Results 1 to 11 of 11

Thread: 1976 R90/6 Valve adjustment issues

  1. #1
    Registered User
    Join Date
    Nov 2009
    Posts
    14

    1976 R90/6 Valve adjustment issues

    I seem to be having problems "keeping" my valve clearance adjusted properly. I'm able to set the clearance initially but after about 20 miles the bike begins to progressively get more chuggy and the valve clearance is way off. Any Ideas on what could be causing this? I appreciate the help.

  2. #2
    MOA #24991 Pauls1150's Avatar
    Join Date
    Apr 2008
    Location
    south of Los Angeles
    Posts
    1,521
    Are they getting tighter or looser?

    Tighter indicates that either the valve seat is worn (or being hammered) or the rear of the valve face is worn. If one condition exists, the other is also likely.

    Looser indicates wear on any (or all) of these: valve stem, valve lifter, pushrod, follower, cam.

    Another possibility is that the head and/or cylinder mounting hardware is either stretching or loose.

  3. #3
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    13,043
    And let's be sure you're setting the valves properly. Each side must be set when the piston is at top dead center on the compression stroke. Once one side is set, the engine flywheel must be rotated 360 degrees to get the opposite side at the same condition...TDC on the compression stroke.

    But 20 miles is pretty bad. The nuts on the rocker arms need to be fairly tight...no torque wrench is needed, but they should be locked down so the clearance doesn't change.
    Kurt -- Forum Administrator ---> 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!

  4. #4
    Registered User
    Join Date
    Nov 2009
    Posts
    14
    Quote Originally Posted by 20774 View Post
    And let's be sure you're setting the valves properly. Each side must be set when the piston is at top dead center on the compression stroke. Once one side is set, the engine flywheel must be rotated 360 degrees to get the opposite side at the same condition...TDC on the compression stroke.

    But 20 miles is pretty bad. The nuts on the rocker arms need to be fairly tight...no torque wrench is needed, but they should be locked down so the clearance doesn't change.

    In what way can I make sure TDC is achieved without relying on "OT" on the flywheel?

  5. #5
    Registered User krpntr's Avatar
    Join Date
    Jan 2010
    Location
    Mt Vernon WA
    Posts
    409
    Did you check the torque settings on your head bolts? Not necessary every time, but after a recent top end re-build on my '92 RT,my valves needed re-adjustment after my break-in ride. Re-torque was also required, but only a slight tweak. My valves became loose after about 60 miles of hard riding in the lower gear range with violent speed changes. Not sure if this helps. How your valves are behaving other than going wrong?

  6. #6
    Registered User
    Join Date
    Nov 2009
    Posts
    14
    Quote Originally Posted by Krpntr View Post
    Did you check the torque settings on your head bolts? Not necessary every time, but after a recent top end re-build on my '92 RT,my valves needed re-adjustment after my break-in ride. Re-torque was also required, but only a slight tweak. My valves became loose after about 60 miles of hard riding in the lower gear range with violent speed changes. Not sure if this helps. How your valves are behaving other than going wrong?
    They seem to be fine. I thought initially the problem was a vacuum leak.

  7. #7
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    13,043
    Quote Originally Posted by pszyjka View Post
    In what way can I make sure TDC is achieved without relying on "OT" on the flywheel?
    Two ways. One is to remove the valve covers, get the rear wheel off the ground, and put the tranny in 4th or 5th gear. Then, standing behind the bike, grab the wheel and rotate it while watching the left side intake valve. When you see it open and then close, you are approaching TDC on the compression stroke. Go to the left side, continue to bump the rear wheel, and watch for the next OT in the window. That's the point you want to set the left side valves. For the right side, do the exact same thing by turning the rear wheel which watching the right intake valve.

    The second way is to remove both spark plugs. The engine will spin easier now. You can use the allen wrench in the rotor bolt on the front of the engine (remove the battery ground before removing the cover) or you can more easily bump the engine with your hand. Put your thumb over the open spark plug hole and wait until you begin to feel pressure on your thumb. You're beginning to compress the air and headed towards OT on the compression stroke. Set the valves on that side. Repeat for the other side.
    Kurt -- Forum Administrator ---> 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!

  8. #8
    Airhead or Nothing
    Join Date
    Feb 2008
    Location
    Shoreline, WA
    Posts
    41
    When you are about to set the side you believe you have reached TDC on, try spinning the pushrods. If one of the two is too tight to spin, you are 180 degrees off (unless your adjustment is really, really bad)

  9. #9
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    13,043
    Quote Originally Posted by 91310 View Post
    When you are about to set the side you believe you have reached TDC on, try spinning the pushrods. If one of the two is too tight to spin, you are 180 degrees off (unless your adjustment is really, really bad)
    "...unless your adjustment is really, really bad..." Which is the reason you shouldn't rely on this approach and just use the proper procedure to ensure you're on the correct side. Then there can be no doubt. IMO.
    Kurt -- Forum Administrator ---> 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!

  10. #10
    MOA #24991 Pauls1150's Avatar
    Join Date
    Apr 2008
    Location
    south of Los Angeles
    Posts
    1,521
    The sure way to make sure you're at the "right" TDC is to watch the valve action as you turn the rear wheel (it's ALWAYS easier to pull the plugs first!). Expanding on Kurt's post:
    At one Top Center, there will be very little (or no, depending on the cam) easily visible time when both valves are closed. This is the "wrong" TDC.
    Get to the place where both valves definitely stay closed (not compressed) for some portion of the wheel rotation - this is the "Flat" of the cam, where the adjustment is done.
    If you want the absolute TDC, gently insert a dowel into the spark plug hole, and find the rotation point where it's pushed out the most.
    Note where the flywheel's scribe marks are (or aren't...) for future reference.
    If you insist on depending solely on the flywheel marks, you may not be in a good spot - some bikes (especially rebuilds) don't have the flywheel mounted in the "right" rotation. If this is the case, a timing light (when checking the points plate) won't give correct results either.
    ALSO note that you MUST turn the engine over one full rotation to do the adjustment on the "other" side - they do NOT all get adjusted at once; find the "other" flat of the cam.

  11. #11
    Registered User
    Join Date
    Jun 2003
    Location
    Northern Front Range, CO
    Posts
    6,429
    I learned to watch one side to see when one valve is closing and the other valve is opening. this should correspond perfectly with an OT reading in the window, and OT on the OPPOSITE side cylinder.
    always remove sparky plugs first- it makes turning the motor Soooooo much easier than with them in.

    going out of adjustment within 20 miles leads me to think you might have a stripped adjuster nut or similar. that is very not normal!
    Ride Safe, Ride Lots

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •