So I need some advice.
First the backstory. I purchased a 2007 R56 S, with a bad engine. Best I can tell, the timing chain/tensioner let go and did the usual damage.

Starting the rebuild, I decided and went with a CP piston set. Initially because they were the best and cheapest option I had. And, because I want to eventually up the boost from stock, and make some decent power with it.
So, I completed the rebuild and here we are.

First off, the piston slap is noticeable. To the point of it sounding like a really quiet diesel.
The oil consumption is tolerable (1qt used/added so far), but the amount of oil being deposited in the intake tract is not. 4k miles and the intake valves are starting to coke up. Oil is pooling in the pipes and intercooler as well.
Now.... I have already ordered a dual catch-can setup and am willing to try that, but should I?
I do have another option, as it turns out. In my possession is another block and head setup. I have rebuilt another engine with Mahle pistons for someone else, and have had really good luck with it. Very stock running and none of the side effects of forged pistons. So, I could go ahead and rebuild that setup with the Mahle pistons and rock on, or I could put this engine back together and run it til it pops, but putting up with the side effects (annoyances)?

What are your thoughts on this dilemma?

 

Used CP's before and oil consumption was nonexistent, so couple of what may seem stupid questions. Was the block bored over with a torque plate? What about new valve seals on the head? Slap with CP piston should only occur on a cold start if clearance is correct, and higher oil consumption is usually a result of rings not seating or the bore not being true all the way down the cylinders.

 

Thanks for the feedback.
The head was rebuilt, but not by this machine shop. As far as I know, everything was new in it.
The machine shop that I use has a good rep and has done good work for people I know, so I would think they knew what they were doing on this job. They did the other engine I mentioned, head included, and it has had no issues so far.

Do you think it would be worth getting a new set of rings, re-gapping them and starting over? How long should it take for the rings to seat properly? I used reg oil and did about a 1000 to 1500 mile break-in.
If they did bore this block too wide, is there any recourse? No re-sleeve. Coat the skirts to try and take up some of that gap? I don't think anyone makes a 78mm piston, so I'm stuck, it seems.
I guess I'll be tearing into this one and taking a closer look.
The engine and car only had 50k miles on them....

 

It would seem that a re-sleeve is possible. Just expensive as hell.
http://www.darton-international.com/mid_04.html

And it also seems that the 77.5mm bore is max diameter. Period.

 

Sounds like you did a good break in. I'd start with a compression and leak down check before anything else. If you do have to pull it back apart pressure check the valves and check the bore taper and roundness with a torque plate installed. If you don't have a torque plate you'll have to remove the crank and check it from the bottom with head installed. Anything over .0005 out of round or .0008 taper would cause me concern. It might be something as simple as the ring gaps lined up during break in though. Darton makes MID sleeves p/n 800-800. Cost is $1100 to $1200 and around $400 to $600 to install, bore and true the block.

 

Gotta agree with Tigger --- sounds like machine shop and / or assembly errors. My CP / Carrillo set caused no grief. Only did about 500 miles of break-in (with reg oil), but it was lotsa hard accel with engine braking for decel, minimum brakes. No problems yet, but still less than 1K miles on it.

My 1st build also had oil in the intake plumbing, caused by piston blow-by / crankcase pressure build-up and resultant turbo oil seal failure --- oil from the turbo getting into the intake compression chamber. I thought the cylinders were round so I didn't re-bore them --- WRONG!

The guys that did my Cylinder Support System might also do sleeves --- http://cylindersupportsystem.com try contacting them?

 

Thanks everyone for the info. I'm kinda in a spot at the moment and needed the advice.
At the moment, I am going to reassemble everything, do a compression check and re-evaluate. I do have 2 oil catch cans that I am going to plumb in and see what happens.
The car is currently being prepped for paint, so $ aren't readily available right now.

I do have another block and head, as mentioned before, so I may take my time and rebuild it using some of the tricks OBW has done; esp the balanced crank. This MINI is supposed to be my new DD, with better MPG than my R53, so going whole hog isn't really in the cards for it. I just wanted something that could get me to work and maybe not be left behind by a modified Honda, etc., if you catch my drift.

 

Well here's an update for you all.
I did a compression check and here are the numbers:
Cyl1

Cyl2

Cyl3

Cyl4


So, I think something is not happy in the engine. Whether it is a machining error, rings or valves not seating, who knows....
Back to square one.

 

Don't get too discouraged about low CR readings, it could be a hose / gauge combination causing them. My CR set has a hose with an extra large ID causing readings of about 110 - 115, when a Pro set reads 160. Gotta love Harbor Freight --- huge selection but mostly for emergency use only --- I got what I paid for.

Your variation between 100 and 120 is marginal at best, and if you have a CR set that's not known to have previously produced good numbers, I'd consider looking for other causes --- maybe a leak-down test? Valve guide seals are always suspect when someone else does the head work.

Best of luck ---