Cam and breather timming

[Garnet Grylls]

Hello All

All my engine parts are all cleaned and lined up ready to go back together . I have decided  that I would like to advance the cam by 6 deg. so that the inlet valve will begin to open at TDC (OT).
My plan  is to turn the cam sprocket 1/2 turn and cut a new keyway in the right spot. How careful do I need to be with the breather timing? Will 6 deg. make a big difference to it, or should I drill a new hole in the sprocket to time it the way it is now ?

Garnet

[Garnet Grylls]

[BenF]

Hello Garnet,

Just wondering why you would want to advance the cam timing by 6deg? Has somebody that you know already done that. Usually when people have installed the timing chain incorrectly, and it's out a cog or two the bike is very difficult to start and when it does start runs poorly.
The problem is that if you want to go back to the original I think you would have to pull the engine again.

regards
Ben

[† odeon8]

Hi Garnet,

changing the timing 10° earlier (crankshaft) is a standard tuning option offered by Uli´s Motorradladen. Its the identical timing of an R27 engine and was changed by BMW according to the model update from the R26. I think this was because the R72 has a higher RPM level and needs this early timing. Uli in Frankfurt reported that the tuning will also be good for ALL RPMs torque, including the lower range. I didn´t make my own comparison on that - only to the 320° racing camshaft that turned out to be an extreme shift of max. torque to the high end....

The breather timing is pretty unsensitive to all the valve timing - it just makes some underpressure in the crank housing in order to avoid oil leakage. The breather shaft does not have any bearing, so don´t mind...

How are you doing the 6° time shift ?
Uli is offering 2 solutions:

• A changed chain wheel
  
• A changed camshaft with a 2nd slot at the opposite side (5° shifted)

Thomas

[Garnet Grylls]

Hello Ben:

As Thomas said above, the R27 uses a very similar cam, only opening and closing 10 deg. earlier. I originally got the idea of changing from Uli's, who sell a "tuning" cam chain wheel that moves the R24-R26 cam to R27 specification.

Hello Thomas:

The R27 probably achieves it's higher RPMs because of the advanced cam timing. In an earlier post from Anselm http://bmw-einzylinder.de/forum/index.php?topic=1604.0 answer #4, he said that the full performance of the R27 was not realized until the later, shorter gearing is used. Since I am Canadian I like to compromise, so I have chosen to only go 6 rather than 10 deg. The 6 comes from a wish to have the intake open at OT as the R50/5 and R60/5's. I like their combination of low end and top end performance. I know that their closing times are much later so my results will be different.

To achieve this I will reassemble my spare engine and use a degree wheel to find the timing I wish for, and then cut a new keyway in the cam chain wheel.

Or does anyone think I should go all the way or not at all ?

Garnet

[† odeon8]

hello Garnet,


i think you SHOULD go all the way...and learn!
(do you have an engine test bench ?)
Dont forget to adjust the valve clearance to 2 mm for comparison..

... their closing times are much later ...

This requires another camshaft with different cams - where do you get that ?

Thomas

[mekgyver]

Hi @ all,
does anyone have diagrams : torque over rpm and power over rpm for those different camshafts ?
I think, it's the only way to have a discussion about those engines. 
Does Uli offer a diagram for his tuning-cam ?
Does Schleicher offer a diagram for their advanced racing cam ?

R27 will find it's power at higher revs. I think, that was possible in modifiing it's camshaft and drive the ignition coil with half rpm, comparing with R26 ... R25.
At lower revs, no need to hide my (original) R25/3 torque-engine comparing a R26 
Greetings, mek

[Garnet Grylls]

Hi Guys!

While reassembling my spare engine, I had this great idea . Because the crank chain wheel is such a tight fit I may leave the key out and press on the wheel at the new timing place. It might take a couple of tries to hit the right spot.

I have no way of testing the output till the engine is back in the bike and running, then it is almost a year since my last ride .

Yes some performance curves would be very helpful.

Garnet

[† odeon8]

Hi Garnet,

mek is right: The base of engineering is measuring, better than feeling 

So here is my contribution to this:

- The R26/R27 comparison in power and torque



- The comparison between the original and the "Schleicher camshaft:



- The power and torque diagram showing the 344 ccm engine equipped with the Schleicher camshaft:

http://www.bmw-einzylinder.de/Start/tips/berichte/thomasfreund/r325-s5.php

I´ve got another plot for my 344 ccm engine, but with the original camshaft and R27 timing - coming soon...

Thomas

[Garnet Grylls]

Hey Thomas!

