My R25/2 restoration - few question

Begonnen von Al Capone, 12 September 2020, 23:22:49

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Al Capone

During the restoration, there were some problems that I could not find answer on the forum. I allowed myself to create this topic in order to be able to cover it here and not to create a few threads.

1. After tightening the upper fork bolts, there is a 2mm gap on the left side.
I can't tighten the screw any more.

2.Do any of you know how the manual gearshift axle is locked inside the gearbox?
I can see one tiny hole there. Maybe some part is missing.

Al Capone


berndr253

Relating your second question:The position of the axle is fixed by a washer and a splint - in fact before the shafts (output and intermediate) are mounted.
Check it the axle doesn`t have too much clearance!
Bernd
Leben und Leben lassen

Al Capone

Hi Bernd

I really don't know what splint and washer are you talking about.  :traurig:
I'm suppose that hand shifter axle should be locked somehow inside. In other way I would might take it out any time. Have a look at second picture.

Krottenkopp

#3
Of course inside!
With a split pin in the little hole and a washer...

https://en.m.wikipedia.org/wiki/Split_pin#/media/File%3ACotter_Pin_(PSF).png




Gruß Heiko/2
Gruß Heiko/2

rolf


Krottenkopp

Gruß Heiko/2

rolf


Al Capone

Thanks, so I should drill the axle right through becouse there is only one hole at the moment.

I had also solved first problem by using 1.5 mm spacer washer 50/40mm.

Al Capone

The work is slowly going but the first effects are visible.

I found a man who can rebuild a devastated rear fender but
I need information.
Can any of you measure your fender in R25 / 2 and provide the appropriate width? I think it is 15cm.
Is the fender narrower at the cardan shaft (13cm)?
Another question is, should the right-hand bracket have a larger bend angle?


Do you have any way to remove the disk from the cardan shaft? I tried to use a 10T press and heat it up but it ended up deforming the tip.

Kurt in S.A.

I checked my '52 fender...installed on the bike.  It does appear to be 15cm near the area around the hinge.  Harder to measure at the cardan shaft, but at the very end of the front par of the fender, I can see that it is more like 13cm.  Of course, there is the molded cutout for the shaft to pass by the fender.

Kurt
Kurt in S.A.

Al Capone

Do you guys have any tips for speedometr needle removal?

This is the only one thread I have found.
https://bmw-einzylinder.de/forum/index.php?topic=522.msg2844#msg2844

4Taktix

Hi Al,
I made a "quick&dirty"-solution which worked for me.
- strip of sheet-metal from on old PC-housing
- M8-bolt + 2 Hexnuts
- ziptie
- the smallest drillbit I could find (slightly unter 1 mm, should go into the small hole of the needle)
I used a lathe to center-drill a hole with the small drill into the face of the M8-bolt. Then glued the shaft of a broken drill of the same size into it.
It has to be hardened/very hard, like the drill-shaft. Any wire woun't do the job and bend.
You can figure out how it's made from the pictures. It can be made much more professional, but I required it only once or twice, and it did what it was intended to.
Don't hesitate, if you got questions.

Regards,
Sascha
Think outside the box !

cledrera

Du bist im Recht; nun sieh zu, wie du da wieder heraus kommst. (v. Chamisso)
Lieber Einzylinder als zwei Fallschirme (v. mir)

Al Capone

Zitat von: 4Taktix am 13 Oktober 2020, 15:18:12
Hi Al,
I made a "quick&dirty"-solution which worked for me.
- strip of sheet-metal from on old PC-housing
- M8-bolt + 2 Hexnuts
- ziptie
- the smallest drillbit I could find (slightly unter 1 mm, should go into the small hole of the needle)
I used a lathe to center-drill a hole with the small drill into the face of the M8-bolt. Then glued the shaft of a broken drill of the same size into it.
It has to be hardened/very hard, like the drill-shaft. Any wire woun't do the job and bend.
You can figure out how it's made from the pictures. It can be made much more professional, but I required it only once or twice, and it did what it was intended to.
Don't hesitate, if you got questions.

