Air bypass screw O-rings

[docc]

For certain, the V11 is exceptionally sensitive to even very minor intake leaks as well as exhaust leaks. These can add up to a maddening crusade to hunt down and eradicate idle issues and the nefarious sub-4000 rpm cough/hiccup.

Ever the Beta Tester, and afflicted with a painfully inquisitive mind , I removed my Air Bypass Screws for cleaning this Decent Tune-up :

Yep, they were really sooty and nasty. Far worse than this "representative image" shows:

Then I got the clever idea that the 20+ year old O-rings could be suspect (green, left: below). One, especially, looks deformed and damaged. So, I locally sourced Viton O-rings in "Standard" size #008. They look (and measure) a bit undersize (black, right: below):

After waiting at a crowded counter at my expert rubber&gasket resource (along with folks repairing bulldozers and well drilling equipment ), the good man sizes the wee O-ring as metric 4mm I.D. x 2mm cross section. The #008 is indeed a bit undersize. He figures Viton is the right choice and orders them for me. (I had him get a dozen so the well drillers would let me live) and asked him what the OEM green O-rings could be. He figured EPR (or EPDM) as used with refrigerant, but no way they could have lasted all this time (me: "thinking" ). 

So, what are the OEM green air bypass screw O-rings? Nitrile?

And, isn't it coming time these hidden leak sources might start contributing to our madness if undetected? 

 

[Tomchri]

Nothing beets new rubber,,, or was the old Oring of better quality. Any leaks is bad, but a tiny leak there ? Thanks docc for finding out. Perfect is nice even agricultural vehicles .

Cheers Tom.

[docc]

I will report back on the results of installing fresh, correct O-rings on the Air Bypass Screws. There are many (many) culprits to exorcise that contribute to the V11 sub-4000 rpm hiccup/cough. As, @Tomchri has said, " the TPS is VERY important ."

Yet, one of the most maddening hiccup/cough sources to contribute to my (ongoing) madness: a very slightly loose vacuum tap and dried out rubber cap:

(Yes. It made THAT much difference. )

 

And, yep, sometimes those superficial intake rubber cracks aren't just on the surface:

 

 

In case we forget that "Ignition" issues can send us down the "Fuel/Air/Map" rabbit holes, this coil -> ignition wire connection failure took a long time to reveal itself . . .

[al_roethlisberger]

14 hours ago, docc said:

I will report back on the results of installing fresh, correct O-rings on the Air Bypass Screws. There are many (many) culprits to exorcise that contribute to the V11 sub-4000 rpm hiccup/cough. As, @Tomchri has said, " the TPS is VERY important ."

Yet, one of the most maddening hiccup/cough sources to contribute to my (ongoing) madness: a very slightly loose vacuum tap and dried out rubber cap:

(Yes. It made THAT much difference. )

 

And, yep, sometimes those superficial intake rubber cracks aren't just on the surface:

 

 

In case we forget that "Ignition" issues can send us down the "Fuel/Air/Map" rabbit holes, this coil -> ignition wire connection failure took a long time to reveal itself . . .

Were you able to just successfully clean it with electronics cleaner?

 

[docc]

48 minutes ago, al_roethlisberger said:

Were you able to just successfully clean it with electronics cleaner?

 

Are you speaking of the corroded coil output?

Yes, it cleaned up, but the wire end had corroded apart and had to be replaced. And, yes, that nasty hiccup was much improved!

[docc]

Correct metric air bypass screw O-rings in Viton, 75 Durometer,(4mm O.D.  I.D. x 2mm cross section), compared to the (U.S. expedient) #008, the inside diameter (I.D.) is especially suspect (loose). The #008 (right) is visibly undersized, yet so very close. 

Correct metric O-rings installed in mySport, now, and awaiting a check ride to see if this issue introduced the nasty hiccup/cough/stumble/hesitation at various new rpm once warmed up, or if I jacked up the TPS setting with my last "Tune-up."

>unscientific< comparison shown in thousandths of an inch.

Original Moto Guzzi green O-rings shown top, left ("probably" Nitrile).  Opening, and zooming, the higher resolution image clearly shows one is damaged.

[Speedfrog]

5 hours ago, docc said:

Correct metric air bypass screw O-rings in Viton, 75 Durometer,(4mm O.D. x 2mm cross section)

I think you mean 4mm I.D. no?

Source?

 

[docc]

8 hours ago, Speedfrog said:

I think you mean 4mm I.D. no?

Source?

 

Haha, yes, indeed! A 2mm cross section with a 4mm O.D. would have no hole would it?

I sourced these at a local rubber&gasket supply, but here they are, in Viton, at McMaster-Carr:

https://www.mcmaster.com/9263K163/

I see that they are more reliable reporting the dimensions . . .

[PJPR01]

Thanks Docc...I just tried to order from them...$11 for a pack of 25 rings, but $39 for shipping!  Wow.

I'll have to find a local supplier...thanks for the technical info...might as well replace the ones I have as well as another "fine tuning" in the tuning process.

[docc]

McMaster-Carr usually is not horrible on shipping ($39 is horrible!) For sure, that was not some kind of expedited shipping (overnight or 2-day)?

With taxes, the O-rings here were $1.54US each, so right at three bucks to take care of a V11.

Bringing a little SpineRaid swag with me to Kentucky . . .

[80CX100]

While trying to find durable heat resistant O rings to seal up the ridiculous "designed on Friday after mucho vino lunch" cross over pipes on one of my Lafranconi exhaust systems; I got schooled on the crazy world of high tech/high cost O rings,which apparently went totally ape shit crazy, after the apparent O ring failure on the space shuttle Challenger?

The lady in charge of parts acquisition at my local Freco Hydraulic shop was extremely knowledgeable & helpful. She had at her disposal every O ring configuration known to man.

If you haven't done so yet, your local Hydraulic Servicing business might be worth checking out as a possible supply source.

fwiw idk

[PJPR01]

I'll have to check, I found something very close at ACE HW...at least the OD is identical, and ID is slightly off, but I think it might work.  For $1 each, that's a good deal.

Now that I think back to my coughing episode with the TPS reset, I recall I had to have the airbleed screws set differently...silly of me not to think of the O-rings as a potential culprit for that slight imbalance between left and right sides.  

Thanks for the heads up here Docc!

[docc]

Further riding this afternoon and I find the change from the #008 O-rings to the 4mmx2 metric made no difference. Seems the #008 will work fine as far as I can tell.

Just make certain the O-rings are fuel compatible (preferably Viton, although Nitrile/BUNA-N is probably fine. Nothing from the ACE plumbing aisle! )

My bad running issues look to be down to a bad TPS setting . . . Close, but no good.

[docc]

TPS posts moved:

 

[docc]

Regarding the air bypass screws, it occurred to me to say that if you have to set one side quite different than the other (like 3/4 and 1 1/4 turns out) to synchronize the throttle bodies at idle, take time to look for a vacuum leak.