The Boxer Engine - A Question For the Historians

[Deletedmemberjdcxxx]

Hi Guys,

I've got a question for the guys who have owned / ridden BMWs for a long time.

I'm going to add the disclaimer that I'm not criticising my own bike, I love it, and the only thing that would replace it is a slightly newer one in the sandrover colour scheme. I'm just interested in how it has developed so no headslapping icons please.

The mechanics of the GS engine seem bullet proof and although the boxer engine is a bit unusual its as simple as any internal combustion engine. Attached to it is what appears to be a convoluted fuelling / engine management system that seems fraught with performance problems. There are hundreds of posts on this site about lean running, booster plugs, remapping, accelerator modules etc. (I've fitted one of the latter.)

Remember this isn't a criticism but I did my DAS on a new Honda CBF 500 which was a pretty dull bike, but it could pull away slowly in first gear with no accelerator and then toodle along forever. As I said there was only ever one bike that I was going to buy and I have got used to the occasional lurch and splutter. So my question is why has the GS developed in this way? I don't want to know how to fix it, I've read all the posts on remaps and bolt ons and the cheapest option has done a very good job for me. I'm just a bit surprised that I would need to fit one. Is there a reason why BMW havevn't addressed the problem?

Having received some very random answers to previous posts I would be really grateful if you could answer the question that I'm asking above and not provide me with an answer that refers me to Google, the IAM, a Youtube video about milking cows, or any answers designed to show how much smarter than me you are.

Cheers.

 

[Jon P]

I have had BMW boxers (and three and four cyl K series and F series) for almst 25 years. I like the boxer - it's the layout I have always associated with the brand. Just like, to me their cars should have a straight six. My first new one was a '91 R80GS and have had just about every one after that.
The carb twins were sweet - the motor did what you told it too. The fuel injected twins however have always had some 'issues'. I bought a new 1100GS from the first batch in the UK and wrote to BMW about it and had an article published in the BMW journal. There are all manner of 'cures' out there but why bother? I just get used to it and ride away. You can spend time and money 'playing' with your bike trying to change / improve but to me it's not an issue.

The K series bikes never had the issues of the twins but to me, the K series bikes never had what I call 'character' either. The F650 was a carb model and was good - I like singles.

I have also had a lot of KTMs, all of them with carbs and they were great but I understand that the later injected KTM twins also have issues.

Over the years BMW have issued all manner of solutions, such as ensuring that valve clearances are spot on and then in 2003 they went twin plugged - that did make an improvement.....but it's still not perfect. I think we are partly to blame by demanding large capacity twins with lots of power (though it does seem that Ducati can make it work). Motors have never been bigger. In real terms it's not that long ago that a 650 twin was a big bike and now we are up to 1200 twins!!

In truth the boxer should have been axed in the early 80s - BMW were going to do so by introducing the K series but the grey beards voted with their wallets so BMW had to make a U turn, bring back the old boxers and start to develop a new one. In terms of mechanical layout I would say that the 'new' boxer was a mess - so many chains, two oil pumps, still used pushrods. Yes, it was a real mess but it worked and has proven very reliable. Of course the more recent ones did go overhead cam but still had lots of chains and now water cooling. What ever next?? So there you are like it or lump it. I like it and just like all my previous BMWs I leave them standard.

 

[Nice 'n' Fat]

As I said there was only ever one bike that I was going to buy and I have got used to the occasional lurch and splutter. So my question is why has the GS developed in this way?

It's the bloody EU with their meddlesome interference on emissions and the like

 

[DrFarkoff]

I am beginning to think this bloke is Trippy in disguise?

!!!

 

[APE]

IMO having owned and put significant miles on one 1150GS and two 1200GSs there are no fundamental issues with the engine. You'll never get inline 4 type power but that's not the point with these bikes.

The only caveat I would add is that the last single cam 1200GS (I believe was 08/09 ?) used the 1200R engine and that ran very lean and a lot of bods fixed it with that accelerator module thingie.

 

[Engineer]

The GS went the way it did because the boxer engine is a marketing success, BMW tried dropping it years ago but the outcry was deafening so they bought it back, modern electronics and advancements in materials and technology have ensured its success.

A boxer engine is relatively simple and has perfect primary balance, it is perfectly arranged for shaft drive and is easily cooled - perhaps most importantly it is different.

 

[2 wheel humvee]

I am beginning to think this bloke is Trippy in disguise?

!!!

The correct use of "there" rules that out-sorry

 

[SteveM]

It's the bloody EU with their meddlesome interference on emissions and the like

Is an emissions test part of the MOT in Europe?
Or are BMW just being green as part of some wider corporate philosophy?

 

[Deletedmemberjdcxxx]

The GS went the way it did because the boxer engine is a marketing success, BMW tried dropping it years ago but the outcry was deafening so they bought it back, modern electronics and advancements in materials and technology have ensured its success.

A boxer engine is relatively simple and has perfect primary balance, it is perfectly arranged for shaft drive and is easily cooled - perhaps most importantly it is different.

So why all the posts about lean fuelling / booster plugs / remaps etc. My 2009 GSA was very jerky until I fitted an Accelerator module. Was it just not possible for BMW to fix what seems a fairly fundamental problem. I've gotten used to it but you would expect a bike designed to go off road to have really good low speed control without a lot of clutch slipping. Again I'm not being critical, just wondering why.

 

[davegs]

Boxers

The lean fueling and booster plugs are there because of the latest emission requirements of the EU and their main customers
in the US. If your bike was that bad it requires servicing and adjusting by your friendly dealer or local ,expert the boxer design goes back to 1927 not quite the same as the modern bikes though.

 

[(RIP) Edvard Munch]

Two even bigger big jugs and twice as much powah as the , admittedly sweet, old things.

