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Old 01-04-2012, 04:07 PM   #391
Midnullarbor
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Steveman, if I may speak for Joel . . . he was not meaning that the "compression ratio" ("CR") was literally unimportant, but that we must not fall into the trap of thinking that the engine's nominal CR is what applies in all circumstances of engine operation ~ nor can the CR be considered as precisely comparable between different engine models/types [in terms of its effect in compression heating of the fuel mixture].
Please allow for some looseness of American rhetoric !


Camshaft timing, engine speed, throttle position, and other factors will affect the actual or "effective" CR (which I am sure you were already fully aware of, in view of your experience with engines).
And you are right of course, in that for any particular engine [without other changes] an 11:1 CR piston will cause less compression-heating than a 12:1 CR piston.

As I mentioned in an earlier post . . . I still don't fancy crossing Peru while cruising at 5000 rpm in second gear, at one-eighth throttle !
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Old 01-04-2012, 04:54 PM   #392
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Quote:
Originally Posted by Steveman View Post
Joel, thats heavy stuff for me as non native speaker, but its very interesting and I think and hope I understood most of it.
However your explanation of CR and that it has nothing to do with tendency to knock more or less is in my opinion not absolutely correct. you are sure right with mentioning other things than CR alone, combsution chamber construction, air inlet, pinch point, spark plug design and thermal value, cylinder temperature etc. etc.

In the early 90ies I spent hours and hours on the Dyno and we did serious tuning of Kawasaki and Honda racing engines. Of course only 4 cylinders. We had serious trouble with the Kawa superbike engines due to high rpm knocking. Maybe you can hear it, we could not, at least not on 4 cylinder engines running on the Dyno with 12 to 14000 rpm. But you could feel it and I have idea how I could describe that.

We have tuned the engines exactly to Kawasaki Kit Engine Specs but Kawasaki was always somehow close-mouthed about deatails not described in the kit manuals. And you know what cured the problems? After a hint from Mr. Rob Muzzy (he owned a Kawa SBK team) he gave me on the phone we replaced the kit spark plugs (40 bucks each in 1993!) with cooler standard plugs and used aircraft fuel with 104 instead 100 octane. No more problems. No knocking, nothing else changed just the fuel. And most interesting, the knocking only occured on engines where we raised compression (at this time 12.5:1 to 12.8:1) as Kawasaki described in their kit engine manual. The standard engine never had this problems. Considering that the kit engines had massive coolers and running with much lower water and oil temperatures the only reason for knocking was the higher CR. I just mention that as you say it plays no role, which imho is not correct. I see high CR's as a major reason why engines knock although they are not overheated and are mechanically healthy....
When you raised the CR, that and VE raised "mean compression". CR has an effect, but it's not particularly useful as a measurement unless comparing apples to apples.

For instance, changing throttle from 5% to 100% doesn't affect CR in the least. It is a static measurement and unaffected by throttle or anything else that affects VE.

As to your description of the Kawi, now I understand.

Terminology isn't 100% standardized but there are between 2 and 4 different names for types of abnormal combustion depending on how you lump things.

Knock, so named because you hear it audibly knock, is the sudden explosive ignition of end gasses. It is only the explosive ignition of end gasses because that phenomenon doesn't occur until pressure is way high due to combustion being already underway. Knock is what makes pistons look like all the ones I have seen here and with my own eyes on exploded F800 engines.

What was happening with the Kawi was not audible because it wasn't knock but rather "pre-ignition". The text book cause of pre-ignition (though there are others) is too hot of a plugs after glowing and starting orderly normal combustion at the wrong (too early) time. You can feel it but you can't usually hear it. It can be felt ok usually on a 4 cylinder but is 3x more feel-able on a 2 cylinder.

This is a good explanation of terminology http://en.wikipedia.org/wiki/Engine_knocking

In any case, raising the CR increased energy density and therefore specific heat which overheated the standard plug. Textbook preignition.

