Nasty Probe
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There are some days when it doesn't seem profitable to come to work. Ever had one of those? A long time ago (1983) when I
was a technician working at the VW dealer, a valve adjustment on a VW Rabbit (diesel or gas powered) cost about $20. The valve
cover added a little to the bill, and $20 doesn't sound like much, but it was fairly profitable once a tech gained the skill
to get it done quickly.
I've seen a lot of balancers slip, but I don't remember ever seeing the pulley divorce its hub and leave home this way. This
was the original problem we had to repair, and after we replaced this part and installed the belts, the alternator and A/C
came online, but our jubilation was short-lived.
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The cam followers on those old Rabbits were like the ones commonly found on overhead cam engines in Toyotas today. But with
the hydraulic lash adjusters (built into the cam follower), the valves on newer OHC engines don't require the adjustment the
old VWs did. The valve springs aren't visible on this type of OHC engine — a cam follower is a small bucket-shaped affair
that fits into a smooth bore with the center of its underside sitting on the valve stem. The top of the cam follower is machined
to accept and hold a shim that can be replaced with one of a different thickness. One of the camshaft lobes rides on the shim,
and with the cam lobe pointing upward, the clearance can be measured with a feeler gauge. If necessary, the shim can be replaced
quite easily with some special tools. All the valves can be done in about 30 minutes.
I drew a ticket one day on a diesel Rabbit that was a routine job, but it smoked my bacon. I had done dozens if not hundreds
of valve adjustments on those cars, and this one had the loosest valves I had ever seen. I had to replace all the shims with
very thick ones to get the valves in spec. After I was done, I drove the car and parked it.
This is the valve train. One external
gear drives each pair of camshafts, with helical gears transferring the rotation from the belt-driven camshaft (exhaust on
the front head, intake on
the rear head) to the partner on that bank. Notice also the spring-loaded "scissor gears" on the companion camshafts, an ingenious
way of keeping gear backlash at zero so as to prevent the rattling noise so prevalent with helical cut camshaft gears.
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When the customer came to pick the car up the next morning, it made a horrible noise while the starter was spinning it and
the noise remained after it was started until it warmed up. The problem was that the cam followers hadn't been going nearly
as deep into their machined bores before I adjusted the valves and now some of them were sticking on the thick varnish in
the previously undisturbed part of the bore. The valve would stick, the piston would contact the valve and pop it shut, and,
well, you can imagine what it sounded like. The customer was apoplectic. I was blind-sided by this, because I had never seen
anything like it, and after I figured out what had happened I took stock and realized that I had a couple of options.
Option 1: I could tear everything down, and clean the varnish from the valve bores, but our friendly customer wasn't about
to pay for that repair and I knew I'd be doing that job on my own time.
Here's the timing mark for the front gear. Notice that the index mark on the gear is 180 out at this point, but we had it
lined up with the mark in the final stages of our repair. The bolt in the center of this gear is the guilty item.
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Option 2: I could put the valves back like they were and send him on his way, which was what I decided to do. I hadn't done
anything wrong on the job and quite frankly I didn't see any point in burning hours and hours of my own time on a problem
that would have blindsided anybody who had drawn this dirty hand. It was what I call a "circumstantial land mine," because
I was strolling along doing everything according to Hoyle and it blew up in my face.
Painful Probe
Turning the camshaft with the wrench, the helical gear, the camshaft and the bolt (center of timing gear) would move, but
the timing gear would remain stationary.
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When my dad was running his shop in the 1960s, he made the remark that whenever he worked on a Corvair he had to do it with
the shop doors closed. When asked why, his answer was that if somebody sees you working on a Corvair, they'll bring you another
one.
With the crank mark lined up and the marks on both camshafts indexed, we went to find where the distributor rotor's firing
window would center on the No. 1 post.
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Most guys I know see Ford Probes the same way. They run good when they're running, but when they come in with a problem, it
can be both expensive and painful. Of course, from the perspective of a tech school instructor, things are a bit different,
because our labor is free and every problem an automotive student has to solve (or see me solve) has a learning application.
Joe brought his Probe to us with an inoperative A/C and a dead charging system, and both concerns had happened simultaneously.
When I opened the hood I saw that the 2.5L had tossed its outboard serpentine belt (the one that drives the compressor and
the alternator) but the inboard belt (which drives the water pump and power steering) was still in place. As the students
and I evaluated the underhood situation, the owner handed me the pulley ring that he had picked up in his driveway one morning
when the two accessory components went offline. The ring was the larger of the two pulleys that are married to the rubber
ringed hub of the balancer on that car, and this balancer had left its partner behind on the driveway.
This would be a simple repair (somewhat). A replacement balancer was easy enough to obtain for about $130, and while it took
some gymnastics with the puller to negotiate the space between the balancer and the vehicle frame, we managed to get it off.
I inspected the part of the timing belt that was visible with the balancer removed (it looked new) and slid the new pulley
on the end of the crank. I then applied the necessary torque to overcome the interference fit, seat the gear and pinch it
against the crankshaft boss. While I was doing this, I explained to the students that the key and keyway that locate the gear
on the crankshaft don't have the strength to carry the load of spinning the cam gear over a long period of time, thus a loose
balancer can bring a delayed reaction disaster. If the balancer isn't properly tightened to pinch the gear, it follows that
the rotational torque of the crankshaft is applied to the key so that it shears. In a case like that, the car will be back
on the hook with the valves out of time.
New belts were installed and tightened, the splash shield and the tire were reinstalled, and the Probe was ready to push some
wind. I fired it up and backed it out of the shop; it ran well. But the next day when the customer started the Probe and drove
away from the shop, he didn't go 300 feet before the engine died. We had stumbled onto a land mine.
