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Faced with a delayed reaction failure

A year and thousands of miles after a routine repair, a failure could have destroyed the engine.
Monday, March 1, 2010 - 01:00

A year and thousands of miles after a routine repair, a failure could have destroyed the engine.

Rich White Car Care Council National Car Care Month

The e-mail began: "I took my 2006 Honda in for new rear rotors and brake pads at a national chain service center (not dealer). It drove away fine. I don't usually take the car on the freeway, as I don't need to on my commute. Last week, when on the freeway, my car would not go over 50 mph, and when I pulled to the side I was met with a burning smell. No smoke, just odor. I took (it) to the dealer, and there were no error codes, so I went home with the car. This past Tuesday, the same thing happened, so I took it back to dealer."

The writer continued: "This time, the service manager and I went on a test drive on the freeway, and the car did the same for him. We pulled to the side, and burning odor filled the car. He said the smell was the brakes. I took it back to the dealership, and they found that the brake fluid had been contaminated with what they believe to be engine oil. That national chain store was the last shop to do any brake work. It turns out that the 'new' rear rotors are not new, nor are the pads. The damage they caused with the oil requires the entire brake system to be rebuilt."

This serves as a reminder that repairs done wrong can be devastating, and some of these situations happen because some shops tend to hire people that haven't been properly trained. The service manager of the local GM dealer says he turns down applications fairly regularly from people who fiddled around and built a 350 or two in their backyard and think they're ready for the shop floor in his service department. But there's no way to tell exactly what happened in the Honda's case. The consequences of the work the outlet did remained hidden for (according to other details I received) about six weeks. This was a delayed reaction failure.

Almost a Year With No Problems

There are other instances like this. Today's Motor Age Garage deals with a Toyota Camry one of my students had done some cylinder head work on about a year ago. The cylinder head was removed and a valve job was done. The car ran like a sewing machine for many months and tens of thousands of miles before the failure occurred.

What is a shop supposed to do in a situation like this?

I worked at a dealership for 15 years under a very sharp dealer principal who had bulletproof integrity. In a dispute, he was always in search of the truth and he was very fair-minded. Service managers at that shop, on the other hand, came and went; some had integrity, some didn't. One day I was called out to have a look at a 1989 Crown Victoria that had been repaired a year earlier by one of our line techs (we had 25 techs at that time).

The Crown Victoria's Thick Film Ignition module (the one that mounts on the side of the distributor) had failed, and the shop that replaced it showed the owner that the module had been broken during previous repairs and subsequently had failed because of that damage. It is not uncommon for careless technicians to pry on that module and break it when they're adjusting the ignition timing on those engines.

The service manager we had at the time usually tried to tap dance out of situations like this one, and so I found myself drafted by the dealer principal as an expert witness. I looked at the module, pulled the file folder on that particular car, found the work order and made note of the tech who had done the work. I put the folder back in the files and walked back out to the car.

"We broke it," I said simply, refuting the slippery service manager's tap dance. The dealer principal refunded the man's money for the module. That's what a shop should do.

Well, we don't charge for labor because we're a training facility, so a refund wasn't in order, but this 2002 Camry very suddenly had developed an aggressive oil leak, and we found that it was coming from the passenger rear corner of the head gasket.

Exploratory Surgery

When we found a rather prodigious oil leak coming from the rear corner of the head, our diagnosis was at least partly behind us. Bert, a student, removed the valve cover, the timing chain tensioner and both camshafts. We checked the cylinder head bolt on that left rear corner and found that it wouldn't tighten; all it would do was turn around.

That was pretty revolting. These bolts were replaced the previous year when we had done the head work because they're torque-to-yield bolts. The oil leak was a direct result of this failure, because the pressurized oil feed to the camshaft journals and the VVT solenoid/servo system passes through the head gasket right next to this particular bolt. The only threads that could have failed were the aluminum ones in the engine block.

