Problem with the engine temperature BMW R26

[Manifesto1984]

Recently replaced the cylinder liner 68mm and new piston rings, new valves with guides and i placed a thermometer oil from Ulis.

Everything has been installed on and set correctly.

The full speed of motorcycle is not over 80km and when push full throttle the engine drowns.

After a trip of 50-60 km with normal speed the thermometer shows over 90 degrees Celsius and the engine performance falls vertically.

Which is the problem?

I think the problem is the metal alloy of the new cylinder liner. Poor job from engineering.


I will appreciate your help.

Thank you!

[Manifesto1984]

[rolf]

Full throttle and new piston???
What is normal speed for you?
90° is not (!) to much....thern the motors starts (!) getting warm.
But it is oil temperature....if the piston seized....this is normally too quick to raise the oil temperature

[Manifesto1984]

Full throttle and new piston???
What is normal speed for you?
90° is not (!) to much....thern the motors starts (!) getting warm.
But it is oil temperature....if the piston seized....this is normally too quick to raise the oil temperature

Full throttle after 1500 km.
Normal speed about 60-70 km/h
I said over 90 degrees. Sometimes 100-105 degrees. I think it's too much.
But why the engine performance falls?

In a little uphill road (with 10% slope e.x) i must put 3rd gear of 4th.

[rolf.soler]

No, oil temperature is definetely NOT your problem. My R27 can get to 120°....1-2 hours hour overland, slightly hilly region ? ...120°, 125°  for sure ! and that's with perfect performance, full power and speed.
But 80 km/h is far out of normal...this is serious lack of power
1500 km may not be enough for running in, depending on how you did it.. Check & improve ignition timing, carburetor settings and then run in in, i.e. drive full throttle until it gets slower, then immediately reduce throttle for a while. Repeat this process many times, every time it should run a bit longer on full throttle, and power should improve gradually. Except if new piston/lining is already damaged...

[Manifesto1984]

No, oil temperature is definetely NOT your problem. My R27 can get to 120°....1-2 hours hour overland, slightly hilly region ? ...120°, 125°  for sure ! and that's with perfect performance, full power and speed.
But 80 km/h is far out of normal...this is serious lack of power
1500 km may not be enough for running in, depending on how you did it.. Check & improve ignition timing, carburetor settings and then run in in, i.e. drive full throttle until it gets slower, then immediately reduce throttle for a while. Repeat this process many times, every time it should run a bit longer on full throttle, and power should improve gradually. Except if new piston/lining is already damaged...

About ignition timing everything have setting and works perfect. I'm sure for that.
About carburetor i tried with 1/26/55 , 1/26/46 , 1/26/112 with various settings but the problem remains.

When the engine is cold, the power is good but the top speed remains at 80 km/h.
When the engine is warm enough, the power falls vertically. The problem with the top speed remains.

This bike was my father. In his youth he tells me trips for 80 and 100 kilometers with full throttle and top speed over 100 km/h without problem.

The problem became after restoration, but i can't understand which is the problem. I have this problem about one year and i can't solve it.

[Manifesto1984]

Some photos of my bike after restoration.

http://postimg.org/image/dvjzg2m0n/
http://postimg.org/image/vkbq7oxrr/
http://postimg.org/image/chsckrmrb/
http://postimg.org/image/hchg5avp3/

[rolf.soler]

well...if timing is correct (early about 40-42°) and carburetor OK (the 46 and 55 at least are original) and a change of carb does not change anything....I'm afraid it goes deeper
- valve timing (chain) is correct ? (check valve opening and closing times)
- you changed piston rings and cylinder liner, but not piston ? If piston changed, is it the correct piston (my R27 had a R26 piston when I bought it)
- how much was piston clearing when new piston was built in (6-7/100 mm correct)
- low compression ? how much is it ? buy compression tester or let it check in a garage.
- when power "falls", does the ignition have lapses ? weak sparks could be a cause....ever tried a new spark plug ? condensator ? coil ?
Your father is right, R26 has > 100 km/h top speed

[Manifesto1984]

well...if timing is correct (early about 40-42°) and carburetor OK (the 46 and 55 at least are original) and a change of carb does not change anything....I'm afraid it goes deeper
- valve timing (chain) is correct ? (check valve opening and closing times)
- you changed piston rings and cylinder liner, but not piston ? If piston changed, is it the correct piston (my R27 had a R26 piston when I bought it)
- how much was piston clearing when new piston was built in (6-7/100 mm correct)
- low compression ? how much is it ? buy compression tester or let it check in a garage.
- when power "falls", does the ignition have lapses ? weak sparks could be a cause....ever tried a new spark plug ? condensator ? coil ?
Your father is right, R26 has > 100 km/h top speed

- I have replace the timing chain with new one and i put chain tensioner. The valve opening have setting perfect (0.15mm in) and (0.20mm out).

- The engineer told me it's not necessary to change the piston it was in good condition and is the old piston from my father when the bike works good.

- I brought to him (it is a honing shop) the cylinder, cylinder head, piston, the new piston rings and the new valves with guides. He did all the work and when he finished i took them and simply place them to the engine.

