Full Answer
How many hours does a 2 stroke top end last?
This often happens after a top-end has so many hours on it, and will get worse/less powerful over time. How many hours on a 2 stroke top end? 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.
How do I know if my 2 stroke needs a rebuild?
Low compression is the most common sign that your 2 stroke needs to be rebuilt. Hard starting and plug fouling are also symptoms of a worn top-end. For a complete list of signs click here .
Do I need to rebuild the top-end of my two-stroke?
Periodically, if you own a two-stroke, there will come a point where you need to rebuild the top-end of your engine. Hopefully, this won’t come as a surprise to you and will be part of your planned maintenance schedule versus experiencing an unplanned engine failure.
How to make a 2 stroke dirt bike last longer?
Starting up your 2 stroke dirt bike and immediately going for a ride is one of the worst things you can do to it. If you want the top-end, as well as the bottom-end to last longer and save you money, you need to properly warm up your dirt bike.
How do you know if you need a bottom end rebuild?
Simply grab the con rod and push and pull it while feeling for any movement. There will always be a small amount of side to side play, but there should be no up and down play whatsoever. If there is play, then the crank will need replacing, which means a full rebuild is needed.
How do I know if my 2 stroke needs a bottom end rebuild?
0:005:05KTM Dirtbike Bottom End Checks and Measurements - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd check it very thoroughly in good lighting if you do discover any damage. And it's been rubbingMoreAnd check it very thoroughly in good lighting if you do discover any damage. And it's been rubbing up against something it would typically mean that the con rod needs replacing.
How often do you have to rebuild 2 stroke engine?
How Often Do You Have To Rebuild A 2-stroke? It is necessary to do that every year. If you are working hard, you will have more time. It is best to rebuild after 50 hours or riding a motorcross.
How long does a 2 stroke crank last?
It's all relative to maintenance and how you ride obviously, but as a rule of thumb, with a good maintenance schedule 250 2-strokes usually can go 100-150hrs on cranks.
How many hours is alot for a 2 stroke dirt bike?
You should be good for another 10-15 hrs assuming PO regularly cleaned air filter and did not abuse the bike. Good news is a two stroke top end is so easy a child could do it. Plus, less actual parts to replace (piston, rings, gaskets - done).
How often should you change a piston on a 2 stroke?
Most modern two strokes / four stroke Motocross/Enduro motorcycles recommend piston and ring replacement at 15 hour or 5-6 race intervals. Just because the kick starter feels firm or it starts easy, it still may be time for maintenance.
Is 100 hours a lot for a dirt bike?
What Is Considered High Hours on a Dirt Bike? If you're a dirt bike enthusiast who casually drives the motorcycle from time to time, 100 hours is considered high hours.
How do I know if my 2 stroke engine is blown?
0:322:30Quickest way to tell if your 2-stroke is blown - YouTubeYouTubeStart of suggested clipEnd of suggested clipPut take this off oh come on come on come. On. Then using a flashlight look straight up the exhaustMorePut take this off oh come on come on come. On. Then using a flashlight look straight up the exhaust port to see if you can see vertical scoring marks on the cylinder.
How many hours is 450 top end?
Always having a clean air filter and fresh oil. What did the manual, service manual say? The 16 KX450 manual says 15 hours for a top end and the same for oil changes.
What is included in a bottom end rebuild?
Replacement components are a major factor to consider, both in terms of cost and engine performance, when diving into a bottom end rebuild. Replacing bearings, seals, gaskets, and refurbishing the crankshaft either by rebuilding or replacing it is essential.
How do I know if my dirt bike needs a rebuild?
The Top Ten Signs You May Need To Rebuild Your Dirt Bike Engine. Hard to Start - This could be due to a fueling issue, ignition issue, decompression system out of adjustment, worn rings, worn valves and seats, a stuck valve, leaking gaskets, or cam timing that is off.
How much does it cost to rebuild the bottom end on a dirt bike?
When you are using OEM parts, which includes all new bearings throughout the engine, a cylinder head, new valvetrain, new crank, new piston, new cam chain and tensioner, and a freshly honed cylinder, the cost comes to $1300 to $1500.
How to know when to rebuild top end?
How Do I Know When To Rebuild My Top End. There are some signs and symptoms that your dirt bike will tell you when it needs attention. Low compression is the most common sign that your 2 stroke needs to be rebuilt. Hard starting and plug fouling are also symptoms of a worn top-end.
