We're not going to lie and tell you that it's easy to build your own motor. Even though you've read other articles in the past and have seen the photos, the amount of work required to put together the engine of your dreams is quite intensive. Instead, we want to show you how to not only build your own 302 short-block, but how to turn it into a stroked behemoth with a whopping 347 cubic-inch displacement (this is relative; remember, considering the short 8.2-inch deck height.)
At first, this wasn't going to be a stroker engine buildup, but rather a 306 buildup (a 302 with a .030-inch oversize bore.) But once we saw how affordable Summit Racing Equipment's 347 kit was, we decided to go the stroker route.
Considering that the cost to machine a stock crank, prep a set of rods and to purchase new pistons, bearings and gaskets was fast approaching $900, we figured that for $600 more, we could reap the benefits of 41 more cubic inches. With Summit Racing's 347 Stroker kit (part # SUM-CSUM347KIT, $1,479.95) and a prepped production block, we ventured off into the world of backyard engine building.
Your first order of business is to locate a good block to start with. The idea here is to keep costs down (since this is a budget stroker motor) but to use the best possible production block out there. The most desirable casting years for roller cam motors are 1986-1995.
From what we understand, these blocks were virtually unchanged in alloy content and casting strength, so any of these stock HO blocks will do.
The good thing about Summit's stroker kit is that its crankshaft is machined for both two-piece and one-piece rear main seals. This allows you to use an older, non-HO block as your foundation. Some of the older high-performance 289 and 302 blocks were much beefier in the number one main area, where the later "weaker" blocks are known to crack. Again, if you have access to an older block, try to get it. But if the availability is low or the cost is prohibitive, just use any late model casting. If it hasn't been done already, tear down the whole motor to the bare block, and inspect it for cracks or damaged threads in important areas such as engine mounting pads and bellhousing bolt bosses.
With your block bare, send it to a reputable machine shop for a good bore and hone, set at 4.030 inches. A good machine shop will ask you what kind of pistons you will use so that they can match each bore for proper piston skirt-to-bore clearance. Don't forget to leave your machinist at least one of the pistons that you will be using. As a general rule of thumb, lightweight cast and hypereutectic pistons should have about .002-inch clearance and heavier forged pistons as much as .005 inches. Lightweight forged pistons (such as Wiseco, JE or Arias) will live happily with .003-005 inches. But always check with the manufacturer of your pistons to make sure what it recommends.
While you are at it, have the block fully boiled, cleaned and Magnafluxed, with new freeze-out plugs and camshaft bearings installed. If extra funds permit, a line-hone of the main saddles would be great, and a good cleanup mill of the deck surface isn't a bad idea, neither.
What You Need
Summit's 347 stroker kit is all inclusive for a complete short-block. That means that you don't have to purchase anything else to put that oil pan on. As a matter of fact, the stroker kit includes a new oil pump, a complete Fel-Pro engine gasket set, a new nodular iron Scat 3.4-stroke crankshaft, a set of H-beam 5.4-inch connecting rods (which appear to be the excellent Eagle "ESP" rods, and a set of Keith Black hypereutectic pistons in 4.030-bore sizing.
Summit states that with these pistons, compression checks in at 10:1 compression with a 64cc cylinder head. If you intend to use a power adder of some kind, perhaps an upgrade to a forged piston would be wiser. As a matter of fact, we like the Trick Flow pistons that are manufactured by Arias. They are available with a dish for 8.5:1 compression, and a flattop for 10:1 compression, and work perfectly with the Twisted Wedge heads. These pistons will add a bit to the price, but consider them mandatory if you intend to lean on the motor hard and/or may encounter any detonation. In the future, we hope Summit offers its 347 kit with a forged piston option for not much more.
No matter which way you go, keep in mind that this kit is not balanced. For the utmost in reliability, especially on high-rpm applications, spend the extra money to have the rotating assembly balanced. We didn't do so because we wanted to save a few extra bucks.
With a freshly machined block in your possession, have it safely mounted on an engine stand, and set it upside down. Hopefully, you've saved a few of the old main and rod bearings so that you can mock up the rotating assembly to see where you have to relieve the block to clear the connecting rods. Because of the added stroke, the bottoms of the cylinder bores will need to be notched. You can do it easily, provided you have the proper tools and the patience to mock up and disassemble the crank, pistons and rods. We used a permanent magic marker (if possible, use machine dye for best results) and noted where we had to grind the block for two cylinders at a time that shared a pin. The crankshaft, rods and pistons were then removed from the block, and set aside.
