To get started a truing stand of sorts needs to be set up. This doesn’t have to be anything special and I used a bench vice, adjuster block, rear axle, spacers, a series of old bearings and washers, and the axle nut. The reason I went to the trouble of clamping the hub in place was to eliminate any possibility of the hub sliding back and forth on the rim, which would make my truing efforts difficult.
In my last blog post I covered how to lace up a wheel assembly with new spokes. This week I’ll discuss how to properly true the rim. Truing the rim is actually not too difficult. Once you understand the interaction between the spokes and rim, you will make quick work of the job.
To get started a truing stand of sorts needs to be set up. This doesn’t have to be anything special and I used a bench vice, adjuster block, rear axle, spacers, a series of old bearings and washers, and the axle nut. The reason I went to the trouble of clamping the hub in place was to eliminate any possibility of the hub sliding back and forth on the rim, which would make my truing efforts difficult.
How many of you become disheartened when spokes break, bend, or a rim becomes permanently damaged necessitating a rebuild of the wheel? I know a lot of people think rim building is a black art and are willing to shell out serious dough to avoid the job altogether. This week I want to debunk the black art of wheel building and provide you with an overview of the process, allowing you to take on your next wheel build yourself. Next week, I’ll cover the second half of the project by showing you how to true the wheel.
As you can see I have a great example of a wheel assembly that is way past its prime. The spokes are bent, loose, and the nipples are mostly all stuck. On top of that, the rim is cracked in a couple spots necessitating further repairs.
Last week I talked about what a compression test is, touched on some of the finer details you should know about when performing a compression test, and provided information on when it makes the most sense to perform a compression test. This week I’m going to wrap up compression testing by providing a step-by-step write up on how to perform a compression test.
Before getting into the step by step how-to a reader left a comment asking for further information on compression testing bikes with electric starters. I actually believe electric start bikes are easier to test than kick start bikes because the rate at which the engine is turning over is more consistent. My recommendation would be to engage the starter for a set period of time. Around 5 - 10 seconds is usually enough time to crank the engine over sufficiently and obtain an accurate reading. When performing the test you will notice the readings on the pressure gauge will be much more consistent as the engine is turning over compared to what you see on kick start engines. The battery should also be fully charged and in good condition. Apart from using a good battery and establishing a time period where the starter is engaged there isn't much more to it.
For clarity, the above tips are only for single cylinder engines. For multi-cylinder engines additional considerations and precautions need to be taken to ensure the engine doesn't start while performing the compression test. All plug leads will need to be disconnected. If the engine is fuel injected disconnecting the fuel pump or injectors is a good idea too so that fuel doesn't build up in the cylinders or inlet tracts after repeating the compression test for each of the cylinders. For multi-cylinder engines the compression readings should be compared across cylinders. As a rule of thumb if there is a 20% difference across cylinders further diagnostic work should be carried out to determine what the problem may be.
Most modern clutches incorporate rubber dampers which help reduce torque fluctuations through an engine’s drivetrain. Single cylinder engines (four-strokes especially) have high peak torque fluctuations since they only fire once every fourth stroke. The dampers situated between the clutch driven gear and clutch basket help smooth out the delivery of power to the gearbox and rear wheel.
The rubber dampers wear out from normal use and in most cases can be replaced. Replacement of the dampers is a fraction of the cost of buying a new clutch basket, does not require a lot of special tools, and you aren’t out anything if the project doesn’t go as planned. Before I get into the details of replacing the dampers, you are probably wondering how you can tell the dampers are worn out. When the engine is running some additional gear noise coming from the clutch may be noted, but honestly this is a problem difficult to diagnose when the engine is together. Finding this problem is much more likely when servicing the clutch pack or performing other work on the engine. The easiest way to determine if the dampers have worn is by trying to rotate the clutch gear independently from the clutch basket. Depending on how worn the dampers are this may take a little bit of force, so it is best to lock out the clutch gear and primary drive gear. Once locked, the basket can be rotated back and forth to check for free play. Alternatively the clutch gear can be clamped in the soft jaws of a vice while trying to rotate the basket back and forth. The clutch basket should not move independently from the clutch gear. In the first photo note the alignment marks are perfectly aligned. In the second photo the marks have shifted about an ⅛” (3mm). This may not look like much, but it will feel like a lot when you twist the basket.
A lot of folks have inquired about compression testing and how to do them. I want to share my thoughts on compression testing with you, as well as provide you with a detailed write up on how to perform one. I’ll cover this topic in a two part series. If you want more in-depth information on the subject, I’d highly recommend grabbing a copy of my book, The Four Stroke Dirt Bike Engine Building Handbook, which has a great deal more of information on diagnosing engine problems and how to rebuild.