I don't expect the bike to be as smooth as a big multi or even a middleweight parallel twin because it won't be.

That said it does a pretty good job of providing enough pep and a still gives a fairly cosseting rider experience.

Whatever the engine configuration there are loads and loads of folk willing to sell you stuff to 'cure' problem(s) you previously never realised were a problem.

BTW if you think Ducati have aced this 'problem' I'd suggest you ride one or two modern examples.

Modern bikes are a piece of piss to ride and the GS is no exception you just have to have enough nouse to know it's not going to be like a big 4, or a middleweight Japanese twin

The so called 'jerky' throttle response on practically all modern EFI bikes is well reported as dewy eyed souls hark back to their smooth old carbed R80 or carbed Jap UJM. Is that what you base your 'comparison' on?

In my opinion they all generally ride, shift gear and fuel very efficiently and you're a mug for buying the tech tat to make 'em marginally 'better'.

IMHO of course.

 

[Engineer]

So why all the posts about lean fuelling / booster plugs / remaps etc. My 2009 GSA was very jerky until I fitted an Accelerator module. Was it just not possible for BMW to fix what seems a fairly fundamental problem. I've gotten used to it but you would expect a bike designed to go off road to have really good low speed control without a lot of clutch slipping. Again I'm not being critical, just wondering why.

All engineering is a compromise be it mechanical, electrical, civil or whatever - large capacity twin cylinder engines have their compromises too - the manufacturer is constrained by many conflicting requirements and what you got with the 1200 is what you got. The compromises could be shifted a little with the twin-cam and it was better at low speed than the previous model - the LC shifts those compromises again.

You can tweak the bike too, but you will shift the compromise - so asking why BMW didn't 'fix' what seems to be a fundamental problem is only meaningful in the context of your viewpoint which is different to theirs. Lean running for example reduces emissions and give better fuel consumption, it is just one of the inevitable engineering trade-offs that you are forced to make.

 

[Bendy toy]

The old R80 was well liked smooth and adequately powerful. The R90S was even better (ignore the spindly forks & weedy brakes. Then BMW couldn't resist making a 1 litre which was always criticised for being less smooth and hardly any more powerful. Since then the boxers got bigger and even harder to make smooth running.

Unlike a 90 degree V twiin the boxer engine does not have perfect primary balance. The con rods have separate journals so the pistons are not directly opposite each other. The power pulses are evenly spaced but the engine still rocks sideway as each side fires alternately.

If during the 1970s BMW had not their heads up their bums, they might have beaten Honda to the boxer four which solves most of the discussed mechanical issues.

Another ides would be to dump the inline, Vee and boxer formats. What about a radial? All four rods on one crank pin = zero vibration. It works well with a forced induction 2 stroke. Oh dear Beemer don't do strokers nit even DI.

 

[seahorse]

It ain't just BMW I can assure you. There are many other big twins from other manufacturers with similar symptoms. As has been said, it is down to emissions regs mainly, but thankfully there are always solutions.

 

[Engineer]

The old R80 was well liked smooth and adequately powerful. The R90S was even better (ignore the spindly forks & weedy brakes. Then BMW couldn't resist making a 1 litre which was always criticised for being less smooth and hardly any more powerful. Since then the boxers got bigger and even harder to make smooth running.

Unlike a 90 degree V twiin the boxer engine does not have perfect primary balance. The con rods have separate journals so the pistons are not directly opposite each other. The power pulses are evenly spaced but the engine still rocks sideway as each side fires alternately.

If during the 1970s BMW had not their heads up their bums, they might have beaten Honda to the boxer four which solves most of the discussed mechanical issues.

Another ides would be to dump the inline, Vee and boxer formats. What about a radial? All four rods on one crank pin = zero vibration. It works well with a forced induction 2 stroke. Oh dear Beemer don't do strokers nit even DI.

It does have perfect primary balance - the 'rocking couple' is not part of the primary balance.

 

[Bendy toy]

Lean running reduces HC emissions but at the expense of NOx which the catalyst is supposed to clean up. In reality NOx has always been a problem. Lean running only uses less fuel on a constant throttle. when more power is called for, it uses more fuel than a richer running engine. That's supposed to be solved with motronics but rarely ever is.

The smoothest lean burn engines are diesels. Sadly a toxic word in bike circles so we get offered generator engines rather than a scaled down TDI.

 

[Mistacat]

Two other culprits.

Compression ratios have increased, running 12 to 1 CR with a 14.7 AFR isn't easy hence knock sensors, complex ignition maps etc.
Combustion chamber design, until the total redesign with the LC this has been hard for BMW to work around.

Reference cheap tat and ad on`s. I have removed a PC5 and Autotune and fitted the BMW-AF-XIED. Early days, monitored it with GS911 and an innovate Lc1 wideband in another O2 bung.
Setting 7 as delivered seemed a little richer than advertised running 13.9 to 1 AFR and setting 8 Running 13.5 to 1 AFR.
This has re- sorted the bike as regards smoothness with a simple plug and play and no setting up.
Cheap Not at £300 delivered from beamer boneyard ( but better value for money than any other options I have tried) .
Plus it will fit any other BMS-K equipped bmw and also 800`s ,1100 & 1150 `s only require one ( nearly half price) with a different cable.

I have no interest in these only that it is nice to find a product that works as advertised and can't be adapted out by the BMS-K.

 

[JohnnyBoxer]

Perfect Primary Balance - who's right?

Engineer or Ben de Troy??

 

[bod]

I once had a Honda CB1300. A smoother, more refined bike you will not find ... But the fuel injection was still snatchy at low speed.

 

[Harry Nicholson]

Perfect Primary Balance - who's right?

Engineer or Ben de Troy??

Engineer

Cheers

Harry