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THE TWO STROKE DIRT BIKE ENGINE BUILDING HANDBOOK IS HERE!

11/24/2017

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Check out the Two Stroke Dirt Bike Engine Building Handbook
I'm excited to announce that The Two Stroke Dirt Bike Engine Building Handbook  is here! We've been working incredibly hard to wrap up the last few details of this project and I'm happy to say we've finally arrived. Book printing is complete, they've arrived at our warehouse, are pre-packaged for shipment, and we've buttoned up the last of the logistical details.

Simply follow this link to grab your copy: The Two Stroke Dirt Bike Engine Building Handbook 
The eBook version of the two stroke dirt bike engine building handbook
I want to thank you all for your support and patience as we've worked to finish up the two-stroke book. When I started working on the book shortly after launching the four-stroke book I never imaged it would take as long as it did!

The two-stroke cycle is my favorite type of internal combustion process and I'm thrilled to share my knowledge on how to correctly build two-stroke dirt bike engines. As an engineer I've always been fascinated with ways in which designs can achieve a lot in terms of function while remaining simple in execution. The two-stroke engine exemplifies this by capturing a complex gas exchange process in a handful of moving parts. 
While simpler than four-stroke engines, two-stroke engines still must be meticulously assembled in order to ensure they run trouble-free and last a long time. Using the feedback we've gotten on our four-stroke book as a starting point, I set out to write a comprehensive guide that delivers all the information a builder needs to complete a major overhaul from start to finish. 

I used three different engines to ensure all the common design variants across manufactures were captured so that the reader will not have a problem tackling any engine build they encounter. 

I've also gone far beyond just capturing the rebuild process and have included chapters on important topics that must be understood in order to correctly diagnose problems, inspect parts, and reassemble the engine. Within the book you'll find info on tests used to diagnose problems, a discussion on premature wear, and a thorough how-to on using all the precision measurement tools necessary for correctly inspecting components.  
The Value Pack of the Two Stroke Dirt Bike Engine Building Handbook
While service manuals tell you when to do things, I've detailed the how and why behind the entire process of what you are doing. My goal with this book is to increase your engine building knowledge, make you a better engine builder, and explain why it's important to execute each step in a precise and predictable way.

As someone who loves tinkering and making engines perform better than stock, I included sections on performance/race engine building techniques, which cover checking/setting port timing, checking squish clearance, and checking compression ratio. 
I hope you enjoy my new two-stroke book and that it makes your life easier. For a comprehensive overview of everything the book has to offer check it out here: The Two Stroke Engine Building Handbook. 

Thanks again for all your support as we've grown DIY Moto Fix from an idea to a thriving community of riders who are passionate about making their machines perform better through their own hard work.

​-Paul
The Two Stroke Dirt Bike Engine Building Handbook
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How The Two-Stroke Exhaust System Works

11/12/2017

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How the two stroke exhaust system works
In my last post, I shared details about how the two-stroke cylinder works, in today's post I want to provide an overview of how a performance two-stroke engine's exhaust system works.

Adding a performance exhaust system can be a great way to increase power and/or alter the power delivery of an engine. I would also argue that optimizing a two-stroke engine’s exhaust system is equally as important as ensuring the cylinder’s ports are correctly designed for the given application. Not all exhaust systems are designed to do the same things, and much like cylinder port design, exhaust designs are intended to alter power in specific ways. Having a basic understanding of how an exhaust system works can go a long way when it comes to selecting the right exhaust pipe for your engine.

Two-stroke exhaust design is complicated and there are many different variables that must be considered when designing a pipe. I don’t intend to go into all of them, but I will share a few of the most critical.
two stroke exhaust layout
Each time the exhaust port opens to release spent combustion gases, pressure pulses are created. Modern pipe designs harness this pulse energy and use it to help scavenge and fill the cylinder. The process starts when a positive pressure pulse is created once the exhaust port opens and combustion gases leave the cylinder. The positive pulse travels down the pipe until it reaches the diffuser, at which point part of the pulse is inverted and reflected back towards the cylinder as a negative wave. This negative wave is very beneficial in pulling spent exhaust gases out of the cylinder and fresh mixture up through the transfer ports. The remaining positive pulse continues on its journey towards the end of the pipe where it encounters the reflector. The reflector acts as the name implies and forces the positive pulse back towards the exhaust port. Once reflected back, the pulse remains positive and, if the pipe is designed correctly, will reach the exhaust port just as the piston is about to close off the port on the compression stroke at the desired RPM for maximum power. Any fresh mixture which has escaped out the cylinder will be forced back in by the positive pressure pulse.

