Valves and seats ... Should I do something ?

[georgesgiralt]

Hello !
My 1982 R65 bought new in '84 has around 200 000 km on it's odo.
The heads have been rebuild in 1994 at around 120 000 km (broken spring..).
The mechanic exchanged the valves, guides, and springs and machined the seats to fit the new valves)
Now, every time I check the valve lash I find one or the two exhaust valves with too low or quite too low gap. (the feeler is difficult to pass or does not pass at all).
What do you think about that ?
I think it is time for new valves but should I change the seats too ?
Hearing your opinion will be greatly appreciated, as always !

P.S. : Since April 2012, I've checked and/or renewed quite everything on the bike except for the con-rod bearings and the main bearings.

[montmil]

Perhaps a visual inspection of the heads may offer a clue. You'd only be out a pair of head gaskets. How often do you re-torque the six head bolts? I try not to do that but once a decade.

[Barry]

If the seats are original 1982 and they were not replaced in 1994 then maybe they will need replacing this time around.  BMW didn't get unleaded seats right until a few years later.  

[Bob_Roller]

As Barry has said, the valve seats, were the problem, the valve recession is the result of the seat issue .
So, if the seats are not replaced you will still have the recession problem with the replacement valves.

[georgesgiralt]

I've checked the 1994 invoice and the seats were only machined not replaced.
I think it's time. If the valves could hold until the spring, i'll be in vacation and far from home. Good time to send them for refurbishing ...

[mrclubike]

Just how much are they closing every 8000 K
How thick of feeler gauge will fit in the gap
If they are only closing .05mm or less that isn't much
Not sure it is really a problem
Glad to hear you have gotten that many Kilometers  out of them

[D Mann]

You could pull the header off and look inside and see how much valve margin you have. If the margin is thinning or looks like a knife edge, it is time to spend some money.

[Kookaburra]

Montmil said-

"How often do you re-torque the six head bolts? I try not to do that but once a decade."

Why is there such a deviation from the recommendations in the BMW manual
(and Snowbum seems to share your view).

Please explain.

[georgesgiralt]

Why ? Because the gudgeons are threaded in light alloy.
So if you have a lighter alloy than planned (a little...) and a not so finely calibrated torque wrench as it should, there is a big risk of destroying the threads in the engine block.
As the thread is longer than usual, Helicoil are special to BMW and the repair needs to be done perfectly so needs a special jig.
In France, this often leads to a new block ... which is... costly...
So it is "common practice" to re-torque the heads only 1000 km after installing new head gaskets.
I do not know why BMW prescribed this schedule for torquing the heads.

[Barry]

Re-torquing the heads on a regular basis is madness in my opinion and just asking for trouble. Once after a new head gasket and once very rarely after adjusting rocker arm axial play is often enough.

How often do you hear of blown head gaskets - almost never so why would anyone do it.  You can't assume that BMW were infallible they weren't and occasionally got things wrong.  Some brand new engines left the factory already helicoiled.

When I do re-torque heads I stop short of the book 25ftlb figure and use no more than 22ftlbs.

[montmil]

Weather's too pleasant to stay inside on the compuKer, so...

What Barry said is on point regarding the unnecessary and continual re-torque of the four cylinder and two head studs. Disregarding the large cylinder-base o-ring and the two smaller rings at the upper cyl studs, all that's left to compress is the head gasket.

I just had the top end off my R100S -which does not utilize the base o-ring- to replace push rod tubes. After the initial torque was done, I waited 24 hours and re-torqued. I would guesstimate that the head gasket compressed enough to a value of approx one pound.

Some owners will check torque again after the first 100 miles. I'm not in that fraternity.

Same procedure done on both my R65s.

BTW, a forum member hereabouts is rehabbing a neglected early R90. Discovered helicoils and/or timeserts in three of the four engine case threaded bores... on the left side only!

The available Airhead shop manuals are not infallible and have not been updated in, well, almost forever. Point: Check the manual's suggested tire pressures. Modern motorcycle tires would be under-inflated if the manual's figures are used.

[mrclubike]

I have been doing this kind of stuff for a long time and this head re-torque thing was very out of the ordinary to me.
I didn't  even know it was done until I went to a tech day and they insisted on doing it before  adjusting  the valves.
  Talk  about being scared. Here I am a journeyman mechanic watching this guy  that thinks he knows better than me torque the head bolts in my aluminum block motor with a Chinese click type  torque wrench.
I was only there to find out about the vibration at 4200 RPM thing and they insisted on adjusting my valves.  
I have always torqued it down per the book and left it alone.
Just for the record I have found a lot of the torque specs in the BMW manuals  to be on the high side.
Some down right scary.   

[Kookaburra]

Thanks all. I am definitely over the retorquing thing. It has I think cost me one stud reseat on the left jug just after I got the bike.  ( Could possibly blame the PO but that may be unfair.) Recently after new rings and pushrod rubbers I torqued progressively to Snow bum's spec. Rode about 100km and retorqued to spec. Have not touched them since and don't intend to.