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Author Topic: Catastrophic CB750 engine failure...what might have happened?  (Read 3724 times)

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flat black

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Catastrophic CB750 engine failure...what might have happened?
« on: August 13, 2009, 08:19:52 PM »
Well, it looks like the engine on my old 750 chopper bit the dust today.

Fortunately, I have a spare one lying around.  ;D

This actually happened to my brother, since I had given him the bike a few
weeks ago. Now before you start thinkin he killed it, he's a pretty conservative
rider. He's not a hotrodder and a hooligan like his brother.  8)

Here's the particulars, for those of you so inclined...

He said he was going down the highway at around 60 MPH. Fourth gear, nice and easy.
Lookin at about 5500 RPM, no big deal. Suddenly he felt it start to lose power, and then
heard some kind of loud metal noise. He said he initially thought something had fallen off
and hit the road.

At that point, flames and smoke started shooting out of the front of the engine, the engine
was making a death rattle, and he pulled off the highway into a safe area.

Here's a picture he sent me of the damaged engine once he got it back to his house.



Just looking at the picture, and not being able to see it myself and know for sure, it looks
like maybe it broke a connecting rod or something. What do you think?
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Offline MCRider

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #1 on: August 13, 2009, 08:28:21 PM »
Ya think?

No one will ever know for sure, but last I was told, you can't get pregnant form a toilet seat.
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Online Don R

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #2 on: August 13, 2009, 08:28:41 PM »
He broke a rod. Or a sniper. Or hit a rock. Or sabotugee. Look in the hole the offender is in there. :'(
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Offline BlackMax

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #3 on: August 13, 2009, 08:35:19 PM »
Quote from: flat black on August 13, 2009, 08:19:52 PM
Well, it looks like the engine on my old 750 chopper bit the dust today.

Fortunately, I have a spare one lying around.  ;D

This actually happened to my brother, since I had given him the bike a few
weeks ago. Now before you start thinkin he killed it, he's a pretty conservative
rider. He's not a hotrodder and a hooligan like his brother.  8)

Here's the particulars, for those of you so inclined...

He said he was going down the highway at around 60 MPH. Fourth gear, nice and easy.
Lookin at about 5500 RPM, no big deal. Suddenly he felt it start to lose power, and then
heard some kind of loud metal noise. He said he initially thought something had fallen off
and hit the road.

At that point, flames and smoke started shooting out of the front of the engine, the engine
was making a death rattle, and he pulled off the highway into a safe area.

Here's a picture he sent me of the damaged engine once he got it back to his house.



Just looking at the picture, and not being able to see it myself and know for sure, it looks
like maybe it broke a connecting rod or something. What do you think?


 I'll take oil starved which caused pistons to start seizing.......eventually snapping a connecting rod, which clanked around in the case for $1000 Alex.
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flat black

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #4 on: August 13, 2009, 08:46:18 PM »
I'll get to find out for sure this weekend. Bummer, really. I had just got
that bike looking pretty good. It was running great too. Good sound, plenty
of power.



Looks like I'm doing an engine swap here in a bit!
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Offline GammaFlat

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #5 on: August 13, 2009, 08:53:43 PM »
Little consolation.. but I love the color.  Glad to hear you have a spare.  Honda bottom ends are generally pretty tough... bummer. 
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Offline Sam Green Racing

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #6 on: August 13, 2009, 09:00:39 PM »
More often than not, rod breakage is down to over revving but if you know your brother's not a revver, it must have been caused by something else. ;D ;D ;D ;D
Glad you've got a spare. When you pull the motor look for signs of a seize up in the piston dept or cam.

Sam. ;)
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Offline BLUE71TURBO

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #7 on: August 13, 2009, 09:20:44 PM »
Low oil level ?  Oil pump failure ?  Dropped a valve ?  Over revving ?  Could be alot of things. Sucks that it happened.  :(
Doesn't it seem to always happen when ya loan yer things to other people ?  That's why i have a sticker on my rear fender that states ;  YES IT'S FAST- NO YOU CAN'T RIDE IT !
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Offline zoo mob

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #8 on: August 13, 2009, 09:24:02 PM »
'round here we call that broke d*ck.
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Offline Trevor from Warragul

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #9 on: August 13, 2009, 09:31:44 PM »
Just needs a bit of JB Weld!
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Offline Patrick

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #10 on: August 13, 2009, 09:44:13 PM »
That was no rod. That was the alien breaking loose...
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Offline Hush

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #11 on: August 13, 2009, 11:06:12 PM »
Bummer dude, nice looking chopper...hint, don't lend it to your brother again. :)
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Offline BLUE71TURBO

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #12 on: August 13, 2009, 11:20:46 PM »
I figured it out !!  He was visited by the MAGICAL ASS RAPE FAIRY !!   
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Offline bryanj

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #13 on: August 14, 2009, 02:48:30 AM »
Depends on wether rod broke or end cap came off, rod broke is overstress sometime and i yet to see a piston siezure snap a rod unless its repeated one, end cap come off is who and when it was rebuilt
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Offline Alan F.

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #14 on: August 14, 2009, 06:18:12 AM »
Quote from: flat black on August 13, 2009, 08:46:18 PM

Looks like I'm doing an engine swap here in a bit!

Well at least you've got a little frame stretch going there, that'll speed up the swap.
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Offline razor02097

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #15 on: August 14, 2009, 07:56:14 AM »
I also vote for oil related...


The only rod that gave out on one of my machines was a .21 engine in my RC truck.  22k RPM then silence.  when the engine was opened there was some metal chunks and a crankshaft... not much else.

Cause:  Blue thunder fuel... highly rated in the lab and highly hated by RC enthusiasts.


moral of the story... word of mouth is sometimes better then what labcoats say.
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Offline MCRider

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #16 on: August 14, 2009, 08:03:28 AM »
Pure speculation at this point on my part, but my experience is: the rod usually breaks right below the pin. Then it becomes a club that the crank drags around, with a hole in the front the usual symptom.

Pretty hard to break a rod without some extra HP. Got a 836 kit or something?
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"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 kos

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #17 on: August 14, 2009, 08:39:35 AM »
As we used to say at M3 Racing....the engine gave itself the finger!

Don't need more power (836cc kits, etc) excessive RPM sometime in the engines life... can and will lead to rod failures.





KOS
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Offline hapakev

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Re: Catastrophic CB750 engine failure...what might have happened?
« Reply #18 on: August 14, 2009, 10:38:48 AM »
I think he must have pissed off the hamster, so the hamster hatched a plan to break free.  They are hard to please!
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