Practical Engine Building: Step 2: Stripping and Inspecting
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Step 2: Stripping and Inspecting
11.38
| 00:00 | - Now we can move onto the second step of our process which is engine disassembly and inspection. |
| 00:05 | And this is an often overlooked aspect of engine building. |
| 00:10 | Often an engine will be hurredly stripped so that it can be sent out for machine work, only to find that a problem with the base components becomes apparent when the time comes to reassemble the engine. |
| 00:22 | This can waste both time and money, but more importantly it can also result in premature failure of the freshly rebuilt engine. |
| 00:31 | In the perfect world we'll be starting our disassembly with a complete long block. |
| 00:36 | In this case we want to go through a methodical approach to stripping the block down into component form. |
| 00:43 | Keeping track of all components and fasteners during this process is really important and there's nothing more frustrating than wasting hours, looking for a specific bolt when you're completing your final assembly later in the process. |
| 00:58 | To help organise my engine parts during disassembly, I keep a selection of clear plastic snaplock bags on hand. |
| 01:05 | These are the sort of bags you'd use to store sandwiches in and can be purchased cheaply from a supermarket. |
| 01:12 | I'll also keep a sharpie marker on hand, and this allows me to group parts or fasteners together, and then label the bag so it's obvious when it comes time to reassemble. |
| 01:23 | For example I might remove all of the bolts holding the front cover assembly to the engine block and store these in a single bag labelled front cover. |
| 01:33 | It might be tempting to be a little more conservative with the bagging of parts like this and perhaps store all of the fasteners from the outside of the block in a single bag. |
| 01:43 | While there's nothing specifically wrong with doing so, I personally find that if you're a little bit more specific with the location of the bolts and fasteners, it will make the assembly that much easier. |
| 01:56 | There's no right or wrong way of approaching this and it's really up to the individual but I'd recommend you develop your own preferred technique and stick to it early in your engine building career. |
| 02:08 | You'll be thankful later, particularly if you've got multiple engines disassembled at the same time. |
| 02:15 | When we disassemble the engine, the amount of attention we need to give it, will depend on what we're intending to do to it. |
| 02:22 | For example if you're replacing the stock pistons and conrods with aftermarket components, then it doesn't make much sense to waste time thoroughly inspecting the original components for faults. |
| 02:34 | Even in this situation I'd still recommend a general inspection for condition and in particular I'd be looking for signs of tune related issues such as broken ring lands and detonation damage to the piston crowns. |
| 02:48 | If the same tuner is retained then you may be able to expect a similar result from your freshly built engine. |
| 02:55 | If you're retaining the engine components, then a more thorough inspection is required. |
| 03:00 | Here I'd be looking for signs of damage to the piston such as detonation damage to the crown and top ring land, and any visible cracking to the piston ring lands, or around the pin bosses. |
| 03:13 | It's also a good idea to confirm that the rings are able to move freely in the ring grooves. |
| 03:19 | While I'm inspecting the pistons, I'll also be carefully looking for any signs that they may have contacted either the valves or the cylinder head. |
| 03:28 | In particular I'll be looking for any witness marks around the valve pockets as well as around the crown of the piston where it may be likely to contact the squish pads in the cylinder head. |
| 03:39 | If the pistons are showing any signs of detonation, then we also want to carefully inspect the cylinder head surface in the matching locations, and look for signs of pitting from detonation here. |
| 03:51 | This is easy to overlook and it can require the head surface to be decked to remove this damage. |
| 03:58 | In severe cases it can result in the head becoming soft in this area, rendering it useless. |
| 04:05 | When the pistons are removed from the conrods, we want to check the condition of the wrist pin bore and make sure there's no significant wear. |
| 04:13 | In high power or high RPM applications, it's common for the wrist pin to flex in the wrist pin boss, causing wear. |
| 04:21 | This may also bend the wrist pin, so these may need to be inspected too. |
| 04:27 | I always test fit a wrist pin back into the piston after the rod has been removed, and ensure it still exhibits a good fit, and still rotates smoothly in the piston. |
| 04:38 | In severe cases you may find that the wrist pin bore in the piston is actually out of alignment by a few thou which may make it difficult to assemble the wrist pin into the piston. |
| 04:50 | The conrods should be visually inspected, particularly with regard to the condition of the big end bearings, and the condition of the bushing in the small end of the rod. |
| 05:00 | We're looking for any sign of lubrication issues here. |
| 05:03 | It's possible that the conrods may become bent if you're close to exceeding their strength in a particular application, however unless the bend is significant, you may not be able to easily see this by eye. |
| 05:17 | A basic check that we can do in the workshop if the small end and the big end of the rod are the same width, is to assemble the two rods onto a single wrist pin and swing one conrod past the other, while ensuring the small ends are butted together tightly. |
