Originally Posted by LAF
When I talked to my Service Manager on this topic and expense at 12,000 he said do not worry about it. At 12,000 we will go over it and listen with a stethoscope and if it sounds fine go to the 18,000 and do it then.
This is why I like this Dealer because he also feels the BMW maintenance schedule is aggressive, and believes that listening, checking the fluids well when drained, visual inspection, and how I feel the bike is running a better gage of maintenance. He told me flat out he will do what he feels in his opinion needs done, and if breaks in warranty, he will fix it, period.
I would think the biggest issue, that I was not aware of until someone on this Forum posted is the LT valves wear tight.
Now a loose valve you can hear pretty well.
I am not totally sure of what symptom (s) of a tight valve would be?
What, combustion wise, would a tight valve create?
I assume that a tight valve is one that is dropping farther into the cylinder, thus getting closer to being able to strike a piston?
I want to get the first one out at the dealer, but from then on I would like to do it. As others have said 12,000 is pretty quick and I sure can live with 18-24,000 checks if it seems safe to do so.
I guess on a used bike you have to do it once to see where you are as a point of referance anyway.
Tight valve clearance is only a couple thousandths, so has no bearing whatsoever on valve to piston clearance. Tight exhaust valves however, can cause premature burning of the valve/seat, which when started will cause valve work to be needed far ahead of normal, which is probably well in access of 250,000 miles if kept adjusted properly.
The reason is that all solid lifter cams are ground with "clearance ramps" which take up the normal clearance fairly slowly until all the clearance is out, then rapidly open the valve. That is to reduce both impact damage and noise. If the valves are allowed to run below normal clearance range, the valve starts to open slowly (relative) on the clearance ramp before being opened on the fast opening ramp. This slow opening causes hot exhaust gasses to blast through the tiny gap at ultransonic speed for much longer than in normal valve opening, and that starts to erode the seating surfaces. Those very tiny, microscopic size erosion pits then fairly rapidly enlarge until you have a noticeable valve leak, which progresses quickly to badly burned valves and seats requiring a valve job.
The valves and seats in the LT engine must be pretty darned robust though, becausee for the several years I have been on this site, I don't recall anyone requiring a valve job! Maybe because we usually preach "don't let your valves run tight!", and most heed the warnings.
Loose valves are not as much of a problem, but on the LT engine (or any cam over valve design) the normal pattern is for them to wear tight, not loose.