did compression test today and have bad rings/cyl. on #4 all cyl. were 150 but cyl. 4 was 120; added some oil and bingo thru the roof . so bad is it to do a quick from the top hone? i'm thinkin' drop the bottom pan , unbolt the piston rod ; clean up the ridge (can't be much only 66000 mls.) push the piston up thru and cover all at bottom well with oily rags and do a quick hone and toss in some new rings . can the coating on the cyl. take a honing or is that better determined on in spection?

 

There is no cylinder coating, there is a grafal coating on the piston skirts which reduces friction.

Unless you had some scuffing due to a siezed ring, you might not have to do anything to the cylinder walls at all, at most a quick few passes with a bottlebrush hone. Given the high-ringed pistons in the MINI engine, most likely your issue is a partially siezed top ring. A leakdown test is more conclusive than a compression test, you'd be able to tell by where the air is coming from if you have ring, valve or gasket issues.

If you can still see the crosshatching at the upper ring travel on the cylinder walls, you wont have to deal with any ridges.

 

i added about a tsp. oil after first test to seal rings . it worked. the compression went right up . good to here the coatings on the pistons . so it shouldn't be a big deal to run a hone down it ;if at all ? then run the piston back down and torque it up ? i don't really want to get into a big rebuild just yet .

 

i will check the rod for any bends. and will check run out on crank but if that's good i'm outta there!