1979 SC Chewed a Valve - Total Rebuild
 

My SC chewed up one of its valves and jammed a cam. I was roaring out of a light (as I usually do) and heard a bang bang as I neared redline in first. The noise quickly stopped and it was time for a tow-truck. Car history at the end of this post.

Now it is all out and apart, and ready to teardown in earnest. I'll post here as I make progress. The two goals are:

1) Determine why it broke.
2) Prepare it for many years of excitement.

Current state is down to the long block and cam covers off. I've fished a good number of metal bits out, and more fall out each time I rotate the engine. I'm working on acquiring the Stomski tool to remove the cam shafts, so in the meantime I'll probably clean up removed parts.

Any ideas on what to watch for, measure, and photograph along the way are appreciated. I'm bagging and labeling each thing as it comes out, and have 6 bins labeled for each cylinder's parts.

There was a lot of oil in the heat exchanger for bank 4-6. Also some oil flooding when looking down those valves.

Photos of current state:
http://forums.pelicanparts.com/uploa...1751732506.jpg
http://forums.pelicanparts.com/uploa...1751732506.jpg
http://forums.pelicanparts.com/uploa...1751732506.jpg

Videos from yesterday (before cam covers came off)
Video from the top. Three is the boomed cylinder.

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Video from the bottom.

<iframe width="560" height="315" src="https://www.youtube.com/embed/HEfylfChkLI" frameborder="0" allowfullscreen></iframe>

History!
This car has 280K miles on it. Originally a California car, its first owner was a female doctor who put 200K on it in 20 years, and then sold it to an Air Force mechanic, this forum's very own Leland Pate (https://forums.pelicanparts.com/members/1761.html). He is a big SC fan and founder of the 911 SC World Domination Plot and Dr. Pate's 101 Tips.
He rebuilt the engine and made performance improvements (head studs, larger bore, higher compression, etc). You can see his many rebuild posts on this forum, as well as his eventual sale post. Third owner was an occasional Pelican, and also sold it via this forum to me.
I'm the 4th owner, and it became mine in 2012. Since then I have made lots of small and moderate fixes, including transmission rebuild, CIS rebuild, fuse box, and fuel lines. But this is the first time in the block.

All things considered, it should have lasted a good many more miles before a rebuild. I hadn't adjusted valves in a few years, I'm not sure if that could have been a factor.

I feel fortunate to have 25 years of posts (the forums records don't go past the year 2000), and hope to make many more years of posts.

Any recommendations on what to use or not use to clean nasty parts? I have some Simple Green, but I'm concerned about de-oiling things that should stay oily, and possibly opening things to rust.

I soak in safety Kleen, scrub brush.
Dry parts, spray with Sam’s club degreaser, undiluted.
Power wash, respray the tough corners
Bruce

Ugh sorry to hear. The intake valve guide boss and the rocker are broken, and the retainer is missing. Hard to tell which happened first, but the dropped valve hitting the piston will make some noise for sure. Let's see what the piston looks like. Hopefully the rod and crank will just need to be checked.

As for preserving steel/ferrous parts after cleaning, spray with some WD40, or better yet dunk in a 50/50 solution oil and mineral spirits. Oil works too of course, just a little messier.

Sounds good, I'll make sure to finish them off with some oil.

Probably had a tensioner failure. The cams are in different positions.

Interesting, I didn't think of comparing cam positions across the two banks. Is it indicated by orientation of one of the nuts at the end of the cam? Or based on the valve positions in the video?

There is a bolt (I think from the valve adjustment) jammed in the 1-3 cam by where it came off at cylinder 3. Could it catching there slammed it out of synch?

If there's anything I can look for now or during teardown to get more info, I'm eager to learn more.

The failure happened while I was accelerating out of a light, and it banged for a few seconds before going silent. It sounded a bit like something had gotten loose on the exhaust, and I was in a tunnel with construction and no place to pull over, so I had been hoping to keep it limping until I was clear.

If a chain jump was the first failure, would it make the banging/rattling noise for a few seconds until something else went wrong?
Or could the chain jump be the second failure, caused maybe by the broken bolt jamming the camshaft?

