Engine Knock Under Load

Discussion in 'Airheads' started by Boxer Metal, Apr 13, 2013.

  1. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    Is this a new rebuild? If so, you'll get a knock if the rods were installed with the pins towards the rear instead of the front.

    If old, no you can't get the heads off without taking the exhaust nuts off and at least pulling the headers out of heads.

    No you can't get to the rods from the pan..maybe on a pre-69 engine where the cam was still on top but I don't think so.

    If the oil pressure stays constant at around 80psi above idle, you've got pressure..if low, suspect the oil pump gears or a clogged oil gallery.

    Might as well pull the heads and get to the rods. Bet you can feel some give when you pull on the rod...only takes a little to knock. Pull the rods, measure, balance, assemble.

    Chris, if you're in a hurry, I have 3 rebuilt short blocks on the shelf (new chain, gear, seals, clutch pack, etc, sitting on the shelf for exactly this situation. Just swap out the short block.
    #21
  2. Plaka

    Plaka Brevis illi vita est

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    You should try pulling the heads with out disturbing the header pipes (except the crossover of course, loosen it). Then you won't have to say it can't be done anymore.:evil
    #22
  3. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    Tried 2 weeks ago on an R100RT..couldn't pull the heads away from the block while the headers held them in. Had to pull the headers out of the exhaust ports so the heads could be pulled away. Pipes just barely stayed in the collector so easy to reassemble.

    The only way I can maybe see this working is to take the mufflers and collector off so the headers just hang from the head.
    #23
  4. Plaka

    Plaka Brevis illi vita est

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    What is this "collector" you speak of?

    Yeah, the mufflers seem like a good idea, makes a long package to handle otherwise. I don't have things like "collectors" (???) or crossovers. Makes all sorts of things a lot easier. But I've pulled /5 heads with the pipes on. Screwing with the crossover was the only issue.

    If the pipes come off easily then of course it's the way to play. But you are pulling the mufflers anyhow unless the headers fall off.
    #24
  5. Lornce

    Lornce Lost In Place

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    Who's there!

    :ear



    I slay me.

    :rofl
    #25
  6. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    No one said what year/model bike we're dealing with..Around 1981 with the R80G/S and later airheads, the headers went back to a collector under the tranny before heading to the muffler(s). The headers curved under the tranny which made pulling the head off with the header on about impossible. Some early models had straight back header/mufflers with a single or dual cross over which may be what you meant.
    #26
  7. Plaka

    Plaka Brevis illi vita est

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    My '83 had dual crossovers. Nothing a sawzall couldn't fix.

    Methinks the "collector" came in with the monos. Still nothjing a sawsall can't fix. I notice making that thing go away is a popular GS mod.
    #27
  8. Rucksta

    Rucksta SS Blowhard

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    G/S collectors are extinct.and they self destructed.
    This could be part of why its a popular mod.
    #28
  9. Boxer Metal

    Boxer Metal Mad Scientist

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    Next week I will pull the heads off and check both rods and while I am in there I will go ahead and replace the bearings. The exhaust will come right off as I just installed them. Thanks for all of the suggestions.
    #29
  10. Plaka

    Plaka Brevis illi vita est

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    I just replaced my big end bearings. I must have screwed up with the plastigauge because when I got my new bearings they were exactly the same thickness as the old ones. I mean dead on with a digital mic. And there was only the most trivial scoring in the old bearing too. I could have run them without issue. Grrr...I put the new ones in 'cause I had bought them and labeled the old ones and put 'em on the shelf.

    Need a smokin' deal on some R100 big end bearings? Half price of new, precisely the same thickness.
    #30
  11. Boxer Metal

    Boxer Metal Mad Scientist

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    I'll take'm.
    #31
  12. Plaka

    Plaka Brevis illi vita est

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    I'll put your name on them. Can get them to you fairly quickly. Do your teardown and look at the crank. If it's borked and you need to grind undersize you'll need first over bearings and mine are stock. Not real likely but worth checking. Get the bungs yet?
    #32
  13. supershaft

    supershaft because I can

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    I tried to warn you that would happen but you were to busy advising others to do as you were doing. It will be a miracle if you didn't tear up your new bearings trying to measure them with a mic?

