"I've never been able to blow one up." Many times, a conversation revolving around a Slant Six engine results in that very quote. It's the Leaning Tower of Power, it's indestructible, and the Slant Six saw duty in everything from the small A-Body to the Ram pickup.
For that reason, we thought that a follow along with a rebuild of one of these engines was in order. Some time ago, we got a call from Chris Holley, an instructor at the Pennsylvania College of Technology, in Williamsport, Pennsylvania, telling us about a Dart that the college had just acquired. We ran a Hidden Treasures article about the Dart in our April 2013 issue, and when the Dart's engine was ready for a rebuild, it seemed like the perfect follow along for us.
As we said in our Hidden Treasures article, the engine is a 225-inch Slant, with a 904 transmission bolted to it. Disassembly was a little harder than planned, as pistons number five and six were seized in the heavily rusted and pitted cylinders. By honing the visible areas of the cylinders by hand, and then hammering the pistons up and down in the cylinder, we eventually freed the pistons. The block was stripped, and during removal of the head, we learned that several of the valves needed some persuasion in their removal as well. The head, block, crankshaft, and rods were then sent to the college's automotive machine shop for the necessary machine work.
The block was decked .060-inch, and the cylinders were opened up to 3.460-inches (.060-inch oversized). The head was also milled .060 inch, and treated to a three-angle valve job. The rods were equipped with ARP rod bolts, and then resized, and new .060-inch oversized cast pistons were then hung on the rods. The factory steel crankshaft was in good condition, so it just needed a good cleaning and a polishing of the journals. The large amount of metal removed from the block's deck and the cylinder head (.120 inch total) in conjunction with a .045-inch crush head gasket, resulted in a 9.37:1 compression ratio. Although some might consider this low, it is actually a nice one-point increase in compression over the factory specs. Since the head and block were milled, the pushrods were now going to be too long. To correct this, the rocker shaft was shimmed .035-inch to correct the rocker angle and not have the valve train bind during operation.
1. The Slant Six looked a little dirty but was in complete and unmolested condition. While the engine looked good, it was later determined that the engine was seized due to the poor preparation for its storage.
2. The lack of attention led to nine of twelve valves becoming seized in their valve guides. Various attempts to free the valves were all unsuccessful, it was quickly determined the engine would have to be pulled for a complete rebuild.
3. All six cylinders were filled with a water/gas mixture. During disassembly pistons five and six were seized in their respective cylinders. It took several hours of hand honing the rust in the cylinders and then using a hammer and drift to drive the pistons up and down a little at a time.
4. The engine was bored .060-inch oversized, to restore the cylinder bores to a true round and pit free surface. The block was decked .060-inch to provide a flat surface and to increase the compression ratio slightly. The factory replacement camshaft was installed into the block in the straight up position.
5. The stock crankshaft was polished and placed back into service, and the short block was assembled to the factory specifications. The new oil pump was packed with Vaseline to help with the priming of the oiling system.
It was now time to install the engine in the Dart, and fire it up. With the engine's oil system pressurized and the fuel system primed, the key was turned and the engine jumped to life. Once running, the timing was checked, and several adjustments were made to the new 1920 Holley carburetor. The engine was run at 2,000 rpm for 30 minutes, to break-in the new camshaft and tappets. The oil pressure remained constant during the entire break in period, and after the break in, the valve lash was checked. Once everything was checked, the Dart was taken for a little spin around the campus. The engine temperature remained steady and on the cooler side, and the Dart had nice acceleration. Back at the shop, the fluid levels were checked again, and the Dart was inspected for any problems or leaks. Everything looked good, and it was time to test the new engine on the dyno.
With the Dart strapped to the chassis dyno, the engine brought up to operating temperature. Everything looked good so we let it fly. With very conservative ignition timing (initial timing was set to 5 degrees BTDC, but the distributor advance slots had been modified to limit the advance, so the total timing was only 19 degrees BTDC), the engine was run at WOT from 1,500 rpm to 4,000 rpm. This gave us a torque reading of 123.683 lb/ft. of torque at 3,150 rpm, and 77.936 horsepower at 3,500 rpm. So now we have a baseline for the start of the aftermarket bolt-on components class.
| PRICE TAG
|Master Rebuild Kit*
|Ignition Control Box
|Ignition Wiring Harness
|ARP Rod Bolts
|Mopar Paint (Red) (4@$8.99)
|Holley 1920 (Reman)
|Intake Valves (6)
|Exhaust Valves (6)
|Valve Springs (12)
|Champion Spark Plugs (6@$1.79)
*Master Rebuild Kit Included: Pistons, Rings, Gaskets, Cam Bearings, Rod Bearings, Main Bearings, Oil Pump, Freeze Plugs, Camshaft, Solid Lifters, Pre-lube, and Timing Set. All machine work was handled at Penn College's machine shop. Block decking, head milling, rod resizing, new guides, valve seat prep
6. The cast pistons were part of a master overhaul kit from Napa. They were attached to the reconditioned connecting rods, and installed.
7. When it came time for a camshaft, a conservative stick was chosen. The Mopar cam has .406 /.4140inch lift, and an advertised duration of 244 /244 degrees.
8. With the addition of the reconditioned head, the long block is complete. The head was also milled .060 inch, and given a three-angle valve job. New valvesprings were installed, and the factory rockers and shafts were cleaned and re-used. With all the decking and milling work performed on the block and head (.120-inch removed) the rocker shafts were shimmed .035-inch to reestablish the correct rocker geometry. The compression ratio was raised to a pump gas friendly 9.37:1.
9. The rebuild is complete, with the addition of the Mopar Performance orange box electronic ignition, the engine oiling system was primed and all the fluids topped off. A new battery was placed on the battery tray and attached to the battery cables. The carburetor is a remanned Holley 1920 with the same part number as the original. The break-in of the engine was successful and a quick test drive was encouraging as the Dart drove very well and there were no strange noises or leaks.
10. In the car, and on Penn College's Mustang chassis dyno, the initial numbers for the Dart's 225 were 123.683 lb-ft of torque at 2,800 rpm, and 77.926 horsepower at 3,600 rpm. Now that the baseline has been established it is time to improve upon the combination with readily available aftermarket parts while maintaining a streetable pump gas compatible engine. We're thinking that a performance camshaft, and intake and carburetor should be next. What do you think?