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      JUST IN!   04/24/2018

      HOW TO: 4-STROKE PISTON REPLACEMENT DONE RIGHT!

XR/CRF80-200

This is the spot to talk about the Honda XR/CRF80, XR/CRF100, XR/CRF125, & XR200. Find new & used XR/CRF80-200 motorcycles & parts for sale, XR/CRF80-200 reviews, and browse owner garages & mods.

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  • Featured Content

    How-To: 4-Stroke Piston Replacement
    We have a used 2006 YZ450F that we're rebuilding step-by-step, and documenting along the way. In this part 1 feature, we'll go over how to replace a 4-stroke piston. Click here to watch the quick tip video to go along with it! The top end in a four-stroke can be split up into two major sections: the head, and the cylinder and piston. They both require specific attention and critical steps to ensure proper opertation once everything is back together. We replaced the worn stock piston with an OEM quality forged ProX piston kit. It includes the rings, wrist pin, circlips, and installation instructions. The pistons are available in A, B, and C sizes, to accomodate for the size of your cylinder as it wears.   Our new ProX forged piston compared to the stock, used piston. Carbon deposits on the crown are common after running hours, but can decrease power and efficiency. Disassembly To prepare to disassemble your head and cylinder, you'll need to remove the seat, gas tank, exhaust system, and carburetor (or throttle body). While not always required, removing the sub-frame, shock, and air boot make accessibility to the engine a lot easier in most cases. Once those major components are removed, you'll need to remove any other components attached to the head or cylinder, such as clutch cable guides, spark plug boots, and electrical connections.   Removing the subframe, airboot, and shock, in addition to the other components, provides much better access to all sides of the motor. Don't forget to remove any cable guides or other items bolted to the head/cylinder. Next, remove the cam cover, loosening the bolts incrementally until they are all loose. With that off, it is best to make sure your camshafts are not fully compressing any of the valve springs before you loosen the cam caps. You can do this by slowly rotating the crankshaft via the kickstarter. With the cam caps removed, loosen and remove the cam chain tensioner next. This will give you the slack to remove the timing chain completely. You can now lift the camshafts completely out, handling carefully. Now you can loosen the head bolts in incrementally in a crossing pattern. Remove the head and place it aside, handling it carefully. Next, do the same for the cylinder bolts, and carefully remove the cylinder. As you remove the cylinder, the piston is going to stay on the connecting rod, so it helps to hold the connecting rod steady as you wiggle the cylinder off the piston. It is always a good idea to fill the opening of the cases with a lint free rag to prevent debris or loose parts from falling in. Remove the cam cover and head bolts incrementally until loose. This prevents the chance of warping.   Finally, you can remove one wire lock from the stock piston using a pick or small screwdriver. Slide the wrist pin out, and remove the piston from the small end of the connecting rod. Be very careful no to drop anything into the cases during this step, and throughout the entire process. Cleaning With everyting removed, you'll need to clean any old gasket material and other residue off your sealing surfaces. This includes the base for the cylinder on the cases, top and bottom surfaces of the cylinder itself, and the bottom surface of the head that seals to the cylinder. For large or difficult pieces of material, it is common to use a razor blade for removal. However, be gentle and careful not to put deep grooves or scratches in the surfaces. Also, don't cut your finger open, or off. Scrape old gasket material off carefully, being cautious of any grooves or scratches in sealing surfaces and personal injury.   Final cleaning commonly consists of using carb cleaner, or a similar chemical cleaner, and a rag to achieve completely clean and flat surfaces. Cylinder Prep Before you go and put that cylinder back in with your new piston, you'll want to inspect it for signs of wear, and measure it to make sure it's within spec (refer to your owner's manual for proper specifications). If there is minimal glazing on the cylinder, no grooves worn in, and it's within spec, you should be ready to reinstall after a good honing. Always use a diamond tipped honing brush for resurfacing work. If you're unsure about performing any cylinder prep work yourself, talk to your local dealer about cylinder shops, where any prep work required can be performed. ProX pistons are available in multiple sizes to accomodate for cylinder wear, so be sure your bore measurements correlate with the size of piston you're installing. Make sure your cylinder is the correct bore size for your piston, and properly cleaned and honed, as pictured here. Reassembly When you have your cylinder prepped and ready, now is a good time to double check your piston-to-wall clearance and ring end gap. For piston-to-wall, measure the size of your ProX piston using a micrometer only. Measure the piston on the skirt, 90 degrees from the wrist pin bore, at the point on the skirt that is 1/4 of height of the piston from the bottom. Refer to your manual for acceptable piston-to-wall clearance range. When measuring ring end gap, install the top ring and second ring (seperately, and if applicable) approximately 1/4" into the bore. Use a feeler gauge to be sure ring end gap is within the dimensions specified in your piston kit instructions. ProX rings are pre-gapped, but it is always good practice to double check. While ProX rings are pre-gapped, it's still a good idea to double check your ring end gap. Install the rings in the proper order and location on your pistons. Refer to the instructions that come with ProX piston kits to be sure you are installing the rings in the correct fashion and location. After this, install one wire lock into your piston, being sure it is properly seated. Click here for our tips on installing wire locks. Use your finger to put a layer of motor oil on the cylinder wall. Next, put a layer of oil on the outside of your new piston (on the outside of the rings, on the ring belt, and on the skirts). You don't want your new piston and rings breaking in under dry conditions. Use the normal motor oil you use in your 4-stroke. Piston installation can be done via more than one method, but in our case, we installed the piston in the cylinder before attaching it to the connecting rod. Either way, be sure your piston is facing the correct direction, meaning the exhaust valve reliefs line up with the exhaust side of the head. There will be markings on the crown of ProX pistons to indiciate which side is the exhaust side. Also, make sure your rings remain in the proper location as you slide the piston into the cylinder.  The arrow shows the marking on the piston crown that indicates that is the side of piston that needs to face the exhaust. Before installing the new base gasket, piston and re-installing the cylinder, make sure the surface is clean and the crankcase is free of debris. While the top end is off, this could also be a good time to make sure your crankshaft is in spec. Next, lay your new base gasket on the cases, lining it up properly. Install the piston (which should remain in the cylinder) onto the connecting rod by lining up the pin bore with the small end bore, and sliding your new wrist pin (put a layer of oil on this before installing) completely through, until it stops against the one wire lock previosuly installed. With the piston secured to the connecting rod via the wrist pin, install your remaining wire lock, and make sure it is properly seated. You can now slide the cylinder all the way down to meet the cases. Note: Make sure you take any rags out of the cases before reassembling! You're now at the point in reassembly where you will install your rebuilt head (details in part 2 of this top end rebuild soon to come) with the proper head gasket, and re-install all the items previously removed. Be sure you are following all proper torque specs specified in your manual. Head back for part 2 of the the top end rebuild, where we'll show you some great tips on assembling a four-stroke head with new valves and valve springs, re-installing camshaft(s) and timing chain, and checking and adjusting valve clearance.   Our new ProX piston and freshened up clyinder successfully installed. Note the dot on the piston crown, indicating that is the exhaust side. Stay tuned, more rebuild tips to come!
    Posted by Rob@ProX on Apr 23, 2018

