Engine How-To: Jeep Dauntless V-6 Overhaul


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All engines run great until they don’t. Once an engine has lost its ability to convert ordinary air and fuel into a thermal energy reaction from which we can harness the power, well, then it just becomes a boat anchor. All science aside though, pistons need to be churning between the framerails to roll the rubber down the road.

In the case of this Jeep, the motor is so worn out that it struggles to start, and a cracked block leaves puddles of coolant in the driveway. The Dauntless V-6 was used in Jeeps as an optional engine from 1966 through 1971, making it 48 years old at best. Chances are there isn’t much pep left in its step, and this Jeep is a prime example. It was apparent that a different engine needed to be sourced for a heart transplant. While the rest of the Jeep world seems to be infatuated with modern fuel-injected V-6 and V-8 swaps, we really have a nostalgic love for the rumbling sound of the old Buick odd-fire 225. Rebuilding a replacement engine that will drop in place was an easy decision for this project.

A rebuildable core was sourced from a local 1971 CJ-5 partout. To keep the rebuild cost down we will be doing all the teardown and buildup in our home garage. At the same time though, we only want to do this job once, so it will be done right. If we are lucky, it will be another 40 years before we have to do it again.

In this first part of the Buick V-6 rebuild we are going to dive into some of the basics of tearing down this engine to prepare it for the machine shop. We will also give you a glimpse of what happened behind the doors of that machine shop when our old mill arrived ready for work.

We spent a lot of time searching for leads on “rebuilt” Buick V-6s in hopes of finding one that had good compression and leakdown tests. Those are two basic tests that can provide confidence in an engine’s condition. Even an engine with paperwork to prove the claimed 10,000 miles fell way short of our expectations when tested. Trust but verify, as they say. At the end of the day, the only way to meet our expectations was to rebuild an engine ourselves.

We started digging into our motor by removing the carb and intake. As usual, we hit a snag almost right away. Without fail there always seems to be one piece of hardware that takes longer to remove than all the other 50 fasteners combined. Be prepared with a penetrating lubricant like PB Blaster, a blowtorch, and some ingenuity. A bolt head on the intake was badly rounded off. A nut had to be welded to the bolt head so it could be removed.

Take lots of pictures along the way. The more you document the teardown process, the less head-scratching you will do during reassembly. On the right side of the engine just the valve cover is removed. The left side has also had the rocker arm assembly, pushrods, and head removed. It’s cool to see the two stages side by side.

Be very observant during the teardown. Don’t rush it. Inspect the parts as they are coming off and make a list of parts you will need. The Buick engines use a mechanical fuel pump that is driven by the camshaft. It is common for the fuel pump eccentric on the camshaft to wear a groove where the fuel pump arm rides. Fortunately, replacements are available through TA Performance, and it has been added to our long list of needed parts to revive this powerplant.

The timing chain did not appear to be stretched or damaged while it was on the engine. Once it was removed, it told a different story. No clue on how many miles were on this timing gear, but it’s obviously damaged and no longer keeping good engine timing. A metal gear design will also wear down, even if it is not as apparent. Timing gear and chain sets should always be replaced during a rebuild.

Each piece of the puzzle was laid out on the workbench as it came off the engine block. What’s lying on the bench is basically the “top end” of the engine, as it is commonly referred to. I always find a box to poke holes into to keep the correct order and orientation of head bolts, pushrods, lifters, and valvetrain as they are removed. Have a box of ziplock sandwich bags handy. Bag and tag each set of bolts from the various engine components so they don’t get lost or mixed up. The heads will end up at the machine shop for a full makeover, while some of the other peripherals will stay home and get a deep cleaning.

