With the Jeep unloaded and parked in John’s garage, I wanted to take a little time and do some fine tuning. The carburetor was still being a bit of a pill and I think it was due to the normally aggressive nature of Holley units. This model series having started it’s life back in the late 50’s as a racing carburetor for the NASCAR boys probably has a lot to do with it too. We knew that the timing was off a bit, that the lifters were making a bit of noise and that we also had a minor exhaust leak going on. The leak in the exhaust tubing was quickly found but there appears to be an exhaust header gasket that might have given up too. We adjusted the timing and made some carb adjustments that seemed to help the idle quality but left a little bit to be desired just off idle. We also had a problem with the idle speed climbing as the engine warmed up, having to manually adjust it down. Mind you these were not major changes but just a little worrisome. The next thing to tackle was the lifter adjustment. When I built the engine and installed the valve train, I went through the firing order cylinder by cylinder adjusting the lifters by rotating the pushrod until it would not do so, then giving the adjustment an additional 1/2 turn. My thought was that I must have been a little light on one or two as I could detect some tapping. To adjust the lifters this time, I wanted to do it with the engine warmed up and running. We made up some cardboard to keep the oil from splashing on the headers and went through each one loosening it until it clattered then tightening it down until it was quiet and giving it an additional 3/4 of a turn. With the valve covers back on, we fired it up again and I was stunned that I could still hear some tapping but very minor in nature. But, when we dropped it in gear, the tapping became far more pronounced. Trying this a few more times, we thought the sound was coming from the lower back of the engine. We shut it off and checked underneath to make sure nothing was hitting anything but that was not the problem.
We decided that it could possibly be an issue related to one cylinder so we disconnected the number 8 plug wire as that cylinder is the rearmost one and tried it again. Other than the misfire you would expect, the sound was gone. We reconnected the plug wire and sure enough the sound came back. Whatever the problem was, it was the number 8 cylinder. After some quick work to find a set of rod bearings and some gasket material, we proceeded to dump the oil and remove the oil pan. Surveying the engine’s internals we could not see anything wrong with the rod or the bottom of the piston – that was a huge relief. Removing the number 8 rod cap and looking at the bearing, you could see that the witness marks showed that there was something going on at the top of the rotation and the bottom of it. Basically it was the instances where the piston is stopped at the top and bottom of the connecting rod throw. For some reason, the rod was actually moving up and down, however slightly on the rod journal. This is normally referred to as rod knock. I didn’t have any measuring tools with me and the rod journal itself looked to be in good condition. All I could do at this point was install a new bearing set and hope that it would take care of the issue. We put everything back together, letting it sit overnight so that the sealant around the oil pan could dry. The next morning was the moment of truth. We fired up the Jeep, tested the number 8 cylinder again and the noise was gone. I have to admit that I was very relieved that this was the case. I think overnight all I could think about was having to take the Jeep back home, pull the engine and go through it again.
I have lost count of the number of engines I have assembled over the years. I have now learned a new lesson and that is to make sure and check every bearing clearance twice. This is something that I do on every one of the race engines, but on a basic rebuild I would normally just check a couple of rod bearings and main bearings. The reason being is that I normally know the condition of the crank as to whether it is standard size or not and obviously would be putting in bearings that matched that size. I have never had a bearing set that was machined wrong as this one was. It now appears that this rod bearing set was marked as a standard size but was actually about .010 undersized which allowed the rod to move at the top and bottom of its stroke. Just to be fair, this one was not the fault of the Chinese. This bearing set was manufactured in Turkey.
Our next issue was really one of engine manners. The Holley carb was simply not the right piece for this build and while we got it a little bit better, we felt that switching to a carburetor more suited for the street would be a positive thing to do. So we picked up a 600 CFM Edelbrock carb and installed it the next day. Purchasing the carb was definitely a three-ring circus as it seems that Advance Auto refused to honor their so-called 10% off everything Black Friday sale. I see it as false advertising but apparently they don’t care. Between this and the problems I had with the solenoids, I think my days in Advance Auto Parts are about done. Anyway to install the new carb, I had to manufacture a new retention device for the throttle cable and move some vacuum lines but tuning wise it only took a few minor adjustments to get the carb to where it was very well mannered. We took the Jeep out for a test run and my only concern was the timing again. The new distributor which was a GM HEI unit was providing too much advance via the vacuum control unit. I decided for the time being to remove the vacuum source to the control unit and just rely on the timing setting and the additional mechanical advance provided by the distributor. An additional test drive indicates that this was the right move to make.
This wraps up the Jeep Project, at least for now. And like most projects I learned a few different lessons along the way. If I were to ever do something like this again, there are a few things I would do differently like pulling the transmission out and setting up the engine/adapter/transmission in a dry run. There were painful issues with the adapter although it all eventually worked out but mocking it all up where I could get to it would have helped a lot. I would also make sure to check every part, especially anything electric or electronic right after it arrives. I lost too much time to chasing bad parts on this build and that added to the frustration. And lastly as much as I like and understand Holley carbs, sometimes they’re just not the right piece. The Edelbrock carb was a snap to setup and I am sure it will provide excellent service.
Overall though, I think the Jeep Project turned out pretty good. It’s a neat little hot rod now.