Make sense?
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Old 01-05-2012, 02:30 AM   #393
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Ok, so it is : Downshift to keep the throttle low and keep the rpm high. Also keeping our exhaust and airfilter stock helps. I don't fancy it either as Midnullarbor said, but at least it is good to know that there is a way to reduce impact.

The only thing i didn't get, due to english not being my native language, is this:
Quote:
Originally Posted by JoelWisman View Post
... Poor mans water injection, repeat ...
what do you mean by that? are you suggesting that we place the air filter back in place while it is wet?

thanks for all the advice
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Old 01-05-2012, 03:34 AM   #394
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Quote:
Originally Posted by roadspirit View Post
Ok, so it is : Downshift to keep the throttle low and keep the rpm high. Also keeping our exhaust and airfilter stock helps. I don't fancy it either as Midnullarbor said, but at least it is good to know that there is a way to reduce impact.

The only thing i didn't get, due to english not being my native language, is this:

what do you mean by that? are you suggesting that we place the air filter back in place while it is wet?

thanks for all the advice
I think Joel made a joke. A true water injection system would lower the temperature and increase the power output as with cool air you're able to inject more fuel without letting fuel/air ratio getting t00 rich.

So if you put in a wet air filter this - as a joke - may raise your power output. A poor mans water injection
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Old 01-05-2012, 03:52 AM   #395
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Quote:
Originally Posted by Midnullarbor View Post
Steveman, if I may speak for Joel . . .
Sure, your (and Joels) explanations are most appreciated!

Quote:
Originally Posted by Midnullarbor View Post
he was not meaning that the "compression ratio" ("CR") was literally unimportant, but that we must not fall into the trap of thinking that the engine's nominal CR is what applies in all circumstances of engine operation ~ nor can the CR be considered as precisely comparable between different engine models/types [in terms of its effect in compression heating of the fuel mixture].
Ooops, OK my fault as I didn't understand it that way. Apologise. No doubt, CR cant be taken as comparable parameter between different engines, thats a fact.

Quote:
Originally Posted by Midnullarbor View Post
Please allow for some looseness of American rhetoric !
Honestly, American rhetoric and spelling is easier for me than British. I worked for Chrysler so many US terms are not so uncommon. Unfortunately the last 15 years I did not need my lingual knowledge and if then it was pure British English. But at least most Brits say "Steve you're talinkg fookin American stop that darn slang!"

Quote:
Originally Posted by Midnullarbor View Post
As I mentioned in an earlier post . . . I still don't fancy crossing Peru while cruising at 5000 rpm in second gear, at one-eighth throttle !
Yep, I fully agree, thats not great fun....

Thanks
Steve
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Old 01-05-2012, 05:18 AM   #396
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Quote:
Originally Posted by JoelWisman View Post
When you raised the CR, that and VE raised "mean compression". CR has an effect, but it's not particularly useful as a measurement unless comparing apples to apples.
Not sure if VE is what I think, I guess (!) that it could make sense in this case if its volumetric efficiency. However, I fully agree with the above said!

Quote:
Originally Posted by JoelWisman View Post
For instance, changing throttle from 5% to 100% doesn't affect CR in the least. It is a static measurement and unaffected by throttle or anything else that affects VE.
100% right


Quote:
Originally Posted by JoelWisman View Post
As to your description of the Kawi, now I understand.


Terminology isn't 100% standardized but there are between 2 and 4 different names for types of abnormal combustion depending on how you lump things.
Additionally it is a problem translating the Austrian/German terms into English as very often the translation is not 100% spot on,

Quote:
Originally Posted by JoelWisman View Post
Knock, so named because you hear it audibly knock, is the sudden explosive ignition of end gasses. It is only the explosive ignition of end gasses because that phenomenon doesn't occur until pressure is way high due to combustion being already underway. Knock is what makes pistons look like all the ones I have seen here and with my own eyes on exploded F800 engines.
Exactly as I understand it. Additionally it can be said that it appears never in the last third of the rpm range but most of the time from low to mid revs. We too just call it "knock" or "engine knock", these terms describe and mean what you said above.