The tuned length of the pipe is dictated by the exhaust port timing, RPM of max power, and the speed of sound. Pulse length and amplitude are governed by the angles of the diffuser and reflector. Generally, steeper cone angles create pulses with more amplitude but shorter duration. Shallower angles generate pulses with less amplitude but longer duration. Given these variables, it is easy to see how a pipe could be tailored for specific applications. An engine converted for road racing may utilize a pipe designed for peak power which incorporates steep diffuser and reflector cone angles so that pulse amplitude is not sacrificed. This peak power would likely come at the expense of a narrowed range of power. An engine tailored for woods riding may feature a pipe with shallower cone angles, resulting in less pulse amplitude, but a broader spread of power.  

The last parameter I want to touch on is how the tailpipe, which is sometimes referred to as the stinger, influences the pipe. The tailpipe creates a flow restriction in the pipe which allows the pipe to have a certain amount of back pressure. Enlarge the tailpipe and the back pressure decreases, make it smaller and the back pressure increases. As back pressure increases or decreases, so does temperature and ultimately the speed of sound. As the speed of sound changes, so does the resonance RPM of the pipe. If the tailpipe is sized too small, cylinder scavenging will be inhibited. When this happens, the cylinder, fresh mixture, and piston will all be overheated.

While engineers and tuners can estimate starting pipe dimensions and tuned lengths, a great deal of trial and error testing is usually still necessary to fine tune the exhaust pipe and optimize the design. Unless you intend on building your own exhausts, this work will have already been done for you.

When selecting an exhaust system, you need to focus on how the exhaust alters the power curve. Exhaust systems are tailored to deliver more bottom end performance, top-end performance, or performance throughout the power curve. Selecting which system is right for you will depend on how you want your engine to perform. If you’ve chosen to modify your cylinder ports, installing an exhaust system that compliments the porting can be very beneficial.

You might be wondering about slip-on mufflers. If you’ve followed along with my explanation of how exhaust pipes work, you’ll notice I made no mention of the muffler. While the muffler can have a small effect on performance, it is not the primary factor. Upgrading a muffler is a good way to reduce weight, but there won’t be a slip-on out there which significantly increases power, in the same way, a properly designed expansion chamber can.

I hope you enjoyed this write-up on key features affecting the performance of two-stroke cylinders. As for Two Stroke Handbook news, we received our first printed proof of the book this last week! Needless to say, we are inching closer and closer to an official release date. To stay updated on The Two Stroke Dirt Bike Engine Building Handbook we created an email sign up for our readers. Click this link to sign up, see the new cover, the Table of Contents, and some sneak peek pages right from the book.

Thanks for reading and have a great rest of your week!
​

-Paul
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Sneak Peek of The Two Stroke Dirt Bike Engine Building Handbook! The Pre-sale Will Begin On...

11/4/2017

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DIY Moto Fix The Two Stroke Dirt Bike Engine Building Handbook
The DIY Moto Fix Team is pleased to announce that we received the first proof of The Two Stroke Dirt Bike Engine Building Handbook this week, so we had to get some beauty shots of the print book out in Paul's workshop to show it off to you! 

First off, this soft cover book is 8.5" x 11" and weighs over 2lbs. We are happy to bring you nearly 300 pages of engine building knowledge and over 300 highly detailed color photos. Take a look at the photos below to learn more about what's packed into the handbook. 
DIY Moto Fix The Two Stroke Dirt Bike Engine Building Handbook
The Two Stroke Dirt Bike Engine Building Handbook features an entire section dedicated to inspecting crankshafts. Within it, a comprehensive overview on how to measure runout, pinpoint surface wear, and true crankshafts is discussed. In the photo below the book is discussing the three types of crankshaft misalignment conditions that can be present on new and used crankshafts.
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The handbook covers a lot more than just engine building technique. We strove to put together a comprehensive reference that helps someone perform a major overhaul on their engine from start to finish. Here's a complete list of all the chapters that you can expect to find in the book:
  1. How To Use This Book
  2. When To Rebuild
  3. Diagnosing Trouble
  4. Leading Causes of Engine Wear and Failure
  5. What To Replace
  6. Engine Building Tools
  7. Service Manuals 
  8. Precision Measuring
  9. Your Workshop
  10. Race and Performance Engine Build Considerations
  11. An Overview of A Build
  12. Engine Teardown
  13. Inspection
  14. Final Assembly
  15. Setting Ignition Timing Dynamically
  16. Engine Break-in
  17. Maintenance Logging
  18. Closing Thoughts​
In the photo shown below, we're one page into Chapter 12 and only about halfway through the book!
DIY Moto Fix The Two Stroke Dirt Bike Engine Building Handbook
Did we mention this book is thick? We went beyond providing basic information and included more detailed explanations throughout the book. Littered within the chapters are detailed sub-sections and pop-outs that we've deemed Race Engine Engine Building Techniques, Technical Takeaways, and Hot-Tips.

