The dreaded blue smoke

Discussion in 'Airheads' started by motog, Dec 30, 2012.

  1. disston

    disston ShadeTreeExpert

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    I don't know why but I thought you had new rings. If not then I was wrong.

    So we are back at you need to do compression and leak down tests. You did say earlier that mileage was unknown? If not improperly seated rings then worn rings. Worn rings = too much blow by = oil dumped by breather into right cylinder.
    #21
  2. motog

    motog Been here awhile

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    Yep, I'm pretty resigned to the fact that I'm probably going to have to do pistons, rings and cylinders. There's really only one way that oil can get into the combustion chamber - by getting past the rings. I'll still do the compression and leakdown tests but I'm pretty certain of what I'll find.

    In the meantime I've been doing a bit of research and found this power-up kit for the R75/5 from Motoren Israel for about $860: http://www.motoren-israel.com/produ...-1000-cc-for-models-up-to-September-1975.html. Which is pretty tempting. The way I figure it, new pistons, a rebore etc will cost me about $650, but if I got the powerkit for only an extra $200, I'll get a new set of nikasil cylinders (that won't wear out in my lifetime), new pistons and a stinking great increase in power and torque. As an added benefit, I can do the change over in one afternoon, rather than having the bike off the road for 1-2 months (riding season is pretty well 12 months of the year here in Oz so this last point is important)

    Does it sound like I'm trying to talk myself into this?

    Has anyone else done this?
    #22
  3. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Ok, so it only got the heads re-worked, nothing was done to the cylinders or pistons. Got it!

    So - how many miles are on the cylinders and pistons?

    Just because rings may be worn out doesn't necessarily mean pistons and cylinders are bad. :huh

    But if you want to talk yourself into new pistons and cylinders, don't let us stop you! I'm just saying there's a very good possibility all that's needed is rings. Just maybe, the ring gaps are aligned and all that's needed is properly orienting them! Cost = zero!

    How many miles does it take to lose a quart?

    I'd like to say that it makes no sense to me the breather could be causing this. For one, the breather dumps into the LEFT side on your bike. If it was dumping excess oil fumes into the engine, it would be the LEFT side that smokes, not the right!

    Another interesting bit of data is that Oak considers the old style breather better than the new one and recommends replacing the disc when it goes bad with a new one cut from circuit board material. I don't know why he feels that way, but it is something to consider.
    #23
  4. motog

    motog Been here awhile

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    How many miles on the pistons? No idea! I've had the bike for about 5 years and probably put about 10,000 miles on it. When I got it the original speedo was long since gone. From the condition of the lands on the rear drive (completely roached, they looked like shark teeth) I reckon it's done at least 100k miles. I have a vague recollection that the pistons had "B" marked on them which suggests they were already 1st oversize.

    How many miles does it take to use a quart of oil? I haven't measured it because I've got in the habit of just topping it up every now and then. I wouldn't be surprised if it was using about a quart (that's about a litre i think) every 1000 miles- at least 2-3 times as much as it should. It has probably decreased a bit since I did the valves but not as much as I expected and it seems to have started to go back up again.

    I hear what you say about worn rings not necessarily meaning worn barrels, so I reckon I'll do the tests and see how they look.

    Wife is taking the kids to the beach for the weekend on Friday so I'm all clear to do a compression test, leak down test and top end tear down (if necessary) on Saturday. Just got to remember where I put the compression and leak down gauges. Probably should have done them when I bought the bike but the price was pretty good so I just wanted to get it out the door before he changed his mind.
    #24
  5. disston

    disston ShadeTreeExpert

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    When you get it torn down you will be able to see how well the pistons fit. I thought mine were OK but they really weren't and when I ended up with new pistons it was what I really needed.