| 05:33 | If either rod is bent then the big ends of the conrod will clash into each other, rather than sliding past each other. |
| 05:40 | Regardless of this test the rods will be inspected in more detail by the engine machinist, but right now we're looking for major or obvious issues. |
| 05:50 | When we remove the crankshaft from the block we want to take careful note of the condition of the bearings and the journal surfaces of the crankshaft. |
| 05:58 | If there is sign of damage to the bearings then it may require corrective work to the crankshaft. |
| 06:04 | If there is scoring on the crankshaft journals that you can feel when you run your fingernail across the journal, this at a minimum will require the journals to be polished, but it can also require the crankshaft to be ground to undersize or replaced if it's been previously ground. |
| 06:21 | In high power and high RPM applications, we also want to take note of the wear pattern on the bearing surfaces. |
| 06:29 | While we may think of the block and the crankshaft as being rigid components that don't flex, in operation many would be surprised just how much these components move around. |
| 06:40 | This can initially show up as light polishing on the outside edges of the main bearings, and may be an indication that a small amount of additional clearance may be beneficial. |
| 06:52 | If the engine has suffered from a bearing failure, then this is going to have a large impact on our requirements. |
| 06:58 | In particular the bearing material will end up distributed throughout the entire oiling system and this needs to be accounted for, particularly if the engine is fitted with an oil cooler. |
| 07:10 | This goes for oil to air and oil to water heat exchangers. |
| 07:14 | The bearing particles from the damaged bearing will end up stuck in the matrix of the heat exchanger and can end up contaminating your freshly built engine. |
| 07:24 | The result is that the new engine can succumb to an unexplained bearing failure almost immediately. |
| 07:31 | I've yet to find a cleaning technique for oil coolers that I'm confident with and my technique is simply to replace these components with brand new units. |
| 07:41 | It may seem like an unnecessary expense, however I can guarantee it will be cheaper than rebuilding the engine again. |
| 07:49 | When the main bearing caps or cradle are removed from the block it's also advisable to inspect the mating surfaces for signs of fretting. |
| 07:58 | Fretting occurs where the two surfaces rub gently against each other as a result of the cap being essentially partially lifted off the block under heavy load. |
| 08:09 | The result is that material will be removed from the mating surface of the cap and the block, leaving a slight surface irregularity. |
| 08:17 | In mild cases this is nothing to worry about and for example it's common to see signs of mild fretting between the two halves of a Subaru block even if the engine is 100% stock. |
| 08:29 | In more severe cases this can affect the location and register of the caps in the block as well as potentially affecting the crush on the bearing shells and consequently the oil clearances. |
| 08:41 | Severe fretting may indicate that upgraded fasteners are required and it may also require the mating surfaces to be machined and the bearing tunnel to be line bored during machining. |
| 08:53 | The other area that's worth investigating during disassembly is the condition of the head gasket as well as the mating surfaces of the block and the cylinder head. |
| 09:04 | What we're looking for here is any sign that the head gasket has been leaking combustion pressure, and this will normally be apparent by a dark staining or marking on the head gasket surface, as well as potentially the block or the head. |
| 09:18 | The most common place to see this is between the head bolts and the staining will extend out towards the water jacket. |
| 09:26 | This may affect the surface of the head and block, requiring these to be machined flat in order to achieve a good seal with a new head gasket when the engine is reassembled. |
| 09:37 | If the gasket has been leaking for some time, it may also cause the head to become soft, which can mean that the head may need to be replaced. |
| 09:46 | If you're dealing with a push rod engine then the block will also house the camshaft and the lifters. |
| 09:52 | Particularly if you're going to be reusing the existing parts, and the engine uses a flat tappet style lifter, it's important to make sure you keep track of which lifter came from which location. |
| 10:05 | The lifters tend to wear to the cam lobe, and hence you want to make sure that they go back in the same location. |
| 10:12 | With a flat tappet lifter it's also advisable to inspect the surface of the tappet to check on its condition. |
| 10:19 | What you're looking for here is a smooth surface with no signs of wear. |
| 10:24 | The lifters should rotate in the lifter bores during operation to ensure that the interface between the cam lobe and the lifter is continually lubricated and doesn't wear. |
| 10:35 | If the lifter doesn't rotate however, you're likely to see heavy wear marks. |
| 10:41 | It's also common to see the lifter worn in a concave shape which indicates a lubrication problem or an incorrect break in procedure. |
| 10:50 | Either way if the lifters are exhibiting wear, they'll need to be resurfaced or replaced. |
| 10:56 | As you can see there's more to the disassembly process than stripping the engine and sending it straight out to the machinist. |
| 11:03 | Spending some time here to thoroughly inspect the components will tell you a lot about how the engine has been treated, what went wrong with it if it suffered a failure, and any additional parts that you may require or additional measures you may want to consider when it comes time to put the engine back together. |
