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1970 BMWR75/5 engine issues

Discussion in 'Airheads' started by Magion, Mar 1, 2021.

  1. Magion

    Magion Adventurer

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    Hello everyone!

    Long time lurking here for help and opinions, thank you all so far for the knowledge.

    So couple years back I purchased a 1970 R75/5. I took it all down to pieces, basically restored the whole bike except for engine itself -cylinders, block stayed untouched.
    My issues lays in engine giving me headache. During my restoration I installed new clutch and replace all seals in there. When I bough the bike oil was leaking from rear main seal. After reassembling the bike I learned it is leaking again! So second questioned my work and went back and replaced it for the second time. Still leaks.
    Later I decided that a timing chain was never replaced so I went ahead and replaced chain. Along all new seal were installed. Now oil is leaking from camshaft seal, just above points. Great. So I have two leaks.
    I went through all possible scenarios in my head.
    here are other issues which I think might be tight to this. Engine oil is getting real black real fast. I measured compression and It was well within specs. I think my engine has a lot of blow by, also because of oil in right tube leading to carburetor. Checked oil pressure valve, seems to be good.
    So I am thinking it is either rings or valves not sealing properly. Or could this have to do anything with timing of the engine?
    There is something that I cannot grasp. When I am setting my timing I get both static and advanced where I want it to be, my other side does not correspond. There is a tolerance (cannot remember now) how many degrees is allowed but on my engine I am just past the tolerance, meaning I am off on on side if the other is set precisely.
    Right side has also lots of carbon on spark plug which could be a result of oil being passed from venting? Or because my timing is off?

    Sorry I know there is a lot. I am not really an engine builder, I am just a guy with lot of passion and I can use my hands to some degree. This has been bothering me well. I came to a point of needing help!
    #1
  2. Plaka

    Plaka Brevis illi vita est

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    you have a bent cam nose. confirm with a timing light shining in timing hole . a double image confirms. if the bike will run smoothly enough to suit you, ignore it.

    crankcase pressure sounds high or you truly suck at installing seals. :D run leakdown and compression tests. borrow gauges from flaps. know procedures.
    #2
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  3. Magion

    Magion Adventurer

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    Thank you for your input!

    I have seen the bent cam nose mentioned around here. It makes sense. I am pretty sure those marks in the window were jumping around quite a bit.
    So what exactly would cause the cam to bend? My bike rides fairly smooth I would say, I have nothing to compare it though. Would you say its best when setting timing to try go sort of in between? Or just set one side exactly?

    As for the pressure and my seals, I think I did good job of installing them, could be wrong too. I will find leak down tester for sure
    #3
  4. mykill

    mykill odd

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    If you were careful and made sure the RMS went in straight and the surfaces are smooth and clean, then I might suspect your breather isn't breathing well. If you have lots of blow-by that pressure has to go somewhere and will push out past the seals.
    #4
  5. Magion

    Magion Adventurer

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    That is kind of what I was thinking, Like I said I went back and installed second RMS to make sure. nice clean surfaces, friend of mine cnc'd me tool to push it in correctly.
    What I did not mentioned initially; I have the /9 and /10 Bings on the bike. I rebuilt them. But I had hard times adjusting them, some backfiring and one side plug is always black - carbon. I am getting confused as this could be because my timing is little off? Or because oil is beiing pushed there? Or just because there is an issue with the carbs itself
    #5
  6. Plaka

    Plaka Brevis illi vita est

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    you said there was oil in the r. intake tube. that is from the breather. if it is dripping to the outside the blowby is significant. this will make the plug black. timing a little off will not do it. a whole4 lot off will. i would ignore the timing issue for now. you have bigger fish to fry. get to it when you can get out and ride.

    the cam nose is a separate piece of metal pressed into the end of the cam. it can work lose in it's bore and whirling around get cocked.

    i would be interested to see a pic of that leak in the front and one of the heads under the rocker covers.

    what were the compression numbers, what kind of gauge did you use and did you take the carbs off?
    #6
  7. TwoShoes

    TwoShoes Carbon-based bipedal life form

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    The one side plug being black, I'll bet it's the right side plug, the breather drips oil into the right side intake when blowby is significant. You can mitigate this somewhat by swapping the breather valve to the more modern reed type and / or installing a deeper oil pan to increase the air volume in the crankcase, but you are describing symptoms of piston blowby / too much pressure developing in the crankcase (black oil, seals that don't want to seal, sooty plug). Compression and leakdown testing should point you in the right direction... My money is on rings
    #7
  8. tsADV

    tsADV Been here awhile

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    Sometimes engine oil can leak past the O-ring under the oil pump cover, which is below the rear mail seal. May be worth replacing as well, when the flywheel is off.
    #8
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  9. mykill