Took of the sump plate and took a few more pictures of the boshed valve. I think I can't do much more teardown until the Stomski tool arrives later this week. Is there something else I could do that I haven't thought of?

So probably the next few mornings are cleaning already removed parts? I guess I'll get a pair of buckets going and dig out my giant yellow gloves. Should I expect to be reusing hardware? Or just assume I'm going to replace all the bolts and washers?

Also, this funky yellowish thing came out during one of the turns I rotated the engine on the stand. It seems almost like ceramic.
http://forums.pelicanparts.com/uploa...1751805644.jpg http://forums.pelicanparts.com/uploa...1751805644.jpg

More pics of the bombed cylinder valve/cam. Note the little nut jammed in there under the cam.
http://forums.pelicanparts.com/uploa...1751805666.jpg
http://forums.pelicanparts.com/uploa...1751805666.jpg

Nothing unusual to my untrained eye under the sump plate.
http://forums.pelicanparts.com/uploa...1751805666.jpg

Best pic so far of the inside destruction.
http://forums.pelicanparts.com/uploa...1751805666.jpg

Watched another video. Maybe I can remove the tensioners now before cam tool arrives? Don't want to lose track of some evidence such as John Walker's note about cam misalignment.

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EDIT:
This guy removes the valves before taking off the cam nuts. Maybe I can do that next and learn something.

<iframe width="560" height="315" src="https://www.youtube.com/embed/SZeKHAQiE10?start=465" frameborder="0" allowfullscreen></iframe>

Wow, looks like a grenade went off in there! Bummer!

I think I see a swivel foot, piston ring pieces, and a piston circlip came out the bottom?

Good luck!

I would guess (with data and pictures supplied) that the last builder used the intake valves beyond their service life. Even with hard impact, you generally don't see the valve head separate with a clean break.

They also had that "bad batch" of valve springs where the outer spring would break. I'm rebuilding a 78 right now that had 3 broken outers. If they were original and never replaced, those little ticking time bombs are still in there.

Especially since he was near "redline in first."

Lots more to learn inside, I'm sure. I am thinking about taking another set of good photographs, then working on removing tensioners and such while waiting for the tools.

I also need to peruse Wayne's book to identify what other tools I should track down.

An impact wrench and 46mm socket gets the cam nuts off. Don't need the Stomski tool for that.

Thanks John, I picked up the socket cheap, should be here tomorrow. I'll have the Stomski for reassembly.

I went ahead and removed the rockers while waiting for the tools to handle the cam shafts themselves. I was especially interested in cylinder 3's intake valve, as that is the one that blew up.

I did note some minor wear on a few other rocker feet, specifically 4 and 6. I'm not sure if that is relevant and merits posting the photos.
This post I'm going to focus on the damage around cylinder 3.

First two photos, you can see the broken rocker arm and the jammed adjustment bolt stuck in the housing between #3 intake and exhaust. Not sure if that constitutes destructive damage to the housing. There's the bolt that jammed, and it has bent the oil supply line (or whatever that is).
http://forums.pelicanparts.com/uploa...1751843140.jpghttp://forums.pelicanparts.com/uploa...1751843140.jpg

Down here you can see rod that the rocker rides on had actually worked itself a good bit out of center. Maybe that was part of the issue? Or maybe it was an effect after the collision occurred? The shock was strong enough to flatten the head of number 3 spark plug and knock the wire off its connector to 3 as well.
http://forums.pelicanparts.com/uploa...1751843226.jpghttp://forums.pelicanparts.com/uploa...1751843226.jpg

Here you can see the removed parts of the rocker and the valve. The head itself is somewhere deeper inside. note the wear on the base of the valve stem, and some damage on that ring's edge as well.
http://forums.pelicanparts.com/uploa...1751843337.jpghttp://forums.pelicanparts.com/uploa...1751843337.jpg
http://forums.pelicanparts.com/uploa...1751843337.jpg

Finally, here is the destruction inside at the base itself. I presume that damage is on the cylinder, and not on the cam header assembly? I fear a lot of damage has been done.
http://forums.pelicanparts.com/uploa...1751843480.jpghttp://forums.pelicanparts.com/uploa...1751843480.jpg

And here's the walk-around video for this side.

