K51/K52 Wethead Valve adjustment observation

Greetings,

I have a 2015 R1200GS Adventure which I purchased new in July of that year. ~ 2 years ago I purchased a 2015 R1200RT which was near new (3100 miles.)

I performed the 12K service on the Adventure back in 2018 and found it kind of odd that clearances on all exhaust valves were out of spec the exact same amount @ .432mm (spec on exhaust calls for .34mm - .41mm (according to my service manual.))

If I understand wear, valves should get tighter as they wear, not looser... am I correct on that? If so, why did all 4 valves read looser than spec by .022mm? I recall thinking that odd when I did the service back in 2018.

What brings this to mind now is that I'm currently starting my 12K service on my 2015 R1200RT and have just measured the valve clearance on both sides. Again, all 4 exhaust valves are out of spec by precisely the same amount, i.e. .022mm loose @ .432mm. Intake valves are, as expected, a bit tight but still in the specification range.

I'm curious if anyone else has noticed this measurement while doing their service. 'Not a big deal to shim things down, but I find this very on on 8 out of 8 exhaust valves.

Again... just curious! Just a note, the bike was running beautifully when I shut it down for the season.

Thanks for any input.

Best,

-l-

How wear is related to valve clearances is complicated. In the most simple terms valve head or valve seat wear will cause the clearance to close up and get smaller. But cam follower wear and rocker arm wear (if rocker arms are used) will cause the clearance to get larger.

I can speak from experience with BMW K75 motors. For many, many miles the wear was offsetting. When shimmed correctly the clearances were very stable, with the engine taking one shim at the 600 mile service, and then only two additional shim changes in 350,000 miles.

But the offsetting wear can't last forever and eventually the valve heads will be thin and deform.

landev said:

…all 4 exhaust valves are out of spec by precisely the same amount…

Click to expand...

I think the odds on that happening, twice, are infinitesimally small. Thus, without any other information, my speculation would be that there is some other explanation for your experience.

Cap

I’m going to add a bit to the title for clarity.
OM

Good point, PG! I can see cam wear leading to in increase in measurement... 'never really thought about that. I imagine that would be something to take into consideration, particularly on a higher mileage machine. It's always nice to add to the knowledge base in my 'lil brain!

The person I purchased the RT from was a meticulous sort... 'owned the scoot for 5 years and had it serviced each year, having logged fewer than 700 miles per year. Service records show oil changes each year, no valve adjustments, so I'm assuming that any cam wear is minimal and probably not applicable... not sure about this. I've maintained my GSA meticulously also. Still the strange measurement and my purely academic posting.

Cap, I agree... the readings don't seem logically possible, hence the post. I have to admit I make a lot of mistakes... a LOT of mistakes! My "degree of precision" here is defined by my sense of touch to the feeler gauges... 'not absolute by any means, but pretty close.

When I'm working on machines, I recheck everything I do multiple times. My method for valve measurement is to measure one side, record the results and move TDC to the opposite side and record. I then go do something else unrelated for a bit, then come back and repeat the process. If I get the same readings, I call it a day, then come back in a day or two and repeat the process. Some days, I repeat dumb mistakes, but rarely two days in a row. If the measurements are consistent over a couple of days, then I prepare to shim the next day. Not trusting myself, I measure once again prior to removal of the cams to make sure. This is fairly compulsive behavior, but it has served me well for many years.

The adjustment to the GSA brought exhaust clearances down between .370 and .381mm. I hadn't realized the bike was previously performing below par until I did the adjustment. It's been running beautifully smooth and strong over the past 6K miles.

Thanks much for the input!

-l-

Cam wear happens on the nose of the cam when the cam is lifting the valve against the spring pressure. There should be NO wear on the base circle where you are checking the clearance as there is, or should be, no contact. A little loose is much better for the valves than too tight. The extra clearance could be caused by cam follower ("rocker") wear.

Frank

landev said:

Greetings,

I have a 2015 R1200GS Adventure which I purchased new in July of that year. ~ 2 years ago I purchased a 2015 R1200RT which was near new (3100 miles.)

I performed the 12K service on the Adventure back in 2018 and found it kind of odd that clearances on all exhaust valves were out of spec the exact same amount @ .432mm (spec on exhaust calls for .34mm - .41mm (according to my service manual.))

If I understand wear, valves should get tighter as they wear, not looser... am I correct on that? If so, why did all 4 valves read looser than spec by .022mm? I recall thinking that odd when I did the service back in 2018.

