New 0ld Airhead - R60/5

[Bengt_Phorqs]

Hey Ken, nice bike!  We seem to be gathering quite a few of the '70's /5 and /6's.   My R90/6S (Monte's idea of nomenclature) has Napolean bar ends and they work very well.  I'll see if I can find a photo of same.  Did you find that bike back home or in Texas when you were here?  Here is one of the throttle side.

[Barry]

Interesting comment about speed - my son took her for a spin and thought she's quicker than the R65 - is this possible?The R65 has more cc's and updated carbs.

On paper there's not much in it with the R60 having 46HP vs 50HP for the R65. Perhaps it feels quicker because of the way the power is developed at lower revs. You've got a milder cam in the R60 with less overlap which will increase the effective compression at low to mid revs so I would expect it to feel strong.

Don't know if you have seen this period road test.

http://www.beemergarage.com/documents/r60rt2.pdf

[Red_Hen]

Hey Ken, nice bike!  We seem to be gathering quite a few of the '70's /5 and /6's.   My R90/6S (Monte's idea of nomenclature) has Napolean bar ends and they work very well.  I'll see if I can find a photo of same.  Did you find that bike back home or in Texas when you were here?  Here is one of the throttle side.

Hi Mike - nice R90!  Found this back home in MN - I just don't see many older BMW's advertised in the Houston area.  Mike V said the same thing - he doesn't see many Airheads for sale in Southern California.  

Sure is a quieter ride with the stock pipes vs the 2 in 1 Luftmeister on the R65!

[tvrla]

One thing that might make the difference versus the R65 is the R60 has accelerator pumps.

Another factor is that the R60 is essentially a long rod motor, especially compared to the R65, which makes for a whole different feel to the power band.

[Red_Hen]

So, Terry . . .

What is an accelerator pump?

Could you also describe a long rod engine and the differences between the R60 & R65 motor - compression? piston size?  What makes them different - I did notice right away that the R60 idles a lot smoother than the R65LS.  The R60 has a type 53 carb vs a CV on the R65.

[steve hawkins]

The other thing of course is, is it still an R60?  You can stretch that motor right up to 1050cc if you have the cash - new pistons/heads/bores etc.  Same bottom end as a R100 in theory.

Rev. Light

[Barry]

Could you also describe a long rod engine and the differences between the R60 & R65 motor - compression? piston size?What makes them different - I did notice right away that the R60 idles a lot smoother than the R65LS.The R60 has a type 53 carb vs a CV on the R65.  

The R65 has a bore and stroke of  82mm x 61.5mm that makes it an over square engine (bore bigger than stroke) which usually means an engine that likes to rev.

The R60 has a bore and stroke of 73.5mm  x 70.6mm which makes it only very slightly over square so together with the fact it develops maximum power and torque at lower revs than the R65 and with the milder cam thrown in it's not going to be such a revy engine as the 65 and is likely to pull better low down.

I can't comment on the long rod vs short rod because the dimensions are not readily available. If anyone has them I'd love to know.

The smoother idle will be down to the combination of substantially milder cam (no valve overlap) and a heavier flywheel.

By comparison the R65 has 20 deg of valve overlap. That is the inlet valve opens before the exhaust closes. This results in inertial benefits at high revs but at idle/low revs a little of the incoming mixture goes straight out of the exhaust which is not conducive to the smoothest idle. That being said 20 deg is still a relatively modest amount of overlap by moderrn standards.

[Red_Hen]

Thanks, Barry.

So, what is an accelerator pump, where is it, and what does it do?

[Barry]

With a normal slide type carb, if you snap the throttle open it produces a big reduction in the venturi vacuum which will reduce fuel flow. The end result is no power to accelerate. Such a carb needs more gentle operation of the throttle to accelerate well.

An accelerator pump is a common way of overcoming this problem by squirting in extra fuel in proportion to the speed with which the throttle is opened.

I've never had a bing slide type carb in bits so I don't know exactly what it looks like other than it's some part of the needle jet assembly. I swear I've seen a diagram somewhere recently and if I can think where and find it I'll post it up.

[montmil]

My itty bitty 50cc SunL pit scooter has a diaphragm-operated slide and an accelerator pump. Little carb has a throat that is less than 0.375" in diameter. 80+ mpg but you need to keep the throttle WFO all the time.

[Barry]

I had a look at a diagram of the Bing slide type carb and the accelerator pump is part of the main jet/needle jet assembly.  As far as I can tell when the throttle is closed it compresses a small coil spring and piston which sits in a cylinder between the main jet and the needle jet. Opening the throttle raises the slide and needle relieving this spring tension which acts on the piston to squirt extra fuel up through the needle jet.

In the diagram linked below the accelerator pump components are items 36 to 40 and they fit inside the cylinder item 35.

http://www.bingcarburetor.com/pdf/T53x.pdf

[Red_Hen]

You guys are amazing bordering on mad scientist.

Me, I'm the nutty professor.

Btw, Barry - I know England is a big province/country - the flooding looks horrible - are you keeping your bikes dry?

[Barry]

Btw, Barry - I know England is a big province/country - the flooding looks horrible - are you keeping your bikes dry?  

No major floods or property damage in my locality Ken.  

Although we did set off for lunch at a country pub last Sunday and came across a car on a narrow lane stranded in 2 foot of water. Undeterred we turned around and found another route. Where there's a will there's a way !

As for keeping the bike dry. Anyone daft enough (me) to still be riding to work at this time of year can't expect to keep totally dry. Once the bike gets dirty I start to think what the hell.  It really is going to need a wash this weekend.

[tvrla]

Barry is right - there's a spring loaded pump at the bottom of the main jet that gets compressed when the slide is closed. When the slide is opened, it pumps a shot of fuel into the carb.

Another little difference between the two is the /5 four speed transmission. Not sure how much of a difference that makes, but the ratios are different.

What's the final drive ratio? I know some of them came with a 32/11 - pretty tall for a low displacement machine.

[montmil]

Before fuel injection took all the fun out of tweaking our 4bbl-carburetor V8 hot rods, we were constantly changing jetting and accelerator pump pushrod lengths. Always looking to trim another tenth of a second off the quarter mile times.

I believe the simplicity of the BMW Airhead motorcycles is what keeps me from owning any of today's latest electronic this n' that FI motorcycles.