The most nerve-wracking part of this engine buildup (or any stroker engine buildup for that matter) is notching the block for clearance. On Ford 289/302 blocks, you need to put a notch about the size of half a nickel into the bottom wall of each bore. On cylinder number five's bore, you also need to massage the pad that mounts the oil pump. Fortunately, this boss is not a major structural member and does not flow any oil inside of it. Just notch it for clearance and forget about it.
With an air-powered rotary tool, we used a carbide bit (similar to what head porters use on cast iron) to remove copious amounts of material. With a well-lubed bit, carefully remove cast iron where you made your marks with the permanent magic marker or machine dye. Try to keep the radius of the notch smooth to prevent any potential stress risers. Once all eight bores have been clearanced, use a Dremel tool with a smooth sanding roll or a fine-grit sanding stone to massage the area. What you want to do is remove any sharp burrs from inside the bore and to again, avoid any weak areas for cracks to form.
After you've finished notching the block, you must thoroughly clean it. We cannot emphasize how important it is to thoroughly go over each passageway to remove any and all machining oils and/or metal particulates. We like to use a whole can of engine cleaner (the foaming type for more entertainment), rinse it off, and then use a brand name hand dishwashing detergent that is strong on removing grease. Lather the engine up, scrub it down with a medium to hard brush, and rinse repeatedly. If you can, get your hands on a set of brushes that are designed for engine cleaning duties. Otherwise, improvise with a set of toothbrushes, like we did, to carefully clean the main bearing saddles, lifters bores, and cylinders.
You can never have a block that is too clean. Even thought we spent nearly an hour scrubbing our block down, when it dried we still discovered some oily residue in the lifter bores. We cleaned it a second time, because we know that a dirty engine results in a failed engine down the road. Use compressed air to blow out all the excess water to prevent the formation of rust on the freshly machined bare metal surfaces. Blow out all the oil passages to make sure they are clean too. Use a lint-free towel of some sort to dry the motor off and let it sit to air-dry.
I Need You Tonight
Make sure that you have at least one friend to help you out, especially if you've never done this type of work before. It also helps to have friends that are helpful rather than playful because their corny jokes will only make you lose concentration. Have a gearhead with you while assembling the motor, not a prankster.
The piston rings that Summit provides are Speed-Pros that require filing for fit. With a trusty hand file and a feeler gauge, we set up each top ring to .019-inch clearance, and about .020-inch for the second ring. We say about because it was hard to be dead-on when it was time to file the rings. When filing the rings, make sure that you cut them flat and that they sit with a gap that is evenly spaced. Number them for each bore, and set them aside.
The pistons and connecting rods need to be assembled next. Since they are a full-floating setup, you can assemble the piston and rod combo by hand. With the pin dipped in oil, it should slide into the piston and the small end of the rod with slight resistance. Make sure it does not bind. If it binds, locate where it is binding, and use very fine sandpaper (800 grit or finer) to smooth out any obstructions or tight clearances. Also, make sure the rods and pistons are phased properly. Since the Ford small-block uses a symmetrical head port design, all the pistons have the exhaust valve notch facing the same direction as the large chamfered side of the connecting rod. Once together, number the piston and rod combo and install the rings for its respective bore.
Engine assembly is now straightforward. Simply lay down the crankshaft, and check for oil clearance. Summit provides plastigage for this operation, but if you have access to a dial bore gauge for the 2.25-inch mains, use it. Otherwise, shoot for a plastigauge reading of .002-.0025 inches. Ours registered at a hair over .002 according to the squish reference paper. Then, phase the piston rings so that the top ring and the second ring gaps are at least 90 degrees away from each other. We had the top ring face the front of the engine while the second ring faced the rear, making them 180 degrees apart. Use a high quality tapered-style piston ring compressor to install them pistons and rods for best results. Some of the foil-type ring compressors are a real pain to deal with. With the tapered-style ring compressor, a lot of hassle is removed. Just remember to get one for a 4.030-inch bore.
The remainder of the lower half assembles just like any other 5.0 bottom end. We torqued down the main caps to 80 ft./lbs. and the rod bolts to 65 ft./lbs. (when lubricated with 10W40 oil, otherwise 63 ft./lbs. when torqued with moly lube.) The oil pump then goes on, but not before its driveshaft is inserted into the distributor access hole and its gasket is laid to the block.
Well, there you have it, a home-built short-block that promises to give you more torque, more horsepower, and ultimately, more reliability. Again, if you intend to lean on it hard with a power adder, we recommend swapping the pistons over to forged units that lower the compression down from 10:1 to 8.5:1. Otherwise, Summit's 347 stroker kit is the easiest way to add cubic inches to your Mustang, without spending cubic dollars.