Race Engine Building Techniques cover topics that would fall outside a normal engine build, but are standard practice for builders who are preparing performance engines. Race Engine Building Techniques are often lengthy in discussion and can span several pages at a time. Examples of these techniques covered in the book include: Setting and Checking Port Timing, Checking Compression Ratio, and Checking Squish Clearance. 

Technical Takeaways are sub-sections that detail the how and why behind specific engine building techniques as well as highlight the appropriate procedure for the given task. Technical Takeaways are often used to introduce repeated tasks once so that they can quickly be referenced later. Examples of Technical Takeaways include: Installing/removing bearings, tightening sequences, and retaining ring installation.

Hot-Tips are quick blurbs that fall outside the normal discussion, but can add incredible value depending on the user's specific situation. Hot-Tips also serve as a way to communicate friendly reminders of things to double check or do prior to proceeding on with the build.
DIY Moto Fix The Two Stroke Dirt Bike Engine Building Handbook
Thanks for taking a look at what The Two Stroke Dirt Bike Engine Building Handbook has to offer!
The Two Stroke Dirt Bike Engine Building Handbook

When does the pre-sale officially begin?

We are excited to announce that our pre-sale will begin on Friday, November 24th (Black Friday) and end on Monday, November 27th (Cyber Monday).

So you will have a four day window to reserve your copy - whether it be print book, eBook, or both - at 20% off the list price.

Feel free to pass this info on to a loved one so you get a holiday present you actually want! Sign up below and we'll email you the moment the 2T book pre-sale is up and running. A huge thanks to those of you who have already signed up!

To stay updated on the 2T Book Sign up below.

We will email you the moment the handbook is available for pre-sale on Friday, November 24th!

Success! Now check your email to confirm your subscription.

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Everything You Need To KNow About The Two-Stroke Cylinder

10/30/2017

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This week I want to talk about two-strokes. Today's post aims to provide an overview of the important aspects of the two-stroke cylinder and answers a couple commonly asked questions relating to cylinder modifications.

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New and Re-plated Cylinder Prep

9/18/2017

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New and re-plated cylinder prep for a dirt bike
Today I want to share some pointers on preparing new or re-plated cylinders that will help ensure your engines run stronger and last longer. 

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Help! Dirt Bike Only Starts When Pushed

3/13/2017

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What does it mean if dirt bike only starts when pushed
​Today I want to talk about a situation I hear all too often. Someone’s bike, whether it be a two-stroke or four-stroke, only starts when it is pushed.

Before I discuss potential causes for this scenario, take a moment to think through the situation yourself.

What mechanical factors would result in either a two-stroke or four-stroke only starting when it is bump started?

In either case, the reason the engine is able to start when it is push started is because it is able to build more compression than it otherwise could when it is kicked or the electric starter is engaged. More compression is achievable because the cranking RPM is higher than what’s possible with the aforementioned starting methods. With a higher cranking RPM for a four-stroke, more air will fill the cylinder on the intake stroke, and for a two-stroke the scavenging process will be improved. With this being the case we must look at reasons why the engine is struggling to build compression in the first place.

Starting problems specific to four-strokes:

1. Valve seat recession - When a valve seat wears out and recedes, the valve moves up towards the camshaft. This leads to diminished valve clearances and if left to run its course, the valve and shim will bottom on the camshaft’s base circle. This can prevent the valve from seating and make the engine hard to start.

2. The valve is bent - A valve with a serious bow to it may get jammed up inside the guide and not return all the way back to its seat. Bent valves typically result from an over-revved engine where the valves contact the piston. Valves can also bend to a lesser extent if they were mated to valve seats that were not cut concentrically to the guides, or they were paired with worn seats.

3. The valve stuck in the guide - This is usually due to the engine overheating.  When the engine overheated the clearance between the valve and guide diminished which caused metal to transfer from one part to the other, ultimately ruining the surface finish on one or both parts. Once this happens the valve may be prone to sticking in the guide until the engine warms up.
​

4. The valves and seats do not seal well - Worn valves and valve seats can compromise the seal between them. Valve and seat wear is a natural part of running an engine but can also be accelerated by ingesting dirty air.

Starting problems specific to two-strokes:

1. The reed valve is worn - Reed petals that don’t close all the way, are chipped, or bent will not allow sealing of the crankcase and efficient gas flow up from the crankcase into the cylinder.

