rocketrich
rocketrich New Reader
6/21/14 7:57 a.m.

Hi folks, Looking for some advice on the motor in our Mini. It's been drinking oil like a rotary for a while now: about 1 quart every 1,000 miles or so -- but not leaking anywhere on the engine, so I know its running through the motor. Lately its been surging under boost, so the acceleration isn't what it used to be. It's got about 52K miles on it now. I've been putting up with this, but now coolant leaks have me thinking its time to put this motor right. Its a blast to drive and gets really good gas mileage considering how much fun it is to drive, so its a keeper. The brakes on this car are amazing!

Haynes manual says the min compression is 116. I get 118,112,109,& 110 dry and 137,133,130,&134 wet on my inexpensive Harbor Freight compression tester. So clearly, something isn't right. I'm not sure if the low compression could be caused by the intake buildup on the valves alone or whether I've got a ring problem as well, but the wet values seem to indicated I could have a ring problem.

So my plan is to remove the head and have a look at the condition of the head/valves and piston bores. Would I have a visual indication on the bores if the rings are shot? In other words, is a ring problem going to be visually identifiable? I hate to rebuild the bottom end if it doesn't need it. No pictures to post yet, as I haven't started.

All advice welcome, thanks. Rich

SVreX
SVreX MegaDork
6/21/14 8:11 a.m.

I don't think there is any visual indicator that would tell you if the rings are worn or broken, unless they have scored the piston wall.

Leak down test?

rocketrich
rocketrich New Reader
6/21/14 10:19 a.m.

In reply to SVreX: Thanks. Yeah, thought about the leak down test, but with the difference between between dry and wet compression I'm fearing I've got a ring issue. Also just noticed that the compression numbers in the Haynes manual shows both 116 and 130 as the minimum for this model year. I think the 116 is a typo as it shows 130 min in two places but 116 only in one. 130 makes more sense if I simply do the math with the compression ratio. With the wet values in the 130 range, I think I've convinced my self I have a ring issue.

docwyte
docwyte HalfDork
6/21/14 11:05 a.m.

That's not a lot of miles for that kind of oil consumption/performance/wear. Is it under warranty?

You're a lot more forgiving than I am. If my car with ~50k miles on it needed an engine rebuild there's NO way I'd be keeping it...

maj75
maj75 Reader
6/21/14 11:07 a.m.

Could it be going out the turbo?

f6sk
f6sk New Reader
6/21/14 12:28 p.m.

I've seen a TON of minis with bad valve guides. This will cause it to burn oil and lower compression. The dealer does not even have a part number for the guides, so you have to adapt some over from SBI.

rocketrich
rocketrich New Reader
6/21/14 12:52 p.m.

docwyte: Ha! Not trying to be forgiving, but rather looking for the lowest cost option out of the issue. We've got other cars to drive, so time isn't an issue. Plus I bought it used and warranty had expired back in '10 - SWMBO put ~30K miles on the car. I'm thinking I inherited the issues from the previous owner. SWMBO has driven it troublefree from Dec '09 to recently. As I do the MX, and drive it from time to time to make sure its running well, I'm the one who identifies the issues. [Clutch went ~30K and the original run flats where in sad shape when I bought the car. I suspect the previous owner ran it pretty hard]

maj75: yes, from what I've been able to research oil is leaking out the turbo seal into the exhaust as well as back into the inlet when not under boost. Strangely its not smoking, but I attribute that to the quality of modern catalytic converters.

f6sk: Wouldn't the valves seat themselves well regardless of the valve guides? I can see how a loose valve guide would allow oil to leak by and run through the engine and maybe even cause surging under boost, but don't understand how I would lose compression that way. I'm guessing that the valve spring would pretty much pull the valve tightly against the seat. I suppose if the guide was misaligned or really sloppy the valve would offset from the seat and cause compression loss. But with the difference between the dry and wet compression test, I'm attributing that to improved sealing at the rings because of the oil. Any more info about these valve guides? Thanks, Rich

Feedyurhed
Feedyurhed SuperDork
6/21/14 4:46 p.m.

Wow.........another Mini with a problem thread. Damn discouraging.

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