5 Signs That Your Dirt Bike Needs A New Top-end – 2 Stroke

If you buy or put a lot of hours on a 2-stroke motocross bike, chances are it will need the top-end replaced. A top-end rebuild is pretty easy to do on a two stroke engine, and the only special tool you’ll need is a torque wrench for most dirt bikes. However, before tearing your engine apart, there’s several signs that can tell you it has a worn top-end. If you have most or all of the symptoms listed below, you can count on replacing at least the piston and ring, and possibly a cylinder and head. Although, if none of the symptoms relate to your bike, there’s a good chance it won’t need a rebuild yet…

It Takes 50 Kicks To Start My Bike…

This is a common symptom for both two and four stroke dirt bikes. Unless you are riding in extreme climate, your bike shouldn’t take more than a few kicks to get started. Certain bikes require more muscle and/or technique to get started, but a solid running engine will only take 1-3 kicks to start, hot or cold. On the flip side, just because your bike takes forever to start doesn’t always indicate a worn top-end. For more info on a ‘no-start’, read this article on Diagnosing A No-Start

My Bike Is Gutless

Does your dirt bike feel like it lost its power-band(sarcasm)? A worn piston/ring will make the engine feel weak and low on power even when WOT (wide open throttle). This often happens after a top-end has so many hours on it, and will get worse/less powerful over time. A 2-stroke piston can last over a hundred hours if the bike was casually ridden and properly maintained, but an aggressive motocross racer can wear out a top-end in less than 20 hours of ride time.

This Thing Eats Spark Plugs

Shattered CR80 Piston
Shattered CR80 Piston

How often are you replacing the spark plug? If you have to put a new one in every ride, stop and inspect before riding again. If the jetting is right, a fouled spark plug can also be caused by a bad top-end or blow-by from the worn piston/ring/cylinder. This definitely indicates a new top-end is required, as well as a new spark plug. I have personally seen a CR80 that fouled plugs because of a bad top-end. It turned out that the piston was cracked and it eventually just lost compression. The cylinder was used again because it was surprisingly still in good shape! Here’s some more causes of a fouled plug.

Look For Scratches

A scored piston or cylinder can be caused by multiple things. A lack of lubrication from not enough 2-stroke oil in the gas or lean jetting can damage the piston and cylinder, as well as the crank assembly and bearings. Scoring is caused by metal to metal contact, which is common on 2-strokes when they aren’t warmed up properly. It makes me cringe when people try to warm up their dirt bike too quickly, and I see it quite often. A lot of top-end damage is done if you start your bike and immediately ride it hard or rev it without giving it enough time to warm up.

A piston has a certain amount of clearance between it and the cylinder wall. This clearance is for “growth”, because it will get bigger as it heats up. The size difference isn’t much, but if the piston heats up too quickly, it will expand faster and get too big to properly fit in the cylinder bore, thus creating scoring, and possibly a “cold seizure”. Read the article in the link above to learn how to warm up your dirt bike without damaging anything. You should also note that forged pistons, as opposed to stock cast pistons, are slightly smaller in diameter and require more warm-up time to expand; so take extra precaution.

You may have to take the cylinder head off to get a good look at the cylinder walls to check for scoring, but there’s a quick and dirty way to give you an idea of its condition without touching the engine itself. Just unbolt and remove the pipe/expansion chamber so you can look in the exhaust port of the engine. Shine a light in there and see if there’s any noticeable scratches. You can look at the piston as well, but any scratches/scoring that looks like something you can feel with your finger nail is damage and will most likely need repair/replacement. If you can’t see the cross-hatching on the cylinder walls then it is worn and probably out of spec.

Top-end Rebuild
Top-end Rebuild

My Bike Is Super Easy To Kick Over

If you don’t know already, this isn’t a good thing. While most 2-strokes are easier to kick over than a four-stroke dirt bike, you shouldn’t be able to push the kick-start lever down with one finger. If it kicks over with next to no resistance, the top-end is probably down on compression. Low compression will usually go hand-in-hand with taking a lot of kicks to start, as well as a weak engine.

A new piston ring may be the only thing that needs replacing if the piston and cylinder are still in good shape. Rings only last so long and eventually go out of spec (refer to your manual). If you have the cylinder off, check the ring gap with gauges and compare to what the manual says. If the gap is too big, replace the ring with a new one. You can usually re-ring a piston once before needing a new piston as long as everything else checks out.