2. An engine seal or gasket has failed - A two-stroke engine requires a well sealed crankcase and cylinder in order for it to scavenge gases efficiently. A worn crank seal, leaky base gasket, or problematic power valve seal can all make starting more difficult.

Two and four-stroke problems:

1. The piston rings are worn - Worn piston rings will allow compressed gases to escape past them.
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2. The head gasket or o-rings are leaking - Usually a leaking cylinder head will be accompanied by white smoke if coolant is being pushed into the combustion chamber, by coolant being blown out the radiator, or both.

I hope you found this rundown of potential problems useful for diagnosing bikes that like bump starting over a kick or the push of a button. Can you think of any other problems that would lead to lack of compression? If so, leave a comment and share them.
​

If you liked this post and want more technical info, be sure to sign up for my weekly eNewsletter. Every week I will send you in-depth technical and maintenance tips when it comes to caring for your dirt bike. 
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Inside KTM's Design Methodology

8/1/2016

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Inside KTM's Design Methodology
While I don't normally re-post articles, one of my mentors lead me to this series of Q & A write ups featuring a few of the lead engineers at KTM. I enjoyed reading them, learning a bit more about how KTM operates as a company, and liked the technical information they shared about their bikes.

If you enjoy this sort of thing - check 'em out. Trust me, there is something for everyone - two-stroke, four-stroke, enduro, and motocross discussion! 

​Engine Development: https://transmoto.com.au/2017-ktm-exc-range-the-engine-guru/

R & D Insights: https://transmoto.com.au/2017-ktm-exc-range-rd-insights/

Design Philosophy: https://transmoto.com.au/2017-ktm-exc-range-design-philosophy/ 

What did you think of the articles? Is KTM heading in the right direction? Leave a comment below and let us know what you think!


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How Much Damage Can An Improperly Cared For Dirt Bike Air Filter Cause?

7/11/2016

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Why you need to take care of your air filter on your dirt bike
I thought this week it would be a good idea to share with you an example of what can happen when dirt gets passed an engine's air filter. This will be a short post, but a picture is worth a thousand words. In my next post I’ll go into detail on how to properly care for your air filter to help ensure that this never happens to you.

The series of photos below shows a sad case where dirt has found its way into the engine and wreaked havoc. The photos are all from the KX250F I bought on the cheap with the sole intention of rebuilding the engine and documenting the process for my book, The Four Stroke Dirt Bike Engine Building Handbook. Honestly, I couldn’t have bought a better bike for the project, nearly everything on the bike was worn out or screwed up from the previous owner.

Here is how the air filter and airbox looked prior to disassembly.
example of a dirty air filter on a dirt bike

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How do You Keep Track Of Where Bolts Go During A Rebuild?

7/4/2016

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Alright guys, this week I just want to share a short and simple tip with you on how to stay more organized during an engine build.

When it comes to major engine maintenance or repairs, usually the engine covers have to come off or the crankcases must be split. The covers and cases are almost always retained using different length bolts. The repercussions of installing the bolts in the wrong order upon reassembly can be very damaging. This is especially true if you install a bolt that is too short for its location and only a couple of threads engage, ultimately stripping the threads when you tighten the bolt.

So what’s an easy way to keep track of cover or case bolts that are arranged in a pattern of different lengths?

My favorite way to organize these bolts is to take a thin piece of cardboard (think cereal box thickness) and then slit the approximate bolt pattern into the cardboard so that the bolts cannot get mixed up. A picture is worth a thousand words so check out the one below. You need not be an artist to apply this tip, simply slit the pattern, add a couple reference points and you’re done!
How to organize bolts during a dirt bike engine rebuild
Do you have any organizational tips you’d like to share? Leave a comment below because I'd love to hear about them!
If you are looking for more helpful tips and engine building info, feel free to check out my book, The Four Stroke Dirt Bike Engine Building Handbook. You’ll find 301 pages filled with crucial and down-to-earth four-stroke engine building knowledge. 

Containing 250 full color pictures, 300 pages of step-by-step instruction, and detailed technical knowledge that can be applied to any make and model, The Four Stroke Dirt Bike Engine Building Handbook is a trusted guide for any expert or beginner.
How to rebuild a 4T dirt bike engine
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Big News For 2016 And Looking Back On 2015

1/12/2016

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DIY Moto Fix Goals for 2016
With 2015 now in our rear view and 2016 in its infancy, I wanted to reflect on the past year as well as share my goals for DIY Moto Fix in the new year. First and foremost, I have to thank you. 2015 would not have been the year it was if it wasn’t for all of you curious and courageous bike owners out there. Thank you for your willingness to learn more about your bikes and for choosing to trust your time with DIY Moto Fix.

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