos5565]

What is important is that you have consistent pressure throughout all four cylinders. You could do as mr Hart suggests a wet compression test. Do you have blow-by? A leak down test will definitely pinpoint if you have issues with piston rings (blow-by) or with valves not sealing properly. I believe that your engine is fine as long you can accelerate on hills and the coloured of your spark plugs is ok in all cylinder and right colour of residue. Enjoy your mini as much as you can.

[@shaneblacklord3313]

Great video, you need to buy a more modern gasket. Just found your channel and subscribed.

[@TornadoCAN99]

My 1275 c.c. engine had 165 PSI per cylinder when I had it inspected prior to purchase two months ago. Appears to have been rebuilt, but like you I do not know any details on what was done. Also like you, I've got a synchro issue, 4th to 3rd downshifts typically grind. One recommendation is to use double de-clutching...something I have yet to master. This will permit good engagements even without any synchros, so should be a good stop gap until engine comes out for a rebuild one day. I see you've got dual carbs. Do you know if there is much to be gained by them over a single (I have a single HS4 now)? Are they worth the added bother of having to synchronize/balance them? I've got a Gunison ColourTune see-through spark plug for settng mixture on carbs...I've used in on my '74 Norton Commando (a true Cafe Racer ;-) to good effect. Not yet used on the Mini.

[@michaelhart5886]

What's the history of the engine. Has it been rebuilt at some stage, if so how long ago. How many kms has it done since. 125psi is at the lower end. Probably not the gauge if it's an old engine that's simply worn. Have you checked valve clearances.

[@CafeRacerLab]

The short motor was supposedly rebuild, but the motor has changed hands a few times so its condition and the quality of parts is questionable. I rebuilt the head myself. I will be checking the valve clearances next, will be interesting to see if that makes a difference.

[@michaelhart5886]

@@CafeRacerLab when the head was off what was the bore size. Do a wet compression test and see what the results are. I.e take all the plugs out and squirt some oil down the plug hole. If the reading is up quite a bit then your compression rings are simply worn

[@hannesczeitschner7590]

Michael Hart it could just be that the compression ratio is low. if that is the case either skim the block or the head to raise it,

[@grahaminaus]

Not tried one yet, but Mini Spares UK have a silicon rocker cover gasket, supposedly better than cork....minispares.com/product/Classic/Engine/Cylinder_heads/Rocker_Cover_Fittings/GUG5038EVO.aspx?100406&ReturnUrl=/product/classic/GUG705009EVO.aspx|Back%20to Cheers! Graham