A very good friend of mine operates a medium-sized farm, among other enterprises, and owns several pieces of heavy farm equipment. One of his farm operation pieces of equipment is a 1968 Chevrolet 1.5-ton stake truck with a hydraulic grain box on the back. The truck, although it is 41 years old, has less than 20,000 miles on it and looks like the day it came off the showroom. Yes, he takes good care of his equipment. The only time my friend, Matt, uses the truck is to run his grain to market during harvest season and to pick up seed or fertilizer in the spring. Thus, it has not accumulated many miles. In fact, if you do the math, he has averaged less than 500 miles per year.

As I said, Matt is a good friend. He rode his motorcycle with me last year across the Arctic Circle and to the northern tip of Alaska and back. We tent camped the entire trip and, therefore, spent many nights around the campfire together. We came to know each other well as a result of that trip.

Together, we rode across snowy mountains and traveled thousands of miles down dirt and gravel roads. Together, we battled the worst of what Mother Nature could offer and, therefore, like two soldiers fighting side by side in battle we came to trust one another implicitly. To say Matt is a friend may be an understatement. We are more like brothers. So when Matt called and said his truck was hesitating on acceleration, obviously I found the time to help him diagnose the problem.

Matt showed up to my place recently at the scheduled time. He wasn’t one minute late. I like that about Matt. We backed the big truck into my shop and started the diagnostic process. Now, I should tell you that Matt is an above average mechanic in his own right. The fact is he has a degree in automotive technologies from a highly respected Michigan college. I figured if Matt was bringing the truck to me for help, we might have to look a bit to put our finger on the actual problem.

A 1968 Chevrolet truck is not the most complicated piece of equipment on the highway by any stretch of the imagination. In fact, is it is pretty simple mechanical stuff by today’s standards. Regardless of the complexity of the system, the best approach to diagnosing any problem is to start with the basics. So that’s where Matt and I started.

If you recall,  Matt’s complaint was a hesitation on acceleration. There are only a couple systems most likely to cause such a concern. They are the fuel delivery system and the spark delivery system (ignition system).

We decided to check the spark delivery system first. Remember, this is a 1968 piece of equipment. Old school technology! We set the new points that Matt had installed to factory specifications and then set the ignition timing. Or we attempted to. That’s when, and where, the interesting stuff began to happen.

I should note it was about this time that the normal “helpers” or “leaners” began showing up. These particular “leaners” are a couple of older retired fellows Matt and I know. Each has great intentions and each is willing to offer up advice at the drop of a hat. Mind you, whether or not you take that advice is a subjective matter deserving of a whole column unto itself.

Now, each of these men is very knowledgeable in their respective fields and I certainly do not wish to take away from that fact. Nonetheless, while facing a diagnostic dilemma, both Matt and I were distracted, somewhat, by their input.  Both men were, however, very useful at fetching tools.

Setting the ignition timing on a vehicle of this generation is not a complex process. With the right equipment, a technician should be able to set ignition timing on a 1968 Chevrolet in a few minutes. “Should” was the operative word in that last sentence and that was not the case with this truck. According to the timing indicators on the truck ignition, timing wasn’t even close to being set accurately. Both Matt and I had a hard time believing the ignition timing was that far off because the truck idled and ran far too good.

Nonetheless, the testing equipment indicated timing was indeed nearly 40 degrees off.  Although I felt that the actual ignition timing was very close to being set accurately, and because of this discrepancy, I knew I had to actually verify what the timing really was. The process would require me to manually, not electronically, check timing.

Matt and I took the necessary steps to verify mechanically what/where the timing was actually set. Once we were certain we had the engine lined up at top dead center with the No. 1 cylinder on compression stroke we found that the timing indicator mark on the harmonic balancer still indicated we were more than 40 degrees off. For an experienced technician this is one of those things that makes you say, “poop!”

We knew that there were only a couple things that could actually be wrong at this point and both required we, at a minimum, pull the harmonic balancer.

So that’s what we did.

We removed the radiator and fan blades in order to get to the harmonic balancer.

We found the water pump bearing was in pretty bad shape during that process.

We both were happy we found the bad pump before it failed on the road. After sending the “leaners” into town to get the correct bolts for the harmonic balancer pulley removal tool, we pulled the balancer.

The balancer itself showed no signs that it had slipped on either the inner pulley of the balancer or upon the crankshaft to which it is mounted.

We both felt, since we had come this far, we might as well pull the timing cover and see what, if anything, was amiss inside. We found nothing!

So, my friends, as unusual a diagnosis as it is, the timing problem on this truck is the result of a slipped outer pulley on the harmonic balancer.

Even though the harmonic balancer shows no sign of slippage, it must have actually done just that. There is no other answer to this problem.

This is a very unusual problem and one that requires removing a lot of the engine in order to verify.

Matt has all the parts coming and we’ll get back to it soon.

Once we reassemble the truck and set the base timing we can get on with finding out why the truck is hesitating on acceleration. We will be sure and coordinate our efforts with the “leaners!”

I’ll update you folks next week.

Nick Shultz is an instructor of Automotive Technologies at Owens Community College. He is an arbitrator for the Better Business Bureau who specializes in cases involving the Ohio and Michigan Lemon laws. He is a certified master automotive technician by ASE, General Motors Corp. and Ford Motor Co. Shultz, a Toledo native, will take questions from readers at letters@toledofreepress.com.

This entry was posted on Thursday, November 12th, 2009 at 7:48 pm and is filed under Auto Sense, Wheels.
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