August 2000 Articles & Features
By Dan Marinucci | August 2000
Dealing with Honda harmonic balances is less of a chore when you know why they fail and how to remove them when they cause charging and a/c system woes.
The dog days of August are here. But if you don't know about a common Honda harmonic balancer failure, diagnosing a Prelude or Accord could become a dog of a job. Here's the word.
A layer of rubber separates the inner and outer sections of a typical harmonic damper or balancer. It's fairly common for this rubber to crack on 1988-91 Preludes and 1990-93 Accords, causing the outer part of the balancer to shift on or spin around the inner part that's bolted to the crankshaft. Photo 1 below shows the engine side, or back side, of a cracked harmonic balancer.
Suppose you can't confirm that the rubber layer is cracked just by visual inspection with the engine off. An easy way to check a suspect balancer is to paint or chalk a mark across the inner and outer sections of the part. Rev the engine and abruptly release the throttle several times. Then shut off the engine and inspect the marks. If they're misaligned, you know the balancer rubber is cracked.
If the problem occurs on an Accord, an undercharge or no-charge symptom may be the complaint that actually gets the car into your service bay. The 'slipping' outer section of the balancer slows down the alternator enough to cause a noticeable charging problem.
The outer section of a cracked Accord balancer often shifts outward as well, allowing it to rub against the power steering belt. Here the telltale clue is the shiny witness marks the power steering belt makes on the front of the balancer. The arrow in photo 2 shows where to look.
A no-charge or undercharge problem can also occur on a Prelude if its harmonic balancer splits apart. But the more obvious symptom of a Prelude balancer failure may be an inoperative air conditioner and an illuminated warning light. On this car, the harmonic balancer pulley drives both the alternator and a/c compressor. Honda has a fail-safe system on the 'Lude that protects the drive belt if the compressor seizes up.
An a/c compressor control unit, under the left side of the dash, monitors engine rpm through the traditional Honda tach terminal (blue wire at the ignition coil). It also checks compressor rpm via a compressor speed sensor. (One speed sensor wire is green, the other is white.) Whenever this control unit senses an ongoing rpm difference between the crankshaft and the compressor, it shuts off the compressor and turns on a red LED to warn you that the a/c system has shut down due to the fail-safe system.
Note that this red LED warning light is located on the a/c On/Off control button itself. Don't confuse it with the regular a/c light directly above the a/c On/Off button!
Suppose a Prelude compressor won't turn on and the red LED on the a/c button is illuminated. First, check for obvious signs of belt slippage due to a glazed belt, leaking compressor shaft seal, etc. If you don't find anything obviously wrong, perform the 'chalk check' on the harmonic balancer that I described earlier.
After you repair the problem that caused the difference in crankshaft and compressor speeds, turning the ignition switch back on and operating the air conditioner will reset the compressor control unit's fail-safe system.
As long as we're on the topic of Honda harmonic balancers, I must make a public service announcement about loosening the balancer bolt. This can be a brutal task! Whatever thread-locking sealer the factory uses here holds so well that unknowing technicians who can't loosen the bolt begin wondering if it uses a left-hand thread. It doesn't!
Some Honda specialists keep a 3/4-inch-drive impact gun on hand solely for loosening these bolts. Typically there's an access grommet or 'knockout' in the inner fender panel. A tech will remove the knockout and slide a 19mm impact socket and an extension through the hole. Once the socket is positioned securely on the balancer bolt, the technician lets his Big Bertha impact gun slowly rap-rap-rap away until the bolt gets loosened up.
Several tools are available for holding a Honda crankshaft steady while loosening or tightening its balancer bolt. These tools engage the big internal hex shown in the center of the balancer in photo 2. Honda sells its own and Sir Tool (800-845-4542) makes tools that resemble Honda's.
However, the simplest, most cost-effective tool I've seen is a new one from Schley Products (714-693-7666). Because this one (shown in photo 3 at left) fits into the most common-size internal hex (55mm), it works on 90% of all Honda/Acura harmonic balancers--including all the high-volume vehicles up through 2000.