Operation of the outboard motor is not only the joy of water walks, but also the responsibility for the technical condition of the unit. Four-stroke engineUnlike two-stroke counterparts, it has a complex gas distribution system (GDM) that requires periodic maintenance, and ignoring routines inevitably leads to power loss, increased fuel consumption and, in the worst case, major repairs to the cylinder head.
One of the key procedures of maintenance is to adjust the thermal gaps of the valves. During the operation of the engine, the GRM parts are heated and expanded, and the lack of free running leads to a loose fit of the plates to the saddles. Adjustment of valves of 4 stroke engine It allows to compensate for thermal expansion of the metal and ensure the correct gas distribution phase, which is critical for the efficiency of combustion of the mixture.
In this article, we will discuss in detail the symptoms that require intervention, the necessary tools and step-by-step algorithm of actions. outboard factory traction and smooth idling.
Symptoms of violation of thermal gaps
You can understand that it's time for maintenance, you can tell by the characteristic signs in the work of the power unit. Most often the owner notices changes in the acoustic profile: a ringing metal tsokot appears, especially for a cold, or, conversely, a deaf knock. Valve knock This is the first and most obvious signal that the gaps have exceeded the permissible values.
But noise is not the only indicator, because the increased gaps cause the valves to open later and close earlier than the phaser should, which reduces the filling of the cylinder with fresh mixture and impairs exhaust cleaning, and as a result, the engine starts to "trouble", twitch at low speeds and gain speed poorly.
⚠️ Attention: If you hear a constant ringing that doesn't disappear after warming up, it's an indication of an excessive gap, and operating in this mode causes the pushers to collapse and the seats in the head of the block to break.
The other problem is the inverse valves, and there may be fewer symptoms, but there are more serious consequences, and the tight fit breaks the tightness of the combustion chamber, and the hot gases start to break out, melting the valve edges, and the engine loses compression, and the exhaust manifold can produce cotton.
Required tool and training
Before you start working, you need to organize a clean workplace and prepare a special tool. Yamaha, Honda or Tohatsu Specific probes are often required, as standard car probes may be too wide for narrow valve mechanisms.
You will need the following set:
- 🛠️ A set of probes for measuring gaps (flat, thickness from 0.05 mm).
- 🔧 A set of carob and cape keys (most often 8, 10, 12 mm).
- 🪛 Screwdrivers (cross and flat) for removing casings and adjusting screws.
- 🧼 Sealer for gaskets (heat resistant, for motor oils) and a new valve cover gasket.
It's also important to prepare the engine. The engine must be completely cooled. Adjustment to hot It will give the wrong results, as the metal is expanded, and once cooled, the gaps will become too large. Remove the upper casing, unplug the candle wires and carefully dismantle the valve cover, trying not to damage the gasket if you plan to use it again (although it is better to replace).
Before removing the valve cover, blow the compressed air area around the candle wells and valves, which will prevent dust and dirt from entering the head of the block when the lid is opened.
Theoretical Basis: Intake and Release
To be properly tuned, you need to clearly understand the difference between intake and exhaust valves, and in a four-stroke cycle, they perform different functions and operate in different temperature conditions. Intake valves They are washed with a cold fuel mixture, so their heating is less.
The exhaust valves take the main heat stroke by contacting the hot combustion products, which makes them expand more, so the heat gap for the exhaust valves is always bigger than for the intake valves, and if you confuse them when you set them up, the motor will not work properly.
The valves are usually located by location, and in most modern outboard motors, the intake valves are located on the carburetor side (or intake manifold) and the exhaust valves on the muffler side (exhaust manifold). OHC They may be in a slew of sleeves or in pairs.
Why do the gaps change?
Over time, the natural wear of the rubbing pairs occurs: the camshaft and the pusher (or skewer). The metal "sets", there is a production. This leads to an increase in the gap; Less often, if the assembly is wrong or overheating, the gap can decrease due to the deformation of parts.
Algorithm for valve adjustment
The tuning process requires attention and consistency, and the main task is to set the cylinder piston in compression stroke when both valves are closed, and only at that point can the gap be measured and adjusted.
Here's the step-by-step instruction:
- Find the VMT tag on the flywheel, and then twist the spark plugs to make it easier to turn the crankshaft.