Regards,
Sascha

It's really looks profesional. Today I have bought 0,8mm drill and it fits properly. Now I have to build my own tool.Thx for advice Sascha! :thumbsup:

Al Capone

The works are still in progress and the first effects are already visible.

Unfortunately, the engine block is damaged and I have doubts. On the forum I found information that the crankcase material is Alsi6cu4 alloy. Can I use a different commercially available alloy? Alternatively, I can purchase another crankcase and cut the needed element.

If any of you know metals, please give me some suggestions.


4Taktix

Hi Al,
considering the common price for a used block I'd think twice, if I really put the effort to repair the missing section by welding.
welding aluminum is tricky, also the section is hard to access. It bears the risk of putting some inner tension and making things worse.
On the other hand the missing section is uncritical from my opinion. It probably makes more sense to "create" a workaround to fix the grid, that's it.
Or you just look out for a used housing, maybe right here. They were dealt for about 50 to maximum 100 bucks on ebay e.g.
More than 100 bucks is cocky !
broken bolts or damaged threads can be fixed by helicoils, but the bearing seats should be within tolerance.

Regards,
Sascha
Think outside the box !

Al Capone

The repair went quite well. I want to keep this engine block for the sake of number matching.
I have some tips when it comes to welding aluminum. I took my first steps here and not everything was successful the first time.

We must remember to first clean the welded area using a low welding current without the addition of a wire. During the casting process, gases are trapped inside which we have to get rid of.

If we have to weld in the missing element, as in my case, it is absolutely necessary to heat the entire element strongly. Otherwise the weld will break.



After the block was repaired, I started assembling the engine.
There is a spacer ring between the bearing and the gear wheel. (No. 18 in the photo) Does anyone know what the size of this ring should be?

4Taktix

Hi Al,
I wonder why you ask. Do you miss this Ring ? Or do you want to avoid mixing it up with #17 ?
-> #17 is chamfered on the inside.
You can by it e.g. here: https://www.ulismotorradladen.de/artikeldetails/Abstandsring-Kurbelwelle-KettenradLager-R24-R253.aspx
Or do you want to make it on your own ?
btw.: excellent repair-weld-job on the housing  :thumbsup:

Regards,
Sascha
Think outside the box !

Al Capone

#18
i bought my R25 / 2 in several boxes and there are still many parts to identify.
I know there is a difference between part number 17 and 18. I found two rings without a groove, one 6,5mm thick and the other 9mm thick that fits over the crankshaft. After installing the 6,5mm ring, there is approximately 1mm missing for the sprocket.
Correct ring size would be really helpful.

4Taktix

Hi Al,
yesterday I browsed all the boxes in my shop and there were some rings, which might be part #18.
But I really can't say certain, if they are or not. Maybe different model or even different brand.
Sadly I have no assembled crank with all the bits and rings on it.
Maybe someone else can doubtless classify this ring and post the measrues ?

Regards,
Sascha
Think outside the box !

Borgward

#20
Hi Al,
I checked it on an assembled R25 crankshaft with a 6.5mm  drill - it fits -

Hubi6_5drill_Hubi.jpg

Al Capone

Thanks! :thumbsup:  The 6.5mm ring is correct. The bearing housing did not go deep enough, so 1mm was missing. Now everything is ok.

What is your experience with Loctite adhesive? The rear bearing seat in the block has a play of 0.05 (side) and the bearing enters without heating. I'm going to use Loctite 648 or 603 glue.
Do you have anything tested by yourself?

Heiko

The rear bearing is the floating bearing of the engine. I would not fix it with glue but repair the motor housing or get another good housing.
Ariel motorcycles... upon which the sun never sets.

Al Capone

hello Heiko

After what you wrote, I read a bit about it.
https://bmw-einzylinder.de/forum/index.php?topic=3841.msg40738#msg40738
# 44

But I still don't know how it works.

Should the rear bearing move in its housing when the clutch is used? This explains why there are two spring washers.
However, if the rear bearing does not move on the shaft, the shaft must move completely.

