You can easily check for drive chain wear by seeing how far you can pull the chain off the rear sprocket (see picture). If you can pull the chain off more than one third of the height of the sprocket teeth than the chain is in need of replacement sooner rather than later. Keep in mind you need to replace the front and rear sprockets at the same time or you will significantly reduce the life of the new chain.
I am sure most of you have noticed a loss in engine performance on very hot, humid days. Why is that? Both higher heat and humidity will reduce the amount of oxygen in the air that the engine ingests. Hotter air temperatures thru reduced air density and higher humidity thru the water vapor displacing oxygen. As an engine uses oxygen combined with vaporized fuel in the combustion process there will be less heat is produced in the combustion chamber there creating less cylinder pressure. Less pressure equals less push on the pistons which equated to less power at the wheels.
Why is it that if you over bore some 4 stroke engines the performance gained is more than what you would expect with the minor increase in actual displacement. As an example a YZ250F with a 2mm larger piston gains only 13cc in displacement yet will likely gain a few horsepower throughout the rev range with no other modifications. The gain actually comes from the larger bore"unshrouding" the valves in the cylinder head allowing for increased air flow. The 5 valve head is especially bad due to the crowding. All the power from a 4 stroke is in the head.
Wow! Attention All you Restoration Guys ! We now offer in House Wet Vapor Blasting for the Ultimate In Surface Finishing. Coming first week November!
Wet Vapor Blasting was originally developed by Rolls Royce to clean delicate turbine blades. With wet vapor blasting you can clean years of oxidation, corrosion, rust, grime and tarnish out of the tightest places while leaving a beautiful long lasting smooth oem satin finish. No other process compares when it comes to not only cleaning but surface finishing parts for a rebuild. You can also clean and restore most plastic and rubber parts. See below for examples !
Had a customer with a 500cc street bike who wanted to put a 2 tooth smaller rear sprocket to increase his top speed by approx 10km per hour. I explained to him that it may do nothing as with everything else being equal top speed is simply a function of how much horsepower your engine produces. As that isn't changing, chances are that gearing is not going to help assuming his top speed now is at approx where his bike is producing max hp.
Pistons always have directional arrows on them showing you which way to install them. Most times the arrow point to the exhaust but there are some weird exceptions (towards PTO, etc) and you need to check before assembly. One obvious reason is locating pin location for 2 strokes and valve size pocket on 4 strokes. There is another reason. The wrist pin is often offset to lessen piston side thrust to reduce wear.
Many manufacturers has built in fault codes to alert of any problems with the EFI sensors that tell the ECU how much fuel to inject at different rpm and load. Most engine sensors emit some noise in their signals and the problem is this value tolerance that the fault code looks for has to be large enough not to trip a false fault code due to noise but also small enough to know when the sensor is causing a problem. To avoid customer complaints generally this tolerance is on the large side so some performance problems can go unnoticed.
We see a fair number of off road bikes with premature engine wear from dirt ingestion. One often overlooked problem is the air filter cage. Many times these cheap plastic cages warp which causes the air filter to not seal tight against the air box. A good solution is to replace it with an aluminum aftermarket unit. Twin Air is one brand that offers this solution.
You may notice the far left Intake camshaft holder is marked with an E1. This unfortunately should be on the exhaust side. This R6 engine was just bought by a customer off Ebay and this is one of the reasons why I would rather rebuild than buy used. This motor ran like this and ultimately caused some damage to the cam and journal. Lesson, you have no idea what your getting when you buy used.
Most quality cast pistons have a silicon content of 18% or so versus a forged pistons max of aprox 12%. This higher silicon content results in less piston expansion and better high heat thermal properties which is desirable and critical in a 2 Stroke engine. The forged piston is stronger due to its grain structure which is desirable for a 4 stroke application.
I have been involved in mechanics and motorcycling from a young age. I formed Cycle Improvements in 1981 and still have the same passion to learn today as when I started. Hope you find this blog interesting and educational.