BIG BRASS SCREW o-ring

[BluegrassPicker]

I can't find these on the fiche, can someone point me to a source?

[Ken H.]

Your local hardware or automotive parts store. There's nothing special about that O-ring. Just take the screw and the old one with you and match it up.

[Selden]

Do these O-rings tend to wear out over time? If so, this is a pretty simple addition to routine maintenance.

 

I'm surprised at how coked up the air bleeds get between tune-ups (as evidenced by the amount of black on the screw, and in the bleed hole).

[Jerry Duke]

A friend came over last night with a 96 (I think) R850R that was idling rough. He had already adjusted the valves so we were prepared for a throttle cable adjustment. Before hooking up the TwinMax I pulled and cleaned both air bypass screws. Talk about soot and dirt....

Cleaned them both, ran them in all the way, gently, and hooked up the TwinMax. With about 1/2 turn out on each, the idle was perfect. Sounded like a sewing machine. The cables were so close we didn't even bother with any adjusting.

I was surprised at the difference just cleaning made.

[tomk99r11]

A shot of compressed air into each of the screw holes is also usually helpful. Need to do my 99 soon again and this step seems to help a lot.

[Selden]

This has been my experience: they coke up, and should be cleaned with every tune up, before attempting a sync. At one point my left was 1.5 turns and the right .5 turns out; after cleaning, each within a quarter turn of 1.5, and smooth idle.

[Ken H.]

Do these O-rings tend to wear out over time? If so, this is a pretty simple addition to routine maintenance.

As a rule, no. But every once in awhile one gets torn or something. I presume that’s what’s happened to the OP.

[ShovelStrokeEd]

They live in a hostile environment to elastomers. Gas vapors, vacuum, long term position followed by being turned. I'm not sure how long they should last but a tip on prolonging their life is to lightly lubricate them. Petroleum jelly is not really the best for this but will do. I use a silicone vacuum grease that both lasts longer and is better for the composition of the O-ring. A hydraulic supply store is a great source for these things. There are a number of materials available but plain old Buna is fine and the cost is usually pennies. If you really want to get fancy, Kalres will set you back about 5 bucks each and won't do any better.

[japachap]

Ive asked this question before on other forums without getting a sensible response, but...

 

If the BBAS operate in a by-pass channel for the main throttle butterfly plate then is all the crud that builds up in them caused by oil vapour that enters the air system from the crankcase breather pipe that connects inside the air filter?

If that is so then has anyone tried fitting a condenstion/vapour trap filter (cars have/had 'em) to the crankcase breather?

Seems like the way to go to reduce crud build-up between servicing, or is the general opinion here that this is also overkill...?

[nrp]

The residual gas pressure in the cylinder after the exhaust valve closes allows some of the exhaust fumes to get into the intake system when the intake valve opens. The intake manifold surfaces are usually cool so there will be a variety of compounds deposited.

[Ken H.]

The residual gas pressure in the cylinder after the exhaust valve closes allows some of the exhaust fumes to get into the intake system when the intake valve opens. The intake manifold surfaces are usually cool so there will be a variety of compounds deposited.

Yes, that’s always been my speculation also. It’s more of a ‘back draft’ issue than an intake air issue. Especially during deceleration.

[ShovelStrokeEd]

While it could be some back drafting during the overlap, the cause is not usually from residual pressure in the cylinder but rather a phenomenon called reversion.

 

Reversion occurs when a combination of cam timing, rpm and intake/exhaust tract length conspire to force exhaust gases back into the cylinder and actively blow them back through the intake tract. It occurs to some extent on all engines and is more prevalent on those with long cam timing and highly tuned exhaust and intake tracts.

[Selden]

Thanks for the explanation, which is as good as I have ever seen. I will continue to clean the screws and passage with each tune up; it's not that much extra effort.

[japachap]

The residual gas pressure in the cylinder after the exhaust valve closes allows some of the exhaust fumes to get into the intake system when the intake valve opens. The intake manifold surfaces are usually cool so there will be a variety of compounds deposited.

