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Practical Engine Building: Assembly Related Failures

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Assembly Related Failures

04.21

00:00 - A common yet easily avoidable reason for engine failure, is those failures that occur as a result of incorrect assembly processes.
00:09 There are literally too many options here to consider.
00:12 Everything from inadequate clearances, to incorrectly fitted piston rings, incorrect fastener torque, and improper bearing installation.
00:21 It's my expectation that at the end of this course, you'll be able to avoid these sorts of failures, but it's still worth spending some time here to cover the most common failure modes that could be attributed to assembly error.
00:36 By far the most common failure I've seen that falls into this class, is simply getting the engine's clearances wrong.
00:43 This could include bearing clearances, ring end gaps, piston to bore clearance, or piston to head and piston to valve clearances.
00:53 A common reason for these sorts of failures simply comes down to not checking every measurement and clearance prior to assembly.
01:02 Instead many engine builders assume that the machinist has performed their work correctly and blindly assemble the engine without performing any further checks.
01:12 One of the key areas here is in regard to clearances between the piston and the valves.
01:18 While understandably we shouldn't need to be concerned with this if we're using stock parts, any time an aftermarket cam is used, a different piston crown profile is fitted, or larger diameter valves are being installed, the piston to valve clearance needs to be checked and confirmed.
01:36 This process will be demonstrated later in the course if you don't know how.
01:41 The next area that we will discuss is when the engine components are damaged during installation and this is not picked up at the time.
01:49 The components we're dealing with are very sensitive and easy to damage.
01:54 This may include a crankshaft journal being nipped or marked by the conrod while the piston and rod assembly are being installed, a ring being bent or damaged during installation onto the piston, or as the piston is installed into the cylinder, or a bearing shell being dropped or damaged prior to installation.
02:15 Any of these scenarios may result in damage that can escalate quickly once the engine is started for the first time and cause extensive damage to your freshly built engine.
02:26 Generally these sorts of failures are going to become evident very quickly and will often show up during the running in process.
02:34 You're unlikely for example to find these sorts of problems become evident after the engine has completed several thousand miles of running.
02:43 You're also likely to be looking at an isolated failure that's centred on just the component that's being damaged which would normally make it relatively simple to decide what the cause has been.
02:56 Another issue that can be introduced during assembly is dirt or debris and we've covered these failures in a separate module.
03:05 The solution to these assembly related failures is already covered thoroughly in this course as well as our engine building fundamentals course, and simply comes down to understanding the underlying principals of engine building, and then careful and methodical application of these principals during the assembly process.
03:26 Never rush the assembly process and always double check your measurements so that you can be 100% confident everything is perfect.
03:36 Some of the warning signs that you should look out for include parts that don't go together smoothly or easily as normal.
03:44 Perhaps one particular piston required more force to assemble it into the block for example.
03:50 This may be a sign that a ring isn't located correctly, and I'd take the extra time to remove the piston and carefully inspect it and the ring pack for any signs of damage.
04:03 Likewise it's always a good idea to develop your own feel for what's normal.