In this first part of the series I’m going to provide a general overview and discuss some of the finer details regarding compression testing that can be overlooked. In the second part I’ll show you how to perform a compression test. What is a compression test? A compression test measures the peak pressure in the engine’s cylinder as the engine is turned over, or a reduced cylinder pressure value if the engine is equipped with a decompression system. How many of you have a service manual for the dirt bike you currently own? If not, do you know where to buy one? An OEM service manual is by far one of the most important tools you can get for your bike and this week I want to talk about where you should get them.
Alright, let's get to it. This week for our Q&A post I’m going to cover the dreaded process of removing broken off bolts from their stuck fortresses. An outline of the process usually entails saying your favorite cursory phrase, repeating this phrase numerous times, then trying to use an extraction tool to get the broken off bolt out. The success of this endeavor varies widely depending on the situation, however I’ll attempt to share some helpful tips with you in case you find yourself in a jam.
Alright guys, it's time to let us know what you think. We are just a few weeks away from launching the Four Stroke Dirt Bike Engine Building print book and we need to decide on a cover. Which should it be?
This week in our Q & A series I’m going to spend some time discussing solutions for repairing damaged threaded holes that occur when rebuilding your dirt bike engine. Hopefully you never have to use any of my solutions, but if you’ve been around dirt bikes long enough repairing damaged bolt holes is an inconvenient truth. Whether you have bought a used bike from a ham fisted previous owner or you buggered up a threaded hole yourself, let’s take a look at how they can be fixed as well as how damaging threads can be avoided in the first place.
Why do Threads Strip or Get Damaged? Over-tightening, cross-threading, installing bolts with dirty threads, and installing the wrong bolt in the intended hole are the primary reasons a threaded hole will become damaged or completely stripped. Most fasteners used on dirt bikes are comprised of a steel alloy and they thread into aluminum holes. This combination of hard and soft materials used to fasten joints leaves the threaded hole particularly susceptible to stripping if the bolt is over-tightened beyond the specified torque spec. Since the aluminum is the weaker of the two materials used in the joint, the aluminum will yield long before the steel bolt is affected, resulting in the stripping of the threads. This post was originally published on ThumperTalk and can be viewed by clicking here. As we wrap up this final post on precision measuring from my Engine Building Series, I would love to take a moment and tell you a little bit about the book I just published, The Four Stroke Dirt Bike Engine Building Handbook. As someone who has been following the DIY Moto Fix Engine Building Series posts, I think you're going to love the in-depth knowledge and information provided in this book on dirt bike engine building. The Four Stroke Dirt Bike Engine Building Handbook provides incredible insight on the process of building a four stroke dirt bike engine. I wanted to bring at-home mechanics the level of expertise present in the industry when it comes to engine building, and do it in a way that is accessible and easy to understand. This book is presented in a format that helps both beginners and experts. I not only write about the correct way to rebuild your engine, but also present the technical reasons why things are done the way they are in the engine building world. In addition, I supply information not found in service manuals for building high performance racing engines. Reading this book will also prevent you from making crucial mistakes that many at-home mechanics unknowingly suffer from when rebuilding. Writing this book has been such a blast and I know you will benefit from its immense value if you are planning a rebuild. Here are a few pages from the book to give you a sneak peak on the massive amount of technical content provided for dirt bike engine building enthusiasts. The Four Stroke Dirt Bike Engine Building Handbook is available in both an eBook format and a printed and bound version. Check the book out and learn more by clicking here. Thanks so much for your support and enthusiasm for DIY Moto Fix. Read on for my final post on utilizing the remaining six precision measuring tools. PlastigaugePlastigauge is one of the only measurement tools you won’t mind throwing away once you are done using it. Plastigauge is a measurement tool used to check the clearance between parts. The plastigauge consists of little strips of plastic which are inserted between two parts. Once assembled the plastic strip is compressed. The amount the strip compresses can be measured and correlated to a chart (supplied with the plastigauge) which defines the clearance for the measured compressed width of the strip. For engine building purposes plastigauge is ideal for checking clearances between engine components utilizing plain bearings. The plastigauge is a great tool for confirming clearance and measurements. Another plus is that unlike most other measuring tools, plastigauge is cheap! Plastigauge is usually sold in an assortment of sizes which cover multiple clearance ranges. Plastigauge strips will come in different diameters and each diameter will be capable of measuring a certain clearance range.
Where to Use: Examples include cam to cam journal clearance, crank bearing to crankshaft journal clearance, and crank pin to rod bearing clearance. Calibrating Plastigauge Finally a measurement tool where no calibration is necessary. Just make sure you choose the appropriate size strip for your application. Also make sure the plastigauge is fairly new. Plastigauge does get old after awhile and using old plastigauge may not yield accurate results. Reading Plastigauge 1. After the plastigauge has been compressed use a calipers to measure the width of the compressed strip. |
InspirationsCategories
All
Archives
November 2022
Favorite Films |