 

Really?? So you're saying that burnt combustion gasses can travel maybe up to six inches from the cylinder back past the the inlet valves back up to the throttle bodies and lodge minute ammounts of goo in the by-pass screw?

 

[X-files Mode On] 'I want to believe' [X-files Mode Off]

 

Why then when I cleaned my Throttles last was there a varnish on the airbox side of the butterfly valve, whilst the downstream side was relatively clean?

Why also no build-up of gunk in the vacuum take-off stub for throttle balancing?

I also refer to my old 4-cylinder Yamaha XJ bike which had a balance pipe connecting all four inlets 'to help scavenge charge via equalisation of intake manifold pressure pulses' or something... This pipe never got blocked or gooed over the 60,000 miles I owned it (120,000 total).

If you also look down in the airbox past the filter grille to near the intake tubes you'll see a slight coating of the same thin goo- how did that get as far back as that?

 

With all due respect, Im unconvinced...

 

 

[RoanokeRider]

The residual gas pressure in the cylinder after the exhaust valve closes allows some of the exhaust fumes to get into the intake system when the intake valve opens. The intake manifold surfaces are usually cool so there will be a variety of compounds deposited.

 

Really?? So you're saying that burnt combustion gasses can travel maybe up to six inches from the cylinder back past the the inlet valves back up to the throttle bodies and lodge minute ammounts of goo in the by-pass screw?

 

[X-files Mode On] 'I want to believe' [X-files Mode Off]

 

Why then when I cleaned my Throttles last was there a varnish on the airbox side of the butterfly valve, whilst the downstream side was relatively clean?

Why also no build-up of gunk in the vacuum take-off stub for throttle balancing?

I also refer to my old 4-cylinder Yamaha XJ bike which had a balance pipe connecting all four inlets 'to help scavenge charge via equalisation of intake manifold pressure pulses' or something... This pipe never got blocked or gooed over the 60,000 miles I owned it (120,000 total).

If you also look down in the airbox past the filter grille to near the intake tubes you'll see a slight coating of the same thin goo- how did that get as far back as that?

 

With all due respect, Im unconvinced...

 

 

Why do you insist on confusing the issue with facts?

[David R]

First, silicone is not good for an o2 sensor. There are different types, and I don't know the difference.

 

Now you are flying down the highway at seventy something for hours.

 

EVERYTHING is hot including the throttle bodies.

 

Intake air is passing the throttle plates. Pull into a rest area and let it idle one minute like always to allow equalization of the heat. Engine is Idling. Vacuum is high,almost all the air is going by the BBS. Oil vapor from the air box is also going by the BBS and gets cooked on it.

 

David

[Ken H.]

Really?? So you're saying that burnt combustion gasses can travel maybe up to six inches from the cylinder back past the the inlet valves back up to the throttle bodies and lodge minute ammounts of goo in the by-pass screw?

 

[X-files Mode On] 'I want to believe' [X-files Mode Off]

 

 

With all due respect, Im unconvinced...

(Shovelstroke) Ed is by far the superior engine engineer that I (he built them for years), so he can explain it better than just about any of the rest of us, but the concept is actually quite accepted. Six inches is a micro-distance for the speed of combusting gases to travel. Exhaust deposits in intakes of internal combustion engines from valve overlap is quite common.

 

The oil vapor deposits in the upstream areas of the air supply from the crank case ventilation system is a totally different issue. Actually it’s basically a design flaw in the oilheads. One that has been corrected in the hex and camheads.

 

[japachap]

[quote=Ken H(Shovelstroke) Ed is by far the superior engine engineer that I (he built them for years), so he can explain it better than just about any of the rest of us, but the concept is actually quite accepted. Six inches is a micro-distance for the speed of combusting gases to travel. Exhaust deposits in intakes of internal combustion engines from valve overlap is quite common.

