This week I wanted to share an excerpt from the Race and Performance Engine Building chapter in my book, The Four Stroke Dirt Bike Engine Building Handbook. If you've been wondering how high compression pistons work and if they are right for your application, read on!

Piston upgrades are normally considered when changing the compression ratio is desired or larger valves are installed. In both instances the shape of the piston is altered either to reduce the volume in the combustion chamber or to allocate additional room for larger valve pockets.

The compression ratio defines how much the original air/fuel mixture which was sucked into the engine is compressed. The following equation shows how an engine’s compression ratio can be calculated.
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In my last post I shared an account of what happens when dirt gets past the air filter and into an engine. This was a telling tale, however I want to go further and discuss key components of what can be done in terms of maintenance to limit the chances of sucking in dirt. Whether you ride a two-stroke or four-stroke, it makes no difference, the importance of keeping dirt out cannot be overstated.

I want to start off by thanking those that left constructive comments in my previous post. Your insights into filter maintenance are much appreciated and help reinforce what I’m about to share.

How often should I change my air filter?
This depends entirely on the conditions you ride in. Dusty dry conditions will warrant more frequent filter changes than a damp riding environment where dust is non-existent. The amount of dirt accumulation that is acceptable is subjective, but I always err on the safe side. As an example, my filters are blue when freshly oiled and as soon as they start to become blotchy and start to turn color I change them.

Can I change my air filter too often?
Yes and no. I say yes only because every time the filter is removed there is a chance for dirt to enter the engine. A sensible changing regimen decreases the odds of dirt getting into the engine as the filter is removed/installed.

What to Use
I’ve personally been using FFT filter oil, however, there are many great options out there. No Toil’s water based oil system is something I’ve heard good things about and would like to try too. Asking other riders or doing a quick search will certainly turn up more great options as well.

Removing the Filter
The main point I want to mention here is to be careful when removing the filter from the airbox so that dirt does not come off the filter or surrounding areas and find its way into the intake. On most bikes, fitting the filter between the subframe is a tight fit and dirt can occasionally come off as the filter is pulled up.

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.

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!

Do you have any organizational tips you’d like to share? Leave a comment below because I'd love to hear about them!

In today's post I'm going to shift focus back to the engine and talk a little about valve technology. Valve technology and manufacturing techniques have changed substantially from the earlier days of engine development and I want to share with you some information about the current valve technology being implemented in your engines. I also want to discuss one way you can get a feel for how much life is left in your valves. Let’s get started.

The following excerpt is copied directly from my book, The Four Stroke Dirt Bike Engine Building Handbook. If you want to learn more helpful tips, which will bring your maintenance knowledge and engine building skills to the next level, I’d like to invite you to pick up a copy of my book by clicking here. Be sure to use the offer code rebuild2016 to get 15% off when ordering!

Alright, on to valves shim sizes.

The cylinder head assembly of most engines will wear out before it resorts to telling you it has had enough by catastrophically failing. Diagnosing these wear signs and knowing when it is time to replace components is the key to keeping the cylinder head assembly from failing. Due to the aggressive camshaft profiles, high compression ratios, and high RPMs required to make a lot of power, the valves and seats typically are the first parts to wear out within the cylinder head. Worn valves and seats will cause the engine to become difficult to start, have low compression, and have reduced power.

I hope 2016 is treating you well so far! This last weekend I participated in the Steel Shoe Fund 3 Hour Endurance Ice Race out on Kettle Moraine Lake. For those of you not living in the northern midwest, last weekend averaged about 0 degrees Fahrenheit and the wind chill made it feel like 10 below. Regardless, there were over 65 teams that raced and the day was a blast. Unfortunately we had a serious injury out on the track and they had to call it before anyone officially completed the race. Last I heard the rider is doing fine now, thank goodness! Hopefully I get a few more ice races in before the winter season is over. 

Today I want to talk about six characteristics that are necessary to have when one sets out to build an engine. I’ve detailed how to tackle many different jobs, but honestly that is only half the battle. If you’re in a rush or lack the desire to understand the reasons behind what you’re doing, you will make mistakes and miss out on important things. Listed below are the traits that I believe can help you take your build to the next level.

