« previous next »
Pages: [1]   Go Down

Author Topic: Chain tight then loose then tight then loose...  (Read 1968 times)

0 Members and 1 Guest are viewing this topic.

Offline Nikkisixx

  • Expert
  • ****
  • Posts: 839
Chain tight then loose then tight then loose...
« on: May 28, 2011, 07:25:16 PM »
So a buddy came over with his bike and had a symptom I had never seen with a drive chain: it runs tight AND loose.  The bike is  73 CB750 with a 3 inch extended swing arm.  He has ridden this bike inthis configuration for about 2 years with no other weirdness.  With the back wheel off the ground when you roll the wheel the chain sags out about 2 inches of slop, then at about 180 degrees from there it gets tight and the chain runs high on the sprocket. Roll it another 180 and everything sags out again.  It does not happen in exactly the same spot everytime.  Just roughly every 180 degrees or so.  It is as if the back sprocket is oval or egg shaped, but it is still round. 


Pulled the chain and it had given up about 75% of its life but it had no stiff spots.  The same with the sprockets - worn on the valleys but the peaks are still flat.  Both need to be replaced soon but can be ridden for a few hundred more miles. Everything is true, the sprockets are strait.  The swing arm bushes seem tight, the rear wheel bearings also seem ok.  When the new parts get here he wants to be sure he has cured the weirdness so he doesn't kill another chain and sproket setup.

Anyone seen this?  Thoughts?
Logged
It is a proven fact that modifying a SOHC Honda in any way will bring on the apocalypse.

Offline aplaceinspace

  • Full Member
  • *
  • Posts: 11
Re: Chain tight then loose then tight then loose...
« Reply #1 on: May 28, 2011, 07:33:59 PM »
Is the sprocket proplerly centered on the wheel?
Logged

Offline madmtnmotors

  • When did I get to be a
  • Really Old Timer ...
  • *******
  • Posts: 6,154
  • Sunny Central Florida
Re: Chain tight then loose then tight then loose...
« Reply #2 on: May 28, 2011, 07:51:58 PM »
Or maybe uneven stretch on the chain. If the chain is overtensioned (to tight) and then the suspension is deep cycled (or even bottomed out) the chain can be unevenly stretched since the swingarm pivot does not align with with the front sprocket (which is nearly impossible to do practically). As the suspension cycles the distance between the front and rear sprockets changes (if only a little). That is why there must be some freeplay in the chain when properly tensioned. I believe the 3/4" freeplay described in the manual I have for my CB750K8 is too conservative. I have had an unevenly stretched chain in the past and have never seen it again since I started using 1" as my target freeplay.
Logged
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                          
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline Retro Rocket

  • Eggs are hard due too a
  • Really Old Timer ...
  • *******
  • Posts: 19,214
  • ROCK & ROLL
Re: Chain tight then loose then tight then loose...
« Reply #3 on: May 28, 2011, 08:19:26 PM »
Quote
Or maybe uneven stretch on the chain.

Exactly, seen it plenty of times before.......
Logged
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline MCRider

  • Such is the life of a
  • Really Old Timer ...
  • *******
  • Posts: 14,370
  • Today's Lesson: One good turn deserves another.
Re: Chain tight then loose then tight then loose...
« Reply #4 on: May 28, 2011, 08:29:56 PM »
Quote from: Retro Rocket on May 28, 2011, 08:19:26 PM
Quote
Or maybe uneven stretch on the chain.

Exactly, seen it plenty of times before.......
Yup. Only fix is a new chain. I went thru the is the sprocket out of round thingy when i first noticed this phenom back in my earliest days. Never happen. Well, maybe, but...never.

Its the chain.

Get a new one and learn how to adjust properly and oil evenly.
Logged
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline Nikkisixx

  • Expert
  • ****
  • Posts: 839
Re: Chain tight then loose then tight then loose...
« Reply #5 on: May 28, 2011, 09:30:27 PM »
Quote from: MCRider on May 28, 2011, 08:29:56 PM
Quote from: Retro Rocket on May 28, 2011, 08:19:26 PM
Quote
Or maybe uneven stretch on the chain.

Exactly, seen it plenty of times before.......
Yup. Only fix is a new chain. I went thru the is the sprocket out of round thingy when i first noticed this phenom back in my earliest days. Never happen. Well, maybe, but...never.

Its the chain.

Get a new one and learn how to adjust properly and oil evenly.

Thanks fellas!  Well, this is my something new for the day.  25 years of chain adjustment and never seen it.  His extended swing arm may have added to the fun and games, based on madmtn had to say. 
Logged
It is a proven fact that modifying a SOHC Honda in any way will bring on the apocalypse.

Offline 754

  • Really Old Timer ...
  • *******
  • Posts: 29,046
Re: Chain tight then loose then tight then loose...
« Reply #6 on: May 29, 2011, 08:34:32 AM »
 very very common if you do lots of burnouts or hard shifting.
 Simple test for worn chain, see how far it pulls away from the back sprocket, towards rear of bike.. new will barely move.
 A caution on worn chains like that, not adjusting at its tightest spot is very hard on the bearings..
Logged
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Markcb750

  • Guest
Re: Chain tight then loose then tight then loose...
« Reply #7 on: June 09, 2011, 07:02:12 PM »
It would be best to replace the chain & sprockets....but you can ct by with just a chanin for perhaps a season, maybe.


Logged

Offline DJ_AX

  • Expert
  • ****
  • Posts: 1,279
  • ?!
Re: Chain tight then loose then tight then loose...
« Reply #8 on: June 09, 2011, 08:45:27 PM »
I had a similar issue a while back. I supposed that both sprockets were a little out of round plus a lame chain. Also had bad bushings in the swing arm. You could change the chain tension just by moving the rear wheel side to side. This all made it difficult to figure out what the change in tension was relative to.  :-P. I ended up replacing  all-a-dat. Making sure of course that everything was lined up and centered properly. Not a prob. anymore! :-D
Logged
~ Vincent . . . '75 CB750 K5 . . . '97 BMW r1100rt . . . had; '75 CB550 K1 (sold) . . .  '73 CB350G (gifted) HELL YEAH!
Disclaimer: I could be wrong. :)

Offline Tugboat

  • Puppet
  • Master
  • *****
  • Posts: 1,778
  • '75 CB750K + '67 CL90 + '71 CT90
    • PseudoMoto
Re: Chain tight then loose then tight then loose...
« Reply #9 on: June 10, 2011, 07:42:48 AM »
Just had to replace the chain on my KZ400 because of this exact same reason. Had just replaced my sprockets a year ago so I knew it wasn't that. Make sure it's loose enough (but not TOO loose)!! :)
Logged
If it's worth doing, it's worth doing twice.
Pages: [1]   Go Up
« previous next »