Roll the engine stand over and remove the oil pan to expose the “bottom end” or “rotating assembly” of the engine. With the windage tray and oil pickup tube out of the way, inspect the connecting rods. The first engine we tore down (yes, there was more than one) was a factory engine that had never been rebuilt before, which was an ideal situation. Starting from the front with No. 1, all of the connecting rods and caps were marked with a numbered punch to identify the block position and mating cap orientation. The second engine was “rebuilt by a reputable shop” but had spun a bearing and was given to me as a core. What we see here is that connecting rod/piston No. 1 is in the No. 2 position on the crankshaft. In fact, five out of the six connecting rods were in the wrong position. Not so reputable of a shop all of a sudden.

Too much RTV sealant is a bad thing. Obviously, someone was attempting to make sure the rear-main seal was leak free, but the excess goop can wreak havoc on an engine or gearbox. When the cap for rod No. 5 was removed, we found RTV bits and pieces under bearings and in oil pathways. Let this be an example of how to not apply RTV; take a more conservative and methodical approach.

As the pistons travel up and down, the rings wear into the block and push material to the top. Over a long period of time a ridge will form at the top of the cylinder wall that can ultimately prevent the piston from being removed when the ring gets stuck on it. A ridge reamer can be rented from your local auto parts store to machine it down by hand. Use some lubricant, follow the instructions, and only ream just enough to remove the piston. You can easily go too deep into the cylinder wall if you are not careful.

Once all of the pistons were removed, the engine block and all of the internal components headed to the machine shop. After a more thorough cleaning and inspection, the machine shop found a harrowing crack in the block between the freeze-plug holes. That sure did throw a wrench into the plans. Most cracks in heads and blocks, even small ones, can easily be seen with a visual inspection. We could have saved an $80 block-cleaning fee if we had been a little more diligent with our own inspection before dropping it off.

While we are talking about inspection, one thing that is often overlooked is inspecting the rough casting areas that are left over from the block casting process. In this photo you can see a piece of casting flash that easily detached with a slight poke of a screwdriver. This could have led to catastrophic failure of our freshly rebuilt engine if it had broken off down the road. A rotary file on our die grinder was used to smooth over all of these casting edges. Just enough to clean things up—nothing crazy.

After reaching out to the local Jeep community, we had another Buick Dauntless V-6 engine delivered to our door about a week after discovering the first block we tore down was cracked. The replacement was disassembled and inspected, and then the engine block, heads, crankshaft, and pistons were dropped off at Chet’s Engines & Performance in Ogden, Utah. Tony, who owns the shop and runs the show, got right to work. Some bore gauge measurements were taken, and soon the block was chocked into the machine and we began cutting chips. This block had been rebuilt before, so we had to bore it out to 0.060 over stock to get things smooth and straight.

The boring operation is actually always done a few thousandths shy of the final desired bore diameter. This leaves room for the final cylinder hone. Honing the cylinder adds the necessary crosshatching that holds oil on the cylinder walls to lubricate the pistons and rings. Without crosshatching at the proper 45-degree angle, there will be a lack of lubrication and significantly accelerated wear. Course-, medium-, and fine-grit stones are all used in this process until the cylinder finish is just right.

Checking the heads for cracks is also a very important step. This is not a Buick 225 head, for the record, but the photo is a good example of a nearly invisible crack being detected. As mentioned before, most cracks can be detected with a simple visual inspection. To be 100 percent sure there are no cracks, you must inspect for cracks with a magnetic particle inspection. This is also referred to as Magnaflux, which is actually the name of a company that sells magnetic inspection equipment and materials. A magnetic field is induced on the inspection area, and then a yellow-colored metal dust is misted over the area. The yellow dust will gravitate to and reveal any small cracks.

Once the heads were confirmed to be crack free, the guys at Chet’s got to work tearing down valvesprings and removing the old valves. There are sleeves in the heads that the valves ride in, and they are called valveguides. An air hammer was used to install new valveguides into the slots in the heads.

During the installation, the thin-walled valveguides tend to distort and shrink in diameter a little. There cannot be any interference between the guide and the valve stem, so you need to ensure that the valveguide is the correct final dimension. This air hammer tool bit has two bulges near the end to do that job. The first knob does the first resize pass, and the second knob does the final sizing pass in succession.

