A mixture of fuel and air is called fuel mixture, which is suctioned in through the "intake valve. The "exhaust valve" discharges the combustion gas (exhaust gas) that explodes, combusts, and expands toward the exhaust system. If the intake and exhaust valves and its peripheral parts are not in good condition, these parts will not work as expected. What is the condition of the old exhaust valves, which greatly affect the performance of the engine?
Identity of used intake and exhaust valves
Used intake and exhaust valves. Carbon buildup on the left exhaust side valve seat surface. The intake valve on the right appears to be in firm contact with the valve seat, but the bite surface is worn and pitted. The carbon buildup and concave valve seat on the bite surface will not maintain "good compression" and will cause compression leaks. Perhaps the engine that incorporated this old exhaust valve was idling poorly. The compression leakage would have reduced the explosive power of each shot.
Reusable with valve face polishing
A US-made machine specially designed to grind valves, which is used to grind and correct the valve faces at a 45-degree angle. Some models cannot be used for narrow valve stems of Japanese motorcycles due to its size, but for old 2-valve engines, this is a very easy-to-use valve grinding machine. The design is ingenious in that even when the valve stem is chucked quickly, it can be easily centered.
High-performance Swiss-made valve seat cutter
Officially, it is a valve seat refacer made by Swiss company Mira, a so-called high-performance valve seat cutter. It is easy to use, automatically shaking and moving the head of the device to find out the center of the valve guide by itself, and then fixing the main unit. Both work efficiency and accuracy are good, and the workability of valve seat cutting is greatly improved.
Actual examples of excessive use and driving.
A valve guide that has been worn out and finally damaged. It can be seen that the center of the guide bore is off-center and unevenly worn. It also causes the hole on the cylinder head side that supports the guide to widen. When the hole on the head side becomes rattled, it is possible to request a new valve guide with an oversized outer diameter to be machined and manufactured. If such a problem occurs, the outer dimensions of the commercially available valve guides will no longer fit. A professional store for machining internal combustion engines is a reliable source.
With valve stem seal to prevent white smoke
Normally, old Harley-Davidson engines are not equipped with valve stem seals, but iB Inoue Boring in Saitama Prefecture, which cooperated in the photoshoot, responded to a request to manufacture valve guides that can be fitted with valve stem seals to prevent engine oil from dropping = white smoke from the exhaust system. The company is also working on a new for Harleys with thicker valve stems, they use japanese produced stem seals for 4-wheeled vehicles. This iB original valve guide seems to be very popular. H-D V-twin engines have been manufactured for many years. It is not unusual even today for internal combustion engine machining requests to modify the side valve age, knuckle head, and pan head. That must be the beauty of Harley.
Interviewed by: iB Inoue Boring https://www.ibg.co.jp/
- Point 1: In some cases, old exhaust valves can be reused by "polishing and reconditioning" instead of replacing parts.
- Point 2: When a bore-up kit is installed, do not restore the parts just because they are compatible with the stock head, but disassemble and inspect each part.
When a specific component is in a "bad situation = malfunction," we should assume that the surrounding components are also affected. For example, when the clutch lever operation feels heavy, there is some kind of problem, and we should assume that the surrounding parts are also affected by the problem. If you have been riding continuously since you purchased the motorcycle and neglecting essential maintenance, the functional parts of the motorcycle will eventually deteriorate in performance. When the clutch lever feels heavy to operate, the first thing to suspect is the clutch wire. By cleaning the inside of the cable and injecting cable oil and grease, the clutch wire that was reluctant to move will clearly feel lighter to operate. Not only that, in some cases, the tightness of the clutch lever pivot bolt also reduces the operability of the lever itself. In some cases, the operation may have become heavier due to lack of grease around the pivot.
In many cases, the feeling of heavy operation is caused not by the clutch lever area or clutch wires, but by poor lubrication of a part called the clutch release on the engine side. Thus, even if the clutch lever is simply "heavy," there is more than one affected part, so it is important to be sure to maintain and inspect the surrounding and related parts as well. Such "incidental" maintenance will surely improve the condition of your motorcycle.
An extremely important component of a 4-stroke engine is the "old exhaust valve". Over many years of operation, the valves and its surrounding parts are subject to considerable wear and tear. The valve that moves up and down in the valve guide is called the valve stem, which is the sliding part (shaft part). In an overdriven engine, the inside diameter of the valve guide that receives the valve stem may become enlarged due to wear. When this happens, the valve guide must be replaced, and such work is requested by a professional store for internal combustion engine machining. Even if the valve guides are not available as genuine parts, an internal combustion engine machining store can be commissioned to manufacture machined valve guides.
If the valve guides were worn out, the operation of the intake and exhaust valves would be in a state of friction, and the bite of the valve seats would be considerably worse.
Generally speaking.
1. Valve seat bite spreads due to overriding.
2. Continuous sliding causes wear expansion of the valve guide bore.
Parts wear out in this order, but beyond that
3. Valve stem is worn out. → Replace the old exhaust valve with a new part.
To prevent this from happening, it is important to perform maintenance as early as possible. In some cases, what could have been a simple seat cut and rubbing may turn into a "negative chain reaction" requiring valve guide replacement, valve face modification, or even valve seat replacement. To avoid such a situation, it is important to always use high-quality engine oil and perform regular oil changes without fail.
When you notice a drop in engine power and want to overhaul the engine, you should not only replace the piston rings and oversize the pistons (boring and honing finish), but also cut and rub the valve seats, and if the valve guides are rattled, replace the valve guides as well. Maintenance with this in mind is essential. This is the first step to a perfectly good engine.
We often hear stories such as "I bored up a MONKEY to 88cc!", but we also hear stories like "the head was restored without modification" because it is a piston kit for a stock head. In such cases, simply removing the old exhaust valves, removing carbon, and scrubbing the valve seats will give you more power, so when replacing parts or performing maintenance, be sure to pay attention not only to the critical repair area, but also to the surrounding area.