    mykill odd

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    I still suspect breather issues. Can you run the bike without the air tubes to see if your breather (hose that dumps into the right carb) is indeed breathing? Do you have access to a leakdown tester? At TDC you'll be able to see and hear what and where blowby is happening. Passing the rings will increase crankcase pressure and it has to go somewhere. I doubt carb settings are contributing to your leaks but with one side different from the other something wasn't done right. If you removed the needles from the slide did you verify they were reinstalled at the correct notch? Was the rebuild simply a soft part change or did you replace needle jets? Did you verify your float levels are the same and correct? Lots of variables. For now, I wouldn't sweat the timing as long as it's close. One last thing... Any chance you overfilled the oil? Correct reading should be below the MAX with the dipstick threads seated but not screwed in. Too much oil is a different kind of bad than too little oil.
    #9
  10. Pokie

    Pokie Just plain Pokie.

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    On the early /5s, the pump plates were made wrong. They had a channel that didn't belong. The o-ring would get sucked in then oil would start leaking.

    PumpCover1.jpg

    The plate on the left is the faulty one.
    #10
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  11. Magion

    Magion Adventurer

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    Again, thank you kindly for your input everyone.

    I highly doubt it would be coming from oil pump cover. I did replaced the seal as well. I do not really remember or have a picture of the cover itself. But probably no notch.
    When looking inside where the oil was coming from, it looked like it is indeed being pushed past RMS and spread out by flywheel. My instincts are telling me blow by also based on everything I read so far peoples input here also. I do not have an access to Leak down tester but I am going to purchase one. I like the idea for the time being to run the engine without intake tubes to see if I have pressure coming from that valve.

    As for the carbs, I mainly followed William from Boxer2valve :
    No I did not replaced the needle. I clean them in ultrasonic cleaner, reseal them. I did not take the butterfly apart. I added the oem BMW spring that came on later models. As for the floats all I did was to verify / bend for them to be level exactly as William shows in his video. I did read the entire thing Snowbum wrote about these carbs. I also positioned the needle according to his article (3rd )
    And for oil level, no I did not overfilled. Oil level is correct, at least according to my dipstick.

    I cannot remember now what compression numbers I saw, all I know that they were within specs of what I found at the time. But not the best gauge and I did not remove the carbs.
    #11
  12. Kiwiabbo

    Kiwiabbo Long timer

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    Cannot do a compression test if the slides are not all the way up unobstructed or carbs removed...
    #12
  13. Magion

    Magion Adventurer

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    really time to do leakdown test properly I guess
    #13
  14. korinthias

    korinthias Been here awhile

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    Just a thought, I have yet to replace an RMS,so no wisdom to impart there, but I have had issues with the engine breather and wondering if you have considered that? My R60/5 had the earlier disc type and made the typical glopperter glopperter noise; I replaced it with the later reed valve, got rid of the noise and usefully found that the motor pushed out considerably less oil...

    Edit – I see it mentioned above, apologies if you have considered it already!
    #14
  15. Disston

    Disston ShadeTreeExpert Supporter

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    I miss the turkey sound.
    #15
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  16. korinthias

    korinthias Been here awhile

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    Ha, true Disston I never minded it! Explaining it to bystanders was another matter though...
    #16
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  17. Magion

    Magion Adventurer

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    Guys,

    so I bought nice leak down tester and proceeded today to do some troubleshooting.

    The result is rather embarrassing. On both cylinders at TDC (i put a straw in the spark plug hole and spun crankshaft until all the way out) the intake valve is OPEN! :O
    This immediately took me back to when I replaced the timing chain. I somehow managed to loose position in between shafts. I panicked little bit but was finally able to find that both sprockets have marks from factory. I was able to find them and what I thought was to align them properly at the time, was not what it seemed. I remember also that when setting timing I ended up in the very end of the slot in the plate. So I am assuming that my timing chain is of tooth or more more.

    How to solve this problem?

    My biggest question now is on how to find the correct position?

    The odd thing to me is that the bike ran ok. It did not seem to have enough power, as one would expect from '70 r75/5. I think it would explain the occasional backfiring on decel. Who knows.
    #17
  18. Pokie

    Pokie Just plain Pokie.

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    Remember, once the sprockets are aligned properly, if you turn the engine over one revolution, the marks will no longer be aligned. The marks will once again realign every second revolution. Usually low power on a 1970 R75 is either leaky valves, bad timing chain, carburetor problems or ignition problems. Backfiring on deceleration is usually running a little on the lean side or an intake/ exhaust leak.
    #18
  19. Plaka

    Plaka Brevis illi vita est

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    they are very rare but watch the flea market....
    #19
  20. Magion

    Magion Adventurer

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    I realize that. Buddy of mine had a good point about checking clearance gap at TDC. If that is ok then valves might be binding and not closing properly. As I said at TDC the intake valve on both sides is somehow open. when I rotate the engine over a bit the sound of leaking air changes but does not stop.
    #20