Project Cappuccino: A Terrifying Problem

Do you know what sound you never want to hear coming from your engine?  Banshee screams.  Anything that sounds like the squeal of an unholy demon spawn coming from your engine bay is probably going to be very expensive.  So when we heard screaming and squealing coming from the engine bay of our 1992 Suzuki Cappuccino, we immediately suspected something terminal.  Follow along as we diagnose and solve the issue.

Cappuccino & Integra
The Cappuccino usually spends its winter on jackstands as I work on routine maintenance and upgrades. At least this year it had my old Integra to keep it company.

This is what our particular banshee noises sounded like.  Interestingly, this sound only occurs when the turbocharger is making boost.  Once boost hits, you get the banshee.  This almost certainly sounds like a turbocharger that is eating itself alive.  This turbocharger is 30 years old with almost 90,000 miles on it and if it was not well maintained the bearings could be going and what we’re hearing is the impeller contacting the turbine housing.  

Or is it?  Way back in grade school I was a music nerd who played clarinet.  The noise coming from the Cappuccino sounds a lot like a clarinet mouthpiece removed from a clarinet and blown through, creating a shrill, off pitched note that pierces the skull (played by a teenage asshole pranking his friends).  It’s as if exhaust gas is leaking from somewhere in the turbocharger area, maybe past a gasket that’s acting like a reed.  Maybe we actually have an exhaust leak around a flange, causing the metal gasket to vibrate and act like a clarinet reed.

Suzuki Cappuccino Exhaust Manifold Heat Shield
We went straight to the exhaust manifold for our diagnosis as it was obvious the problem was coming from this area of the car. We removed the exhaust manifold heat shield to start searching for exhaust leaks. These will show up as soot marks on both the exhaust and anything nearby. Lucky for us, the problem turned out to be here. It is faint, but a line of soot shows up on the inside of the heat shield (see the arrow). This area is inline with the flange between the turbocharger and the exhaust manifold.
Suzuki Cappuccino Exhaust Manifold Bad Bolts
We grabbed a socket and sure enough, the turbocharger mounting bolts were loose. A couple quick turns and the noise was gone. Talking to a few Cappuccino owners online, it turns out these bolts have a tendency to unwind over the years. The problem is, Suzuki went cheap here and the three M8 bolts don’t provide enough clamping load. A combination of not enough bolts, too weak a material, and being too small means they are prone to stretching. As they heat cycle, they slowly loosen until you get the banshee scream. Note how there are no markings on the head to denote the grade of bolt. These may not even be Grade 5, yet they have to deal with the heat and vibration of a turbocharger making up to 14 psi of boost.
Drilled Turbo Bolt
Fortunately, there is an easy enough fix to prevent this issue from recurring. Simply remove each bolt individually, drill through the head, and safety wire the bolts in place. When applied correctly, the safety wire will prevent the bolts from losing torque. A simple, effective way of preventing a scary issue that will eventually melt things in the engine bay.

7 comments

  1. Ever play with the Stage8 locking washer system? Wondering if you had a preference of that vs drilling and locking wire?

    I’ve honestly got that on some header bolts, the Stage8 stuff, but it was a one-time install and never looked back. So I can’t really compare to say it’s good or bad.

    1. I had not seen that system before. Would be a lot easier than drilling for safety wire that’s for sure. Doesn’t look like they have the bolt lengths I would have needed though.

      My original plan was to fix it with tools and parts I had. That all went out the window when the last bolt broke its threads coming out.

  2. Short length cobalt drill bits are about $2 each, and are the only way to go for drilling for safety wire. Buy at least 5, and you won’t worry about occasional bit breakage that would halt the job in the middle. The short length bits are much stiffer and less prone to breakage than the standard/jobber length.
    Standard high speed steel drill bits are just a waste of time and money for drilling safety wire holes.

  3. Probably smart to at least mark the heads with paint to know easily if they are loosening without having to wait until you hear banshee screaming.

  4. If I were you, I’d still safety wire them – though that’s my bias of fixing helicopters bleeding through. At the very least, use some torque stripe so you can monitor them.

Leave a Reply

Your email address will not be published.

*
*