valve deposit. BIG TIME

[Cinciride]

I am hoping this is not as bad as I think it is.  I pulled the carbs off my bike today and peered in at the intake valve.  I will post a picture when I am at a computer, but what I saw concerned me.  There was a level of build up on the valves that made me think either the 70k + miles of pump gas has been unkind or I am getting some oil past the piston.  

Either way when it is thick is it time for valves and seats?

[montmil]

Pictures will be an assist, Cinci. Remain calm, all is well... Animal House.

Monte

[Red_Hen]

Hi Cinciride,

I don't know how long Airheads can go before they need overhauls but from what I do read on the forums is usually around your mileage a top end overhaul may be in order - like rings, pushrod seals and a valve job.

But - my grandfather used to say "if it runs good leave it alone."

Paul Glaves, from the MOA forum periodically suggests running the Chevron Techron fuel treatment through the gas tank before an oil change - his experience is this product helps remove some of the carbon - exactly from where - I don't know.

If it was my bike and it was running good, that's what I'd do before pulling off the heads but if the pushrod seals are leaking, I'd probably be inclined to to a top end job - once done, the bike will run like a new motor and if you plan to keep the bike awhile, your protecting your investments.

My 2 cents.

Oh, btw, why did you pull off your carbs?

[Dave 2]

Monte, what are you smoking today? [smiley=mad.gif] D22222222

[Cinciride]

Thanks for the responses.  Pushrod seals have been replaced, and I had a  mechanic look at the top end and it was deemed fine (Autobahn Craftwerks).  

Part of my concern is that after my last service (perfomred by the shop) I checked my oil just before a long trip and it was empty.  I suspected that it was not filled because I put oil in, and after (and during) my trip the oil did fine.  I did commute on the bike for several weeks before I noticed the absence of oil (2-3).

My bike does not smoke when it runs, unless it is left on the sidestand, but it has done that since it was new.  

Anyway, this is what I saw.  Carbs are off for a rebuild.  

[tvrla]

They look wet, like maybe oily? But the build-up isn't bad. I was expecting a large ball on the stem or something like that. The carbon doesn't bother me, but the wet does.

[Cinciride]

They look wet, like maybe oily? But the build-up isn't bad. I was expecting a large ball on the stem or something like that. The carbon doesn't bother me, but the wet does.

I had the same thought.  I have never seen the backside of a valve before that had carbon buildup.  I expected some, but not the way those look.  My bike has been running rich, and I have been riding it recently, so maybe it is just some fuel.  Other than smoke and oil consumption anything else to watch for as a symptom of oil getting past the rings?

Correct me if I am mistaken, but the 80 r65 cylinders can not be easily bored over for new pistons and rings secondary to the nikasil linings.  If it is worn or burnt rings, would just a new set of rings fix the problem if there is oil getting past?

Cheers. [smiley=bmw_smiley.gif]


I am photographing my carb rebuild to post later.  Right now I am trying to source parts.   [smiley=bmw_smiley.gif] I have an email out to bing.  Also considering Bobs and a&s, though I can't find needles on anyone's site except Bing.  Any other suggestions?

[tvrla]

The best (and cheapest) place for parts is the dealer. If none are close and you do mail order, go with Max BMW or Countryside in Chicago (they'll give a 15% internet disount).

What's happening that the cylinders need boring? Are you sure it can't just take new rings? Or are you just considering worst case scenarios?

There are other alternatives - such as sourcing some low mileage nikasil pistons and cylinders. For a couple hundred bucks you could be all set!

Also, your pistons will work in nikasils, if the correct size - but the rings aren't the same for nikasil as cast iron.

With 70K on the bike, your rings are probably fine. It is at a mileage when valve guides tend to need work, though. The best diagnostic procedure is a leak-down test. Lacking that, we're just poking in the dark and this could get needlessly expensive for you, besides causing more problems than you started with. As a corollary to not fixing what aint broke, it's a good idea to know what aint broke before trying to fix it!  

How much oil does it use between changes?

[Cinciride]

I am with you.  I am not interested I getting into fixes for the sake of fixing things.  

It was using exceedingly little oil between changes prio to my last oil and filter change.  The problems at the lst change (done by a garage that specializes I old BMWs), there was no oil in it when I check 3 weeks later.  I use this bike as a daily commuter.  There was no oily puddle anywhere and no smoke to suggest that I burned off an entire pan of oil.  I think they forgot to fill it when they made the change.  I used to do all my changes because I lived no where near any BMW service folks, and I enjoy ding it.  However, when I moved to Cincinnati I found a great garage and my job and kids activities left me very little time to do the work myself.  

Now my job has changed again and I will be doing more of the work myself.  

All of my questions at worse case scenario questions.  My plan is to rebuild the carbs, put it back together, ride it and see how the oil survives until my next change.  If there is a problem, I will be looking into solutions.  

Cheers

[Barry]

You know I can be guilty of worrying  about something that really isn't broke. I have a bit more carbon on the left piston than the right and sometimes it looks wet while the right is dry. I put it down to the engine breather favouring the left side for some reason.

The thing is it burns so little oil it's hard to measure - it must be doing at least 6000 miles per pint, the plugs are fine and both look the same, the bike runs perfectly and gets exceptional mileage so I quit worrying about it.

Do I still look down the plug hole when I take the plugs out  - yes of course I can't resist. In between services I forget about it.

As to how you might shift that carbon I hesitate to suggest this as I'm not convinced it's proven yet but as an alternative to a specialist fuel treatment you might consider dosing the fuel with high detergent TC-W3 2 stroke oil which is claimed by some to clean up valves and combustion chambers over time. Lou had a bad experience with I think the diaphragms when using a specialist fuel treatment. This stuff should at least be harmless in that respect.

Here's a link to the TC-W3 thread

http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1321295478