Practical Engine Building: Step 7: Short Block Assembly
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Step 7: Short Block Assembly
06.17
| 00:00 | - Now we're finally at the point where we can begin the assembly process of the engine short block. |
| 00:05 | The short block consists of the engine block, and internal components, minus the cylinder head. |
| 00:11 | This step is one of the largest steps in the process, and for simplicity we can actually break it down further into a number of smaller steps which we're going to go through here. |
| 00:22 | The first step before we actually fit parts into the engine block however is to confirm all of the clearances match what we require. |
| 00:32 | This is an area that many engine builders leave to chance, assuming that the machinist has performed their task correctly. |
| 00:40 | Ultimately it's always the responsibility of the person assembling the engine to ensure that everything is correct and to their liking, so don't take chances here. |
| 00:50 | The critical clearances we need to measure and confirm include the piston to bore clearance, and the bearing oil clearances for the main and big end bearings. |
| 01:00 | While we're at it we also want to check the condition of the bores, looking for any sign that the bores are out of round or tapered. |
| 01:08 | We also want to check and confirm that the thrust clearances of the crankshaft is within specification. |
| 01:15 | You can refer back to the relevant modules in the practical engine building skills section for information on how to complete these tasks. |
| 01:24 | An often overlooked clearance that we also need to check is the side clearance between the big end of the conrod and the crankshaft. |
| 01:33 | This can be checked with the conrod assembled on the crankshaft by sliding a feeler blade between the conrod and the crank. |
| 01:41 | This shouldn't be a concern with stock components but I've dealt with a few sets of aftermarket conrods where the clearance has been too tight, and the conrod needed to be machined to achieve sufficient clearance. |
| 01:54 | If any of the clearances are outside of specification, this will usually require another trip to the machinist for corrective work. |
| 02:03 | Obviously if the clearance is excessive, then this is a little bit harder to correct, and may require new or different parts. |
| 02:11 | This might not be an ideal situation however finding this out now prior to assembly will avoid potentially much more expensive problems later. |
| 02:21 | As an aside I find that when your machinist realises that you'll be double checking all of their clearances, they will tend to provide you with a better product as they don't want to be shown up. |
| 02:33 | Our next steps include filing the piston ring end gaps to suit your particular application, fitting the pistons onto the conrods, and then installing the rings onto the pistons. |
| 02:44 | Again you can refer to the relevant practical engine building skills module in the course for more information on these processes. |
| 02:53 | With the piston and conrod assemblies ready to go, we can now fit the crankshaft into the engine block for the final time before moving onto the last step, where we can fit the piston and conrods into place to complete the installation of the rotating assembly. |
| 03:10 | If you're building an engine that uses parts that deviate significantly from the specs of the factory parts, such as high compression pistons, or agressive cam profiles, then it can be a sensible option to perform a dummy assembly where the parts are trial fitted to check aspects such as valve to piston and piston to head clearance. |
| 03:31 | In this instance it would be normal to leave the rings off the pistons and only temporarily fit the wrist pin to make it faster to disassemble the components if corrective work is required. |
| 03:44 | The dummy assembly is also important when you're fitting a stroker crankshaft or larger aftermarket rods to ensure that there's no interference between the conrods and the block. |
| 03:55 | Often a dummy assembly will involve just the piston and rod from one cylinder to confirm clearances, and then any corrective work will be applied to the remaining components before final assembly. |
| 04:08 | For complete accuracy and thoroughness though, it's always better to perform a complete dummy assembly and confirm clearances on every cylinder. |
| 04:19 | If you're assembling a push rod engine, then the block will also house the camshaft and the lifters, so these need to be installed before we can move on. |
| 04:28 | The camshaft will be housed in its own set of bearings and these need to be inspected and replaced if required. |
| 04:36 | While replacing the cam bearings is not an impossible task to complete at home, it does require some specialist equipment, and requires care to ensure that the oiling holes in the bearing shells align correctly with the oil galleries in the block. |
| 04:52 | For this reason I'd recommend asking your machinist to complete this task for you during the machining process. |
| 04:59 | It'll add a minimal amount to your bill, and you can then be confident that the bearings are installed correctly. |
| 05:06 | The lifters locate in lifter bores and run against the camshaft. |
| 05:11 | There's a variety of types of lifter ranging from flat tappet hydraulic lifters, through to mechanical roller style lifters, which would be a common choice for a performance engine build. |
| 05:23 | Particularly if you're using a flat tappet style lifter, this does require some special attention. |
| 05:30 | For a start if you're resuing the lifters and cam, then these must be kept in the correct order, since the lifter will tend to wear to the cam lobe. |
| 05:39 | It's also important to generously lubricate the lifters and the cam lobes with a quality moly based lubricant to prevent any wear during startup. |
| 05:50 | These lifters also require some special precautions during engine break in, which we'll touch on later. |
| 05:57 | If you're replacing the cam then it's advisable to replace the lifters at the same time, so that the lifter isn't exhibiting any wear that can affect the cam lobes. |
| 06:07 | At this point the engine short block should be complete and we're ready to move onto preparing the cylinder head. |
