Author Topic: Lower end making grinding noise when under heavy load- what's up? cb550k '76  (Read 1019 times)

0 Members and 1 Guest are viewing this topic.

Offline kippstakes

  • Hot Shot
  • ***
  • Posts: 266
If I put too much pressure on the engine (ie starting into a hill, juicing it a bit and opening the clutch quickly, etc.-- it doesn't take much, anything but the most gentle acceleration will produce the effect) the engine will bog down and try to die like something is binding and preventing free movement inside the lower end. This is accompanied by a hair-raising grinding/wrenching sound that seems to emanate from the crankcase or transmission- it can be felt right up through the handlebars; it is tough to miss.
This phenomenon has persisted over two clutches, so I think we can rule that out. Despite clean carbs and 135 compression on all four cyls the bike still runs like it's towing a dead elephant, which makes me wonder if something is binding somewhere.

Any ideas?
Thank you
Strength is just an accident arising from the weakness of others.
-J. Conrad

Offline Redline it

  • Hot Shot
  • ***
  • Posts: 561
  • thread killer
I don't know too much, but if you keep riding it, the problem will eventually fall out of the case, then you'll know what it was. Already 2 clutches? It's way beyond any worries. Probably something minor.

Offline scottly

  • Global Moderator
  • Really Old Timer ...
  • *****
  • Posts: 16,304
  • Humboldt, AZ
Crusty, rusty, worn-out, too-tight chain and sprockets? Thrashed rear wheel bearings?
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline kippstakes

  • Hot Shot
  • ***
  • Posts: 266
Wheel bearings are solid and both sprockets are in good shape, chain is up to tension. The noise is definitely coming from the crank case somewhere.
I just did a top end rebuild about nine months ago, and would be crushed to have to tear the whole thing down again to rebuild the bottom- it would be great to avoid that.
Strength is just an accident arising from the weakness of others.
-J. Conrad

Offline Redline it

  • Hot Shot
  • ***
  • Posts: 561
  • thread killer
was it 2 clutches in 9 months also? 9 months is good, I usually gotta take everything back apart after an hour.

Offline kippstakes

  • Hot Shot
  • ***
  • Posts: 266
Haha no I replaced the clutch that came on the bike- because of this very noise.. It's been making this noise for years, but has gotten much worse over the last month or so.
Strength is just an accident arising from the weakness of others.
-J. Conrad

Offline Duanob

  • Bold Timer
  • Old Timer
  • ******
  • Posts: 4,009
  • Gotcha!
Crusty, rusty, worn-out, too-tight chain and sprockets? Thrashed rear wheel bearings?

Chain rubbing against the cases is my first thought. Take the cover off and see.
"Just because you flush a boatload of money down the toilet, doesn't make the toilet worth more",  My Stepfather the Unknown Poet

1974 CB360T
1976 CB550K2 Resurrected
1976 CB550F2 Barn Find
1979 CX500 VG "HONDA-GUZZI"
2007 Moto Guzzi Breva 750ie
2015 BMW F700GS
Another 1976 CB550K Cafe?

  __o
_- \_<,
(*) /' (*)

Offline jonda500

  • I may be crazy but I'm not stupid!
  • Master
  • *****
  • Posts: 1,804
  • With our thoughts we make the world (Monkey Magic)
Sounds similar to the problem I have with my 500 - the only way to avoid the gnarly grating noise and vibration is to completely avoid putting any load on the engine unless the revs are at at least 5000rpm.
Personally, I am convinced that my primary chain is slipping but I wont be able to verify that until I pull it apart. John
Remember that an ignoramus is only someone who doesn't know something you just learned yesterday!

A starter clutch thread:
http://forums.sohc4.net/index.php/topic,122084.0.html
1972 CB500K1 original 4 owner bike
1972 CB500K1 returned to complete/original condition
1975 CB550F built from parts - project thread:
http://forums.sohc4.net/index.php/topic,149161.msg1711626.html#msg1711626
197? CB500/550 constructing from left over parts
1998 KTM 380 (two stroke) recent impulse buy, mmmm...

Offline kippstakes

  • Hot Shot
  • ***
  • Posts: 266
I had considered that, except that my bike seems to bind up and lose power when the noise occurs, like something is trying to lock up against something else in my crankcase. My guess would be that if your primary chain slipped, the bike would rev UP, due to the temp loss of load. Does your bike rev up when the noise happens?
Strength is just an accident arising from the weakness of others.
-J. Conrad

Offline jonda500

  • I may be crazy but I'm not stupid!
  • Master
  • *****
  • Posts: 1,804
  • With our thoughts we make the world (Monkey Magic)
The engine doesn't rev up much when it happens - stays the same or slows down if anything, maybe due to the uneven transmission of power from the engine to the gearbox and the chain riding up on the teeth?
Once the revs are over 6000rpm, I can give it full throttle without it happening.
At idle speed my primary chain rattle sounds really awful when cold and even worse when hot.
John
Remember that an ignoramus is only someone who doesn't know something you just learned yesterday!

A starter clutch thread:
http://forums.sohc4.net/index.php/topic,122084.0.html
1972 CB500K1 original 4 owner bike
1972 CB500K1 returned to complete/original condition
1975 CB550F built from parts - project thread:
http://forums.sohc4.net/index.php/topic,149161.msg1711626.html#msg1711626
197? CB500/550 constructing from left over parts
1998 KTM 380 (two stroke) recent impulse buy, mmmm...

Offline Redline it

  • Hot Shot
  • ***
  • Posts: 561
  • thread killer
It's surprising how much speed can be produced by gear ratios, and how much power can be robbed from a worn bushing.