R100 knock on acceleration

Discussion in 'Airheads' started by Kspit, Jun 22, 2013.

  1. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    It looks like the crankshaft is still in the engine casing. The rods were send off to machine? What machining operation is needed on the connecting rods?

    There are some folks online who have completely disassembled the engine and rebuild the lower end. The engine (and optionally transmission) need to come out of the frame to remove the crankshaft. Looks like the job is mushrooming. Good luck!
    #41
  2. Kspit

    Kspit Adventurer

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    I was told by my local guy to have them trued and potentially re-sized. He told me that every time he has seen an boxer lose a big end bearing the big ends were out of round. Sent them off to be cleaned up and checked for true. The machinist, who had to have been over 70, definitely knew what he was doing.

    Mushrooming, potentially. I will see how well the crank cleans up I think. If I do end up just bolting it back together we will see how long it runs for I guess, and in that period time to source a new crank/find a short block to set up to be transplanted if/when she does go... Since the machine shop is so busy I have a while to figure these things out it seems. I really do wish I had a garage right about now! Damn apartment life.
    #42
  3. disston

    disston ShadeTreeExpert

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    I work on my bike on the street. When I have to have large pieces of it off for repairs I merely put a cover over it when I'm away. I've gotten away with it so far. Apartment building parking lots often have their own rules, I know.
    #43
  4. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    You may want to keep an eye out for used connecting rods. It may be that only the right rod is out-of-round due to knocking and needs to be replaced. If the rod hole is honed or machined round the diameter will increase which may require a larger outside diameter bearing that also has an oversize ID.

    The rod bearings that I have seen online w/BMW part numbers are only sold in oversize ID. I have never seen a BMW part number for oversize OD rod bearings, but there may be a bearing company that makes them. I would make sure the oversized (both OD and ID) rod bearings are available before spending money on truing the rods after they are checked. Good luck!
    #44
  5. robtg

    robtg Been here awhile

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    Resizing a rod big end involves grinding the cap and rod where they meet and then honing back out to the standard B/E bore size. Standard size bearings are then fitted.
    #45
  6. Kspit

    Kspit Adventurer

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    Hm, I guess I assumed the oversize was for the rods, since BMW recommends against resurfacing the crank at all. I'm going to give a call to my pal and see what he meant. The machinist and even Sullivan said they probably wouldn't need to be machined, more just cleaned up(Hopefully) but Sullivan said just to throw standard size bearings back in it and run it. Let me get all of my facts straight and hopefully things work out. Finding a new rod wouldn't be a problem I'm sure. The bay area is littered with dead airheads it seems(mine shouldn't be included in that statistic)

    Cheers all.
    #46
  7. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    Yes, that makes more sense. I expect the bearing retaining tang is also machined. Obviously, I have not done this operation (or had it done in a very long while). My bad.
    #47
  8. Kspit

    Kspit Adventurer

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    Well that makes even more sense. I was freaking out there for a second but that makes total sense. The machinist wants me to drop off my wrist pins so I'm going to do that later this week and just ask for a rundown on his rod resize process. I know he knows what he is doing, but it will be nice to hear.

    Cheers.
    #48
  9. robtg

    robtg Been here awhile

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    Very little is removed in the tang area. The groove is much deeper than the tang is high. I spent 15 years as automotive machinist and have done a lot of them. The machinist should also check and straighten the rods after the machine work is done.
    #49
  10. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    And unless that rod has been majorly abused, the big end bearing opening shouldn't be elongated. A couple of simple measurements should tell.

    I'd take the parts to the qualified and experieced shop, give them the history of the engine and a "scope of work" (what I ~think~ needs to be done) and let them have at it.

    I typically find that the bearing inserts on a high-mileage engine will have minor "wiped" areas, presumably for the few times that a really HOT engine has been started and revved before oil pressure built up. I did that on the last top-end on my engine, and even Plastigauge'd it (not obsessed, I had a pack of it and extra time and curiosity).

    --Bill
    #50
  11. Kspit

    Kspit Adventurer

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    @Bill Harris - The Machinist said pretty much the same thing. It wont take much work at all.

    So my rods are still at machine. They are super busy and the machinist said he would squeeze my work in when he had a similar setup/tooling ready to go, to save me money. I guess he was impressed a guy in his 20's was rebuilding a motor, pretty cool.

    BMW SF has all the parts I need for a rebuild, pretty cheap too. They would need to order out for 2 sets of rings. I think I'm going to replace mine and hone my cylinders while its all apart. May as well. I'm pretty sure my bores are iron as well. I'll look into it.

    I did end up sanding down my rod journal with a strip of 2000 grit sandpaper. Almost all of the discoloration on the journal is gone, the potentially sharpest grooves are definitely a gradual mound now, as opposed to a peak. But as I said, they were barely if at all catchable with the back of my fingernail. All in all, it feels much better. It got a very thorough rinse out with brake clean, and yes, the oil pan was off. After that I sprayed it all down with WD40 and have just been cleaning my grease off the case and cylinders. All I really have to do now is get the carbon off of my heads, and maybe inspect why my tach doesn't work.

