It's an R100RS, Sept '81. I ran out of Valvemaster about a couple of thousand miles ago and kept checking the valve clearance for the following thousand miles, all seemed well, no recession. I checked the clearance again yesterday and there was no clearance on one exhaust valve, I couldn't spin the pushrod at TDC when cold. I must have been just in time because there's no damage to either the valve or seat, the surfaces seem uniform all round the faces. Oh, when I say no damage to the seat, that's only half right, it's recessed about 20 thous, 0.020" or half a millimetre.
Given the date of manufacture, ie around the time BMW started to try various seat materials I can't say whether mine are to the new specs. but after 90,000 miles I'm thinking that 20 thous recession is quite reasonable and that there's no point in putting new seats in providing I start using Valvemaster again.
I must say that, once again, I am surprised at how little wear there seems to be on the engine, rocker faces, valve tips, pushrod ends, cylinder bores (ok, they are Nikasil) are like new, and there's less than .0004" wear on the vale stems. There's little side play on the valve heads so the guides seem fine too, but that's a matter of judgement of course. Good to see that every time I do some work on the engine I am struck by how well it looks inside. Oh, hang on, that's apart from the gearbox, that needs new bearings, we'll see how that looks when I open it up in a few days ...
Anyway, back to my question: any point changing the valve seats, or just cut them back a touch to clear the step?
Given the date of manufacture, ie around the time BMW started to try various seat materials I can't say whether mine are to the new specs. but after 90,000 miles I'm thinking that 20 thous recession is quite reasonable and that there's no point in putting new seats in providing I start using Valvemaster again.
I must say that, once again, I am surprised at how little wear there seems to be on the engine, rocker faces, valve tips, pushrod ends, cylinder bores (ok, they are Nikasil) are like new, and there's less than .0004" wear on the vale stems. There's little side play on the valve heads so the guides seem fine too, but that's a matter of judgement of course. Good to see that every time I do some work on the engine I am struck by how well it looks inside. Oh, hang on, that's apart from the gearbox, that needs new bearings, we'll see how that looks when I open it up in a few days ...
Anyway, back to my question: any point changing the valve seats, or just cut them back a touch to clear the step?