So I have a 1974 1.8L and I am starting to think about winter projects - she goes on stands on Nov 15th.

I'll do a compression test (I have a gauge) - What should good to great readings be? How low is bad?

I can get a leak down tester. What % is good, great, poor, etc? What would I learn with this test before I go into motor that comression test won't tell me? Tester is ~ $70

Still more to learn.

like this
http://www.jcwhitney.com/autoparts/Product.../p-2318/c-10101

With a compression tester you test to see how well your compression is compared to your other cylinders. You look to see how good your compression is. On a leak down test you can check to see where exactly air is leaking and how much of it is leaking. You need an air compressor for the leak down tester. You put the cylinder at it’s TDC on the compression stroke and make sure your car won’t move when you pump that cylinder full of air. Then it’ll give you a percent of leak down. Then you can listen into the crank case and exhaust to see where the air is leaking. If you take off the oil cap and you hear air then your rings are bad. If you listen at the tailpipe and you hear air then it’s your exhaust valve, and finally if you listen at your intake and you hear air then you have an intake valve leak. Leak down gives you more information.

As for the numbers, I have no idea on a range for a type IV for a compression test. You want them to be consistant. I think +- 10%. For the leak down tester it'll tell you on the guage. It'll have a different color (i.e. green is good, yellow is rebuild soon, and red is rebuild now, car is not feeling well). Hope this helps.

well if this helps my 90k 1.8 motor is averaging in the 120 range but i have the max at 132 and min at 122. this is with the motor just slightly warm and it should be hot.

just make sure your valves are set right

scott t

ps the motor get new rings at 70 k miles
and its for sale with fi that runs and is complete