It's an interesting side note that removing and reinstalling the head on this particular engine is a 17-hour labor charge, and once you've done a couple of them you can beat the heck out of that. The job just isn't that hard. Be that as it may, there are quite a few steps and tricks, a lot of bolts and so on. And this isn't a free spinning engine, so valves will bend if you foul up getting the train in time.

An hour later, Bert had the head off the car and on the bench, and we had a neat little aluminum spiral in hand. The threads in the block had sheared off in a very peculiar fashion, and it had taken a long time for the failure to occur. But why?

Well, the answer to this puzzle would have its roots in the bottom of the bolt hole. The previous student who had done the job had, as I teach all my students in engine repair, blown each hole out with air to remove any standing fluid. But there must have been some standing liquid in that hole when he torqued the head bolt. That's a very deep hole, and a simple rubber-tipped blower won't get all the fluid out every time, particularly if it's oil in cool ambient temps.

As the clamping force was applied to that gasket, the hydraulic lock of that fluid against the tip of the bolt began to exert many tons of pressure on those threads. The weakest threads were the ones in the block, and they began to shear, but that's all they did on that particular torquing. The clamping force against the head gasket was sufficient to contain the oil pressure for quite a few heating and cooling cycles (dozens if not hundreds). Finally, with the expansion and contraction of the head and the fluid in the hole (lots of temperature swings), the threads eventually gave way, and it happened very suddenly.

This was the only head bolt on that engine where the failure occurred, and if this sudden failure had happened on a long trip, the engine would have welded its rotating components together before the driver even knew the lube oil was being jettisoned. As it was, the Camry simply made a mess on the owner's garage floor.

So what now? We could replace the engine block (which would be kind of expensive) or we could recondition the hole to receive a new head bolt. In a word, the most sensible in-vehicle repair for that damaged block was to helicoil the hole. Simple job, right? Not so fast!

That head bolt hole travels several inches through the aluminum block before the bolt reaches any threads. The torque-to-yield fasteners need some length to do their stretching, and that element had to be preserved. Now consider the fact that the 11 mm head bolt was passing through a 12 mm hole on the way to those threads, and that the helicoil was larger than the upper part of the hole. So the hole had to be enlarged, but how much would be safe? And how tough would it be to come up with a drill bit exactly the right size to accommodate the helicoil without weakening the engine block and causing some future failure?

We ordered the helicoils and used a 5/8-inch drill bit to bring the upper part of the hole out to a workable size. Now we had to drill out the remaining threads in the bottom of the hole, tap helicoil threads, insert a helicoil, break off the drive tab and reinstall the head, all while hoping the helicoil could take the punishment of the initial torque plus another 90 degrees. The first one didn't. We removed the head again, worked the ruined helicoil out of the hole and tapped the threads deeper. The next helicoil held, and Bert put the Camry back together.

Round Two

We started the Camry, but the oil leak was as bad or worse than before, and I discovered that Bert's overzealously powerful hands had twisted off the 6 mm bolt that holds the VVT actuator in the head. This actuator is right above our original oil leak and appeared to have popped out of the hole when oil pressure rose to a commanding level.

So I worked for a while on that hole installing a helicoil and a larger bolt to hold it in place. That operation was a success, but we still had a nasty oil leak. We removed the head again, and while Bert had installed the gasket correctly the first time, he was kind of rattled and distracted on the second go-round and managed to put the gasket on upside down, leaving the pressurized oil passage part of the block-to-head surfaces completely naked, thus the nasty leak.

With the gasket on right, the head reinstalled and the helicoiled hole holding a bolt, we finally got the Camry back in the wind. It was a wild ride, a job that will stand Bert in good stead at the Toyota dealership, where he now works full time. I always hope that mistakes made in my shop will make my graduates wise enough to work with a more seasoned hand when they take a turn in their own service bays.

Richard McCuistian is an ASE-certified Master Auto Technician and was a professional mechanic for more than 25 years. He is now an auto mechanics instructor at LBW Community College/MacArthur Campus in Opp, Ala. E-mail him at

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