V8 Engine - a free 3D model from Shapekit

A V8 you can watch from the inside. Turn the handle on the front pulley and the crankshaft drives eight pistons through their rods, while two gears turn the camshaft at half speed. The cam lobes push sixteen lifters and pushrods, the rockers tip and the valves open and close, cylinder by cylinder, in the 1-8-4-3-6-5-7-2 firing order of a small-block. The barrels are cut open so you see the pistons, the crankcase is open underneath, and there are no valve covers, so every valve is in sight. Eight velocity stacks and a distributor finish it off. It stands on its own stand, and every part prints without supports.

Parts (each STL is already placed the right way up for printing)
- v8-engine-block.stl: Both cylinder banks at 90°, five main bulkheads, the camshaft tunnel and two rails for the lifters. Each barrel has a window on the outside so you can see its piston, and the crankcase is open between the bulkheads. Print: Standing on its bottom rails, no supports: the banks lean 45° and every hole prints round or pointed.
- v8-engine-main-cap.stl (print 5): Holds the crankshaft in the block: one under each bulkhead, two M3 × 20 screws each. Print: Flat face on the bed.
- v8-engine-head.stl (print 2): Valve seats and guides, spring seats, holes for the pushrods, four pedestals for the rocker shaft, exhaust ports and spark plugs on the outside and intake spigots on the valley side. The same part fits both banks, turned round. Eight M3 × 20 screws hold it on. Print: Face down (the side that sits on the block). No supports.
- v8-engine-crank-nose.stl: The front main journal and the D-shaped snout that takes the timing gear and the pulley. Print: Snout down, standing up.
- v8-engine-crank-throw.stl (print 4): A web with its counterweight and a crank pin, which carries two rods. Its keys only go together one way, so the four pins end up at 0°, 90°, 270° and 180°. Print: Web down, pin up.
- v8-engine-crank-web-1.stl: The web behind pin 1, with the next main journal. One dot on the counterweight. Print: Web down, journal up.
- v8-engine-crank-web-2.stl: The web behind pin 2. Two dots; its key is turned 180°. Print: Web down, journal up.
- v8-engine-crank-web-3.stl: The web behind pin 3. Three dots; its key is turned 270°. Print: Web down, journal up.
- v8-engine-crank-web-4.stl: The last web, with the rear main journal and the snout for the flywheel. Four dots. Print: Web down, journal up.
- v8-engine-rod.stl (print 8): 48 mm between centres. The big end slides onto a crank pin before the next web goes on. Print: Flat on its side.
- v8-engine-piston.stl (print 8): Ø29.4 mm in a Ø30 mm bore, with two ring grooves and bosses for the wrist pin. Print: Crown down.
- v8-engine-wrist-pin.stl (print 8): Ø4.8 mm: a snug push fit in the piston, free in the rod. Print: Lying down, on its flat.
- v8-engine-camshaft.stl: Sixteen lobes, one for each valve, on five journals. It slides into the block from the front and turns once for every two turns of the crankshaft. Print: Standing on its back end, with a brim: it is 172 mm tall.
- v8-engine-cam-gear.stl: 32 teeth on the front of the camshaft. Its dot faces the dot on the crank gear. Print: Back face down.
- v8-engine-crank-gear.stl: 16 teeth on the crankshaft snout: it drives the cam gear at half speed. Print: Flat.
- v8-engine-pulley.stl: The front pulley, with the handle you turn the engine by. Print: Back face down, handle up.
- v8-engine-flywheel.stl: The flywheel with its starter ring, on the back of the crankshaft. Print: Back face down.
- v8-engine-lifter.stl (print 16): Flat-bottomed tappet that rides on a cam lobe, with a cup for the pushrod. Print: Standing on its foot.
- v8-engine-pushrod.stl (print 16): Ø3 mm with round ends, from the lifter up through the head to the rocker. Print: Lying on its flat. A brim or a glue stick helps it stay down.
- v8-engine-rocker.stl (print 16): 1.5 : 1 rocker arm: the pushrod lifts one end and the pad on the other end opens the valve. Print: On its side.
- v8-engine-valve.stl (print 16): Ø10 mm head on a Ø3.4 mm stem, with a groove at the top for the retainer. It opens 2.2 mm. Print: Standing on its head. Print them all at once so each layer has time to cool.
- v8-engine-retainer.stl (print 16): A small washer with a slot: it slides sideways into the groove on the valve stem and holds the spring. Print: Flat.
- v8-engine-rocker-shaft.stl (print 2): Ø5 mm, through the four pedestals and eight rockers of one head. Print: Lying on its flat.
- v8-engine-velocity-stack.stl (print 8): An intake trumpet. It slides over the spigot on the head. Print: Standing on its base.
- v8-engine-distributor.stl: For the looks: a distributor with eight towers, pushed onto the peg at the back of the block. Print: Standing on its base.
- v8-engine-stand.stl: A base with two cradles. The engine sits on four pegs and lifts off when you want to show the inside. Print: Flat on the bed, no supports. It needs a 220 × 150 mm bed.

Also needed (not printed)
- 16 small compression springs for the valves: about 5 mm outside (at most 6, at least 4 inside), 0.5 mm wire, 12 to 15 mm long. A spring assortment box usually has them.
- 26 M3 × 20 screws: 10 for the main caps and 16 for the heads. They cut their own thread in the plastic.
- A drop of superglue for the crankshaft keys, and a little grease or silicone spray for the bores and the cam.

Print settings: 0.4 mm nozzle, 0.20 mm layer height (0.12 mm for the small valve train parts), 3 walls, 15% gyroid infill, PLA or PETG material.

Assembly
1. Print the parts: Nothing needs supports. Print the camshaft standing on its back end with a brim, and the valves, pushrods and retainers in batches. Clean any elephant's foot off the pins, journals and keys so they slide.
2. Pistons and rods: Push a wrist pin through a piston and the small end of a rod, so it sits in the middle. Make eight.
3. Build the crankshaft: Glue the first crank throw onto the nose. Slide the rod for cylinder 1 and then the one for cylinder 2 onto its pin, then glue crank web 1 (one dot) onto the pin's key. Carry on the same way: throw, two rods, web 2, throw, two rods, web 3, throw, two rods, web 4. The keys only fit one way, so the pins end up at the right angles.
4. Fit it in the block: Lay the block on its back. Lower the crankshaft in and guide each piston into its bore; the bores have a lead-in at the bottom. Put on the five main caps with two M3 × 20 each and check that the crankshaft turns freely.
5. Camshaft and gears: Slide the camshaft into the tunnel from the front. Turn the crankshaft until the dot on the crank gear points up, push the gear onto the snout, and fit the cam gear on the camshaft with its dot facing the first one. Then the pulley and, at the back, the flywheel.
6. Valves in the heads: Push a valve up through each seat, put a spring over the stem on top and press it down until you can slide a retainer into the groove. Drop the sixteen lifters into the rails in the valley.
7. Heads, pushrods and rockers: Screw each head onto its bank with eight M3 × 20. Drop a pushrod through each hole until it sits in its lifter. Slide the rocker shaft through the pedestals, threading on the rockers so that each cup sits over its pushrod.
8. Finish it: Push the velocity stacks onto their spigots and the distributor onto its peg, and set the engine on the stand. Turn the handle clockwise, as seen from the front, and watch the valves open in the firing order.

Safety: The engine has many small parts: keep them away from small children.

License: Creative Commons Attribution-NonCommercial 4.0 (CC BY-NC 4.0)
https://creativecommons.org/licenses/by-nc/4.0/
Print it, remix it and share it, as long as you credit Shapekit and don't sell the files or the prints.