Thanks for the R26/R27 engine data. That is something I have not seen, but is very helpful. It shows that the R27 has about 25% more torque between 4 and 5000 RPMs, which is my 80-100 kph cruising speed.

I will have to advance the crank chain wheel about 2.6mm or the cam about 1.3mm to achieve 10 deg advance. I may be able to make an offset key to do that.

Garnet

[Rütz]

Hi Garnet,

...I will have to advance the crank chain wheel about 2.6mm or the cam about 1.3mm to achieve 10 deg advance...

Attention!
You will have to advance the crank chain wheel 10 deg or the cam 5 deg.
But the ammount in mm will be the same (maesured on the outer circuit of the wheels).
It's nearly exact a half tooth.

I would not neglect the breathertiming.
The produktion of underpressure is just a by-product and not the reason for the breather valve. It prevents the engine from doing "pump-work" ("Pumpverluste"). This may cost a lot of power.
For example try to move a bike in 2nd or 3rd gear (without ignition) and then slowly open the throttle:
Closed throttle: The air/gas in the cylinder ist just compressed (to and fro).
Open throttle: The air/gas is being pumped, and it needs much more force to move it!

Good luck!
Anselm

[Garnet Grylls]

Hello Anslem,

I did not describe my actions well :-[. The diameter of the crank where the chain wheel presses on is 30 mm.
So 30 x 3.14 = 94.2 mm circumference.
Then 94.2/360 = .2616 mm per degree.
For 10 degrees of advance I can rotate the chain wheel 2.6mm measured at the keyway.

But I did make an error on the cam. It has a D of 16.9mm where the chain wheel presses on.
16.9 x 3.14 = 53.07/360 = .1474mm per degree.
For 5 degrees I will need to move it .737 mm, hard to do accurately.

Garnet

I will try this on my spare engine first to check my math. I can also check to see how much change it will make to the breather.

[Garnet Grylls]

Hello everyone !

I have spent the last couple of nights pressing the the chain wheels on and off my spare engine and have learned a couple of things

I tried to make an offset key for the camshaft but it was so small and fragile that it broke when I pressed the chainwheel on the cam

My cam is a few deg. advanced (almost to R27 spec) in it's the original position .

I have carefully marked the crankshaft and crank chainwheel and left the key (scheinbenfeder?) out. Then heated the chainwheel too hot and installed it in an advanced position. (Very hard to pull off afterwards)

The easiest way to "read" the cam is from maximum lift rather than opening point. The stock setting should have max lift for intake at 110 after OT and exhaust at 110 before OT. The R27 spec for intake is 100 after OT and exhaust is 119.5 before OT.

I even read a couple articles and found that advancing a cam 4 deg lowers power range by about 200 RPMs. It also raises compression because the intake valve closes sooner. (You were right Anselm )

More to follow in a couple of days.

Garnet

[Dave]

Any photo's of your progress Garnet?

- Dave.

[Rütz]

Hi Garnet,

i also think you may leave the key ("Scheibenfeder", correct! a very old german meaning of "Feder" ) out.
It's for marking and easy mounting purposes and can't transmit no force anyway.

..advancing a cam lowers power range ..?

That sounds surprising (to me). Do they have any explanation for this?
Where else did the R27 get it's finally higher power range from? 


Anselm E(ager about undocumented R27 features )

[Garnet Grylls]

Hi Dave and Anselm,

Sorry Dave but I am very analog. I can barley use a computer let alone a digital camera :-[.

I lifted this from CraneCams website:

"How does Advancing or Retarding the camshaft's position in the engine affect performance?

Advancing the cam will shift the basic RPM range downward. Four degrees of advance (from the original position) will cause the power range to start approximately 200 RPM sooner. Retarding it this same amount will move the power upward approximately 200 RPM. This can be helpful for tuning the power range to match your situation. If the correct cam has been selected for a particular application, installing it in the normal "straight up" position (per the opening and closing events at .050" lifter rise on the spec card) is the best starting point. "

Also read similar comments in other performance cam catalogues. These are all marketing American V8 parts, but I think the basic principal is the same. I think that the closing of the valves is more important than the opening. The later that the intake closes allows more air in at high speed than at low.

I also am confused where the R27 gets it's higher RPMs from.  Perhaps better ignition system and more compression? When you look at the power curves that Thomas posted above, you can see that the R26 and R27 reach max torque at just over 6000, but the R27 is much stronger at 5000.

Garnet O(pen to new ideas)

Good article on how to "degree a camshaft"
More cam basics http://www.cranecams.com/?show=faq&id=2

[Garnet Grylls]

Hi Guys!

