Valve Adjustment Hot Bike

[MichiganMike]

Question here, did the valves on a 93 R100GS, Sounded perfect when I got done. Took it out on the road and all was great, Rode out to my son's house stopping for gas on the way, about 20 miles into the ride. Shortly after the fuel stop and restart I seemed to lose power and felt a miss. The left intake valve adjuster had not been properly tightened and was loose. I had all the tools required and pulled the valve cover and set about adjusting that valve.

Now the major question???? What would the experts have set the gap on that valve at with a hot engine?

The only tool I did not have was a good maglight or similar small flashlight with a good beam. I had removed that from the bike with some other extra tools the day I did the valve adjustment in the comfort of the pole barn workshop.

:banghead

[cjack]

I would have just used the stock settings.

[AnnapolisAirhead]

I'm not an expert, but I would set them a bit wider than normal to get myself home and let her cool off for the morning. Not hugely, just a bit more room than normal without being able to slop the guage back and forth. Might be a tad noisy, but I think that'd work. And easy does it getting back home.

These bikes have an amazing tolerance.

[vanzen]

I'd set them to spec as usual ...
knowing that I would then need to sneak up on the old twin next morning
to re-adjust properly while cold.

[RecycledRS]

This is an interesting question. I have read about other bike owners (band name forgotten) that have carefully set the valves cold and measured the gap when hot. The result was that it had not changed significantly. The theory was that the cylinder had expanded at approximately the same rate as the push rods leaving the clearance the same. The fear that valves can only be set on a cold morning may be unjust.

Has anyone had the inclination or time to measure this on an airhead??

[RoboRider]

The gap is present so that when the metals expand with heat, the gap diminishes, becoming smaller at operating temperature. If you set them hot, the gap will be too large. So I would have set them at spec, not more or less.

However, I would think it would be fine to get home and then check cold the next day. And, I can't say as I've ever done a "hot vs. cold" check as suggested. Maybe in real life it doesn't change much. It's an interesting question.

[vanzen]

... The fear that valves can only be set on a cold morning may be unjust...

That's a good one :brad

I'm in no way trying to suggest that valves need to be adjusted on a "cold morning",
but rather,
any later in the day ... and MY bike will be ridden, i.e. engine warm !
... and therefor too late to: ADJUST WHEN ENGINE COLD
as per the BMW manual (who's info has mostly always been "just" by me)

[MichiganMike]

Okay, I appreciate the comments, Now here is what I did, since this was the first time ever that I had something come loose like that, I set that valve at .009 and rode home. Power and sounds were all great. It is supposed to rain here tomorrow so first thing Monday will be a check and re-set if required and I will post what I find for the group. The only thing I can think of was I was showing another airhead owner what a valve adjustment program was and possibly I got distracted on that valve when I was tightening it up. The 32 mile trip home was a great ride but I was listening closely to make sure nothing changed again.

[RecycledRS]

Okay, I appreciate the comments, Now here is what I did, since this was the first time ever that I had something come loose like that, I set that valve at .009 and rode home. Power and sounds were all great. It is supposed to rain here tomorrow so first thing Monday will be a check and re-set if required and I will post what I find for the group. The only thing I can think of was I was showing another airhead owner what a valve adjustment program was and possibly I got distracted on that valve when I was tightening it up. The 32 mile trip home was a great ride but I was listening closely to make sure nothing changed again.

I would be interested in knowing what the valve is at when cold before you re-adjust them.

[R90S]

I would measure the other side's settings and match them.

They should be at the same temperature, right?

[20774]

I would measure the other side's settings and match them.

They should be at the same temperature, right?

Now there's somebody with their thinking cap on!! :thumb

[DennisDarrow]

good thinkin jon-lars............if out on the road and have a full set of feeler guages rather than just the one in the tool kit.........

[MichiganMike]

Okay, final result here. Opened it up again this morning with a cold engine and the intake that had come loose was dead on at .009. That was where I had set it with the engine hot after a 20+ mile ride. I adjusted it back to a cold .006 now and will leave it there.

Final result for this engine at this time, the intake valve setting was the same with a hot engine and then checked later with an overnight engine at about 65 degrees this morning.