 

The oil vapor deposits in the upstream areas of the air supply from the crank case ventilation system is a totally different issue. Actually it’s basically a design flaw in the oilheads. One that has been corrected in the hex and camheads.

 

I didnt mean to imply that Ed wasnt correct in what he said, just that I considered the oil vapour issue to be the primary factor. Oilheads may use half to a litre of oil between services and whilst some of it invariably gets past the piston rings, I just felt that the majority of it will exit via the airbox and subsequently through the throttles/BBASs. This quantity of oil seems to massively outweigh gasses flowing back from the combustion chamber, for whatever reason!

 

What is the setup in the Hex and Camheads? Im looking at the parts fiche, and I see a breather pipe from the cylinder/head, but not where it goes to- airbox, maybe? How is this different to the Oilhead- or are you referring to the 1200s not having the BBAS and therefore not having the problem? Surely you're still getting some oil vapour baking onto throttle parts though???

 

Not wanting to divert the thread away from 1100/1150s and BBASs, but do you 1200 riders blast your throttle bodies through with carb cleaner every(/other) service? And, if not- why not?

 

I may not be able to access BMWST for a while, so dont take it that Ive ducked and run...

[Ewell D.]

This thread has answered a question I didn't know how to ask for fear of sounding stupid.

 

A week ago I installed the left cam chain tensioner upgrade and in doing so noticed buildup on the throttle body downstream of the butterfly valve. I have been wondering what the source of that is and whether I should be worried. Sounds like a periodic cleanup is all I need to concern myself with. Is that right?

 

How much buildup of deposit in the throttle body throats would it take to affect performance?

[japachap]

Anybody tried modifying the intake pipes (between the throttles and airbox) so that carb cleaner can be sprayed into the inlets/throttles without dismantling the tubes- ie 'quick-cleaning', or with the engine running..?

 

Sounds like a project...

[nrp]

How much buildup of deposit in the throttle body throats would it take to affect performance?

It won't affect max performance, but the idle air supply settings could be compromised by gook.

[Ken H.]

Here’s the key point – the deposits seen in/on the BBS’s and their ports isn’t oil, it’s carbon.

 

Without getting into a big long discussion, the crank case breather system in the hexhead is significantly different than in the oilheads. The oilheads vented the oil containing crankcase via a dual passage affair around the rear main crank shaft oil seals. It is all one big chamber where lots of anatomized oil particulate is always present. The hexhead’s crankcase on the other hand is a dual upper/lower chambered design where the likelihood of oil anmatomization is much reduced in the first place. Then the external ventilation pick up point is in the left hand head cam chain area, farther from the actual crankcase volume. The hexhead’s ventilation system is not susceptible to the oil pick up that the oilhead’s is.

 

ISFSA cleaning deposits on the inside of a throttle body, IMHO that’s just being AR. Think a second about the math – what % of flow capacity is that thickness of deposits going to reduce the volume of the TB? 0.001%? If we were talking about a highly tuned racing engine, well then I might entertain the idea. But we’re not. We’re talking about a emissions de-tuned street bike. You’re likely to do more damage mucking around inside of one with cleaning stuff than you’ll ever gain. If you must – run some injection clear in a couple of tanks of gas.

 

The servo controlled air bypass ports in the hexheads don’t seem to be susceptible to the carbon deposits issue of the oilheads. Some change made to the TB design as to the location of the port I’m presuming. I’ve had several (higher mileage) steppers out and the plunger (replacement for the BBSs) doesn’t show any signs of deposits. So one way or another it appears BMW is past that issue.

 

[BluegrassPicker]

Wow 3 pages on an o-ring question

 

Thanks for the suggestions. Mine were looking worn, but still usable. I will replace them next oil change. My bike is running smoother since I cleaned them.

[David R]

I do not disagree about the back flow of combustion products in the intake.

 

We do have some good discussion here.

 

AND everyone is polite.

 

I like that

 

David

[nrp]

flow capacity is that thickness of deposits going to reduce the volume of the TB? 0.001%? If we were talking about a highly tuned racing engine, well then I might entertain the idea.