I found this article that adds to the confusion:

"Some cars use a device that can advance the valve timing. This does not keep the valves open longer; instead, it opens them later and closes them later. This is done by rotating the camshaft ahead a few degrees. If the intake valves normally open at 10 degrees before top dead center (TDC) and close at 190 degrees after TDC, the total duration is 200 degrees. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins. So the valve might open at 10 degrees after TDC and close at 210 degrees after TDC. Closing the valve 20 degrees later is good, but it would be better to be able to increase the duration that the intake valve is open. "

Above the writer claims "rotating the cam ahead a few degrees." will hold the valves open longer, which I think is incorrect. If the cam is moved forward, the valves will close sooner.  Terminology aside, later valve openings are used on variable valve timing engines to give high RPM power while earlier opening times are used for lower RPM ranges.

So I still cannot explain why the R27 has more RPMs than the R26. :-[

Greetings
Garnet S(earching for answers)

[Garnet Grylls]

Hello all you Single Minded out there.

I have my crank and cam in and set at just over 9 deg advanced and I am dizzy from watching the degree wheel and dial gauge spinning around.

I still can't understand how the R27 gets it's extra RPMs but Will report on how these settings work.

Garnet

[Rütz]

Congratulation so far!
Perhaps the different R27 Muffler does play a greater roll.
It's smaller front chamber should/could support higher revs.

Anselm

[† odeon8]

Hi Garnet,

Anselm is right - the fine adjustment of the muffler and the intake pipe
has a fundamental influence on the engines´s behavior, additional to the
valve timing.
I changed my R34/4 toilet inlet tube (40-45 mm diameter)
to a slightly shorter rubber hose with
a constant diameter of 35 mm, keeping the K&N air filter.
The engine was completely different on torque - much more on low RPM
and slightly reduced at high RPMs (what i am not so interested in).
I found this to be quite funny because the distance from the intake valve
to the K&N was a little SHORTER 

(...) later valve openings are used on variable valve timing engines to give high RPM power while earlier opening times are used for lower RPM ranges.

I think it is vice versa - early timing for high RPM because
the gas resonance timing is almost the same and early valve timing synchronises better to the faster piston movement....
Actually workin´ on my R34/4 balance. See later on the documentation in
the corresponding thread.

Thomas

[Garnet Grylls]

Anselm:

"Perhaps the different R27 Muffler does play a greater roll.
It's smaller front chamber should/could support higher revs."

I wonder how the R69S muffler I am using will affect things I had no idea that the R26 and R27 had different insides!

Thomas:

Did you find any Tungsten?

Greetings
Garnet

[† odeon8]

Hi Garnet - i did not and did not want to.

I decided to have a more flexible solution and will send some pics in the
"R26 balancing Threat" later... pse be patient.

Thomas

[Heiko]

Hi Garnet,

Mek told me yesterday, that he found tungsten! Ask him! 

Heiko 

[Rütz]

Hi Thomas,

..I think it is vice versa - early timing for high RPM because..

Meanwhile i think, no.
Like described in your american tuning link about the correct (and eventually reduced) inlet diameter (don't find it now), i think the gases can't follow the piston movements at high revs in real time and therefore need later Valve times. Especially late closure times.

@Garnet:
Look also the results of our "Muffler Exploring Group"
http://www.bmw-einzylinder.de/Start/tips/Bauanleitungen/Stroemungssimulation/endtopf.php

If you messure from behind with a rule, the R26 "Prallblech" ist ~ 30 cm deep, with R27 it is ~ 40 cm.

We didn't know this either before we did these explorings . I think many R27 ride with a wrong exhaust (including me). The first "aftermarket" mufflers were R26 type, but offered for R26/27.

Greetings
Anselm

[Garnet Grylls]

Hi Anselm

I have spoken to a few auto mechanics who agree that advancing the cam closes the valves sooner and improves low RPM power. Variable valve timing engines retard the cam(s) at high speed for more power.

Very good project on the mufflers . I need to take more time to translate better to fully understand. My R26 came with a stainless steel muffler from an R69S. It's baffle is 30cm from the rear.

I began to mount my new 15mm oil pump tonight and found that it hit up against the lower engine mount tube (inside the crankcase). . I was able to take a bit of material from around the flat screw that holds the oil pump together, and from the inside of the case near the lower engine mount tube and make it all line up.

Next I will shorten the oil pump drive by 10mm and soon be ready to go back into the frame!!!

Garnet S(lowly makeing progress)