Hi All,

A BMW Club UK member has emailed me regarding decoking the cylinder head of his K1100RS.

He wanted to replace the valve seals (25 years old) and clean up the head, including lapping in the existing valves/seats. In the BMW manual there is a note that any machining of the valve seats requires new valves to be fitted. Motorworks sell the exhaust valves for £126 each!

Would that be the case for just lapping the old valves as opposed to a full seat re-grind?

What method have you used to refit the valve seals?

At his stage I don't know what state the old valves are in (burnt out etc).

Thanks in advance.

Mike

When I did the head on one of my 16 valve K100's I just cleaned the valves with a brass brush and solvent(I think it was carb cleaner).  A propane torch helped the brush get the coke off the surface of the head.  I didn't go nuts on it figuring it was just going to coke up again.  I just got the worst of it.  Think about the stuff you didn't get as helping to raise the compression ratio./s

To protect the valve stem seals, it's recommended to use a plastic soda straw.  I couldn't find one that fit over the valve stem.  I just polished the stem with Scotchbrite and coated it with assembly lube.  A little bit of twisting and gentle pressure as the tip of the valve went through the seal got them in without damaging the seals.  Just be careful when the the notch for the keepers goes through the seal.

Thanks for the feedback Point-Seven-Five, I've passed it on.

Mike

The old-timers' enthusiasm for decoking and lapping in the valves as a routine procedure doesn't really apply any more. Not saying your mate is an old-timer though! If cylinder compression is good, then there's nothing to improve. If the stem seals are suspected of leaking, meaning the valves have got to come out to replace them, then you could justify a very light lapping with the fine grade of paste to make sure the seal is one hundred percent on reassembly. I've just sadly had to scrap a head because of clear pitting on some of the valve seats. Even attacking it with a spare, sacrificial valve and monster grade lapping paste couldn't remove the pits. What it did do, was to widen the valve seats, and wear away the valve head quite noticeably. This is something you really want to avoid, and it didn't take much doing at all!
On the other hand, I've just stripped down the replacement head for examination. The valves and seats are evenly coloured, with no signs of embedded debris, or uneven mating. I'm reluctant to lap them, but it's probably a good idea because I've disassembled and disturbed everything - and I only did that because the head came to me with all sorts of storage crap in the ports which I feared might have found its way trapped between valves and seats. I'll use the fine grade paste, and do the absolute minimum - maybe only six or seven rotations - and stop soon as the valves and seats are an even, smooth colour.
As you can probably guess - I've been massively berated in the past by someone with a lot more know-how and ability than me, for being too keen to lap valves!

Well it wasn't me!

your right on the lightest touch to 16 valve seat lapping twb.

dont forget that 16 valve versions have under bucket - or built in shim thicknesses to the lifter and unlike the 8 valve cousins where shims are easily got at ,,,,,its pull the cam after measuring carefully and fit a new - exchange bucket of the correct thickness 

thankfully not much valve regressions is noted on most of those machines 

just a note worthy of reinforcing

Hi Chris846 and Charlie99,

Thanks for the information. 

He hasn't got the head off yet, so don't know what the inside state is like. He is waiting for parts before removing the head, and now has a friends R1200R that needs a new clutch, so that will be done first!

I'll post an update when he strips the head (I'll be supplying the various tools from our club's Tool Hire facility).

Mike

As written here before, lapping valves is not adequate on these engines. Valve seat metal is very strong, the only way to get an acceptable result is to proceed with a valve seat cutter to re-shape the angles - and to do the same thing on valve. It's an accurate job requiring specific tools and skill.
The good old trick with sanding paste has a chance to spoil the valve and seat contact ring, you can't control angle, width or flatness proceeding with this, and it may spread surface irregularities all around instead of reducing them. And as the valves diameter is very small compared to old engines, their spring rate is also light and won't compensate any defect on the contact ring, so they need a very precise machining.

Did I read some place there is sodium inside the valves?

Not these valves, or they're the cheapest sodium valves ever sold!