The idle air flow can be met with only a few thou of throttle opening. A little contamination in that crescent can go a long way to effect the airflow.

 

It isn't just oil that comes out of the breather system. Really it is a witches brew of crankcase blow by gasses - mostly CO2, water vapor, unburned or partially burned hydrocarbons, and a whole host of other combustion products.

 

I agree the throttle body shouldn't be casually disassembled. The alignment and area around the throttle plate is particularly critical.

[japachap]

 

I like piccys...

[ShovelStrokeEd]

In answer to a comment about silicone being bad for the O2 sensor back a page or so. Yes, it is true, however, the amount of silicone involved is so minuscule as to be insignificant. The proper method for applying this grease to an O-ring is to apply a tiny amount (about 1/2 a match head) to the fingers and then rub the fingers together to create a film on the fingers. The O-rings are then rubbed between the fingers as well.

 

I use this grease on the O-ring seals around the glassware on our mass spectrometer equipped instruments and have never seen silicone or any fractions on a scan and I can see parts/billion.

[Ewell D.]

OK, so just clean the brass screw things at the next throttle body balance, maybe think about having the injectors cleaned and forget about the carbon on the throttle body!

 

I do occasionally run some injector cleaner in a tank of gas but mostly try to use chevron or shell gas.

 

Informative thread, thanks!

[Selden]

 

I like piccys...

Worth a thousand words.

[philbytx]

Jeez!

How many miles was that......

[japachap]

Sorry for late reply- Ive been far, far away...

 

Well, my 12,000 was done Sept 05 by a dealer I trust implicitly- so it should have been done then, but...

 

The 18k was in Aug 06 by a new-to-me dealer.

 

24k in Mar 07 by same dealer...

 

30k in Oct 07 by me- I didnt know about the BBAS at the time...

 

36k (34,600mls) feb 09 by me, still not checked BBASs

 

35,500 mls Apr 09 BBASs finally checked as per photo above.

 

 

Depending on how thorough the dealers were before me, the crud build-up pictured ocurred over somewhere between-

 

12,000miles/2years (assuming good dealer service)

and

24,000miles/3.5years (assuming my old trusted dealer did a good job)

 

So, a minimum of 12,000, but possibly 24,000 to get this gunked up!

 

 

[Selden]

No pic, but they do gunk up pretty quickly. I back the screws out and clean them at the same time as every valve adjustment.

[AndyS]

I can't find these on the fiche, can someone point me to a source?

 

Back to the question.

If you give me the diameter (section) of the O ring material [someting like 1.78mm/2.62mm / 3.53mm],

And the ID of the O ring (in the order of 8mm) I should be able to furnish you with the BS number of the viton O ring required.

 

Andy

[ragtoplvr]

I also clean the port in the throttle body.

 

I take off the vapor canister hoses, put a rag under it and spray cleaner into the BBS hole, the first few seconds do run black.

 

You want to undo the hoses for a drain. The cleaner will not hurt things but restarting after cleaning is much easier if you let the stuff drain out.

 

You can pop off the Air Filter cover and filter, use a long to to spray in the intake while running, you will need a bit of throttle to keep it from stalling. Lots of smoke.

 

Or just use Chevron Teckron cleaner in the gas.

 

Rod

 

 

[jeffm]

I would be really interested to know these measurements also.

 

was there any response to this?

 

 

[Selden]

You want to undo the hoses for a drain. The cleaner will not hurt things but restarting after cleaning is much easier if you let the stuff drain out.

Nice tip. I haven't been doing this, and can confirm that the engine can be a bear to start.

 

With some trepidation, I have been using a wood-stick cotton swab to clean out the bore. The cotton tip came off once, but I was able to carve "hooks" onto the end of the wooden stick and fish it out. Pulling the vapor canister hoses and flushing with copious amounts of cleaner spray seems like a better approach (or at least, less likely to go wrong).