R27 cylinder barrel & head on R26

Begonnen von BSA Bob, 08 März 2021, 02:36:32

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BSA Bob

I have an R27 barrel & head. What do people think of fitting these to an R26? I'm thinking it would give better lubrication & if the head were rubber mounted R27 style that might damp out some vibration.
Pleased to see your thoughts.

BSA Bob



OldsCool!

Hi Bob,

That should fit, but to mount the head with the rubber mount, you would need an R27 frame  ;)
Also I doubt that it will give a bigger advantage given the fact that you still fix the engine case old-fashioned.

Best regards,

Steffen
Ich bin auf dem Dorf aufgewachsen. Ich wurde nicht erzogen, ich habe ÜBERLEBT!

4Taktix

Hi Bob,
you have to get a matching piston, as the R26 conrod is 125 mm long, whereas the R27 is 120 mm.
The barrels do have equal height, but the pistons are different, due to the different conrods.
Check out our "Vergleichsliste" ( comparison-list ):
https://www.bmw-einzylinder.de/Vergleichstabelle/default.html
You should urgently check your crankshaft, as there were two different versions used in R26.
One does have an aluminum-conrod and small counterweights, the other has the stock conrod and stock (bigger) counterweights.
But there are some out there with the heavy stock conrod and the small/light counterweights, notorious for bad and heavy vibrations.
Commonly known as the "Schüttelwelle" which maybe literally translated as "wobble-crank".
Remove the oilpan and take some shots with different crank-positions. Then post them here.
We will tell you then what you got.

Regards,
Sascha

Think outside the box !

Taz

Hello both of you, Bob and Sascha.

If following the link like this: https://www.bmw-einzylinder.de/Vergleichstabelle/default.html#en

this will lead you directly to the English version...

Kind regards, Ute

Ich hab noch nie einen Sarkasmus vorgetäuscht


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berndr253

Vibrations will not change if a barrel/cylinder-system from a R27 is mounted on a R26-engine.

Bernd
Leben und Leben lassen

rolf.soler

#5
yes. The engine is still fixed to the frame with the long rods... R27 anti-wobble technology needs rubber all around...Crankcase and gearbox fitted with the rubber blocks. To add one on top does not help and involves weldering on the frame.

As the piston height is determined by conrod length, why should a R26 piston in the R27 Cylinder not work ? 
forget ist, the R26 piston on a R26 conrod would rise up to the top in the R27 barrel, but the lower point would be too low...as the stroke (the "Hub") is different)...so for the R27 barrel you would need a shorter R27 conrod and R27 piston...


BSA Bob

Thanks for the help folks. I realise the main mounting points are where the vibrations are transmitted.
The crank is emerging as the biggest worry in this project. Unfortunately the engine's seized as well (not my fault, I lent it to a small museum who went broke & neglected it) so  I can't rotate the crank to look at it. Depending on the position the crank's in it might still be possible to get an idea with the engine still in the bike. 

4Taktix

Rolf, are you sure about this:
Zitatas the stroke (the "Hub") is different)
All 250cc BMWs do have equal stroke - 68mm stock.
An R26-Piston w. R26-Crank will work in an R-27 barrel, but due to its lower compression height it woun't reach intended TDC and thus lack compression.
So - no good idea.
@Bob: Remove the oilpan and the grill you will find below the crank. Take a shot and post it here.
I attach 2 pictures, just to give you an idea, how to determine the different cranks by the shape of the webs.
Attention: picture '4T-crank-light' shows the notorious combo with the stock steel rod.
The rare and original Aluminum rod looks beafier and is easy to identify with a magnet, in case of doubt.

Concerning the 2 oil supply holes in an R27 barrel we highly recommend the bigger oil-pump for sufficient volume.
If the crank-subject is cleared, we will take care about that.
But lets do it step by step.  ;)

Cheers,
Sascha
Think outside the box !

rolf.soler

Zitat von: 4Taktix am 09 März 2021, 12:10:02
Rolf, are you sure about this: All 250cc BMWs do have equal stroke - 68mm stock.
No at present I am not sure of anything anymore  ??? I'll make a new thread with questions about my R27 crankshaft (the one with the additional ?woodruff-key slot...)
I thought if the conrod is longer, then the piston will move farther up and down, so more stroke (Hub), but it depends of course also on the position of the conrod pin in the crankshaft...So the stroke is the same ?

rolf

Conrod maybe 3m long....the stroke is the same

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