R26 Racing Modifications

[ALTBMW]

I have purchased an R26 which I am planning to turn into a 250cc racer for track use only.  I am seeking helpful suggestions for this project with special interest to the engine and transmission.  With regard to the engine issues are: improvements in lubrication, R50S piston (?), larger valves, larger carb, switch to electronic ignition, etc.  With regard to the transmission, I am thinking about replacing the wide-ratio gearset with a close ratio gearset from a two cylinder.  Any help will be appreciated.  Thank you.

[ALTBMW]

[Rütz]

Hi,

improvements in lubrication..

Look here:
http://www.bmw-einzylinder.de/forum/index.php?topic=1097.0
and here:
http://www.bmw-einzylinder.de/forum/index.php?topic=1079.msg7339#msg7339

R50S piston (?)..

Is used quiet often (including myself). To get full performance of this piston you have to shorten the Zylinder too. About 1.0 mm from top (on a lace).

larger valves, larger carb

I would not recommend that. The cross-sections (Querschnitte?) of Valves and canals(?) are already nearly as great as possible and cracks of the cylinderhead are often enough.


Further:
You can quiet easely change the valvetiming to R27 by advancing the camshaft a half tooth.
This may be done with a modified mounting of the camshaft sprocket.

There are (or were) also special race camshafts (z.B. Fa. "Schleicher"), but i don't know where you can get them. Ask member "Odeon8", i think he has one in his "R44/3".

Very common is to lighten the Flywheel. In Germany http://www.rabenbauer.com sells an alloy flywheel (1.9 kg).

Gearset:
"Odeon8" realised a very radical solution
http://www.bmw-einzylinder.de/forum/index.php?topic=1518.msg12915#msg12915

So long
Anselm

[† odeon8]

Hi "ALTBMW",

i have got this "Schleicher" Camshaft with more stroke and
more overlap. I measured the camshaft using a rotary table and a spreadsheet program for visualisation. The result can be seen (PDF)
I tried this and found the engine characteristics to be
too much "race-like", e.g. the real torque comes at 5000 RPM, see diagram
This was not what i wanted, so i switched back to the original camshaft, but with R27 timing.
After having this bike since 28 years now my idea was always "reduce RPM" which is successfully realized now. The engines needs 4300 RPM for making 100 km/h and has enough torque to keep this speed even on ascending roads.

If you are interested in the "Schleicher" camshaft give me a note....

Thomas

[Garnet Grylls]

Hello!

Mark Hugget has a R25-R26 "Sport Cam" 11 31 0 031 000.1 for 385 CHF.
With 328 deg overlap compared to 300 deg for the stock R27 cam he claims better power for an R26 than advancing the stock cam to R27 spec.

Has anyone tried it?

Garnet

[Rütz]

i think this is the "Schleicher"- Camshaft, which odeon8 refers to.

Look also here:
http://www.bmw-einzylinder.de/forum/index.php?topic=831.0

[Heiko]

Hi,

you can get the camshaft here: http://www.schleicher-fahrzeugteile.de/index.htm

It is possible to order the camshafts directly there! 

Heiko R(26 Thunderbird)

[Garnet Grylls]

Hello all!

Has anyone worked out what the compresion ratio (factor) with the R50S piston installed? How much more after shortening cylinder 1mm?

Greetings
Garnet

[† odeon8]

Hi Garnet,

there was already a discussion about this topic in our forum.
Look here: http://www.bmw-einzylinder.de/forum/index.php?topic=154.msg750#msg750
You also can see the formula for calculating the compression factor there.

Are you still interested in my tuning camshaft ?
If yes, you can give me an offer using the forums mail system...
If you don´t like the camshaft - its no problem because another pal here likes to have it.

Regards - Thomas

[Rütz]

Hi Garnet,

In my R27 a "No Name"-R50S piston together with R26 pushrod did not increase the C-ratio (8,2:1), though promised ( ).
Therefore i calculated and shortened the cylinder by 1.5 mm (!). By that i got ~9.3:1 and she was runnig pretty well with 98 oktan fuel.

Ten years later, i did a little overhauling: New OEM-R50S-piston (Kolben-Schmidt) with slightly smaller "valvepockets" (?) and a cylinderhead-overhaul (welding a crack and new valve seats):
This small changes let the compression ratio increase  to over 10 !!
Which was definitly to much.
Now i ride with a 0.6 mm cylinder foot gasket, slightly reduced preignition and a compresion-ratio of 9.5:1 .

So it's difficult to predict exactly, what compression ratio you will get. It depends very much on individual differences in the combustion chamber.

Anselm G(reased lightning)

[Garnet Grylls]

Hello!

Thomas: Thanks for the offer on the "camshaft". I still cannot make up my mind. :-[ Unlike "ALTBMW" my goal is keeping up with todays traffic on the street.

Anselm: I have orderd a "KS" R50S piston. The best fuel we can buy here is 94 oktan which is good for R69S at 9.5/1 but not good for R60/5 at 9.2/1 It must have something to do with combustion chamber shape. I will not make my cylinder smaller and see how it works.

Good Day
Garnet (waiting for parts)

[Rütz]

Interesting!

is good for R69S at 9.5/1 but not good for R60/5 at 9.2/1...
...must have something to do with combustion chamber shape..

...or with the "effective compresion" in contrast to the geometrical one.
Here my "personal theory" to calculate such phenomens :

http://www.bmw-einzylinder.de/forum/index.php?topic=1419.msg11730#msg11730

(I have no valve timing data of R60/5, but perhaps it's similar to R60/7..)

