Snap goes the cam shaft

[vigman]

Ok guys.. here's the deal.. my girlfriend's roomie has a 1979 C3.

80K on motor.. coming back from the beach.. gettin on the freeway..
A belt tosses off.. puts a dent in the hood.. total power loss.. 2 hr's later

Up on a flatbed it went .. and PLOP in my driveway.

To make a LONG story short ( er )
She noticed a belch of smoke that came out the back ( noticed in the rearview mirror )

So there was NO OIL in the block when it arrived. and what was on the stick was NOT pretty
( Can you say burnt coffee ?)
We tried to start...The distrib would not turn.. the rotor had a HUGH crack in it.
The engine DID spin over.. but no spark ( for obvious reasons ).
Fuel BELCHED out of the top of the carb as we cranked.

Now here's where it get's weird ( er )

I removed the valve covers
spun the engine
ONLY the first rocker on each side went up and down.
the rest of the valve train.. static.. not even a quiver.

The gear on the back of the distrib is fine & meshes and has ALL IT's TEETH & the pin is in tact..

There ARE at least 4 bent pushrods

and one isn't pretty at all

YE GADS~

I told her this.. and showed her this..and did a VERY BRIEF ENGINE 101.. but she didn't want to hear ANY OF IT!

So My thinking is... the cam SNAPPED behind the 2nd lobe ( of 4 ) between the first & second bearing supports...


So here are my questions

I have lost timing cam before on some NON VETTE Chevy small blocks in the past ( Thanks GM for that Nylon wonder )

But a tooth or 2 only.. nothing like this where I suspect valves & pistons were gettin FUNKY....Doing the bump & bend.

So anyone had a similar DIRECT experience.... not a " Well I heard from my 2nd cousin Luke".

I have NEVER seen a cam SNAP in a street car.. but if the CAM timing went totally out.. I can picture that.

So My " suggestion " was just replace that motor.. based on the potential amount of rework.. it would be cheaper to get a crate motor & toss it in.

Her " racer " friend thinks this CANNOT HAPPEN.. and is feeding her a line of BS ( IMHO )

So I open this up to the forum....

Thanks
Vig~

 

[SIXFOOTER]

Wow, never seen a cam break. Only thing I can think of that would do that is if a cam bearing seized.
If the car is a numbers car, I would say start by trying to rebuild it. Otherwise a crate motor is called for.

 

[Artsvette73]

I have only seen 1 camshaft broken in half. But it was due to the car hit dead center around a tree.

 

[Yoda]

Vigman it's nice seeing ya back in print yahooo

As you already know.... I KNOW NOTHING about engines, I just want to give ya shout (You may have noticed... I'm not in California anymore .... then again you may not of noticed

Bud

 

[wishuwerehere82]

It's not much consolation I know, but camshafts are very brittle. They are great in compression because they are heat treated, but not so good in torsion or deflection. I'm sure the comination of no oil and crud all over exceeded the bearings capaity to resist rotational friction. Snap goes the camshaft.
You have your work cut out for you if you decide to rebuild it.
In additin to the pushrods being bent, the valves and the pistons are going to be damaged too, unavoidable.
I would get the crank magnafluxed to make sure it didn't crack too.

 

[vigman]

More info

It WAS an L 82 ( BTW HEY BUD! )

I'm just not sure if I want to .. participate... in the rebuild.. autopsy...

I was told.. by her EXPERT that it was IMPOSSIBLE for that to happen....

So I thought it would make for some interesting.. dialouge here..

Since I've been twisting on things for a LONG TIME and NEVER seen anything
like this in my life.

I'm tempted to pop the intake manifold.. just to have the last laugh.. and that at best would take about 1 hr ( at the present disassembly point )

So keep the input coming.

Thanks
Vig~

 

[vigman]

The further theory

The chain jumped

Ms Valve met Mr Piston
crank continued to turn
cam didn't...Since Ms Valve & Mr Piston reached an impass.. and I'm SURE
that not just 1 valve got in the mix due to 4 bent pushrods.

Chain did not break( but probably took ALL the nylon off )

Torque continued via crank & chain until cam let go since it looks like #5 exhaust is the MOST TWEAKED and locked the cam....

It's the ONLY theory that makes sence ( in my head ).

 

[Hib Halverson]

The symptoms posted are pretty convincing.

Anyone who says it's "impossible" for a cam to break doesn't have much experience. Yeah, it's unusual to break a camshaft but, no, it's not impossible.

Considering all the bent valve train pieces you found, you can bet there's more bent/broken stuff inside that motor.

