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Old 01-18-2013, 09:49 PM   #31
motog OP
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Thanks Charles

Re bottom-ends, that's what I understand too.

I have written responses from both Motoren-Israel and Siebenrock that the R75/5 power kit cylinders they sell don't require any changes to the motor, valves or carbs, which seems a bit strange - I would have thought that you would at least need to re-jet to suit the larger cylinders. The /5 power kit is specifically machined for that model so that no machining of the block is needed - ie. spigot at base of cylinders is 97mm, not 99mm.

I might just be being paranoid but before I lay out $1000 I'd like to know if it's going to work
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Old 02-17-2013, 07:09 PM   #32
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So, did the top-end teardown after the compression test showed a problem. Found a few interesting things:
  • left cylinder and piston were stamped 'A', while right side was stamped 'B'
  • Rings were definitely out of spec by more than I'm comfortable with
  • Bore was definitely out of spec
At that point I had to make the call: new pistons and barrels or new pistons and rebore.


After I did my sums, the difference between the two options wasn't very much (about $200 more for the Siebenrock powerkit). In return I could look forward to more power and torque, lighter pistons, Nikasil lined bores that are supposed to never need reboring, etc. Just as important to me was the fact that I could do it in one day and wouldn't have the bike off the road for weeks waiting for parts, rebore etc.


So I went for the Siebenrock powerkit.



Kit arrived last week and I fitted it yesterday. Total installation time about 4 and 1/2 hours (including topend teardown, parts replacement and rebuild. Doesn't include two trips to the local auto parts store because I'm a doofus and didn't get all the things I needed before I started). Have done valve clearances but haven't yet checked timing and carbys (hey, it was 37 degrees C (100F) and I wanted a beer!).



Job was pretty straightforward and would have taken less time except for three things:
  1. the instructions from Siebenrock are in German (eventually found a translation on the web when my German proved not to be good enough)
  2. Standard BMW cylinders have got a good bevel on the base of the cylinder flange that makes fitting pistons with rings into the cylinders easy (you can do it with your fingers). The Siebenrock cylinders didn't have that bevel so you need to use a ring compressor. I don't have a motorcycle ring compressor and couldn't find one anywhere on a Sunday so I ended up jerry-rigging something out of a big airconditioning hose clamp.
  3. It wasn't clear to me if the cylinders were handed (ie. cylinders are matched to sides of the bike and should only go on the correct side). After a fair bit of farfing around and test fitting I was able to convince myself that either they weren't handed or I had them on the correct side by chance.
Took it for an initial 1mile test run and it went beautifully. Took it for a 20 mile test run and I couldn't wipe the smile off my face. Bike is running fantastically, a noticeable increase in power and torque (even with the very gentle riding I was doing), pulls higher speeds at lower revs and there is significantly less side to side vibration.


I'll do the timing and carbs on the weekend but I did notice two things that I need to address:
  1. Carbs definitely need to be done - idle speed is too low and bike keeps cutting out even after warm up. That may be a result of the higher compression or maybe even just getting back to compression that is more equal on both sides
  2. The starter motor is struggling. I suspect that the 41 year old starter isn't able to handle the greater compression. It seems to kick over fine most times but was completely unable to turn-over the motor a couple of times. I suspect it's struggling to turn the motor over when a piston is approaching TDC on compression.
I'll do the timing and carbs and see if those two issues can be sorted out. But I get the feeling I'm going to have to get the starter rebuilt or get a new one that has a bit more power.

If anyone else is considering this I'd recommend it. Assuming that there is no big problems that crop up later, this was a straightforward and worthwhile task for those who have a reasonable amount of motorcycle mechanical knowledge. I wouldn't recommend it for anyone who has minimal mechanical experience unless you're willing to take a lot of time or get some help.

If anyone wants more detailed instructions on how I went about it, just ask.

Jim
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Old 02-17-2013, 07:10 PM   #33
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Forgot to say......

.... and no more blue smoke.

Should have also said: I got the powerkit from Motoren-Israel and found them good to deal with. Questions that I emailed them in either German or english were answered promptly, parts arrived quickly and everything was as ordered

motog screwed with this post 02-17-2013 at 07:39 PM
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Old 02-17-2013, 07:33 PM   #34
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[QUOTE=motog;20749300 pulls higher speeds at lower revs and there is significantly less side to side vibration.



[/QUOTE]


Replacing your top end changed your gearing? Explain that please!
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Old 02-17-2013, 07:52 PM   #35
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Did you do any specific break in for the kit?
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Old 02-17-2013, 09:24 PM   #36
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Originally Posted by JonnyCash View Post
Replacing your top end changed your gearing? Explain that please!
Yeah, could have said that better. What I meant was that it got up to speed much quicker and with less throttle needed - eg. 60km/hr came up quicker and much smoother.