Quote:
Originally Posted by JoelWisman View Post
What was happening with the Kawi was not audible because it wasn't knock but rather "pre-ignition". The text book cause of pre-ignition (though there are others) is too hot of a plugs after glowing and starting orderly normal combustion at the wrong (too early) time. You can feel it but you can't usually hear it. It can be felt ok usually on a 4 cylinder but is 3x more feel-able on a 2 cylinder.
OK, I see you absolutely understood what I tried to describe. Unfortunately what you describe as "pre-ignition" is in our laguage also called "knocking", in fact "high rev knocking". Which is literally and physically wrong. Its not knocking and it makes no audible knocking sound. So pre-ignition is correct but menas something different translated to our language. Whatever, we both now know what we are talking about. This pre-ignition stresses the pistons, bearings, rods etc. and leads to a power loss. I am sensible so I can feel it, even on the Dyno but I can not hear it as in fact it makes less noise than common knocking and additionally the exhaust noise, wind, etc. makes it difficult to hear anything. I believe if you say you can hear it on a twin or single cylinder due to the reasons you mentioned above and the fact that these engines normally dont rev so high.

Quote:
Originally Posted by JoelWisman View Post
This is a good explanation of terminology http://en.wikipedia.org/wiki/Engine_knocking
I'll read it. Thanks.

Quote:
Originally Posted by JoelWisman View Post
In any case, raising the CR increased energy density and therefore specific heat which overheated the standard plug. Textbook preignition.

Make sense?
Yes Sir, absolutely!

Thanks for sharing your knowledge, most appreciated. And thanks to you all for not flaming me because of my lingual deficits

Steve
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Old 01-05-2012, 05:58 AM   #397
roadspirit
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Quote:
Originally Posted by Steveman View Post
I think Joel made a joke. A true water injection system would lower the temperature and increase the power output as with cool air you're able to inject more fuel without letting fuel/air ratio getting t00 rich.

So if you put in a wet air filter this - as a joke - may raise your power output. A poor mans water injection
ok! :)

Anyway, trying to lower my fears I was thinking, probably there are numerous F8GS out there doing road trips in S.America and in Central Asia, globetrotting in general, going to places that good fuel is hard to find and chances are that you will get crap fuel.

How many F8GS make it safe? How many break? So far, cases that I know of, are Alberto's and Naomi's here, Raymond Behm's bike (http://behm.lu/blog/en/home/) that also broke down in Peru, and Uli's F8 (http://www.alser-on-tour.de/english) that broke down in Alaska.

Are there other known stories of broken F8GS on the internet? (other forums, other blogs etc) ??
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Old 01-05-2012, 12:56 PM   #398
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You know those expressions 'Back in the day" or "When I was a lad"? Well, bein an old fart, I gotta try one. Back in the day we were proud owners of all kinds of "Beaters". This classification covers all those $200 vehicles we would buy and, seemingly drive for an eternity. I've had and seen friends drive heavy knocking cars, and I mean real lemons, pouring smoke and running on 7, 6, or 3 and all we'd do is add more cheap oil (recycled Nugold here in Canada) and change the plugs. Countless miles put on these pieces of crap. So, what happened? How did technology reach such a state that the smallest mistake can convert your $15000 brand new happy ride into your nail biting worst nightmare.
This thread has turned into such a detailed philosophy class on high tech mechanics I thought I'd just expand on it a bit.
God, give me back my good ol Blue Flame (67 Blue Volvo station wagon with telltale smoke.)
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Old 01-05-2012, 01:12 PM   #399
JoelWisman
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That old 140, unless u were a cool kid with an 1800 or ancient even then 544, made 108 HP from 1.8-2.0L of displacement, a tun of Hydrocarbons and ran on leaded gasoline.

Throw away the catalytic convertor and run leaded gas in the F800 and it will make 85HP from 0.8L and be at zero risk of detonation.

All the high tech wizzbang makes the F800 sip fuel while making massive power but it is true that it's not as tolerant of putting the wrong stuff in the gas tank.