How is this possible if the front bearing in the housing does not move and is screwed on?

Heiko

#24
Hello,

no, not only when the clutch is used.
The front bearing is the fixed bearing. As a floating bearing, the rear bearing is intended to take over the expansion of the crankshaft and the housing when it is hot.
If the front bearing were also a floating bearing, the crankshaft would not be fixed, or if both bearings were fixed bearings, damage would occur somewhere.
Ariel motorcycles... upon which the sun never sets.

Al Capone

#25
Recently, I have been trying to get to know this problem better. The floating bearing can run on both rings depending on how it was designed.


Here are some of my own thoughts. I will be grateful for participation in the discussion and help.

1. If the outer ring is held in place (loctite) and the shaft moves due to the temperature increase in the inner ring. The wave washer between the shaft and the bearing will be compressed and the other wave washer between the bearing and the flywheel will be loose.

2.If the bearing is permanently mounted on the shaft (assuming that the heating of the shaft and the inner ring is the same), then during operation the shaft expands and the bearing moves inside the housing (outer ring) What role are the wave washers based on the inner ring to play then since he is not moving?


3. I have read a bit about it and I am wondering about one thing. Can a NU floating roller bearing be used instead of a 6206 ball bearing? Such a bearing itself allows the "inner ring to float. You would probably have to give up the wave washers that rest against the inner race. For example, the NU206-E-XL-TVP2

I note that these are just my guesses and considerations. I try to get to know this topic as best as possible.

bullet

Nobody seems to have noticed you are asking questions here.  I'll give it a try, as this might lure the experts back.   8)

1.: On the rotating shaft the load point between shaft and inner ring also rotates (take the perspective of the shaft here).  If there is not a tight fit, the fit would wear out and the bearing become too lose.  If the fit becomes too lose, this might be the right place to apply Loctite 648 or similar.  There should be bearings with undersize inner rings available, which would also cure this.  But...

2.: ... I do not know what these washers are supposed to do, as I haven't seen such a construction elsewhere.  I would expect solid rings there.  Shaft and inner ring are thermally tightly coupled due to the tight fit, so you can expect even heating.

3.: NU roller bearings were used by Deutz in their single cylinder tractor engines on the flywheel/clutch end of the crankshaft.  These engines where built from 1936 to 1950 and are among the most durable engines of the era.  I would consider this a legal technical solution in the BMW engine, but I think these bearings are more expensive and were thus not chosen by BMW.  These bearings can also carry higher loads, which is not necessary here.  A drawback is that the outer ring needs to be locked into position somehow, e.g. using circlips or Seeger rings, if there is no tight fit.  I do not know if glueing into place using Loctite 648 is sufficient, as you said that the fit in your crankcase is alread too lose.  There should be oversize outer rings, which would give a sufficiently tight fit.  But this could mean to rework (i.e. machine finish) the bore in the crankcase.

Bullet

Kees

One thing against roller bearings is the flex of the crankshaft. These BMW crankshafts flex quite a bit during higher revs. On the R68 they even had to go to a barrel roller bearing. A Deutz tractor engine doesn't run at higher revs.

Al Capone

In the end, I decided to use an NJ roller bearing. Time will tell if it was a good decision.

The new cylinder and piston are already in place. I put the timing chain on today but it seems to be too loose. I found the chain among other parts in cardboard boxes and I don't know what its condition is. Should a new timing chain be stiff even without a tensioner?

I am uploading a short video to illustrate.

https://youtube.com/shorts/jkTakwIyWy8?feature=share

Eppo

Hy Al,
can't watch the video because it is marked as 'private'.

Precautionary I added the chain tensioner from the R27 to my R25/2 Engine.
There are some benefits of using this tensioner e.g. preventing the chain to get in contact with the aluminium block and reduce the noise from the moving chain.
I don't know how much a new chain cost in your case, but I brought a new one when rebuilding the engine
and I think it is worth the money.

Greetings Eppo
Geht nicht, gibt's nicht. Einfach kann ja jeder 😁.

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