Just to let you know Kustom Kraft has just finished up it's YZ250-301 Big Bore! 73mm of pure joy and fun to go with it. Check it out at www.kustom-kraft.com
YZ Aftermarket Thread YZ250-301 Big Bore.
I went with a friend of mine to look at and ultimately purchase a used 2007 CRF50 last week. While originally checking it out, I noticed that the idle would hang a bit after letting off the throttle (basically after the throttle is open and then closed, the engine will stay at a high RPM and not settle back down to normal idle for different amounts of times - sometimes just a few moments, other times up to 8-10 seconds), I figured it would be something minor like the throttle cable or gummed up carb, so I told him it was good and he bought it. I took it to my house to go over it and see if I could figure the issue out, but have been unsuccessful. I changed the oil, spark plug and filter (the filter and interior of the air box were pretty sopping wet with oil when I first opened it up). I also took the carb apart and rebuilt it fully with an all balls kit. None of this changed the mannerisms that I described above. I checked the cable and it seems fine, I also could actually see the slide opening and closing with the throttle tube in the carb. I've been told that this issue might be due to an air leak after the carb. I sprayed carb cleaner all over the intake in an attempt to find a leak, but I wasn't sure if I did. There were a few times that I sprayed and the idle hopped up, other times it didn't. I did set the fuel/air screw and idle screw at the factory setting after the rebuild as well.
I feel bad because I went to look at the bike with my buddy and told him it was good, and now I can't get it straightened out for him. Any help or suggestions would be much appreciated. I can give a better description or put a video up of it if that would help. Thanks!
By Bryan Bosch
Wiseco introduces the Racer Elite series pistons. The pistons were designed for the serious rider or racer looking for the best performing shelf piston they can find.
Racer Elite 4-Stroke pistons feature an asymmetrical skirt design that keeps contact with the cylinder wall minimal, as well as keeps the weight down. They also feature ArmorGlide skirt coating, ensuring friction is staying as low as possible. Racer Elite 4-stroke pistons are fully machined billet, allowing for the best weight optimization and the ability to machine the boxed under-crown structure with precision.
Racer Elite 2-Stroke pistons are forged out of a 2000 series alloy that offers more tensile strength than the more popular 4000 series. Pistons are coated with ArmorPlating, a Wiseco surface treatment covering the crown, ring groove, pin bore, and under-crown. ArmorPlating protects against wear caused by heat and detonation. ArmorFit skirt coating adapts to the proper piston-to-wall clearance during initial operation, and remains at that clearance, reducing operating friction throughout the life of the piston. A unique benefit of having ArmorFit on a 2-stroke piston is the ability to eliminate the need for A, B, C piston sizing.
R&D developed Dyno proven power gains Asymmetric skirt design Improved wear and even loading on major thrust skirt Precision fit ring 100% billet machined Custom lapped compression ring for improved power Superior strength to weight ratio and optimized fit High compression Maximum torque and throttle response Dome design Improved flame travel to maximize air/ fuel burn efficiency DLC coated piston pin Reduced friction, improved scuff resistant Enhanced pin oiling Improved lubrication and reduced friction Pressure seal groove Reduces ring lifting and power loss ArmorGlide® skirt coating Reduced friction, quieter operation, improved scuff resistance
By Kevin from Wiseco
Proper engine break-in is equally as important as a proper rebuild. Here, we'll go over a checklist to make your build will last, as well as a step-by-step break-in process.
Putting in the time and money to rebuild your motorcycle engine is both a critical job and a prideful accomplishment. The feeling of an engine failure right after a rebuild is a sinking one, and will most likely stir up a mixture of frustration and disappointment.
We want to help as many people as we can avoid that feeling. So, we've put together a review checklist for your rebuild, followed by a general engine break-in procedure, because your motorcycle should bring joy and fun to your life, not take tufts of hair out of your head.
We'll start with a quick review on the motorcycle top end rebuild. Be sure these critical steps and precautions have been taken. If you find any concerning discrepancies, it's worth it to pull back apart and double check.
Be sure that you have proper piston to cylinder clearance. Recently, a cylinder was bored with requested .0035” clearance. This machine shop has been in the area for over 30 years. When complete, it looked like it was tighter. He slipped the piston through the cylinder a few times and said, "It's okay." He was asked to check again, which he refused, and said that it was correct, and that he was too busy. Back in the Brew Bikes shop, it was double-checked, and clearance was .0015”. Yes, way too tight. Don’t just take someone’s word that clearance is correct, always double check it!
Always double check your piston-to-wall clearance.
Was the honing of the cylinder properly done? Honing is required to be done after boring, and if the cylinder was not bored, it still is needed to deglaze the cylinder for proper ring break-in. Different honing tools are better used for different applications, with common tools being brush hones and flex hones. Safe grits and hone materials depend on the cylinder finish, so check your manual or with the cylinder shop for a recommendation. Be sure that the crosshatch is at 45 degrees. The proper crosshatch will retain the proper amount of lubricating oil while allowing the rings and piston to break-in. Too little of crosshatch or too much will not allow the rings to break-in correctly and never get the proper sealing they were designed for. Read our full guide to cylinder prep.
