FAQ: Series I SC Harmonic Balancer Diagnosis/Installation

Yay! FSMs finally showed up. Merry Christmas to me!!

As I've posted HERE, I've been chasing an intermittent misfire through my 95 SC Riv. I've managed to trace the problem to a cracked keyway on the harmonic balancer. That's where my adventure begins.

The first balancer I got was a Dorman 594-161. As it turned out, that is the first design. Having been told by the counter person at NAPA that this was the only balancer listed for the 95 Riv SC, and not knowing any better yet, I hurriedly installed it at work without a thorough look-over to make sure it was in fact the same. When I started the car, I had a bit of belt noise but nothing major. When I started home, however, it became clear that something was not right. V-I-B-R-A-T-I-O-N! I found a happy spot in the RPM at about 1500, and nursed it home.

It seems that GM, in their infinite wisdom, decided to change the balancer design on the Series I SC during the model year. Therefore, there are two different part numbers listed for the 95 Riviera. The dealership parts dept. has a note on the parts diagram to check the casting number on the original balancer to determine which one is the correct balancer. If your car has the factory HB on it, that's not a problem. However, if yours has already been replaced, like mine was, it becomes a bit more of an issue. I even asked if they could look it up by VIN and figure out which one is correct, but was told that was not possible.

So I learned that the first design, GM P/N 88960265, has a smaller counterweight than the second design, GM P/N 88960264, which is what it turned out my car takes. Here's a photo of the two side-by-side:

If I had taken the time to look, I would have never installed this one on my car. I have measured both balancers, and other than the counterwight, they are identical.

The Dorman part numbers are 594-161 for the first design (small counterweight), and 594-122 for the second design (large counterweight). The RockAuto catalog page HERE lays it out very well as far as design numbers, but doesn't list the second design Dorman. I found a 594-122 at Advance and installed it, and it is back to being smooth as silk.

Learn From My Fail and compare your new and old balancers if you are unsure of the numbers, since the difference is very obvious.

The good news for you here is that if you have the second design, you also have a chance of having the series 2 oil pan, different cam end cap, and lighter series 2 crank. The lighter S2 crank in the series 1 = rare factory freak for power.

Update - SOLVED!!

Once I got my FSMs around Christmas, I spent time poring over diagnostic flow charts, studying wiring diagrams, and performing wire traces to the PCM. Using the manuals, I figured out that all the wiring was acting as it should. Since starting my new job I haven't had much time to actually do any work on my car, but the 40 minute drive each way sure gave me time to think about it. The more I thought about the conditions the problem occured under, the more I began to think it was a mechanical issue. It happened mostly while under throttle, but went away when a higher RPM was reached. Sometimes it happened less if the throttle was applied at a constant rate, or the problem would come and go. The biggest thing that was consistent was that it wouldn't happen when the engine was cold, but only happened intermittently when the engine was hot.

A couple weekends ago, we worked a half day at the shop. Afterward, I decided to pull off my balancer to make sure the crank sensor hadn't been damaged. I noticed that the balancer pulled right off without the assistance of a puller. Here's what I found:

I also noticed these grooves in the timing cover from the 3X and 18X crank triggers. The picture is not that great but I have indicated the grooves.

What I think was happening was when it got warm, the cracked keyway would allow the balancer to "walk" on the crankshaft, pulling the crank triggers away from the sensor. The tension of the serpentine belts would hold the HB toward the back, making the grooves in the timing cover, but leaving the crank sensor undamaged (fortunately), but still pulling the triggers far enough out of the sensor to make it mis-read.

After a grand adventure with the new HB (link), I finally got the correct balancer installed and have had no problems since. Hopefully I got the problem solved for good!

Karma wrote:

The good news for you here is that if you have the second design, you also have a chance of having the series 2 oil pan, different cam end cap, and lighter series 2 crank. The lighter S2 crank in the series 1 = rare factory freak for power.

Hmmm... Not knowing how to tell the difference off the top of my head, what do I look for?

I was wondering if there was a performance or lightweight balancer for the series 1 engine?

Yes. But expect to pay around 600$ for it, and you will have to determine if your engine is large or small opposite key weight. ATI makes it and if your really want I could find the part number. (Its around somewhere.) It will be a slight overdrive(larger on SC belt) that would be similar to dropping a SC pulley size.

I really havent thought about that yet foing a port match on the heads, intake plenium and exhuast ports. And also doing yella terra rockers so I really cand say what size... Dont want to over do it. Any suggestions?

When reading the question in this thread, my immediate reaction is, Why?

Yeah, the only reason I looked into it is that I needed an 8 rib balancer for my m112 swap. For a "normal" series one, no point in wasting money.

just wondering got a extra block bout to put back together trying do everything to it that a can while its apart

if you are really serious about it, do a stroker kit on it. that negates the ati balancer since the rotating mass is balanced for a series two balancer. ie.save the 600$ and put it towards the stroked kit.

Hi,

I took my '95 due to a growling noise. I thought it was the water pump. Aside from this it ran perfectly. The mechanic told me it was the harmonic balancer. He showed me the old one and the rubber was torn completely. The repair was made. I drove half a mile and took it back because it ran rough and vibration came through the steering wheel. He is going to put in another HM. I hope this cures the issue.

When I brought it in for the original issue, I suggested replacing the cam and crank sensors. The mechanic said he needed a special tool to adjust the sensors and he didn't have one. Is this true? Is it really a big deal to change these sensors? Could he have damaged the crank sensor during HM removal/installation causing the issue described above? Should I insist replacing both sensors while the HM is off?

Any help would be appreciated. I know I need to find a new mechanic.

Thank you.

I think 95 Rivs came with 2 different harmonic balancers depending on the manufacturing date. When I swapped transmissions when my old one went bad, I had a pretty heavy RPM related vibration caused by the new flywheel that came with the transmission. It was a weighted flywheel and we swapped in out with my old non-weighted one and the vibration was gone. Might be something to look into. Im not sure which came on the early/late models though

th: you hit the nail on the head. my mechanic figured out and verified just what you said. he ordered the other hm and will install it Monday. he's pissed because his parts supplier did not notify him of the two types so know he has to do double the work (that's usually my job). thanks for your accurate and quick response.

I asked him to change the cam and crank sensors and he didn't have a $300 tool to calibrate the crank sensor and that I didn't need new ones so he won't/can't. i'm kind of peeved about that and am thinking of looking for a new mechanic. it seems a shame not to do the preventative part swaps while it's exposed.

thanks again.

Hi Ren,

Cam and Crank sensors are definitely NOT considered PM items. They should only be break/fix replacments. Often times the sensors are still good but the wiring has become brittle/cracked, so they even get misdiagnosed frequently. IIRC (if I recall correctly) the Series I 3800 did not need calibration of the cam and crank sensors, or perhaps there is a GM only tool. It's hard for any mechanic to keep up with the constant barrage of specialty tools and software required these days so I can understand his reluctance to buy yet another specialty tool if it's not a requirement.

Hope this helps (and that someone can confirm my Series I memory of the cam/crank calibration)

-Derek

Thanks Derek. That's what my mechanic said. I pick my car up tomorrow. He said it runs great. This is a great forum. I wish the forum for my 1988 Olds Toro was 1/4 as good.