Valve Adjustment

I just received my new BMW Owners manual for my R75.

The valve adjustment measurements state .15 and .20 for intake/exhaust, which differs from Clymers. I'm assuming the BMW manual is correct, any input from the forum?

Yeah, the information in the BMW manual came from BMW.

As for Clymers, who knows?

I'll guess that your Clymers says 0.10/0.15. The value settings have changed, even from BMW, over the years. The lastest service bulletin that I can find (ca 1984) set the clearances to 0.10/0.20 intake/exhaust after break-in. But the 0.15 for intake is a good thing to do. It doesn't detract noticeably from engine performance but does allow the valve to rest on the seat for a fraction of time longer, helping with heat transfer. The intake valve needs this less than the exhaust valve due to the in-rush of cooling air-gas mixture.

Not that I quote Paul Glaves as the end all of information; but he discusses valves in depth in the July issue of "The News". He is much more in touch with bulletins, etc than I will ever be..........on page 30, "The latest bulletin calls for all Airheads to be set at 0.15 intake and 0.20 exhaust".


Thanks Paul........Dennis

BMW moa article

Thanks that article was right under my nose the whole time.

FWIW, Snowbum's airhead top end manual says to set intake at 0.006 in and exhaust to 0.010 in.

Manfred said:

FWIW, Snowbum's airhead top end manual says to set intake at 0.006 in and exhaust to 0.010 in.

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That would be Oak's topend manual. The 0.010 seems a bit much and will result in a bit more noise. Probably OK but 0.008 works just fine. FWIW, Snowbum has discussed using 0.0085 for the exhaust. I think he does it like others have mentioned...0.009 won't go but 0.008 will slip through.

Did you get your answer ?

Howdy Pete !

Looks like you need to set em where you like !

Heck, I've always used .006 and .008 as I thought that was "correct" for an R75/5. Come to think of it, I can't recall where I got those specs.
Old age sucks.

Airhead Valve settings

ebeeby said:

Heck, I've always used .006 and .008 as I thought that was "correct" for an R75/5. Come to think of it, I can't recall where I got those specs.
Old age sucks.

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According to my master tech. (he was a BMW mech in those days) .006 intake and .008 exhaust is correct for my 84 R100RS don't know about the others.

Matt Parkhouse.

DennisDarrow said:

Not that I quote Paul Glaves as the end all of information; but he discusses valves in depth in the July issue of "The News". He is much more in touch with bulletins, etc than I will ever be..........on page 30, "The latest bulletin calls for all Airheads to be set at 0.15 intake and 0.20 exhaust".


Thanks Paul........Dennis

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Matt Parkhouse, "Keep 'em Flying", recently recommended this setting as I recall, not Paul Glaves. BMW recommends 0.10 mm for intake and 0.20 mm for exhaust, but as pointed out in post #3 by 20774 there are benefits to a "looser" intake setting. I use 0.15 mm intake and 0.20 mm exhaust ; a little more noise perhaps but I love the sound.

whoa......I am ever bad......MATT......sorry for getting the credit wrong.............one of those old ages moments I guess........But at least I was so impressed with the information from YOU that I remembered that..........God bless the old guys......Dennis

Cams are ground with acceleration and deceleration ramps on the lobes. The purpose of these ramps is to start lifting the lifter and valve gear slowly to overcome the inertia of the valve and valve gear as it begins to move and lift the valve off the seat. Then the lobe basically whacks the valve nearly to full lift and there is a ramp slowing the rate of lift as the valve reaches full open. This is to keep the valve gear from floating away from the cam and overlifting the valve, maybe tagging the piston. As the lobe begins to rotate out from under the lifter there is a ramp that starts the lifter slowly down, once it is moving the lobe drops off real fast and almost closes the valve. Now here it the point of this long winded post. The lifter gets to the deceleration ramp that slows the rate of drop (valve closing) and gently sets the valve down on the seat. If you arbitrarialy increase the valve clearance adjustment beyond what the engine/cam designers intended, the valve slams into the seat before the deceleration ramp is finished doing its job. This pounds the seat and valve and causes the adjustment to close up a lot faster than normal seat/valve wear. Going from .10 mm to .15 mm doesn'r seem like much, but it is a 50% increase in valve clearence.

0.15 mm vs. 0.10 setting for intakes.

