BMW R1200RT/R1250RT Forum

I own a 2009 BMW R1200RT with 95k miles on it. In that 95k miles, I've lost performance and fuel economy twice. This is to stay that on two occasions that engine failed compression and leakdown tests. The last time, it made 150 lbs. compression with 9% and 11% leakdown in each cylinder. So, I love this motorcycle, and I want to save it. I'm tired of putting new rings in it, only for them to fail in 20k miles.

So, I decided to send the cylinders and heads to a machine shop - one that shall not be named yet. I told them I want the heads redone, new Wossner pistons and rings, and cylinders plated, bored, and honed to match. They say that they can do it. Great!

Well, the machine shop removed the brass plug that blocks the oil galleries on the #1 cylinder (right-hand side). They even drilled and tapped the hole that remained. I didn't recall removing any fastener from the hole, and I reserved myself to the fact that I would find it as I reassembled the bike. Well, I found out what was missing very quickly when I started the bike up, and it gushed oil all over my lift.

I didn't want to tear the bike back apart and waste $1500 for new gaskets and o-rings, so I plugged the hole with a screw, crush washer, and some red threadlocker.

Anyways, I break-in the new top-end only to discover that the bike is more of a dog than it was before. A compression and leakdown test proved that the bike now makes 130 lbs. compression and 10% and 20% leakdown. It's worse than it was before with a brand new top-end! I'm livid! When I tore the top-end apart again, the bottom spark plug was wet with oil. As I dug deeper, the exhaust valve is coated with burnt carbon. There is no sign of any oil that has bypassed the valve seals. The head gasket is fully intact and looks brand new because it is brand new. There was a puddle of oil in the combustion chamber sitting at the bottom of the piston where it meets the bore. The top of the piston is coated with oil-soaked carbon and has a nice film of oil all over it. There is a bit of wear on the bottom of the bore from the piston skirt.

The pistons appear to look fine. The top ring looks like it sealed evenly and completely across the bore. The second ring is worn about halfway across the bottom, e.g. if you hold the ring horizontally, only the bottom half of the ring shows wear.

I box everything up and send it back to the machine shop. It takes them two weeks to look at the parts after they received the shipment, even after I called them twice. They say, "Everything checks out. We think that you have a timing issue." Are you serious? A timing issue? How can a timing issue introduce oil into the combustion chamber? The bike is properly timed.

It wasn't until I got upset with a representative of the machine shop that they presented me with these numbers.

#1 Piston
3.975" piston size
3.9762" bore size
top ring end gap .015"
2nd ring end gap .020"

#2 Piston
3.9745" piston size
3.9764 bore size
top ring end gap .015"
2nd ring end gap .019"

Anyone have any thoughts here? I have my own.

An interesting read and a coincidence, after 67K miles, my 1980 Yamaha XJ650 is undergoing a top end overhaul. I'm "honing in" on the piston ring end gaps. On the 650, the piston ring end gap was outside of the installed (new) limits but within the service limit. The cylinder bores have been lightly honed and a new set of standard piston rings is being fitted. This has reduced the piston ring end gap by half and is now within the installed (new) limits and 25% of the service limit. The oil rings were seized in the piston grooves. There was blow-by the piston rings and the compression was well down on standard. The engine restorers were not keen on using anything other than genuine Yamaha piston rings.

Looking at the Haynes manual for a Hexhead, the top and second piston ring end gap should be 0.004" to 0.012" with a service limit of 0.032". The machine shop measured piston ring end gaps are all above the installed (new) limits and ~45 to 60% of the service limit.

If oil is getting into the combustion chamber, could the oil rings be the problem.

A cylinder compression of 130 psi is within the "normal" range of 125 to 145 psi.

Are the materials of the Wossner piston rings and cylinder coatings compatible with each other. From what I have been told, the piston rings are "sacrificial", as has been proved to be the case with my 650. The cylinders did not require re-boring and oversize pistons fitted.

95K miles is not excessive, viewtopic.php?t=6737&hilit=survey

I had a 2007 Hexhead which after 10K miles, partially seized on both cylinders. At the time BMW were experiencing a problem with pistons.

It is usable for the bottom spark plugs to look more sooty. It left on the side stand for a while they can also become slightly oily