These tips are only guidelines. Nothing is set in stone, as every bike is different. Just because your bike is hard to start doesn’t mean it will always need a new top-end. It could be something completely different, such as a dirty carburetor because the bike hasn’t been started for months. I put this list together because these are the most common symptoms of a bad top-end when all of the simple problems have already been checked.

Have fun, and ride safe!

-Tom Stark

How To Replace A Dirt Bike Clutch – CR125 2-stroke

If you want to ride or race dirt bikes for the rest of you life, there’s some things that you need to learn how to do and fix on them if you want to save time and money. Replacing the clutch should be one of them, and it’s bound to happen if you’re racing or putting a lot of hours on your bike throughout the riding season. Don’t worry, it’s actually a pretty easy job.

If you’re scared to work your motocross bike, I strongly recommend getting an OEM service manual for your bike if you don’t have one already. The factory manual will have pretty much everything you need to know for maintaining or repairing your dirt bike. There’s dozens of diagrams, specs, maintenance intervals, tips on adjusting suspension, and much more.

First thing is to start out with a clean bike and work area. If the bike is not clean, you run a much higher risk of getting dirt or foreign objects inside the clutch/engine, so at least wash that part of your dirt bike. Having a cluttered and filthy shop area is annoying, and can be dangerous if it’s hard to walk. Make enough room to comfortably work on the bike with clean parts and tools.

CR125 Clutch Cover Bolts
CR125 Clutch Cover Bolts

Once you’re all set up and have the proper tools, it’s time to take the clutch off the bike. The clutch cover is on the right side of the engine, and most covers have about 5 bolts holding it on (This bike is an ’01 Honda CR125).

After you get the cover off, you’ll be able to see the basket/plates. There’s five more bolts holding them together. This is where you may need a special tool to hold the clutch to prevent it from spinning while loosening the bolts. If you don’t have one, a cordless impact can be very handy to get it off, although you’ll want something to properly torque it back down.

CR125 Clutch Hub
CR125 Clutch Hub

All of the disks and plates will come out with the pressure plate. This is when you need to check the basket for wear/notching. It will be pretty clear if there’s notches from the disks. This basket does not have notching or appear to be broken, so it can stay right where it’s at!

CR125 Clutch Basket
CR125 Clutch Basket

Next we can measure the springs and plates to see what’s in spec. Refer to your OEM manufacture’s manual for minimum length on the clutch springs and minimum thickness of the metal plates. The min. length of each spring for the CR125 is 35.2mm (1.386″). I measured mine with a dial caliper and it read about 1.430″ (36.2mm), so they’re still within spec.

Measuring Clutch Spring
Measuring Clutch Spring

Next you can measure the metal plates. If they’re still in spec, feel free to use them as long as they don’t show signs of overheating (discoloration). I just bought a complete kit for this bike, so I’m putting in all new plates and disks. Sometimes you can just get away with replacing the fibers/friction plates since they usually wear out faster.

Most clutch plates you will have to soak in oil prior to putting them back on the bike. If you start and run the bike with them dry, you’ll greatly increase your chances of breaking or damaging the clutch. I just take bucket, pour a little engine oil in, and one-by-one place each plate and disk in, swirling the oil around so it covers all of them.

Soak Plates/Disks In Oil
Soak Plates/Disks In Oil

Now you’re ready to put them back in. You’ll start with a friction plate, and alternate until they’re all in. There’s one more friction plate than metal disk, so you’ll start and end with one.

 

CR125 Clutch - Friction Plate
CR125 Clutch – Friction Plate

 

CR125 Clutch - Metal Disk
CR125 Clutch – Metal Disk

After the plates and disks, it’s time to put the pressure plate and springs in. Now you’ll need something to hold the clutch assembly again so you can torque down the bolts. Again, check your service manual for proper torque specs. This CR125 requires 7 ft. lbs. for the pressure plate bolts.

All that’s left is to put the cover back on and fill ‘er back up with oil! Before starting the bike, pull in the clutch a few times and make sure everything feels right, like it’s disengaging and engaging. On the first start, warm the bike up properly by letting it idle for at least a couple minutes. It’s not unusual for the clutch to drag at first; it just needs to be broken in.