Quote from George R.:If you arbitrarialy increase the valve clearance adjustment beyond what the engine/cam designers intended, the valve slams into the seat before the deceleration ramp is finished doing its job. This pounds the seat and valve and causes the adjustment to close up a lot faster than normal seat/valve wear. Going from .10 mm to .15 mm doesn'r seem like much, but it is a 50% increase in valve clearence. ; unquote.

Great post George and informative. But if so many "gurus" recommend the .15 vs. .10 have they not considered any ill effects? I have been using the .15 on intakes and detect no negative consequences as yet. Matt Parkhouse does say in the July "Keep 'em Flying" ,and I paraphrase, " You can use a tighter setting than the .15 intake if you so choose.", referring to the .10 gap, I suppose.

Your thoughts pleas, as I really resp[ect Matt's opinions and advice.

An interesting debate. I use the .006/.008 clearances myself (saves memory, among other things, as my Commando uses the same settings), thinking that looser is better (more time to cool on the seat), although maybe not so important for the intake valves. I have an 84, so want to fend off the inevitable rebuild as long as I can.

Will be interested in everyone's views/experiences.

No question about it, if your valve clearances are too small, you can burn a valve prematurely, but this takes time. If you set your clearance too large, your valves get hammered bouncing off the seats and the valves can break in less than 10 miles. The moral of the story is that either too little or too much clearance is bad. Too much clearance can go bad really quickly. It is not that .15 is too much for the intake valve, but don't run off a think that .25 must be even better. I saw a lot of people make that mistake when building modified car engines. Oak suggests that the clearances be opened a little extra for the first 50 miles to give the valve seats a little room to bed into the heads (.20mm intake and .25mm exhaust), which I am sure is a reasonable idea. Then he suggest running at .15 intake and .20 exhaust for the rest of the engine life. This seems reasonable based on my VW Beetle and Porsche experience too.

carockwell said:

No question about it, if your valve clearances are too small, you can burn a valve prematurely, but this takes time. If you set your clearance too large, your valves get hammered bouncing off the seats and the valves can break in less than 10 miles. The moral of the story is that either too little or too much clearance is bad. Too much clearance can go bad really quickly. It is not that .15 is too much for the intake valve, but don't run off a think that .25 must be even better. I saw a lot of people make that mistake when building modified car engines. Oak suggests that the clearances be opened a little extra for the first 50 miles to give the valve seats a little room to bed into the heads (.20mm intake and .25mm exhaust), which I am sure is a reasonable idea. Then he suggest running at .15 intake and .20 exhaust for the rest of the engine life. This seems reasonable based on my VW Beetle and Porsche experience too.

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Great post and one that makes a lot of sense. Thanks. I will continue to set at .15mm intake and .20mm exhaust. As mentioned by George Ryals "going from .10mm to .15mm is a 50% increase. As such, it seems .15mm intake, is the limit for a "loose" setting.

BMW Gurus

jamesdunn, I too have the utmost respect for Matt and the other airhead mechanics who have shared their years of experience and knowledge with the rest of us who maintain our airheads as a hobby.
Even though intuition says that having a valve on the seat longer is good for transfering heat, my intuition is not enough to make me believe the engineers that designed these engines got it a little wrong. The way I look at it, is if the valve needed to be on the seat a little longer the engineers would have discovered this during the months of dyno runs they must have done before releasing the design for manufacture. One other thing to think about on this theory of more time on the seat to cool the valve being good or necessary, if the valve needs more seat time, "why would BMW manufacture long duration cams for these engines?" They hold the valves off the seats a lot longer than the cams most of us are running.

Why sacrifice a little valve lift and duration if you don't REALLY have too?

I have been using the 006/.008 clearances for all my airheads over the past 20 odd years. Have found no ill effects. Not found it has made any difference as to when the inevitable valve job needs doing. And when they need doing, I just take the heads off and have them done. Part of owning an Airhead, or any engine for that matter. They all need a valve job eventually.

shire2000 said:

I have been using the 006/.008 clearances for all my airheads over the past 20 odd years. Have found no ill effects. Not found it has made any difference as to when the inevitable valve job needs doing. And when they need doing, I just take the heads off and have them done. Part of owning an Airhead, or any engine for that matter. They all need a valve job eventually.

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As I said earlier, I'm a .006 and .008 guy (though I can't recall why, old age, yada yada)
That said, I really don't understand where this .10 and .15 is coming from. This is news to me. I have NEVER hear those used until I read this thread. So is there some sort of metric/thousandths disconnect going on here?
Inquiring minds want to know....