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http://forums.pelicanparts.com/uploa...1751861948.jpg

What's the deal with the texture on the yellow thing ?

Upon closer inspection, it appears to be gasket/sealant compound of some kind. I think the marks are fingerprints from it being molded. Maybe it was supposed to be on a suspected oil leak scratched joint area? Not ceramic.

http://forums.pelicanparts.com/uploa...1751891750.jpg
http://forums.pelicanparts.com/uploa...1751891750.jpg

Morning of surprises here! I decided to try to take off the bank 4-6 tensioner, seeing as 1-3 had been tight when I tried it yesterday. Bank 4-6 came off easily, so I bagged it and went back to 1-3 with renewed optimism.

Back on bank 1-3's tensioner, I was reaching in trying to get some wiggle in the tensioner seating. And I brushed against the giant 46 mm nut... and it was LOOSE! The nut was loose and easily spun off with my fingers. The cam itself is locked into position, held tight by the bolt jammed under it at cylinder 3. I pulled off the giant nut, pushed out the pin in the sprocket (forgot to rotate the engine, it fell somewhere deeper within). The washer also warped a good bit after removal.

http://forums.pelicanparts.com/uploa...1751892285.jpg
http://forums.pelicanparts.com/uploa...1751892285.jpg

I then removed the locking washer-thing behind the sprocket, and it was quite scraped up.

http://forums.pelicanparts.com/uploa...1751892305.jpg

The chain was still very taught, so I went back to work on the tensioner. I found a good angle to pry and protect my fulcrum from damage, and eventually got the tensioner off. Then I noticed a small cap-and-spring from the tensioner were loose, and a small ball-bearing type ball fell out when I picked it up. There was also some scoring on the tensioner pivot shaft.

http://forums.pelicanparts.com/uploa...1751892328.jpg
http://forums.pelicanparts.com/uploa...1751892328.jpg

Is this what a failed chain tensioner looks like? Did we find our culprit? John Walker suspected tensioner failure earlier in the thread.

Also, how can I get this camshaft out seeing as it has a bolt jammed under it, digging into the housing down by cylinder 1?

The big washer is a “spring washer” and is supposed to be like that.

I think you can remove the cam housing without removing the camshaft. Remove the three bolts that go through the camshaft thrust plate, then remove the nuts that secure the camshaft housing to the heads. That should give you enough room to pop it up and slide it out of the chain housing. You may also need to remove the chain housing.

That looks more like the camshaft stopped dead and everything between it and the chain was stripped to hell as the chain kept spinning. I don't think those tensioners failed, I think they did their duty to the bitter end.

The locking washer thing that's chewed to hell is what actually holds the sprocket to the cam, and the threads on the big cam nut also look pretty shiny...

Edit: As for getting it out. If it were me (and I can only judge by the pictures) I think I'd try rocking the camshaft back and forth a bit while alternating with light taps at that jammed nut with a hammer and punch. It got jammed in there in one direction--maybe in the other direction it'll loosen up.

Maybe the rocker arm broke first, and jammed the camshaft thus stopping it dead? The tip of spark plug 3 was hammered down, so something slammed it hard.

Tonight I can take some pictures of the sprocket in more detail.

Update: Maybe the shaft on which the intake rocker #3 rides slipped and led to the jam/break? Or maybe resulted from it?
http://forums.pelicanparts.com/uploa...1751843226.jpg

I can only speculate, but I had highly accelerated camshaft lobe wear from misaligned rocker shafts in the past. When the shaft is out of alignment the rocker starts to ride on the ends which are wider due to the through-bolt's compression, and the rocker stiffens up on the shaft. Maybe at a certain point it locked in place and the valve couldn't, or took too long to, close, leading to interference?

The loose nut on the end of the camshaft also seems pretty wild to me. Maybe it got loose first, leading to the damage to the hub teeth, eventual timing slip, and catastrophic results? But wouldn't a chain slip result in damage to all the valves on that side?

Or could the nut be knocked/shaken loose by the cam getting jammed at high RPM?