These old engines were being used at a time when leaded gas was the norm. The lead additive in the fuel provided a cushioning effect as the valves were opening and closing. Modern engines are designed to operate with unleaded fuel. We chose to machine the heads to be able to install hardened valve seats for our exhaust valves to bring our Dauntless up to date. The engine will run fine without hardened exhaust valve seats for a long time, but it will definitely lead to premature valve seat wear—eventually resulting in leaky valves and lower engine compression. The cost of the hardened valve seats is reasonable and easy to justify.

The intake and exhaust valve seats were all finished off with a three-angle valve job. At Chet’s Engines & Performance, each valve is numbered and set up to fit perfectly in its designated spot to make sure the best seal possible is achieved. Put into a simple terms, the 30-degree angle cut on top reduces flow restriction through the valve, the 45-degree angle cut in the middle is where the valve actually seals, and the 60-degree angle cut on the bottom helps the flow pattern through the valve when it is open. This three-angle configuration will flow at a higher CFM and provide much better performance than the typical straight 45-degree valve seat angle cut by the factory.

Engines see a lot of hot-to-cold, cold-to-hot temperature cycling while they are in service. It is safe to say that the majority of engines have seen some overheating in their heyday as well. These thermal cycles can warp the heads. To finish off the head service Chet’s “decked” or “cut” the heads flat again. Only the bare minimum of material is removed to make them flat. About 0.0005 inch of material is removed with each pass, while the operator is keeping a close eye on the progress. They had to slice 0.006 inch off to make our Dauntless heads true again.

Here is a teaser of what is to come. With all of the machine work done on the heads, they were cleaned of all debris and brought over to the assembly table. The numbered valves were installed in the correct spot for final assembly. Then, new valve seals were lubed and pushed into place, followed by new Comp Cams valvesprings. A valvespring compressor is used to compress the spring down enough to be able to install the spring retainers and keepers on each valve stem. With that done, the heads are complete.

Connecting rods cannot be overlooked and need some love and reconditioning. The connecting rod caps are carefully set up into the machine. The machine cuts the cap ends down a few thousandths to make sure they are flat and true. The main connecting rods also go through this process so that the mating surfaces of both the cap and rod are perfect.

When the ends of the caps and rods are cut down, it effectively reduces the bearing diameter of the connecting rod assembly. The rods were reassembled with new studs and run through the rod hone to resize them back to factory specs. Through each step of the process on all of the engine machine work, the guys at Chet’s Engines & Performance were constantly checking measurements to be sure every component was within the factory specifications.

After the block was bored and we knew the size of the pistons we needed, we made a phone call to Egge Machine in Santa Fe Springs, California. We ordered a 0.060-inch set of the company’s trick 9.5:1 high-compression pistons for the Buick 225 (part number L2226). Once they arrived, the machine shop went to work installing them onto the reconditioned connecting rods. The rod ends are heated in a rod heater to expand the wristpin journal. When they are at the right temperature, a push tool is used to easily slide the wristpin though the piston and connecting rod. There is a “forward” mark on the pistons to help make sure all of the pistons are correctly oriented on the connecting rods.

Between a full teardown on a core motor and all of the machine work, there was a lot to cover in this first part of the Buick 225 V-6 rebuild. We hit all the high points with as much helpful detail as possible. After all of the machine work was done, we had all the measurements we needed to order new components. We needed to order 0.060-inch-over pistons and rings, and 0.010-inch-under rod bearings and main bearings. Chet’s Engines & Performance sent the crankshaft out for polishing, and it looked brand new when it came back. Stay tuned for the second part of the Buick Dauntless V-6 rebuild, where we talk about the performance parts we ordered and go through all the details of the assembly process in our home garage.

Sources

TA Performance

Scottsdale, AZ



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