Kt-88 the Siebenrock instructions say to follow the break-in procedure in your manual. My copy of the /5 owners manual says:

"Even the most carefully machined parts require a certain break-in period. The performance and longevity of your motorcycle depends to a great extent on how carefully it is broken in. The surest method is to:
1. Never exceed the permissible maximum speed in each gear
2. Ride mostly on winding country roads; avoid turnpikes
3. If turnpikes cannot be avoided, try to vary your speed constantly; do not operate at a constant speed for long periods.
4. Always approach the maximum allowable speed and immediately back off.
5. The maximum allowable RPM up to 600 miles is 4000; from 600 miles to 1200 miles it is 5000."

That's probably being overly cautious given it's just one part of the engine being broken in but I'll stick to it, particularly the bit about winding country roads.

I've read other things that say the most important thing is not the maximum revs you run to but that you vary the revs and don't rev the bejesus out of it.

The only other thing I did was that I turned the engine over carefully by hand a few times both before and after putting the valves back on, prior to starting the bike the first time. While doing so I listened to the motor with a mechanics stethoscope. I'm not a 100% sure what I was listening for or even if there was any point in doing this but my grandfather told me to do this everytime I put a motor back together and I never argued with my grandfather.

I'll do a compression test when I do the timing and valves just to give a base line that I can compare back to over time.

Thinking more about the carbs: I recall that they were almost impossible to balance properly with the old cylinders (with low compression) so they're probably miles out now - I recall a little backfire on the test ride yesterday. Probably a good idea to do the timing and the carbs as soon as possible

motog screwed with this post 02-17-2013 at 09:40 PM Reason: Forgot something
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Old 02-18-2013, 05:10 AM   #37
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Originally Posted by disston View Post
This is I think the heart of the current problem. The rings are not seated. They need higher revs and they were improperly broken in. Most builders today do not oil the cylinders or the rings on a rebuild. The idea is to wear the rings into the cylinders fast. Thus they will be seated and they will seal.


I've followed this thread since the beginning because I have a set of rings which refuse to seat. Hoping you have not just come full circle w/ the break-in procedure...
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Old 02-18-2013, 05:49 AM   #38
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Question More info - rings won't seat??

Quote:
Originally Posted by ozmoses View Post
I've followed this thread since the beginning because I have a set of rings which refuse to seat. Hoping you have not just come full circle w/ the break-in procedure...
Curouis on what the rings are doing are you burning oil?? Bad gas mileage?? How many miles do you have on the unseated rings?? Cylinder bores what kind??
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Old 02-18-2013, 06:12 PM   #39
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Ozmoses: I didn't oil the cylinders or pistons and only put a small amount of light oil on the rings (mainly to help with fitting) that would have burnt off within seconds. It's early days yet and I've only done 30 miles but it feels to me like they've seated properly and are working as expected. I've only had rings not seat properly for me once in the past and that was pretty well immediately obvious.

I probably won't stick religiously to the break-in procedure from the manual and I've read a few things that say it's important to run the motor all the way up and down through the rev range. What I won't be doing is cracking the throttle wide open and revving the hell out of it really quickly
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Old 02-18-2013, 07:05 PM   #40
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Quote:
Originally Posted by motog View Post
I probably won't stick religiously to the break-in procedure from the manual ...
Just curious, what is the break-in procedure they suggest in the manual? My Siebenrock kit didn't come with a manual.
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Old 02-18-2013, 07:25 PM   #41
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I think he is referring to the break in procedure for a new bike that is mentioned in the BMW owner's manual or rider's manual.
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Old 02-19-2013, 01:43 AM   #42
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The break in price endure in the manual is for all the wearing surfaces in the bike, from gearbox to camshaft, remember that the only new surfaces that need to be broken in are the rings and the piston pins. Your break in should be making sure that the rings seat properly.

There can be some discussion as how to do that
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Old 02-19-2013, 03:23 AM   #43
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There can be some discussion as how to do that
I'm all ears.

Always willing to learn
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Old 02-19-2013, 06:11 AM   #44
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I'm sure SS will tell us how to do it.
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Old 02-19-2013, 07:12 AM   #45
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I'm a firm believer in not revving it too high for the first 1000 or so, but still loading the engine hard in both directions. Let it brake hard down hills and give it plenty of gas going up them. Vary the RPMs plenty and don't spend a long time idling the thing when you fire it up the first time. Give the carbs a rough setting so that it'll run and immediately hop on and load the engine.
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