- My piston wearing 3 compression rings (2 x 68mm x 2mm  and 1 x 68mm x 1,5mm) and 1 oil ring (68mm x 4mm). I took them from Stemler, it's the correct size and fits perfect.

- I think the compression is good. I don't know exactly how much is it but it's good.

- I haven't problem with sparks. Are very strong and when the engine is worm. I changed the spark plug and condensator with new one.

- I didn't try to change the coil. You think this may cause the problem?

[4Taktix]

Hello Manifesto,
- valve clearance OK, but what about the timing ?
  in other words: Did you doublecheck, if both sprockets were in correct position, after you replaced the
  timing chain ? (timing offset by 1 tooth is a common rootcause for lack of power )
I recommend to check rolf's questions/advice carefully, as suppositions woun't help nobody here.
Don't take it personal, but statements like "I think it is good" don't proove nothing in the end.
On the other hand, I never heard of cylinder-liners for the 250 cc singles, maybe it's worth to focus on this.
How does your bike behave when engine is warm/hot: Does it achieve 80 kmh in third gear ?
Did you already change motoroil after the first kilometers ? ~ 50
How is your points-clearance / ignition timing ?
How did you check this ? with a check-bulb cranking the engine by hand, or with a flash-gun on the
running engine ? Is it prooven, that the flywheel (and therefore the timing-marks) is in correct position
and did not shift on the crankpin ? -> compare t.-marks vs. piston-position through spark-plug-hole.
Does your timing-advancer work OK ? Did you disassemble it ?
If your exhaust-pipe is chromed yet, did it change colour since the engine-maintenance ? (yellow or blue)
How long does it take, until power breaks down ? (average)
Remove the generator-lid and have another try: Does it take longer now ? -> coil
Try the following, if you notice power decreasing while riding:
- press the light/ignition switch-knob down -> any change ? --> contact-spring/balls worn out
- push the primer-knob on the carb (while throttle is still open) -> better or worse ?  -> jet/carb-setup.
- take the throttle back just a bit -> faster or slower ?
Should be enough to check for the first bit, waiting for your results on this.
Best Regards,
Sascha

[rolf.soler]

Thanks Sascha
if all these things are right/correct then your R26 runs 105 km/h and your tachometer is wrong 

- I have replace the timing chain with new one and i put chain tensioner.

that's very nice, but dit you put the chain on the sprocket wheel in the proper position ? or shifted by one tooth ?
Valve clearance is OK , but I meant valve timing ("inlet valve opens at x° after OT/closes at y° before OT, autlet valves opens....."etc etc. )Check this with the values in the workshop manual

you see: basically it's still true: if max. speed ist 80 km/h, then the power is NOT good, no matter what it feels like
even it performs even worse after a while at full throttle, the "basic power/speed = 80 km/h" is already insufficient - something is wrong.
could be compression, could be wrong valve timing, could be ignition lapses at high RPM/temps (coil is a possibility, as is loose contact in the keyhole assembly) could be that it is simply not yet run in,
- and of course ignition timing (at high RPM ! with stroboscope ?), carb settings, not completely opening carb slide, etc, which you say are all OK

Saschas questions are important, try to check all and  reply
quantitative statements would be helpful, e.g. "early timing is 42° before OT, late is 6° before OT", "outlet valve opens at x° before OT"

This is probably not your basic simple stupid problem ("oh, I noticed that the throttle cable opens the carb slide only half....") , as you tried many things already .....but it still might be...
So only precise data help,.short from a visit by another onecylinder-driver

[isie]

among a 1000 other points (see above)
1. be sure ignition is fimly "nailed" to "F sign in window" at time if above some 1800 rpms.
2. ... and ignition contacts at plate in lamp have full contact all time.

[rolf]

1800....take 3000 U/Min

[isie]

from me out

1800....take 3000 U/Min

[Manifesto1984]

I'm waiting a BMW engineer.
I will inform you as soon as possiple for the results.

Thank you.

[4Taktix]

You should provide our recommendations to that engineer and go through it item by item.
Otherwise all our hints were useless - and maybe your bike still runs just 80, allthough the mech says: "everything OK".
Regards,
Sascha

[rolf.soler]

yes, hopefully he knows more than the forum  (not all engineers do...). He has the advantage of seeing & touching your bike
we'll wait for a feedback; good luck !

[BamBam]

@Manifesto1984

BTW - do you live in SoCal??? Have not much to do this sunday

[Manifesto1984]

@Manifesto1984

BTW - do you live in SoCal??? Have not much to do this sunday

I live in Greece

[Manifesto1984]

Which is the correct compression for R26. The manual says 7.5:1 but how many bar or psi?

Thank you!

[rolf]

Compression rate has nothing to do with bar (neither psi)....it is a mathematic data

[Manifesto1984]

Compression rate has nothing to do with bar (neither psi)....it is a mathematic data

Ok but how i will measure the compression?
How many bars or psi is the correct value for a BMW R26?

[skeewde]

Ok but how i will measure the compression?
How many bars or psi is the correct value for a BMW R26?