Anselm

[Garnet Grylls]

Hi Anselm

Intersting theory on cam/compresion ratio or "volumetric efficiancy" or how much % of the engine volume (250cc) that the intake can draw into the engine.   Those measuremnts that you made staticly (engine not moveing) will change as engine UPMs increase.

As we know shorter valve opening times give more power at low UPMs because the cylinder fills fuller when the valves open and close at or near the top and bottom of the piston movement.

The faster the piston moves the later and longer the valve openings can be, because the intake gasses are rushing in faster and the intake valve can stay open while the piston has started to move up. The momentum of the rushing air fills the cylinder fuller (higher compresion) than it would at low UPMs.

This is very hard to measure without complex equipment.

You have probably coverd this topic already.

Garnet

[Rütz]

Hi Garnet,

of course this theme is -in reality- much more complex.

I think (not know ), that this "momentum of the rushing air" assisted by airbox resonance etc... is a kind of Precompression, like the compression in the crankcase of two strokes.
And the wamth from this precompression does not arise in the combustion chamber but somewhere before (cylinder foot, inlet, etc..).

Two strokes and modern sport bikes often have compression rates over 10:1 and nevertheless run with normal gasoline!

My theory is, that only the part of the stroke after the inlet has closed is relevant for the oktans needed.
And the theory seems not to be so wrong, as your example with R69S and R60 maybe shows (i'm sure this sentence is a grammatical desaster, hope you understand.. )


Anselm L(übke)

[Garnet Grylls]

Hi Anselm,

Your English is better than my ability to expalin myself

On some engines, at just the right UPMs, the "momentum of rushing air" can actually put more than 250cc worth of gasses into the cylinder, thus raising the compression number higher than measured by theory.


I don't know how to explain it, but I think you know what I meam

Garnet G(rasping at straws)

[† odeon8]

Hi Garnet,

some month ago i found this very interesting link concerning the intake manifold (intake porting). Thats identical to what i found on my R25 due to the so called "expert" opinion: Making the inlet larger is a real desaster for the "every day" usage. Aditionally having 4 valves instead of 2 makes the engine feel weak and tired at the lower RPM range. I had the same experience with my PEUGEOT 406 (16V) when i changed from the old 405 (8V). 

Without wanting to push you: Still interested in the 320° camshaft ?
Somebody else likes to have it - so please let me know....

Greetings from the thundering Bavaria, Thomas

[Garnet Grylls]

Hey Thomas!

Thanks for the performance link. 

Your camshaft: One day I just have to have it, the next, I want the steady pace of the original. If you have someone who wants it sell it to them. I want my bike for the street so the lower UPM power will be better.

Garnet
( Greetings from the rugged west coast of Canada )

[Rütz]

Hi Garnet,

..On some engines, at just the right UPMs, the "momentum of rushing air" can actually put more than 250cc worth of gasses into the cylinder, thus raising the compression number higher than measured by theory..

Sure! I know what you mean (even before ). On "molar base" the compresson is much higher. I did'nt want to deny that.
"My formula" is not to describe the overall or "real" compression, but to describe the part of compression, which is only relevant for the oktan need.

As the fresh gas is compressed it becomes hotter and may selfignite.

But i say the "compression heat" in the combustion chamber only arises from the compression done by the piston itself:
When the piston is down and you fill in 500cc into the 250cc room it means, that the gas is already compressed, otherwise it wouldn't fit in 250cc.
The warmth which this "precompresson" (500 -> 250cc) has produced is already on the way out. The fact that there is more gas in the cylinder will not increase the heating during compression.
Of course after ignition the temperature in the combustion chamber will be much higher because of this extra load.

That is what the modern sport engines take advantage of:
They have high geometrical compression ratio plus high extra compression done by "rushing air momentums" and even though need relatively less "oktans", 'cause of the wide valve times:
The overall compression is not only done by the piston alone, but takes place in several single steps. Thus the "compression offal" (heat) is not cumulated in one point (combustion chamber) but also spread.

puhh...

Anselm G(rasping for english technical terms )

[Garnet Grylls]

Hi Anselm!

I think we actually agree with each other but don't know it The way you explain it is good. I allways thought that the extra charge of gasses from the intake would raise the "compression heat" causing the need for higher oktan.

But you are right about so many new engines that are higher than 10/1 and are less sensitve about fuel than our old bikes at 9/1.

By the way did you read that link that Thomas put in his last post. Interesting method of keeping that extra charge in the cylinder.

Garnet G(lad to have your help!)

[Rütz]

...By the way did you read that link that Thomas put in his last post

Sorry, i didn't. But now glanced over it.
Also interesting his 8 phases of the 4 stroke cycle:
http://www.mototuneusa.com/the_8_phase_motor.htm

But imho he sells truisms as sekrets... Subscribe?? Sekret Links?? for what? (the site design makes me even afraid of dialers... nevertheless is hard to read)

Anselm O(ver-suspicious)

[Garnet Grylls]

Hi!

I did not subscribe either. There is little for free in this world  (except Einzylinder-Zentrum, Thanks Karl)

Thomas: did you sign up for more sekrets?

Garnet.

[† odeon8]

@Rütz: Thanks for this interesting link !
@Garnet: No, i didn´t sign anything. Like in this forum i want to have this kind of informatin *free* - even i have bought a lot of books, most of them being written in between 1950 and 1960.

My actual project is an electric blower driven by my 600 Watts alternator; something similar is realized at http://www.z-engineering.com/

So by changing back to the original camshaft the the engine feels really stronger, but looses torque in the high RPM area. The gain is having 20% more torque al over 2000 to 5000 RPM. I will show the results of this project here in the forum, even if not successful..

Greetings from a rainy Bavarian night - Thomas