Once the bike is warm, ride the bike around for a few minutes to make sure everything is still functioning. After that, you’re good to go! I recommend changing the oil after a few hours of riding if not sooner to get rid of any shavings from the new engine parts.

Click Here To Buy My Clutch Kit!

-Tom Stark

CRF250X vs. CRF250R – Which Dirt Bike Should I Buy?

Looking to buy a red dirt bike but not sure which one is better? While the CRF250R and CRF250X started off on similar platforms, there are some major differences between the two that make each better in its own way. The first question you should ask yourself is, “What kind of riding are you looking to do with it?”

Suspension – Racing or Trails?

Having the right suspension for the job will make all of the difference between two bikes. While this isn’t the only difference, it’s probably the most important. The CRF250R is a motocross bike; therefore it will have stiffer suspension and valving set up for racing on a track with big jumps and whoops. It’s still not going to fit you perfectly right out of the box, but it’s going to be a lot better of a starting point than if you were to get the 250X.

If you’re looking for something more than the typical, boring, air-cooled four-stroke trail machine, the CRF250X may be just the answer. It began production with the same frame design and style of the CRF250R, including the higher performance inverted-fork and shock set-up. While it may have better and more easily adjustable suspension than most other trail bikes, it’s still going to be pretty soft so you can go on long trail rides without getting worn out from stiff suspension bucking you around.

Engine

CRF250R
CRF250R

Do you like a fast-revving, high-horsepower, race engine, or do you want something that’s smoother with a broader power-band so it won’t scare you? For having almost the same engine design, there’s yet again some major differences between the two. The 250R has a larger stroke (smaller bore), a little higher compression, hotter camshaft, a close-ratio transmission, and EFI starting in 2010. These things all add up to making the motocross version of Honda’s 250F more snappy and begs the rider to twist the throttle.

On the flip-side, the CRF250X still has the same basic engine design. A less-radical cam makes it more trail friendly for smoother power, along with the lower compression. A wider transmission ratio also makes it great for trails, both tight and high-speed. A lower-flowing intake and exhaust set-up combine to make this bike tamer for the beginning riders in mind. The exhaust is considerably quieter, and has a spark-arrestor for state trail riding.

Light-weight vs. Trail Amenities

CRF250X
CRF250X

The more trail riding you want to do, the more accessories you’ll want to have on your bike. However, lightweight is the reason why the CRF250R handles so well. The options that are exclusive to the 250X that add the most weight are a kick-stand, electric start/battery, headlight/tail-light, airbox, larger-capacity gas tank, and exhaust system. Most of these mentioned are highly desirable for trail riding, but you will feel the weight difference if you ride both bikes back-to-back.

So the question is, what are the options worth to you, and how much off-road/trail riding will you be doing? A lot of riders that like the race form of the 250R will take it and add a few things to make it more ride-able in the woods and absolutely love it. However, if you are older and prefer E-start, a kick-stand, and soft suspension, you will enjoy the 250X more, even if it is down on power a little.

-Tom Stark

My Favorite Motocross Channels on Youtube

Youtube has become the new Internet TV, and it is as close and real to being live TV as it gets, except with edited footage! There are hundreds and thousands of dirt biking channels out there, but none of us have 12+ hours in the day to sit on the computer watching them all to find out which ones are the best. Well, at least most of us don’t…

I’ll show you my favorite Dirt Bike related channels from Youtube. Why? Because many of them deserve a lot of views after all of the hard work put in to making and editing them. Besides, it will give you more channels to subscribe to and you’ll be able to watch awesome motocross vids the minute they’re posted. Other than my own Channel for Motocross, the following are my Top Five channels that upload videos regularly that I look forward to watching.

999lazer:

999lazer posts weekly videos of local racers and motocross tracks. They are based in the UK, and are big fans of two-strokes. Why are they on this list? Not only is the footage good, but some of the edits are just plain entertaining, as well as some of the commentary from the riders themselves.

team404:

You want some of the sickest edits of off-road riding from a local filming duo? Team404 has been making professional motocross shorts, as well as photography for the past couple years. Check out some of their latest work; you won’t regret it!

