2011 RCZ THP200 midlife makeover

[gwest]

When I was trying to organise some bits of paper I have accumulated dealing with the EP6 engine I came across some more instructions on the camshafts- this time from the former newtis site dealing with the MINI N12 engine. I attach scans taken from the descriptions for the intake and exhaust cams. They are consistent in describing how the plastic rectangular oil rings should be lightly oiled, but that for the exhaust camshaft adds that the "plastic plain rectangular compression ring is maintenance free and does not have to be replaced".

Who do you believe? BMW designed the valve gear and have used it previously in their engines. Yet the French advice (no oil, replace seals when disturbed) is the opposite to that of the Germans!

 

[gwest]

Early on when I was checking for oil leaks I was concerned at all the oil on the wiring harness coming through the rear side of the block from the oil pump. There is a rubber seal in the wall, but is very hard to see because it is covered by the lower rear engine mount. In the end I decided that the oil on the wiring was probably coming from above, as it sits under the timing chain tensioner.

Later, when I had the engine out and removed the sump I discovered that the oil pump loom had in fact been modified- it had the extension kit mentioned in MINI service bulletin SI M110112 of June 2012. This bulletin would have you check for capillary movement of oil through the harness to the ECU, as well as just leakage at the seal. The former is disastrous, but my car must have just had a seal leak, resulting in the addition of an extra section of wiring and the old harness being pushed into the sump. The end connector had no signs of oil in it and the seal looks ok so I might just leave it alone. But if it ever did leak again it would be a real pain, requiring removal of the RHS driveshaft and the engine mount.

 

[gwest]

The only reason I was changing the piston rings was in case the original 2-piece gapless oil control rings were contributing to the high oil consumption. There was nothing wrong with the compression on this engine, and a check of the used compression ring end gaps showed that while they were just out of the range for new rings, they were within the wear limit.

Piston ring end gaps (mm)	cyl 1	cyl 2	cyl 3	cyl 4	Specs (BMW N13)
1. top ring	0.7​	0.7​	0.7​	0.7​	0.2-0.40, limit 0.95. Side clearance 0.01-0.07 mm
2. 2nd ring	0.6​	0.6​	0.6​	0.6​	0.3-0.55, limit 1.06, side clearance 0.01-0.06 mm
3. Oil control ring	gapless​	(0.10-0.40, limit 0.82, side clearance 0.04-0.10 mm)

The pistons showed a little scuffing on the thrust (inlet) side but using a feeler gauge to check the clearance between the skirt and the cylinder bore on that axis came up with a gap of around 0.002”, which was within the BMW range for running clearance of the piston (0.03 – 0.07mm, 1 – 3 thou). I could still see some cross-hatching on the bores but I’m no judge of whether it is satisfactory so I will leave them alone- I have no experience with honing.
I had bought a set of rings on eBay that came from the USA but turned out to be made in China. The surface finish on the under-side of the compression rings looked a bit rough, so I ordered another set from Kmotorshop in the Czech Republic. They weren’t that different and their end gaps were actually wider than the Chinese ones.
But I stuffed up very badly. When compressing the rings and inserting the pistons into the cylinders, the thin oil control rings were inclined to emerge through any slight gaps at the bottom of the ring compressor tool. On one cylinder I managed to damage the end of one oil scraper ring- I was alerted by the resistance involved pushing the piston down. When I removed the piston there was a significant vertical gouge on the cylinder wall. Very dispiriting! I would have been better off leaving the rings alone.
I was so disgusted I just replaced the damaged ring and proceeded to reassemble the engine. In hind-sight I should have sought advice. The engine has done just 30 kms on the new rings – I used Penrite 15W-40 running-in oil and will change if after about 1000 km. It also has just tap water as coolant and I will replace that after about 600 km. It appears to be running ok but it’s early days.

 

[dimistyle]

From what I understand you can't hone the bores on the EP6 engine due to the coating used on the bores, something similar to motor cycle engine bores. So you've done all you could do anyway and reassemble the engine

 

[DoubleChevron]

From what I understand you can't hone the bores on the EP6 engine due to the coating used on the bores, something similar to motor cycle engine bores. So you've done all you could do anyway and reassemble the engine

how do you bed new rings if you can't put a nice sharp cross hatch on the cylinders

 

[dimistyle]

Well nope I'm wrong, there is supposedly an oversized 77.5mm piston according to the North Americans, a good Pdf engine description attached in this thread on the BMW/Mini R56 engine

Engine rebore possible ? - North American Motoring

R56 :: Hatch Talk (2007+) - Engine rebore possible ? - My 07 turbo engine has suffered a broken piston and the cylinder bore looks to have a few nasty score marks Can someone confirm if this engine can be rebored I have read the piston cylinders have nikasil coating therefore its not possible to...

www.northamericanmotoring.com

 

[Selekta]

NewTIS still works, ignore the legal mumbo jumbo and log in using the login form at the top right hand side of the page. If you need an invite, let me know.