    The white O-ring would be the first thing I looked at. I have fixed knockers like that without taking them apart at all other than fixing the oil filter setup. They were still running fine thousands of miles later so they were fixed good enough for the owner anyway. Cheaply enough too I might add.
    #33
  14. Boxer Metal

    Boxer Metal Mad Scientist

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    I finally had some time today to work on my own projects. I installed a mechanical oil pressure gauge and at 200 degrease(oil temp) I have 30 pounds of oil pressure and it does not fall off when I rev the motor. I'm thinking rod bearings.
    #34
  15. Plaka

    Plaka Brevis illi vita est

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    30 is low. But what RPM did you test up to? if you got 30 at 4000rpm definitely some sort of problem.

    What weight oil?

    Where are you measuring the pressure and temperature?
    #35
  16. Boxer Metal

    Boxer Metal Mad Scientist

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    30 at idle 70 above 3000 RPM's. 20/50 BMW oil and the temp is measured at the dip stick(doesn't really matter it is just a reference) and oil pressure was right at the oil switch.
    #36
  17. ME 109

    ME 109 Long timer

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    Definitely low pressure across the rev range.
    Have you discounted other potential leaks such as the oil filter o-ring as SS suggested?
    I'd look at it before pulling heads off.

    I'd check the oil filter bypass spring as well, to see that it is intact.
    A piece of broken spring can find its way to the rear/front main and score the shit out of it.......low oil pressure.
    #37
  18. Hookalatch

    Hookalatch Born Under Bad Sign

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    I didn't see any info on the history of your engine. If it is something that has run without the knock in the past this definitely doesn't apply and is probably unlikely anyway. But I thought I would throw it out as a possibility anyway. When I recently rebuilt my engine I got most of the parts from our local dealer. I asked for a set of rod bearings and they asked me did I want standard or oversize. I assumed standard since I knew the engine had never been disassembled before. Fortunately I had the rods and old bearings with me and Ozzie suggested we check the size. They were the first oversize. I was unaware and surprised to learn that some bikes came from the factory with oversize bearings. Apparently this was not very common because the shop had not sold any for over 10 years. The computer said they had some but it took Emmi to find them. Had I just asked for standard size or ordered over the net I would have the same symptoms as you. Just food for thought.

    Chuck
    #38
  19. Plaka

    Plaka Brevis illi vita est

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    I'd do the checks 109 proposes and otherwise leave it alone. OilGuy is stating 10psi/1000rpm and you have well more than that. http://www.bobistheoilguy.com/ He also stresses flow over pressure. interesting reading.

    I'm used to 60-65 psi full load running pressure on a /5. (regular castrol 20/50, measured at the switch) If you get a flickering oil light at idle then go into the bottom end and/or check the rotor clearance on the oil pump.

    I always check the conrod big ends if I have the jugs off. it's worth the bolts. Basically I don't want to score the crank although minor scoring or a pit here and there won't hurt. But it's worth the bolts to make sure there isn't anything inbedded in a bearing. I also pull the pan, partially because it makes it easy to flush the bottom end when building and partially to clean it. Just a bunch of bolting and unbolting. Pain doing it on the floor, I wanna lift!.


    I intend on using my pressure/temp gauges to find the lowest viscosity oils I can run. I want to be using that oil filter bypass as little as possible. This means keeping cold starting pressures as low as possible.
    #39
  20. Plaka

    Plaka Brevis illi vita est

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    When you take it apart you always plastigauge it to check the clearances. (use the old bolts) Then mic. the journals on both parts if you can to check for roundness and size. Then go get parts (if any).

    I did this recently, screwed up the plastigauge work and ended up thinking the shells were worn. Turns out they weren't, at all, at about 100k miles.

    More often you replace them to loose some embedded crud rather than for wear.

    If the factory screws up the grind on a crank they'll salvage it by grinding first under and then compensating with the bearings. The machines aren't blueprinted so nobody knows. You have to check everything by measuring.
    #40