MisterBigWheel:

Looking for some humor to enlighten your day? MisterBigWheel combines casual sarcasm with adventurous riding trips into the arctic lands of Alaska. If you enjoy dry humor and watching average Joe’s crash and break stuff, this is another great channel to subscribe to.

Danny Stuart:

If you haven’t seen some of his videos already, you’ll find that Danny Stuart likes to take his filming and editing skills, and make some of the coolest videos of local and national pros riding. Whether it’s at his home track (MX207), or a secret riding spot, you’ll be in awe with the high-quality footage that he captures and edits. Music is something that most people don’t want to hear on a motocross video, but somehow Danny is able to pick the right songs that seem to flow well with his videos…

Wozwick:My Favorite Motocross Channels on Youtube

Also known for MXPTV, Matt Wozney is a full-time professional film-maker in the motocross industry. If you just want hardcore motocross footage with some of the best amateurs around the country, head on over to wozwick’s channel on Youtube. He uses the latest in technology for cameras, video editing, and puts together the finest footage of Motocross racing I’ve come across. Both two and four-stroke, mini’s to full-size bikes, he gets them all. For not being on TV, this is as close to Nationally Televised as it gets, and he was ever so close to bringing the Ricky Carmichael Amateur National to us live. I’d bet that he’ll want to try again in the near future…

Honorable Mentions:

The five channels listed above are not the only videos that I watch from. In fact, there are many more that I subscribe to for more great entertainment. The ones below also have a knack for getting great dirt bike footage. Reasons they didn’t quite make the cut could be that they don’t upload very often, they still need to sharpen their shooting skills, they occasionally fail to keep the audience captivated, or there just plain wasn’t enough room on the list… If you feel like a channel should be added to the list, feel free to leave a comment!

  • bq365
  • 7th Gear Pinned (yz440)
  • RoadandDirt
  • lpmultimedia
  • MXWebCam
  • ZachAtk1

-Tom Stark

I Rebuilt My YZ125 In A Closet!?

It was more like a hallway, but the work area was still smaller than I wanted. I picked up a 2003 Yamaha YZ125 that had some major frame damage. The bike ran well but was not ride-able. The two options were to scrap the main and sub-frame, or take the time to bend and weld them back to their somewhat original form. Either way I would have to strip the entire bike down to the very last bolt and tie-strap. Just by looking at it I could tell this was going to be a difficult, yet exciting project.

I got to work tearing down everything on the YZ125, starting with taking the engine out of the frame. There were a lot of nuts and bolts from the plastics, engine, radiators, frame, and other miscellaneous parts that I had to organize into little zip-lock bags so I wouldn’t lose track of where they went when I put them back on the bike. In the middle of this process I got the sub-frame bent back and welded so that it would fit like normal. Being me, I decided to go the more challenging route of getting the main frame welded instead of paying a couple hundred for another one. Once I took everything off of the main frame my dad helped me by welding it.

I wanted to make this bike look good when it was finished, so I sanded and cleaned off the main frame to get it ready for painting. It took a while, but I managed to find some paint that was close to stock color shade. I then painted it with a few coats to make sure that it wouldn’t peel or chip right away.

Tear Down Process
Tear Down Process

The rebuilding process began just after the paint on the frame dried. This is the part where I had to move everything inside…. I started with the foot-pegs, front-end, rear shock, and swing-arm. Those went on pretty easily, so I then took the whole engine and bolted it up to the frame. The rear-wheel and handlebars with controls were next to go on. After that it was just the electronics, carburetor, plastics/tanks, seat, and a few miscellaneous things, such as the exhaust system.

Rebuild Process - Frame painted, front-end, rear shock, and swing-arm on
Rebuild Process - Frame painted, front-end, rear shock, and swing-arm on
Rebuild Process - Engine in, rear-wheel, handlebars on
Rebuild Process - Engine in, rear-wheel, handlebars, and controls starting to go on

After working inside for some time, this project was well worth the outcome. In the end I think the bike looks good, and I learned quite a bit more about rebuilding these modern dirt bikes (Check out my other article, “How I Built A YZ250F With A Box of Scraps” if you liked this one). Let me know what you think, and if you want to see more projects like this just give me a shout. Thanks!

-Tom Stark

Finished '03 YZ125 Project
Finished '03 YZ125 Project