    "B" on the cylinder is the mark for B cylinders, I think. There are A, B and C sizes. Then with in these three sizes there is 1st and 2nd over size. Do you remember what the number was stamped on the top of the piston? This number tells you much more than the letter B. I'm actually not sure a B on the piston is important. I thought the letter was on the cylinder.
    #25
  6. JonnyCash

    JonnyCash turd polisher

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    I think the letter is both on the piston and the cylinder, that's how they're matched up. the way I understand it, it's a way of working with the variable tolerances of production. Some come out bigger than others.
    #26
  7. Biebs

    Biebs BMW Airhead

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    Rings wear check all tolerences and replace rings sounds like your problem. You had the heads done 2 years ago so you are good - now replace the piston rings and Connecting rod bearings while you have it apart and ride!!!

    As stated in your original post power is good.:clap
    #27
  8. motog

    motog Been here awhile

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    I did the compression test today. Left cylinder 125psi. Right cylinder 127 psi (dry). Wet test (yes I know that you're not supposed to do wet tests on boxers but it's force of habit) right 145psi, left 155psi.
    Haynes manual says 109-123 psi is poor 123-145 is normal and anything over 145 is good for R75/5. I had a short moment where I thought it was at the top of the normal range till I realised that R75/5 compression figures in the manual are higher than most other models.

    Was going to do the leak down test but couldn't find my leakdown tester. Was thinking about pulling the heads off but then my mate (who's garage I was doing this in - I live in a 4th floor apartment) offered me a beer and it just went downhill from there.

    So it looks like I'm only just above poor. Add that outcome to the blue smoke and I'd say that it's time for the top end to be stripped down and either new pistons, rings and rebore or one of the top end kits from Germany.
    So I'll go back to my earlier question: does anyone have any experience of either boring out the cylinders on an R75/5 to fit early R80 pistons (which is about half the price of R75/5 pistons)? Alternatively does anyone have any experience of fitting the 1000cc power kits for the R75/5 from Siebenrock or Motoren-Israel?

    I'm pretty tempted to just keep feeding it oil until summer and autumn are over and do the teardown in winter
    #28
  9. motog

    motog Been here awhile

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    Now in the final throes of decision making. Got some ch coming in soon so need to make a call. Had almost pushed the button on buying the Siebenrock kit when someone in the local BMW club said that he'd seen three occasions that bigger cylinders had resulted in smashed crankshaft bearing housings. Admittedly this was putting BMW 900cc cylinders and pistons on a R75/5 rather than Siebenrock cylinder kits.

    Does anyone have any verification of this?

    Has anyone used the Siebenrock 1000cc kit on a R75/5?

    Thanks
    #29
  10. chasbmw

    chasbmw Long timer

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    The bottom ends of these bikes are pretty well the same whether or not you have a 600 or a 900, so I dont think that the extra power from the Seibenrock kit will be much of an issue, but do bear in mind that various components in the later /6 range were upgraded to take into account the extra power of the 900s. (I know that your bike is pre 900). I don't know for sure fitting bigger cylinders would result in smashed bearing housings, but I have never before heard that this was an issue.

    Boring out 750 iron cylinders to 900cc was often done back in the day, but the results were often less than good with the thinner liner. Have you double checked that the Kit will fit the /5 without any crankcase modifications. Earlier power up kits did not fit /6 models unless some minor machining was carried out to the crankcase ( I think). You could check both issues with Motoren israel
    #30
  11. motog

    motog Been here awhile

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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
    #31
  12. motog

    motog Been here awhile

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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
    #32
  13. motog

    motog Been here awhile

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    .... 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
    #33
  14. JonnyCash

    JonnyCash turd polisher

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    #34
  15. Kt-88

    Kt-88 I like everything.

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    Did you do any specific break in for the kit?
    #35
  16. motog

    motog Been here awhile

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    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
    #36
  17. ozmoses

    ozmoses Ride On

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    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...
    #37
  18. Biebs

    Biebs BMW Airhead

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    Curouis on what the rings are doing are you burning oil?? Bad gas mileage?? How many miles do you have on the unseated rings??:huh Cylinder bores what kind??
    #38
  19. motog

    motog Been here awhile

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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
    #39
  20. Airhead Wrangler

    Airhead Wrangler Long timer

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    Just curious, what is the break-in procedure they suggest in the manual? My Siebenrock kit didn't come with a manual.
    #40