Topic: Primary Chain Failure - Has this ever happened to anybody else?

[danarchy77550f]

Hi Guys,

 I recently had my top end rebuilt on my 77 CB550F and after about 45 miles in she died on me.  I pulled the clutch and killed the power and rolled to a stop.  I kicked it while turned off in neutral and it spun freely, catching nothing.  I got about a quarter turn either way when i pulled on the crank beneath the points cover so i was relieved it hadn't seized.  I looked through my manual and began to suspect Primary Chain Failure.  I thought of this because i had no clue that this apparently never happens.  Once i drained the pan and dropped it, sure enough links everywhere and a chain hanging off of her like an umbilical cord. 

  What could have caused this?  the mechanic replaced a shaft seal but could that have led to complete failure?  I'm not sure how much damage is there but there are bits of something besides the chain.

[HondaMan]

Hi Guys,

 I recently had my top end rebuilt on my 77 CB550F and after about 45 miles in she died on me.  I pulled the clutch and killed the power and rolled to a stop.  I kicked it while turned off in neutral and it spun freely, catching nothing.  I got about a quarter turn either way when i pulled on the crank beneath the points cover so i was relieved it hadn't seized.  I looked through my manual and began to suspect Primary Chain Failure.  I thought of this because i had no clue that this apparently never happens.  Once i drained the pan and dropped it, sure enough links everywhere and a chain hanging off of her like an umbilical cord. 

  What could have caused this?  the mechanic replaced a shaft seal but could that have led to complete failure?  I'm not sure how much damage is there but there are bits of something besides the chain.

Can you post a picture of the chain bits? There are 3 chains inside: 2 are primary chains, and have large links. I've never seen one break, but there's always a first, I guess. The cam chain is another matter: it has small links about 1/2" long, and especially those where someone replaced the OEM endless type with a riveted masterlink type, they can part. NEVER use a riveted cam chain in the SOHC4 engines, because the chains are pretty stressed and run unsupported for a little too much of their travel. This tends to make them hit their rollers hard, which often loosens the rivet-type link pins.

[KRONUS0100]

had an original 76 750F motor send the primary chains thru bottom of case, after repeatedly being told it was cam chain noise.

[Tim2005]

This thread is referring to a 550f's single Hyvo primary chain, isn't it, or am I missing something? Seems rather trippy so far.

Anyway, it'd be interesting to hear which seal was recently replaced & hence whether that involved a crankcase split, those Hyvo's can stick some serious neglect and abuse in normal usage.

[danarchy77550f]

it was the big boy chain who shredded apart.  found little chunks of the inside of the case in the pan as well.  hoping it wont be a total loss and the easiest fix i can think about would be replacing the case off of another engine