- Rotate the crankshaft clockwise (usually behind the flywheel nut) until the "T" (Top) tag is combined with the risk on the crankcase.
- Check the position of the sterns. If both valves are "swafting" (there is free travel), then you are in a compression stroke. If one of the valves is pressed, this is the exhaust stroke, you need to turn the shaft another revolution (360 degrees).
- Reduce the control screw counternut, insert a probe between the valve stem and the skewer.
- Rotate the adjusting screw until there is light resistance when the probe moves. The probe should walk with little effort, but not get stuck.
- Holding the screwdriver tighten the counternut. Be sure to double check the gap after tightening, as it could have gone off.
☑️ Checklist before launch
Repeat the procedure for all cylinders, following the order of operation of the engine (usually 1-3-2-4 or 1-2-4-3, specify in the manual of the particular model).
Table of allowable clearances
The heat gaps are strictly regulated by the manufacturer. The use of arbitrary numbers is unacceptable. Below is a table with averaged data for popular outboard motor series. Accurate data Always look at the service manual of your model.
| Engine model | Intake clearance (mm) | Release clearance (mm) | Type of BRM |
|---|---|---|---|
| Tohatsu/Nissan (MFS Series) | 0.10 – 0.14 | 0.17 – 0.21 | OHV / OHC |
| Yamaha (Series F) | 0.10 – 0.12 | 0.16 – 0.18 | OHC |
| Honda (BF series) | 0.08 – 0.12 | 0.16 – 0.20 | OHC |
| Suzuki (DF series) | 0.09 – 0.13 | 0.17 – 0.23 | DOHC |
Please note that for engines with a system VTEC The procedure may be different and require special tools, in which case self-adjustment without experience is not recommended.
Frequent errors and nuances
Even experienced mechanics sometimes make mistakes that can negate all work, one of the most common is the pulling of the counternut, and with a lot of force, the screw can turn around, reducing the gap to a critical minimum, and this will lead to a very high level of damage. valve burn in the first minutes of work.
Another nuance is the condition of the probes: the use of bent, rusted or worn probes is unacceptable, the error of 0.02-0.03 mm for the valve mechanism is significant, and you should not use too thick probes "by eye" in an attempt to compensate for wear.
⚠️ Attention: Never adjust valves if the engine is warmed to less than room temperature or, conversely, still stores residual heat after operation.
Remember to check the condition of the valved skewers themselves and the ends of the rods. If they show production, holes or bullies, simple adjustment will not help - you will need to replace parts or laundry valves.
High-quality valve adjustment returns the engine to 10-15% of lost power and significantly reduces fuel consumption, making the engine quiet and smooth.
Conclusion and verification of the result
After assembly and installation of all the casings, you need to conduct a test start. The engine can stall for the first few seconds until the oil pressure rises and the ECU adapts (if any), Let the engine work at idle speeds for 2-3 minutes.
Listen to the sound. The metallic twitch should disappear or become barely visible in the background of the general noise. If the knocking is still there, perhaps the gap is still wide. If there is a hissing sound or clapping, check the exhaust valves, they are probably clamped. It is critically important not to leave the engine with signs of valve knocking under load.
Regular maintenance of the GRM extends the life of the outboard motor by hundreds of hours, and do not neglect this procedure, and your engine will delight with reliable traction on the water.
What do you do if you don't have probes?
In an emergency, experienced motorists use a piece of copper wire of a certain diameter or even a razor blade (about 0.1 mm thick) as a temporary reference, but this is a risky method that requires high qualification.
How often should the valves on the outboard motor be adjusted?
The regulations vary by manufacturer. Usually the first check is done after 20 hours (break-in), then every 100 hours or once a season.
Can the valve be adjusted on a hot engine?
It's not recommended. Thermal expansion of the metal will cause a significant error, and the gaps exposed to the hot one will become too large after cooling, leading to noise and impact.
What happens if you don't adjust the valve?
The increased gaps will cause noise and loss of power, and the clamped valves will lose their tightness, causing edges to burn, compression to fall, and eventually requiring expensive valve group replacement.
Do I need to change the slats of the slats?
Yes, 90 percent of the time, it's better to replace the gasket with a new one. The old one often deforms after removal and can leak with oil. Use a quality heat-resistant sealant for reliability.