After proper honing and deglazing, your cylinder wall should have a consistent, 45 degree crosshatch.
If the bike is a 2 stroke don’t forget to chamfer the ports. If it has a bridge in the exhaust port, most pistons require this area to be relieved. READ the piston specs, and if you don’t understand, be sure to reach out to Wiseco for specifications. Read our guide to relieving the exhaust bridge in 2-stroke cylinders.
A critical step in 2-stroke cylinder prep is port edge relief and exhaust bridge relief. This will help ensure smooth piston and ring operation, and combat accelerated ring wear.
Be certain that the ring gap is within specification. Don’t assume it is correct, check it.
Always double check your ring end gap. With your compression ring in the cylinder, measure the end gap with a feeler gauge to ensure it's within the spec included in your piston instructions.
Proper cleaning of the cylinder. Before you start cleaning make sure the gasket areas are clean with no residue of gasket or sealers. First, use a cleaning solvent with a brush and then again with a rag. This is not enough, and you will need to clean with dish soap and water. Using a clean rag you will be amazed on how much grit from the honing is still in the cylinder. Be sure to clean the piston also.
Thoroughly cleaning your cylinder for a rebuild is critical. Be sure all old gasket material is removed, and use a 2-step cleaning process of solvent with a brush and rag, followed by soap and water. When the cylinder is clean and dry, you should be able to wipe the cylinder wall with a clean rag and not see any honing material residue.
Then before assembly, use plenty of assembly lube on the cylinder and the piston. Don’t forget to lube the piston pin and bearing along with the rings.
Assembly lube on the piston, rings, cylinder, pin, and bearing is important for proper break-in.
Many rings have a topside for proper sealing. Double check this and be sure the proper ring is on the proper landing on the piston. Again, read the instructions that came with the piston.
Piston ring markings vary, but the marking should always face up when installed on the piston.
The gaskets and quality play an important part of engine rebuilding. If a gasket is thicker than the original, it could result in a loss of power. Worse yet, a gasket thinner than the original will result in less deck height (piston to head clearance). This reduced clearance may result the piston to come in contact of the head causing permanent damage. After placing the gaskets, be sure while assembling the piston in the cylinder that the ring gaps are in proper placement. Check your engine manual for proper placement of the piston gaps. Then, install the head.
Many motorcycle manufacturers have a desired head nut tightening sequence. Refer to their procedures while doing this. Most companies give the head nut torque rating with the washers, nuts and studs being clean and dry. That means if you use oil or a thread locking compound the studs will be over-stressed due to the over-tightening of the head nuts. Engines have been damaged by this. Now you know, follow what the engine manufacturer recommends!
Regardless of the type of motorcycle engine you're working on, there should be a tightening sequence and torque spec for the head nuts. Pay close attention to the specs in the manual, as these are critical to prevent damage and for proper operation.
Use the proper engine oil and fill to the proper level. The fuel you use should be fresh and of the proper octane. If your engine is a 2 stroke, mix to the proper fuel/oil ratio. For just about any 2-stroke, whether vintage or a newer, a 32:1 fuel/oil mixture is very common, but check your manual for the recommended ratio. Not only is it important for piston lubrication, but also for the crank bearings and seals.
After all this work has been done, and you feel confident with the rebuild, what else can go wrong?
PROPER ENGINE BREAK-IN!
So many mistakes can happen while breaking in the piston and rings, resulting in rings never properly sealing or/and piston galling. Many builders have their own procedures, but most all do heat cycling for breaking in engines.
Before we get into it, please note that this is just one of many methods that work well for engine break-in. Many people have many different effective methods, this is just one example that has worked well for us.
Use this break-in procedure as a guideline for your next fresh top end:
It's important to ask yourself if the rebuilt engine is still using the same carburetor, air cleaner, exhaust system, cam, compression, or if a 2-stroke, the same port work configuration? Any changes can result in air/fuel mixtures to be either too rich or too lean, resulting in engine damage. If your engine is fuel injected and in good working order, the ECU and O2 sensor should keep the air/fuel mixture correct. If you have access to an air/fuel meter, or if a 2-stroke, an EGT (Exhaust Gas Temperature) gauge, check the air/fuel mixture. Even with these tools, spark plug readings are still recommended.
Spark plug readings are a sure-fire way of knowing if your engine is running too lean or too rich. We'll get into more detail in a later article, but generally the plug will look white when it's too lean, and dark brown or black and wet when too rich.
At first start up, keep the engine just above idle and give it a few revs up and down. This power on and power off RPM breaks in the piston and rings evenly on the intake and exhaust sides. If air cooled, once the engine builds up heat where it becomes too hot to touch, shut the engine off. If water-cooled, once the engine coolant starts rising in temperature, shut the engine off. This initial warm up takes just a couple minutes.
Now wait a few minutes until the engine is slightly warm to the touch, repeat #2, letting the engine get slightly hotter. Be sure to keep the engine RPMs above normal idle and keep the RPMs going up and down slowly. Let it cool again till it is slightly warm to the touch.