For laughs, pull the intake. Let us know if the cam broke where you think it did.

Bottom line: overhaul or replace the motor.

 

[wishuwerehere82]

C'mon Vigman, you have to take a look inside!
Isn't the curiousity just killing you?

 

[vigman]

Well yes & no

It's not my ride...

I TRIED to do a favor.

It's a few hours of my life that I'll never get back ( that I could be wrenchin on my other rides )

But that Nayh Nayh factor is tempting.

The problem is.. if I get in THAT FAR... she will really have a KIT CAR

And mechanics don't like to piece back the puzzle
Which means I'll get STUCK doing the motor.

She has NO BUCKS which means.. pulling stuff @ Pick your part.. trying to
piece it back together...

Like I don;t have ENOUGH to do.....

It's complicated

 

[vigman]

And Hib

Your RIGHT ON THE MARK!
There is NO OTHER REASON that the first two rockers ( on on each side )
would move... normally and the rest of the valve train is static.. including the Distrib gear on the back of the cam.

Modern Physics allow no other conclusion.

Well except the automotive black hole theorys...
Where the heck did that socket ( or other tool ) fall down to theory.

Nissan 300ZX I dropped the clip for the fuel injector.. down there.. and it's gone theory.

and the underneath the car.. mess with anything and the dirt or the tool
will gravitate to the center of either eye, which is closer to the object messed with.

Vig~

 

[6880 Mike]

...Bottom line: overhaul or replace...

My advice is to rebuild the original L-82.

 

[gmjunkie]

I snapped a Cam in a Early model L82, and it left nothing usable except 1 head!!The only thing left holding the engine together was the Oil Pan and the fact it was bolted to the motor mounts in the chassis!! I never seen a SB Chevy split right down the middle,It even broke the Intake, Water Pump and Bell Housing!!! But Damn,it was running good before it let Loose!!

 

[bradfordsvettes]

I have seen it a couple of times once in 2 pieces and 1 time in 3 that one fell into the crank not a pretty picture steve

 

[pbcanney]

sounds like the timing chain jumped 1/2 dozen teeth. Thats what happened to mine. Did enough damage to initiate the rebuild to 383

 

[vigman]

OUCH.. this is what I'm TALKING ABOUT

Thanks for that.. how many valves were TOAST?

 

[67HEAVEN]

Vigman,

I dropped by my local garage this afternoon (like I do every few days for a chin-wag). I dropped the question on the mechanic.

Yes, he's seen a few split camshafts in his day, and it ain't never purdy.

 

[grumpyvette]

Ive seen 4 camshafts that broke in 35 PLUS years of racing and building engines
in most cases theres a good deal of internal engine damage , think about it, if the cams rotation is NOT synchronzed with the cranks rotation theres almost certainly a couple valves held open when the pistons reach TDC, when that happends the piston will bend the valves and probably spin the cam, resulting in additional cylinders bendiing valves, bent valves can and frequently do result in damaged rods, bent rods, broken pistons and cracked heads, bent rods tend to beat the crap out of the block, ETC., usually the valve covers and rocker arms, possiably the damper and water pump are salvagable

 

[vigman]

Here Here

I agree.. this is PROVING my theory.....

Well looks like I'll have the owner read this thread....

My take.. reguardless of the the INTERNAL DAMAGE.. just the FACT that there was NO OIL on the dipstick.. requires a rebuild.. due to bearing damage.. and all this repair ( read machine shop time ) just to get the block back in ONE PIECE would outweigh her budget. A crate motor would be the best choice on limited funds....this ASSUMES that the BLOCK is salvagable. I'll further assume that the heads are toast due to valves beating back up.. out of position.. the car coasted for a time ( automatic )
so things were rotating for a bit LONGER than healthy.


It's NOT just throwing in a timing chain....


My best guess.. is the cam just sheared.. and did not break in two pieces.

That being said.. thinking about the torque... I agree that a FULL inspection of the block is in order...

It was enough to toss belts and poke a HOLE in her hood.. which IMPLYS
the engine STOPPED turning for a brief time. The A/C belt was FLIPPED OVER.. which is quite the trick on a V belt.

It's really sad.. another Vette is teetering on the edge of non use.. and maybe being a "Car's in Barns" victim.

Hmmmmmmm

Thanks all so much for chiming in......

Vig~

 

[GerryLP]

....For laughs, pull the intake. Let us know if the cam broke where you think it did...

If I was a waging man I would bet you one beer or a beverage of your preference (which could be due whenever you and I meet next time in person) that the cam went flat.... just to keep things interesting

Vigman, Let us know! otfl