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Discussion Starter #21
Thank you so much for your efforts to help me. I’ll try to answer your questions.

- The exhaust stud in question was not the correct part, but a lookalike from a fastener distributor. Shame on me.

- The manifold doesn’t seem to be damaged. I’ll remove it as you suggest and take a closer look.

- My engine mounts are new, so I did not think to look at them. I will now.

- Sump guard is fitted. I’m fairly sure the car didn’t bottom out.

- Yes, the vibration is curious and worrisome. Has me worried for sure. I can’t even imagine what it could be. If I didn’t know better, I’d guess bearing damage, but a) I can’t fathom what a pothole would have to do with that and b) I’d have expected the engine to have seized by now if that was the case.

I’ll pop the cam cover and take a look later. It occurs to me to start the engine again and post a video of the vibration, but I wonder if I’m just inviting more damage by running the engine without knowing what’s wrong.
 

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Just a hypothesis, of course, but if you bottomed out on the exhaust, you would have put tremendous strain on the exhaust manifold and studs. Possibly enough pressure to affect stud integrity in the soft aluminum head, compromising the gasket seal and worst case scenario, damaging the head. I am not meaning to sound doom and gloom but just spitting out possibilities. A bottom out causing all these issues just makes me think there is something unseen up to this point....
 

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There's a lot to be said for having a good look.
Like others, I struggle to see a link between a pothole and engine damage. Breaking or moving a fitting or mount or the exhaust is another matter.
Do you have car ramps?
Since you say it starts and idles fine, you probably aren't risking anything by crawling underneath and having a look/feel/listen for a short while while an accomplice revs the car a little. Start with the last thing you touched...the engine mounts.
If it's a structural failure, my guess is that something should appear obvious, and will lead to a relatively simple solution. Fingers crossed...
The only other thing that springs to mind is that something in the fuel delivery system (or even spark) may have been moved/jolted/broken, upsetting fuel supply or spark above idle...you never know, but this still seems more likely than an internal engine failure.
 

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I'll add my 0.02 Lira's worth here, agree with the others, it sounds like you bottomed the exhaust somewhere, probably the big rolled flange on the middle silencer - hard enough to break that mild stud and most likely touch the body somewhere else due to deforming the pipe - that'll give you a noticible vibration & a sonic boom into the cabin if you did a *decent* job of walloping it.... Guess how I know...

Be aware that if you jack the body up to see underneath you might jack the pipe off an axle etc - the best would be sitting square on all 4 wheels with weight in the driver's seat on the 4 poster at your local exhaust shop, after all they are going to be repairing it right ??

Aye
Greig
 

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Discussion Starter #26
A bit of an update here for you guys:


  1. The sump guard definitely took an impact. It is slightly concave. Still lots of clearance between it and the sump (thank you, new motor mounts!). Sump is definitely undamaged.
  2. No visible evidence as far as I can tell that the exhaust impacted the road, but that doesn’t mean it didn’t happen.
  3. No evidence of oil/coolant mixing under the cam cover or anywhere else. Whitish frothy substance (approx 1 tablespoon) in the breather tube evidently due to normal operation.
  4. Broken exhaust stud is replaced. Exhaust manifold is bolted back on. No apparent damage to the manifold or head.
  5. Started the engine, but it seems I have reused my cam cover gasket too many times, and it is leaking now. No doubt I overtightened the cam cover and crushed the $h!t out of the gasket. Won’t do that again.
  6. New valve cover gasket ordered from Classic Alfa. Since the shipping to Toronto comes to about $50 USD, I figured I’d order their 123 electronic distributor and a new blue coil to go with it so I won’t have to pay shipping a second time when I inevitably go for electronic ignition. Gonna need the forum search tool to figure out installation there, for sure (not to mention curve selection).
  7. Could only run the car for a few moments due to the leaking cam cover, but it seems some part of the exhaust underneath the car is rubbing the chassis, causing an awful noise, but no longer causing a serious engine shake. I will do as Ranz suggests and explore under the car with a helper at the gas pedal to find the source, after the new cam cover gasket is in. Below 1500RPM everything seems completely normal, which leads me to believe there’s nothing more happening here than some rubbing.
  8. I still can’t completely rule out a head gasket failure. The area of a head gasket that I thought might be leaking is directly beneath one of the cam cover leaks, so I must first replace the cam cover gasket. If oil residue then stops appearing around the exhaust manifold I’ll know I’m good.

Gasket to arrive in two days. Will let you know!
 

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A bit of an update here for you guys...
Gasket to arrive in two days. Will let you know!
Thanks for the update!
Good to know the broken stud is out and a proper one is back in place; can you tell us how you got the broken one out in the end?

When you remove the cam cover to replace the gasket, check it on a level surface for warpage...those cover bolts take very little torque, 10.3 - 14.8 ft-lb, and overtightening can warp it or worst case strip the cam studs.

stick to around 10-12, and then after a few hundred kms, check by hand that they haven't worked loose....the ones on the 4 red paper gaskets can do (hopefully you got those 4 new, as well as the 1/2 moon rubbers at the back?)
 

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Discussion Starter #29
Thanks for the tip on measuring cam cover warpage. I’ll do that.

There was no broken stud fragment to remove. It was simply AWOL. I cannot explain. User error seems probable.

Red paper gaskets and half-moon seals have 300 miles on them. I hope they are okay to reuse. I didn’t reorder them.

Bianchi, what do you call those? I’m not sure what to Google.

Thanks!
 

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A lot of the problem with aftermarket studs is they can have a different heat/expansion/contraction ratio. That can cause broken studs,loosening nuts, etc. whatever you use make sure its heat characteristics are compatible with your aluminum head and exhaust manifold. My Nissan had this issue from the factory. I replaced them with 300ZX studs and cured the problem.
 

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BTW,

How did you repair the broken stud?

Vin
 

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Discussion Starter #34
This problem is now resolved, and I’m a very happy guy.

After failing to identify where the exhaust was rubbing on the chassis, I built some wooden stands to get the car high enough so I could have a proper look. The car fell off my jack stands a couple of weeks ago and I don’t feel good about using them for any lifts beyond 6” or so anymore. Thank heavens, there was no damage to the car. Oh, and I’m ok too.

A close look quickly revealed no contact between exhaust and chassis. Hmm, weird. Motor mounts are tight, too. Can’t be the exhaust after all, it seems.

So I refreshed my memory on the prybar-as-stethoscope trick on this forum and on YouTube, and went at it. A couple minutes later I had traced the source of the vibration to the sump, getting more and more depressed as I honed in on it.

Then I noticed, “the sump does get kind of close to that transverse chassis brace (the one painted in body color, on all cars I presume, or is it just mine?) — maybe there’s some rubbing there, somehow, even though the relative positions of sump and chassis couldn’t really have changed.

Crawling right under there, I start looking. Plenty of clearance. Hey, what’s that? Motherbrother.... the missing exhaust stud is wedged solid between sump and chassis brace, transmitting engine vibration directly to the chassis.

I wrestled it out with some needle nose pliers. It was really jammed in there.

Start ‘er up, never sounded better, winds up smooth as a turbine.

Thanks to all who gave their technical and moral support!

Incidentally, @SkiBum, your point is well taken. On replacing the missing stud I discovered another one that was very, very loose. Both are now replaced with original studs cannibalized from my old cylinder head. Lesson learned!
 

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Thanks for posting your final solution, so many don't often after much input from this BB and that PMO.

ciao

Ken
 

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Thanks for posting your final solution, so many don't and that PMO often after much input from this BB.

ciao

Ken
+1

Unfinished threads is a pet peeve of mine.

Thank you,

Vin
 
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