This time, start and run longer until the engine gets near operating temperature. If air cooled, be sure you have a fan pushing air from the front. You now can rev the RPMs up a little higher, being sure not to hold it at a sustained RPM, but revving it up and down.
Let the engine cool completely. Check all fluid levels to be sure there is no loss of engine lubricant, or, if water-cooled, engine coolant. After engine is cool, do a plug reading to be sure it is not running lean. Because the engine has run a few heat cycles, the gaskets may have compressed. It is VERY IMPORTANT to be sure engine is totally cooled down, and then check the torque of the cylinder head nuts. Most times the cycling head nuts will need some re-tightening. DON’T over-tighten; just tighten to manufacturers’ specification as you did when assembling the engine.
Next, warm up the engine for a couple minutes as you did in the other procedures. Ride the bike, revving the engine up to normal riding RPM. Be sure NOT to keep the RPM too low and don’t lug the engine. These low RPM’s actually puts much more stress on the engine parts. If this is a dirt bike, running on a track is best due to the up and down RPMs the engine will experience. Don’t be afraid to run it normally. If this is a road bike, a curvy road is best due to the RPMs going up and down, this is a must! Don’t lug the engine and don’t go on an open highway that keeps the engine at a sustained RPM. This first initial ride will only be about 5 minutes. Let the engine cool till you can touch the engine.
Follow the same procedure as above, but this time running for 10 minutes.
This will be your last break-in run. Follow the above procedure and run for 15 minutes.
Now is the time to let the engine totally cool down again. Check the fluids as you did before after the engine has completely cooled down, and do another spark plug reading. It is now time to do another check of the cylinder head nuts for proper torque. Sometimes no additional tightening is needed, but don’t be alarmed if you need to, because this is normal
Check all your fluids once more after the engine cools, inclduing coolant and oil level. At this time, the rings and piston should be broken in. Go out and ride it. The first few times, just be sure not to get the engine overheated, but your ride times are not restricted. It never hurts to do another spark plug reading and double-check the head nuts after your first long ride. Enjoy your rides, and be safe!
Hi all, long-time lurker, first-time poster here. I've learned a ton from reading this forum, now I could use some specific help.
I’m a relative newbie, I think my countershaft cracked while I was riding and I lost the nut. Somehow the sprocket didn’t slide off until I parked. Now I need to get it fixed…I don’t think this is something I can do myself. I’d love some guidance on what I need done so I don’t get taken for a ride by the shop.
It’s a DRZ400SM from 2006, new to me as of a few months ago. The other day I took it out to clean/lubricate the chain, which was overloaded with gunk and dirt. I cleaned it with kerosene and lubricated with one of those overpriced motorcycle chain sprays. I also removed the C/S sprocket cover and cleaned around there before lubricating. Everything looked good, there was no play in the sprocket nut. (I don’t know if the previous owner did the loctite fix, but I’m guessing not.)
In the morning I took it out for a ride on the freeway. It performed wonderfully at indicated speeds up to 140km/h. I parked at a rest stop, drank some coffee, tried to walk the bike backwards out of a parking spot and the rear wheel locked up. I looked down and saw way too much slack in the chain. Got off the bike, opened the sprocket cover, and found this:
After removing the dangling front sprocket:
Spent the next few hours waiting for a tow and reading this forum to try to figure out what’s happened. Seems to me like the countershaft cracked and I lost the threaded part, so the only way to repair this is by replacing the countershaft. And from what I gather, that means removing the engine from the bike and opening up the bottom end. At least that's what I learned from this thread, although I'm not positive I'm facing the same issue:
Is my diagnosis correct that it's a cracked countershaft? Am I correct in thinking I need the countershaft replaced, and that this is a big job that includes removing the engine from the bike and opening it up? Does this mean I need a "bottom-end rebuild"? Or does that term imply more than I really need here? Even if I could get by with less, does it make sense to try to do so? Or should I just bite the bullet and have a mechanic do a full review and possible overhaul of the bottom end once I’m paying for it to be opened anyway? Bear in mind the engine is from 2006 and I’m the eighth owner…who knows what else is worn out and could use replacing? Does all this also imply a top-end rebuild? Or can the bottom end be done on its own, saving time/money? And if it can, is that recommended? I intend to stop by a local shop or two and show them pictures and see what they say, but I'd like some pointers beforehand so I know what to expect. I don't really have the skills or knowledge to verify that they know what they're doing and are being honest, so any pointers like questions I should ask them or red flags to avoid would be a huge help.
Bonus round if you’re still reading and want to speculate:
How the *** did I make it to the rest area in one piece? It seems to me like incredible luck that the sprocket didn’t come off while riding, which probably would have meant a rear lockup and lowside on the freeway. What causes this to happen? Was it weakened by my cleaning/lubricating the night before? Just coincidence? Would the loctite fix have prevented this? Or was it just the high speed on an already damaged countershaft? Thanks again to all you experts who take the time to share your knowledge with strangers on the internet, really. The internet is an amazing thing, the way communities form and people help each other out. Never ceases to amaze me.