Ironically, it's a lack of 1980's technology (knock sensor) that makes the F800 less tolerant of bad fuel then the Volvo B18 and B20 power plants were through sheer inefficient mass.

P.S. A round the world trip in a B20 powered Volvo will cost you more then a new engine for your F800 at todays fuel prices, and be a whole lot less fun, so modern technology isn't entirely without merit :)
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Old 01-05-2012, 09:07 PM   #400
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Quote:
Originally Posted by roadspirit View Post
ok! :)

Anyway, trying to lower my fears I was thinking, probably there are numerous F8GS out there doing road trips in S.America and in Central Asia, globetrotting in general, going to places that good fuel is hard to find and chances are that you will get crap fuel.

How many F8GS make it safe? How many break? So far, cases that I know of, are Alberto's and Naomi's here, Raymond Behm's bike (http://behm.lu/blog/en/home/) that also broke down in Peru, and Uli's F8 (http://www.alser-on-tour.de/english) that broke down in Alaska.

Are there other known stories of broken F8GS on the internet? (other forums, other blogs etc) ??
Mark 'Radioman''s F8GS engine went tits-up in Tucson, Arizona. The story here
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Old 01-06-2012, 06:52 AM   #401
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I mentioned one here in Veracruz that was only dealer maintained, ran premium fuel here, and every bearing in the motor was finished and BMW replaced the motor but the owner paid for dismounting the old one and mounting the new one.
The motor was supposedly sent to Germany for further study. As a side note, the owner of that bike had replaced every other bearing on the bike, front wheel, steering head, and rear wheel and all were bad and some with catastrophic failure that resulted in the bike being trucked home from one trip. It was an early 2009 build date with some differences from other 2009 models like the front brake master cylinder being a cloudy plastic finish and the rear axle left side being a different arrangement. That bike never detonated that I know of and just was worn out after 30,000kms of dealer service.
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Old 01-06-2012, 06:19 PM   #402
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There are some BIG QC problems and one needs to take a few steps to prevent low fuel quality damage but many of these engines are going far.
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Old 01-14-2012, 10:24 AM   #403
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I know 6 BMWs F800GS belonging advriders.

I know 6 BMWs F800GS belonging advriders.
These motorcycles have about 40к-80к.
2 from them were often used in offroad.
Any serious malfunctions to them hasn't occurred.
One case occurred in Morocco is known only.
In fork there was a rupture of sealants.
But it has been connected with an error at service.
In a fork the superfluous quantity of oil has been filled in.

I am very happy with this motorcycle,
It is very reliable.

In Russia this motorcycle is on sale for gasoline 91RON.
83HP / 91RON (min).7500rpm

In my opinion breakage of engines in Peru has been caused by bad gasoline,
Probably it was gasoline worse than 87.
I am glad that BMW nevertheless has made the decision on repair at own expense.
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Pate screwed with this post 01-14-2012 at 10:34 AM
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Old 07-21-2012, 07:37 PM   #404
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After seeing Nick Saunders 50.000 mile strip down on his Yamaha XTZ1200 Super Tenere,
and him doing both directions in the Americas,the moral of the story is;Avoid anything Rotax
designed,wether it be BMW or KTM!
Saunders Yamaha was like new inside,i given that he rides a lot harder than most,it's a testament
to quality engineering........i know where my money would be going!
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Old 07-22-2012, 09:41 AM   #405
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The two issues I have seen on F800/F650 bikes with high mileage (over 80,000kms) is alternator failure and cam chain stretch. The cam chain stretch now appears to be a much easier fix with the aftermarket sourced split link and corresponding chain. The alternator failure is interesting and there could be a remedy for that. BMW could fix both of these problems but why bother when they can con people about the "legendary performance and reliability" and then sell them a big ticket repair?
I have seen other lower mileage failures that are simply substandard parts and poor assembly.
The Super Tenere is an interesting option but you'll probably find less support for it than even the F bikes in the developing world.
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