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Thread: 1972 r75/5 engine knock

  1. #1

    1972 r75/5 engine knock

    I been tuning up my /5 and getting it ready to ride to the rally at springfield. So I've adjusted the valves, put in new points, condenser, plugs and also put on a new diode board. It started and ran fine so
    later in the day I thought I would go for a ride. A few miles into the ride a kept hearing a knock from the left cylinder so I got turned around and headed home before I got back I was hearing a knock from the right cylinder. All kinds of bad things were going through my head on the way home. The worst of which was piston slap. Does any one know what piston slap sounds like? Any suggestions?

  2. #2
    Liaison 20774's Avatar
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    Welcome to the forum! Sorry it is on such a troubling situation. Try reading one of the threads in the Similar Threads pane below about knock on an R90/6. I would go back and recheck the valve adjustments just to be sure those didn't change. Also check the up/down movement of the rocker arms to be sure it is not excessive. Noises from the valve train are more high pitched, so likely not the source of a knock, but still something to check. If you have a mechanics stethoscope, try and isolate the location of the sound with the motor running.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Quote Originally Posted by 20774 View Post
    Welcome to the forum! Sorry it is on such a troubling situation. Try reading one of the threads in the Similar Threads pane below about knock on an R90/6. I would go back and recheck the valve adjustments just to be sure those didn't change. Also check the up/down movement of the rocker arms to be sure it is not excessive. Noises from the valve train are more high pitched, so likely not the source of a knock, but still something to check. If you have a mechanics stethoscope, try and isolate the location of the sound with the motor running.
    I had an issue with my 73 that I thought was detonation except it would happen at RPM and Throttle opening's that were not where you would expect detonation. After throwing a lot of time and effort at the problem turned out to be a cracked lifter. Since you mention hearing the noise after a valve adjustment. If your sure everything is correct with your rocker arms and adjusters might take a few minutes to pull the lifters on that side.
    Gator

  4. #4
    Quote Originally Posted by DEANTRIMBLE View Post
    I been tuning up my /5 and getting it ready to ride to the rally at springfield. So I've adjusted the valves, put in new points, condenser, plugs and also put on a new diode board. It started and ran fine so
    later in the day I thought I would go for a ride. A few miles into the ride a kept hearing a knock from the left cylinder so I got turned around and headed home before I got back I was hearing a knock from the right cylinder. All kinds of bad things were going through my head on the way home. The worst of which was piston slap. Does any one know what piston slap sounds like? Any suggestions?
    Always go back to the last things you did. You said you adjusted the valves. Assuming you didn't adjust the rocker arm play, then check your valve clearances again.

    You DID rotate the engine correctly when setting them, right? (CW viewed from front)

  5. #5

    Check your points

    Check your points for gap, burning or factory defects. Where did you get the points? If no knock before the work, something you did is very likely the culprit.

  6. #6
    Quote Originally Posted by gator View Post
    I had an issue with my 73 that I thought was detonation except it would happen at RPM and Throttle opening's that were not where you would expect detonation. After throwing a lot of time and effort at the problem turned out to be a cracked lifter. Since you mention hearing the noise after a valve adjustment. If your sure everything is correct with your rocker arms and adjusters might take a few minutes to pull the lifters on that side.
    Gator
    Thanks i'll check that out.

  7. #7
    Nick Kennedy
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    Kurt mentions a MECHANICS STETISCOPE.
    Great tool - don't need to spend any money
    a 24"-36" piece of old garden hose works great
    Nick

  8. #8
    Registered User STEVENRANKIN's Avatar
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    How many miles

    How many miles on the bike? Unless you have been abusing it while riding, I doubt you have piston slap if you have less than 90K. I could be wrong but I think it unlikely.

    Like most of the folks, I always say check the last thing you did. Knocking could be caused by ignition timing issues. Good luck in the hunt, I know I hate it when I do a repair or maintenance only to have to put the bike back on the lift because something else turns up. I REALY hate it when the something else turns out to be me induced. St.

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