I'd look at the threads on that nut, they look very shiny from the photo. If the sprocket were spinning while the cam was frozen it might have stripped the nut. Same with the keyed sprocket on the cam being chewed up.

This is spitballing, I bet someone can chime in that's seen this same thing before.

Stomski tool in route for Wednesday delivery. Sent you a PM with tracking.

Good luck on the rebuild; there’s some serious damage there.

Best,
Rutager

Thanks, I'm really enjoying the challenge and hopeful to solve the mystery and get it back on the road.

That is probably epoxy that was applied during a rebuild to plug a potential leak/thin spot inside the case. Doesn’t look like it was applied correctly.

Looks like your tensioner collapsed and timing skipped causing the valve to contact the piston.

Wouldn't a collapsed tensioner be more... well... collapsed? He mentioned having to take a prybar to it.

The big nut backed off because the cam stopped. (Remember, the cams spin CCW on these engines) Once the cam stopped, the timing chain kept moving and the big nut backed off.

After some thought, I have what I think is a reasonable theory.
1) Camshaft giant nut starts to loosen. Maybe not tightened to spec, or some other reason.
2) Nut loosens enough that the sprocket hub behind it gains some play and begins to wobble, resulting in some of the damage we see to the hub.
3) Running near redline, the sprocket's wobble became enough that the cam is just out of sync enough for #3 intake valve to collide with the piston, slamming it back and breaking the end of the rocker and freeing the valve adjustment bolt.
4) That's when I start hearing the banging, as the timing for the entire bank 1-3 is slightly off and the chunks of rocker are bouncing around. Cylinders 4-6 are still fine and keep things moving for a few seconds.
5) The loose valve adjust bolt lands in between the cam and case and slams bank 1 camshaft to a stop. The force is enough to jump the sprocket a few more nubs on the camshaft, resulting in further damage to the hub.

So the precipitating failure would be the loosening of the camshaft nut, leading to a loss of timing, collision of intake valve 3, and catastrophic effects of loose bits.

I'm no expert, but this seems more likely than the rocker breaking on its own, and I don't see how a tensioner failure could have led to the loose nut.

I'll pull off the cam housing tonight and we should be able to see more. Maybe I can then get the camshaft out of its housing, once the housing is off the engine.

Missed your response while I was typing mine.

I didn't realize the spin direction was that way, so I guess my theory is off.
The cam jamming was caused by the bolt, which was freed by the wrecked rocker, which was impacted by the valve collision...

So then the first damage was a valve collision caused by the tensioner allowing a slip of the chain? And the hub damage was from the slam to a stop?

I’m not sure. The tensioner ball and cage were damaged, but that could’ve happened while trying to remove it.

It is hard to wrap my head around a cam nut loosening up on its own. Have you ever heard of that happening?

I don’t think the cam nut just loosened up on its own. I think the tensioner collapsed , the engine lost time, then the valve hit the piston, the valve and spring broke, the rocker arm broke, the cam was then obstructed by the broken pieces and then I don’t know what the hell loosened the cam nut or stripped the keyed gear because the engine shouldn't the engine have stopped turning at that point? Maybe the car was still in gear.

Really not sure. Hard to say without touching the parts myself, but my gut is eyeing that misaligned and broken rocker very suspiciously. If that froze up and wouldn't let the valve back up everything else could result.

I was in first gear during the initial bang-bang-bang. I did try re-engaging when I thought it was still running, to see if I could get speed to clear the tunnel and construction zone. I think that was when I confirmed the engine had stopped.

It was an awful spot to have something go wrong - construction in a tunnel. I have a lot of what-ifs looking back at it. What if I'd cut power as soon as it sounded off? I did end up having to push the car out the last bit, but I made it most of the way out before then. I'm glad I didn't end up run over in the dark.

http://forums.pelicanparts.com/uploa...1751919892.jpg

What? How do the cams turn counter clockwise when they are chained to the crank, which rotates clockwise?

Edit: I'm going to leave this idiotic comment to remind myself to reanalyze the reply before hitting submit.... Duh.

There's a reducing gear between the crank and cams that changes rotation.

Edit: Ask a 996 owner, it's their favorite part!