1. Being Detail Oriented
What’s worse than getting started on a build only to realize you didn’t buy an important replacement part? Focussing on the details of a project can feel tedious at times but can pay off in the grand scheme of things. Before I get started on a project I spend a hefty amount of time researching what parts I’m going to replace and where the best prices are. Also, I will have a solid idea of the sequences I’ll use for disassembly and assembly. Another good habit for the detail oriented is to take notes throughout the build, which you can use at a later date should the need arise. When you have an appreciation for all the small details that go into a build, it will make for a much smoother project.

2. Having Patience
Have you ever been in a rush to do something and after you’re done you realize if you had spent just a bit more time the project could have turned out much better? I was this way with so many of the things I did when I was younger, but have learned to slow down and be patient as I work. Engines don’t go together instantaneously and being patient throughout the process, especially when things aren’t going as planned, is very important. There is nothing worse than making a huge mistake because you’re in a rush. Imagine finishing a build and realizing you left an important part on the table, depending on where the part came from, you just bought yourself another few hours of work. Trying to skimp on time more often than not costs you more time in the long run. Have patience and enjoy the process.

3. Being Observant
Just about every mechanical thing is gleaming with a story, and that story only reveals itself if you know what to look for. An engine is no different. From the parting lines on a component left by the casting tooling used to create it to wear patterns on a piston, there are hundreds of observations that can be made while working on an engine. As you work, keep an eye out for subtle anomalies that may tell you why something failed or broke. For example, things like snail tracks across a gasket, raised edges on gasket surfaces, or covers that don’t sit flat on a table - these are all good indicators of why a particular part was leaking.

4. Being Curious
Perhaps more appropriately titled, “a desire to understand mechanical workings”. It is incredible how much can be learned about the engine just by studying how specific parts interact within it. An engine is composed of many different subsystems and they must all work in order for the engine to function. By looking at the various interactions of the parts within an engine, the condition of the parts and reasons for any failures can be more easily understood. The next time you build an engine, challenge yourself to learn how all the different subsystems of the engine work. Once you learn this, diagnosing problems and identifying all the faulty parts becomes much easier.

5. Being Meticulous
The necessity to be thorough and meticulous throughout a build cannot be overstated. Whether it be taking extra steps to inspect components, measuring new parts, or taking extra time to ensure the condition of surrounding subsystems are okay, having meticulous tendencies can pay off. As an example, on more than one occasion I’ve purchased new parts that have been mispackaged or out of spec. Had I not made the choice to carefully measure the problematic new parts, I could have ended up with an engine that was destined to fail. While it may take more time to be meticulous throughout a build, there is a lot at stake, both in terms of time and money, making it all the more important to ensure everything is done correctly.

6. Having Ambition
Building an engine can be hard, things can go south unexpectedly, and projects can easily stall. Being ambitious and having a can-do attitude is important to ensure the engine doesn’t sit half torn apart in the garage never to be completed. Until you tear into the engine, you never know what you might find. I’ve disassembled engines many times in the past only to find I need to replace a lot more parts than I had planned (this seems to be my luck when I shop for bikes on Craigslist as of late). This can be a huge downer, but keeping the end goal of getting back out and riding in mind and having the desire to push through any and all obstacles is a must.

Do you have any engine building characteristics you want to share? Leave a comment below and tell everyone what you think it takes to build a great engine!

For those of you that believe you possess the characteristics of a good engine builder, be sure to check out my book, The Four Stroke Dirt Bike Engine Building Handbook, to learn more about the how and why behind engine building. Whether you want to be taught about the relationships between all the various parts within an engine, you are in need of pointers on picking the right performance parts, or you would like to see examples of wear patterns found on engine components, my book is here to guide and help you throughout your build.

In my last post I covered what a leak down test is and how it can be used to determine engine problems. Today I’ll go through and detail how to do a leak down test on your dirt bike engine step-by-step.

Determining how healthy an engine is can be tricky business. I’ve previously covered compression testing (pt 1 here and pt 2 here), but now I want to discuss what a leak down test is and how to perform one on a four-stroke dirt bike engine. This will be a two part series, with the first part emphasising the details of a leakdown test, and the second part explaining in detail how to correctly perform a leak down test. Let’s get started!

For this week’s Q & A I’m going to talk about why changing the engine’s oil is particularly important for high performance dirt bike engines. Dirt bikes and their engines must contend with all sorts of nasty elements including dirt, mud, water, and sand to name a few. The exposure to these elements, the fact that four-stroke dirt bike engines don’t carry a lot of oil, and their high state of tune all necessitate the need for more frequent oil changes than traditional automotive or motorcycle engines.