Compression Test Results

[1972TCCOUPE]

Hi All,
Got a bit of a misfire. I have ruled out sparks and petrol so decided to do a compression test. Results are
Cyl 1 155
Cyl 2 155
Cyl 3 110
Cyl 4 180

Retested with a little oil in and got mostly the same results apart from cyl 3 which went up to 155. This I believe points towards piston rings. My manual states a cranking pressure of 170. I assume this is the figure to aim for.

What should I be looking for as a result? Why the big difference between 3 and 4? Is it time to take my head off.

Thanks Glen

[balmy]

Could be a valve not seating properly-burnt out / bent etc. but with increase with oil in I'd guess ring.

Whatever I reckon head off to check.

[MarinaCoupe]

If no. 3 comes up to the same as nos. 1 & 2 with a drop of oil then I would say definitely rings/bore for no. 3.

As for no.4 a reason for being high, I would think that it would point to a past repair. If at some point in the past someone had re-bored and ringed just no.4. It sounds weird but it was a low cost fix in the 70s/80s, rather than reboring all four cylinders. With the head off you can use a mic to check the diameter of all the cylinders. Take several readings at different points if the clock to establish whether any have worn oval.



Chris

Sent from my iPhone

[1972TCCOUPE]

Thanks chaps,off with his head to have look and measure.
Glen

[dazza2623]

Before you take things apart you could try this to prevent work.
Get engine to temperature,remove air filter,rev car to about 2000rpm & sprinkle droplets of water through the carbie.
If the rings are stuck,this can free them.
I have used this in the past & it works more than it doesn't.
You still can't beat a rebuild.