What brings this to mind now is that I'm currently starting my 12K service on my 2015 R1200RT and have just measured the valve clearance on both sides. Again, all 4 exhaust valves are out of spec by precisely the same amount, i.e. .022mm loose @ .432mm. Intake valves are, as expected, a bit tight but still in the specification range.

I'm curious if anyone else has noticed this measurement while doing their service. 'Not a big deal to shim things down, but I find this very on on 8 out of 8 exhaust valves.

Again... just curious! Just a note, the bike was running beautifully when I shut it down for the season.

Thanks for any input.

Best,

-l-

Click to expand...

In my experience, tightening valve clearances are a bad thing. For this to happen, you have to have valve seats and or valve surfaces that are experiencing wear faster than the cam followers. Back in the day, excessive valve seat wear in "air-head boxers" was common as fuel transitioned from lead to lead-free. Pre-lead-free engines had valve seats that were designed to be lubricated in part by the lead in gasoline. In order to prevent this, hardened valve seats had to be installed in the older air-cooled boxers else the valve seats would eventually wear away allowing the valves to collapse the seat. Sometime in the 80s BMW did harden the valve seats for unleaded fuel. I put 123k miles on my old 1984 R100RS and the valves always loosened slightly and rarely needed adjustment... especially after I dual plugged it. I'd rather have clearances that loosen slightly than tighten. Changing a worn cam follower is a lot easier than changing a worn valve seat.

I maintain my 1250RT myself. When I did the clearance check it at 12k, they were almost dead center between the lower and upper spec four all eight valves. When checking clearances on a "wethead", you also need to pay very close attention to the top of the cam lobes. There is a known issue where the cam followers fail and cause the cam lobes to wear prematurely. When it starts, it happens very fast and ruins the cams. The fix are a new cam follower design which all the 1250s have. I think the 2018 1200s have them as well, but I'm not 100% sure. This is not detectible when checking the clearances as the procedure checks valve and cam follower wear and not cam wear.

https://advrider.com/f/threads/2017-r1200gs-cam-failure-again.1370262/

https://static.nhtsa.gov/odi/tsbs/2019/MC-10165251-9999.pdf

Thank you Frank and Scott for your input... excellent information about the lobe wear issue. That makes perfect sense and is something I'd never have thought of. Very valuable and appreciated, having that addition to my knowledge base!

Sounds like the general consensus is to leave be, the "loose reading" valves and just attend to the two tight intake valves. I'm quite willing to do less adjusting rather than more.

I'm now interested in what my Adventure's valve clearance looks like after adjusting them down. It'll be a while until that happens... need to free up the lift!

Thank you very much for your help!

-l-

In case you missed this area- https://forums.bmwmoa.org/showthread.php?70623-Wetheads-Accessories-Mods-and-DIY-s
Good luck.
OM

Another thought: have you calibrated your feeler gauges?

I have feeler gauges (that I use for a different purpose than motorcycles). I discovered, via calibrated micrometer measurement, that they are not entirely accurate. I measured them, and now use the actual values, not the stated values.

Valve Clearances and Timing

I have worked on a number BMW's recent boxer engines and continue to be suprised that at 10,000kms how often the valve clearances are out of spec and valve cams are out of time. Quite often the can position sensor is not in the correct position as well. I always set valves that are out of spec as close to the center of the spec as possible and then every 20,000 kms measure and record the drift. Generally about 80,000 - 100,000 kms some of the valves will have to be re-adjusted but then they tend to remain quite stable. This is a simple task and when the valve clearances and timing is right the bike runs smoother, quieter and seems to have more power (seat of pants feel). The one thing that some people don't do is use a cam chain tensioning tool when they check the timing. The chain tensioner works on oil pressure so if you don't do this your cam timing may look out of spec but may be OK.

All 4 of my 2017.5 GS exhaust valves were tight from new. At 60, 600, then at 12K I changed them out to just about mid point but a bit tighter then mid.

My cam timing and cam position sensor was off at 60 miles and I did that.

My 15 RT was always stable and in middle spec in the 26K I rode it. Never changed.

I had always heard the BMW shim stayed in place very well. At 18K they were the same as when I changed them and my 24 will be soon so will be my second check in 12K on the new shims.

As to the OP I worry that you have two bikes with exactly the same "issue". It is pretty far out on the coincidence side of things. I would make sure of your feeler gauges and any math you may have to do.

If you were afflicted with the soft cam and follower issue you would know seeing it. If you can feel anything with a nail on your cam lobes you have issues. If not cam wear is not throwing off your measurement. Nor should it as we are not against it in measuring valves. But for TDC you would see the wear as soon as you looked to be sure your lobes were at TDC.

Let us know what you find out.