    I am very anxious to get back on my airhead. I'm hoping riding it for a while after work everyday will rack up the miles for my breakin so I can give it a nice long ride again before my "Summer"(relative being in California...) is over!
    #51
  12. Kspit

    Kspit Adventurer

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    Welp, Got my internals back. Machinist said all looks good! Rod big ends are re trued and bored to standard. small end bushing and wrist pins micropolished, the machinist told me the clearances on the wrist pin, crazy, like .000 8/10 inches. I cant even fathom that. He said from the factory the rods are end over end balanced perfectly and didn't do any balance work

    :clapSuper pleased

    Had another go at my crank with some 2000 grit. Its super smooth now. It is definately quite nerve racking sanding your crankshaft... But i'm glad I got it more perfect. rinsed the shit out of the crankcase with the oil pan off again, and may do it a 3rd time just to feel better about myself.

    I am planning on putting my oil pan back on first, but I was considering attaching a magnet inside, or maybe buying a magnetic oil drain plug? I was thinking of getting a torch with some map gas or something and burning the oil out of a spot on the pan, then epoxying a small magnet to collect any particles. I have been looking a little bit on this subject, just curious if anyone has done anything similar.

    Hopefully I'll have my finances sorted out well enough to have her back on the road at the end of the month!


    Edit : Also, on my right hand cylinder, my bottom right stud turns in place, when correctly spaced. This one doesn't have an o ring on it, I think. So I can assume that one is a safe passage to helicoil?
    #52
  13. Airhead Wrangler

    Airhead Wrangler Long timer

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    They're all "safe" to helicoil, just need to make sure oil passage isn't blocked for the UPPER studs.
    #53
  14. Kspit

    Kspit Adventurer

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    Thanks airhead wrangler !
    The top 2 carry oil in and the pushrods are the "drain" correct?

    Maybe I'll get to helicoiling this weekend!
    #54
  15. Airhead Wrangler

    Airhead Wrangler Long timer

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    Correct. Just be careful to drill it straight and mind where your chips go. Greasing up the drill bit and the tap really well will take care of most of it, but still be sure to exercise some caution.
    #55
  16. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    Regarding the magnet: The bearings are non-magnetic with the crankshaft being magnetic. As you noticed, the crankshaft journals have worn very little. So, any metal or abrasive bits are non-magnetic and a magnet won't hold them.

    FWIW, I would change the oil and filter after the first 50 miles and again at 500 miles - just because the engine has been sitting opened. Good luck!
    #56
  17. Kspit

    Kspit Adventurer

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    Awesome. I think I'll have someone over with more helicoil experience to monitor my work. He has some 10mm helicoil kits so that will work well. Since my oil pan is still off "off" cleanup will be a breeze.

    Also, thanks for my lesson in Airhead magnetism Stan! I will definitely be doing some frequent oil changes the first week, depending on how much putting around I can do.

    I guess I should try and get my tach to work. I was considering buying something electric and cheap for my break-in. When I got the bike, I have a tach with no needle, still doesn't; but the cable was disconnected, and doesn't spin with the motor. I have been trying to do some preliminary research on what drives it, I know it is off the camshaft, but can that drive gear or whatnot fail? I assume I just have a broken cable.

    Today is another day of scrubbing carbon out of my heads, and beer. lots of beers.

    Edit - Assumption correct. The cable is broken somewhere. I was able to pull it out of its outer cover. Hopefully the gauge still works as well! I'll have to fit a new needle, but that should be easy enough.
    #57
  18. Kspit

    Kspit Adventurer

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    Revived from the depths!

    Today I ordered new piston rings, and Saturday I go in to pick them up! Along with my assortment of gaskets, bearings, o-rings and bolts! SF BMW is great, so many airhead parts. Only thing I'm missing are exhaust nuts, which I am trying to source locally and used. Got 2 oil filters for my first 2 oil changes and I'm trying to settle on a break in oil. I'm leaning towards just a straight 30 weight for the first 50 miles before I do my first oil change...

    Anybody who has sealed up a early /7 without the o ring... I have heard permetex's super grey is a good sealant for the cylinders, anybody have experience with yamabond at all?

    Hopefully my next post is a victory video of the first startup!
    #58
  19. JStancampiano

    JStancampiano PhotoJoe

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    Used Yambond 4 several times...works well.

    Joe
    #59
  20. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    Yamabond is a popular sealant for the cylnders to block. I have always used hylomar, but may switch to yamabond. Only a thin film is needed, per the directions. The upper cylinder studs have an o-ring for the rocker arm oil path which should not be covered in sealant.

    Regarding the oil and my opinion: I would use some Valvoline 10W-40 or Castrol 4T 10W-40 regular motorcycle oil for the break-in. Both oils are reasonably inexpensive (I think Walmart carries the Valvoline 10W-40). Both have sufficient ZDDP for the cam and are motorcycle oils. I might consider the 30W if it was specifically for flat-tappet engines and only used for ~ 50 miles.
    #60