There is some confusion here! It is important to use the correct term, which is compression ratio!
This is simply the relationship between the volume of the combustion chamber with the piston at TDC (top dead center) which is rated at "1" compared to the volume of the combustion chamber plus cylinder when the piston is at BDC (bottom dead center), in your case "7.5" which gives a ratio of "7.5:1".

Best regards,
David

[Manifesto1984]

There is some confusion here! It is important to use the correct term, which is compression ratio!
This is simply the relationship between the volume of the combustion chamber with the piston at TDC (top dead center) which is rated at "1" compared to the volume of the combustion chamber plus cylinder when the piston is at BDC (bottom dead center), in your case "7.5" which gives a ratio of "7.5:1".

Best regards,
David

Thank you very much David but i didn't unerstand what exactly you mean.
7.5 bar is the correct compression?

[skeewde]

Thank you very much David but i didn't unerstand what exactly you mean.
7.5 bar is the correct compression?

No, as Rolf wrote earlier, the compression ratio has nothing to do with bar or psi - which are both methods of measuring pressure - but is simply an indication of the maximum petrol/air mixture that can (theoretically) fill the cylinder on the induction stroke of a normally aspirated engine and the degree to which it is then compressed at the time (approx.) of ignition. The higher the compression ratio, the higher the amount of (mechanical) energy that can be attained from a given amount of fuel.
Too high however and the mixture will detonate before the correct ignition point (knocking).

David

ps. maybe this picture helps?

[Kurt in S.A.]

I've always used this rule of thumb to compute the general compression for an engine using the compression ratio.  For a 7.5:1 engine, add 1 to 7.5 to get 8.5 then multiply by 14.7 psi (for living near sea level).  I get around 125 psi.  This should be a target value for check compression.

Sorry to bring in a relationship between compression ratio and compression!   

Kurt

[skeewde]

I've always used this rule of thumb to compute the general compression for an engine using the compression ratio.  For a 7.5:1 engine, add 1 to 7.5 to get 8.5 then multiply by 14.7 psi (for living near sea level).  I get around 125 psi.  This should be a target value for check compression.

Sorry to bring in a relationship between compression ratio and compression!   

Kurt

Hello Manifesto1984,

sorry, I think we've been talking at crossed purposes and I've been barking up the wrong tree a little.

@ Kurt: thanks for bringing this back to earth. I can't say how accurate your method is but it certainly sounds like a good rule of thumb.

However unless the results of a compression test are really low (<100 psi, which would seem to indicate a major mechanical problem) I wonder how much value a compression test has on a single cylinder engine, as it only indicates how much pressure the engine itself can generate but not how well it is sealing. A compression test generally has more value when used to compare cylinders on multi-cylinder engines.
In this instance I think it would be better to perform a pressure loss (or leak) test, which should be able to show how well the engine can hold pressure and if it cannot, where the leak(s) are happening and which components are actually responsible. The escaping air can generally be heard fairly clearly - valves, rings, head-gasket etc.

David

[Manifesto1984]

I think i found the problem with engine.
I measure the cylinder compression with warm engine.

It's almost 3 bar 
I think is very low compression.

[rolf]

Put a little bit oil into the Sparkplug hole.....compression getting higher?....Piston
The same to the head to the 2 valves----higher?.....valve settings
a little bit = half a glas of a little Whisky

Kurt: target value...ok...but not more

[rolf.soler]

compression ratio is calculated - in your case 7,5 : 1
the pressure at maximum compression, usually called plainly  "compression" is measured in bar and is approximately 1 more that the compression rate -> 7,5 + 1 = 8,5 bar. This is what you measure with the compression tester....no need to convert it to psi...except if the etster shows only psi...
To measure correctly, screw the tube in the spark plug hole and push the motorcycle around 20 m in 2nd gear with full open throttle, or let it roll downhill in 2nd gear a short distance  (using the kickstarter can give low values, although not 3 bar....).
If it's still low (say below 8 ), put a bit of oil in the spark plug hole, repeat procedure - better ? (piston rings) if not good, continue  searching for leaks ...Valves...spark plug hole....cylinder head tears....as above, by applying oil at the mentioned places, visual inspection of cylinder head...valves tightness with petrol...

[Manifesto1984]

compression ratio is calculated - in your case 7,5 : 1
the pressure at maximum compression, usually called plainly  "compression" is measured in bar and is approxiomately 1 more that the compression rate -> 7,5 + 1 = 8,5 bar. This is what you measure with the compression tester....no need to convert it to psi...except if the etster shows only psi...
To measure correctly, screw the tube ind the spark plug hole and push the motorcycle around 20 m in 2nd gear with full open throttle, or let it roll downhill in 2nd gear a short distance  (using the kickstarter can give low values, although not 3 bar....). If still
If its still low (say below , put a bit of oil in the spark plug hole, repeat procedure - better ? (piston rings) in nit good, continue  seacrhing for leaks ...Valves...spark plug hole....cylinder head tears....as above, by applying oil at the mentioned places, visual inspection of cylinder head...valves tightness with petrol...

How much oil to put in the spark hole? About 50ml?