How many hours can you ride a 125cc 2 stroke?
Not only do they have considerably more low-end torque, but you can usually ride them about twice as many hours as a 125 or 150cc 2 stroke before needing to tear down and replace top-end parts.
How to make a top end rebuild go smoothly?
In order to make your top-end rebuild go smoothly, you need to have a clean dirt bike and a somewhat clean and organized work space . This doesn’t mean you need to have a large shop that is spotless, but having enough room to get around your bike and a small bench really helps.
How to check piston ring wear?
To check a piston ring for wear, place it by itself in the cylinder and use a feeler gauge (Amazon) to see how big the gap is. Checking the ring end gap.
Why is cross hatching required on cylinder walls?
Cross-hatching is required on the cylinder wall because it holds a small layer of oil that lubricates and seals it to the piston ring (s). If the cross-hatching is worn, the compression will be lower. About to hone this bad boy. Cylinder tolerances looked good; just need a light honing.
When tightening a cylinder and head stud nuts down, do you need to do it a certain
Proper Torque In A Pattern. When tightening the cylinder and head stud nuts down, you need to do it a certain way. If you tighten each nut down one at a time then you may warp the cylinder or head, and then you will blow the gasket and cause major problems in a hurry.
How to get a cylinder off a cylinder?
To get the cylinder off, you may need to remove the power-valve cover and remove a nut or bolt to disconnect it. If the cylinder is stuck, don’t try to pry it off with a screwdriver or pry bar. That will surely damage the mating surfaces.
How long does a 2 stroke piston last?
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.
How many kicks does it take to start a bike?
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.
Why does my piston have a score?
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.
Can you cold seize a dirt bike engine?
Don’t cold-se ize your engine by doing this! Starting up your 2 stroke dirt bike and immediately going for a ride is one of the worst things you can do to it. If you want the top-end, as well as the bottom-end to last longer and save you money, you need to properly warm up your dirt bike. Click here to learn how.
Do dirt bikes work the same?
Not all dirt bikes work the exact same. 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.
Is it better to kick over a dirt bike with one finger?
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.
Do piston rings need replacing?
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). I. If you have the cylinder off, check the ring gap with gauges and compare to what the manual says.
What to do when you see dirt in your intake?
When you see dirt in the intake, you’ll need to tear down the top end to check for damage. A damaged cylinder may need reconditioning or replating. The same goes for when you find your intake boot and airbox was not sealed properly. Anytime you find leaks, you’ll want to tear down and inspect for damage.
Do quad bikes need to be refreshed?
Many race vehicles are refreshed at strict intervals to ensure top performance. Your recreational bike won’t need to be refreshed at such a strict schedule, but it may also be a little lax on routine maintenance.
Pre-Teardown
Diagnosis – Before tearing the engine apart, are there any signs that a specific problem exists? If so, are there any diagnostic tests such as compression or crankcase leak down that are worth performing?
Disassembly
Limit Contaminants – Once the cylinder has been removed wrap a clean, lint-free rag around the top of the crankcase. Dirt is one of the leading causes of engine wear, and limiting the opportunity for dirt to enter the crankcase is very important.
Inspection
Reed Valve – Don’t forget to check the condition of the reed valve petals, cage, and any stopper plates. Most service manuals will detail the acceptable clearance between the petal tips and cage as well as the stopper plate height. Ensure any rubber coatings on the reed cage are in good condition.
Sourcing New Components
When freshening up the top-end in your two-stroke, it’s important to reassemble with quality components. A deglazed and honed or bored and replated cylinder is a critical component to ensuring reliable performance from your new top-end.
Measurements
The number of measurements that should be taken throughout the top-end rebuild will be discretionary. At ProX, we strive for excellence and err on the side of caution when it comes to engine building, so our builds consist of numerous measurements and inspections prior to reassembly.
Prep Work
Cylinder Cleaning – Once the cylinder has been deglazed or has come back from replating, it should be cleaned one final time. There is almost always leftover honing grit that will need to be removed.
Installation
Piston – On the top of the piston, an arrow will be imprinted, which typically denotes the exhaust side of the piston. Consult your service manual to confirm the proper orientation of the arrow and piston. Apply a light amount of assembly lube to the small end bearing and wrist pin bore on the piston, then install the bearing.