    Hammerhead Designs Brake Clevis
    In the world of motorcycles, 50 bucks is something that can dissipate very quickly. One can blow that much on food & drinks at the races or the gas it takes to get to the track or trail. That said, in a world with $10,000 dirt bikes, is there anything that a measly $50.00 can be spent on that really improves the performance of your machine? One great option is the Hammerhead Designs Brake Clevis Kit. While it does add some satisfying bling to your bike, more importantly, it serves an important purpose of improving the feel of your rear brakes, improving braking accuracy and modulation. Installation The Hammerhead Designs Brake Clevis Kit for the YZ125 eliminates the need for the long and poorly functioning return spring that attaches to the backside of the brake pedal. This was good news because I managed to rip the stock spring off battling my way through the woods. The Hammerhead kit comes with a beautifully machined & richly anodized aluminum brake clevis, return spring, pin, & snap ring retainer. No instructions were included, but have no fear; this is a very easy, straightforward process. With a little deductive reasoning and a quick google search, I was able to install the kit in just a few minutes with typical hand tools. I had a small hiccup with installation that required me to slightly grind down the backside of my brake pedal to maintain clearance for the pedal to operate smoothly, I am not sure if this is the same with all OEM pedals, or if mine may have been tweaked slightly, but either way, it was an easy modification that took only a few minutes. Once installed and after a brief brake pedal height adjustment, I was ready to hit the trails to see how this bolt-on mod performed. How'd it work? The original rear brake set-up on my YZ125 left a lot to be desired. It had a very vague and light feel in the first half of the stroke which often led to premature or panicked slamming of the pedal in order to gain some sort of feel in the bottom half of the stroke.  My initial response after installation of the Hammerhead brake clevis was very positive. Pedal feel was greatly increased in the first portion of the stroke, as if the master cylinder had been upgraded with a larger piston. Pushing through the stroke maintained consistency and improved my braking effectiveness. Without any dramatic changes to my braking technique, the improved brake pedal feel & action gave me a confidence boost that allowed me to push a little harder into corners and slower sections  without the hesitation caused by lacklustre brake feel.  No more panicked slamming of the brake pedal in hard braking situations, just smooth and consistent pedal feel.  How's it held up? The Hammerhead Designs Brake Clevis Kit is extremely well made and that's good because I'm not easy on bikes! I have a history that includes more than a few broken parts. Despite this, the Hammerhead brake clevis shows no signs of wear or damage, pretty much looking like the day I installed it. I'll report back as the hours pile up, but my expectations is that this part will go the distance. Bottom-line - 4.5 out of 5 Overall, the Hammerhead Designs Brake Clevis Kit is a fantastic product. For the price, you can't go wrong! This is such a quick & easy way to improve your bike's rear brake feel & control, something that directly translates to increased control & speed. I can only image the improvements when paired with other brake upgrades such as an oversized brake rotor or upgraded master cylinder.
    Posted by ThumperTalk on Feb 23, 2013

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