Not sure what this proves but was very interesting to me as I had never had this experience before with several airheads.:usa

[tvrla]

The manuals all say to adjust when dead cold, but an expert life-long bmw tech here will adjust the valves a couple hours after the bike was running, if time is tight. He says the important thing is to have it cool enough to handle. I've never checked what clearance was when hot, but that's a good idea to check the other side. Another possible solution would have been to check the clearance of the exhaust valve to see how much it had changed and adjust the intake proportionately.

I'd think .009 was a bit too much clearance for the intake. Maybe .005 if you wanted some extra, but not more than double. The only damage from running too wide a clearance is hammering the tappets, and in a short distance that would have been minimal.

[RoboRider]

I appreciate you posting this but you've destroyed all I thought I knew about valve clearance procedures!

[swall]

If you have a valve clearance spec, at say, .008" cold, the amount of expansion in going to 150F or so is very small. You won't detect the difference with a feeler gauge.

[vanzen]

If you have a valve clearance spec, at say, .008" cold, the amount of expansion in going to 150F or so is very small. You won't detect the difference with a feeler gauge.


... which brings to mind 2 questions:

1) Why does the BMW specify adjusting the valves with a cold engine ?
and
2) Given that all parts in the engine will expand with heat, if only an immeasurable amount –
how many parts must be associated before the cumulative difference is measurable ?

[AnnapolisAirhead]

If you have a valve clearance spec, at say, .008" cold, the amount of expansion in going to 150F or so is very small. You won't detect the difference with a feeler gauge.

I'm thinking 150 is about when you can turn the enricher/choke off. Surely it gets much hotter than that in the valve train and inside the engine, no? Has anyone ever taken an infrared thremometer to a bike after a 10 mile ride?

:scratch

[RecycledRS]

Okay, final result here. Opened it up again this morning with a cold engine and the intake that had come loose was dead on at .009. That was where I had set it with the engine hot after a 20+ mile ride. I adjusted it back to a cold .006 now and will leave it there.

Final result for this engine at this time, the intake valve setting was the same with a hot engine and then checked later with an overnight engine at about 65 degrees this morning.

Not sure what this proves but was very interesting to me as I had never had this experience before with several airheads.:usa

I was a bit skeptical about others observing the same gap cold/hot thing with different engines. I guess manufacturers just want to start with a base line temp orrrr...... they've just always done it that way!:thumb

[carockwell]

Fortunately, I have actually done this little experiment. The valves stay the same, hot or cold. Don't believe my results, repeat my experiment and see if you get the same results (was it Albert Einstein who said that?).

Adjusting the valves cold is a deal we airhead mechanics like to tell the service writer so we can take another coffee break...

[keelerb]

I thought the whole idea of clearance when cold is because that clearance shrinks when hot - the reason the intake valve needs less clearance than the exhaust (which gets hotter)?

[woodgrain]

According to a former BMW dealer from California, the reason the BMW factory wanted engines cold when adjusting valves, was because of a problem with /2 and earlier model heads being unstable when hot. The /5 and later model heads were/are stable and don't have this problem. You can set the valves hot or cold without worry. Oh joy, oh bliss.

Woodgrain

[20774]

According to a former BMW dealer from California, the reason the BMW factory wanted engines cold when adjusting valves, was because of a problem with /2 and earlier model heads being unstable when hot. The /5 and later model heads were/are stable and don't have this problem. You can set the valves hot or cold without worry. Oh joy, oh bliss.

Huh?? I've never heard of such a thing... The technology is the same on my /2 as a /5. There were other problems with the mid '60s heads having to do with changes to the metallurgy and/or the way the molds were cleaned that created the "butterheads", but that had nothing to do with how one sets the valves, cold or hot. The rocker blocks would slowly, very slowly, settle into the heads over time creating a change in clearances. This was fixed with the "LK" heads of the late '60s.

[04R1150RS]

Yeah, go ahead and adjust your valves when hot if you want to, but is it worth taking a chance of burning a valve. Hearsay or not I'm doing mine when cold!!!! I never never do while hot, not even warm.
All the cars I've had with mechanical valves spec to do when cold. Except my Toyota (22RE engine), which specs to do when hot. Screws me up every time on that one.