Overhauling Auto Lube Pump, The Core of Yamaha 2-stroke Engine Lubrication

The oil pump is the heart of lubrication in two-stroke engines, which burn a mixture of fuel and engine oil. Yamaha was the first company in the world to commercialize an oil pump. The pump, which is the cornerstone of the separate oiling system named Auto Lube, is extremely reliable and durable, but some problems can occur over time on older models that have been left unattended for long periods of time or otherwise poorly managed. In general, these parts are replaced by assemblies, but here I will try to restore the performance by overhauling.

Auto lube that automatically adjusts oil delivery rate according to engine speed and load

Yamaha HS1 oil pump. It has many parts, but the key to preventing oil leaks are the four oil seals (although three are visible in the image). The distributor and plunger in the center of the pump were introduced in the 1960s and remained almost the same until the R1-Z in the 1990s.

Auto lube pump that was not submerged in water but had corroded on the inside of the oil pump cover, this was the condition of the motorcycle when I tried to revive it after 30 years of neglect, examples like this are not uncommon for out of print and older motorcycles.

Whether it is a 50cc scooter or a 250cc racer replica, the oil tank is located in a separate place from the gas tank, and it is common sense for 2-stroke vehicle owners to refuel when the oil light in the meter comes on. This is because there is an oil pump inside the engine, just like a 4-stroke engine, and the oil is automatically supplied.

However, if you go back in the history of the 2-stroke engine, it was not equipped with an oil pump from the beginning. In the old days, 2-stroke oil was poured into the fuel tank every time the engine was refueled, and the engine was working as a mixture of oil. Therefore, it was necessary to calculate the amount of 2-stroke oil to be injected and mix it according to the amount of fuel, and if the mixing ratio was too thin, there was a risk that the engine would burn, and on the other hand, if the mixing ratio was too thick, it was normal for the burnt oil to be emitted as white smoke from the muffler.

expressed autorouteThis is the Auto Lube. The Auto Lube uses a plunger pump that operates in synchronization with the crankshaft to pump the engine oil, and the stroke volume of the pump (discharge volume) is variable according to the throttle opening. The Auto Lube has succeeded in balancing the contradictory conditions of reducing white smoke while preventing seizure.

Auto lube achieves separate lubrication in contrast to the mixed lubrication method where oil is directly injected into the fuel tank. It's no exaggeration to say that the invention of Autolube led to the development of separate lubrication by manufacturers other than Yamaha, which in turn led to the introduction of the racer replica models that boomed in the 1970s and 1980s. Autolube was such a revolutionary system.

The beauty of the Auto Lube is that the core of the mechanism - the plunger pump and distributor - has remained virtually unchanged since it was first introduced and has been passed down through the generations. In the 250cc class, for example, the auto lube pump on the 1964 Yamaha Sport YDS-3 and the 1992 R1-Z are nearly identical in appearance. The performance of the engine itself was greatly improved by the addition of reed valves and YPVS and water-cooling, but the basic aspects of engine lubrication were nearly perfected by the time the engine was introduced in the 1960s.

As expected, the appearance of the pump was drastically changed at the stage of the V-type engine TZR250R, which completely changed the engine shape, but there is no doubt that the Auto Lube was the core technology of Yamaha's 2-stroke engines.

If the pump body is disassembled, the oil seal can be replaced with a standard product.

The gap between the plastic starter plate and the oil pump body is small, but wide enough for moisture and humidity to seep in. Changes in temperature and humidity cause rust to start under the plating on the distributor shaft surface and spread to the rubber oil seal and aluminum pump body surface.

The pump cable, which is split from the throttle cable, is connected to the adjusted pulley on the opposite side of the starter plate and rotates. The amount of stroke of the plunger increases or decreases depending on the amount of rotation of the pulley, and the larger the throttle opening, the more oil is discharged. The guide pin for the pulley set in the pump case cover is pinched with pliers.

Before pulling the distributor shaft out of the pump case, the rust should be removed to some extent on the oil seal side because the rusty tip may damage the bearing of the pump case. With this much rust, even a new oil seal with a flexible lip would not be able to stop the engine oil in the case. It is not a fixable level and needs to be replaced.

When the engine starts, oil is supplied from the oil tank to the inside of the pump, and is discharged into the carburetor by the plunger that is constantly stroking, which is the basic operating mechanism of the auto lube. As the engine speed increases, the amount of fuel increases, so the amount of engine oil discharged must also increase accordingly. On the other hand, even when the engine speed is low but the load is high, such as going up a steep hill in a low gear, there is a risk of seizure if more engine oil is not added.

There is an added benefit of the throttle position factor here, as the wire linked to the throttle cable rotates the adjusting pulley, increasing the stroke of the plunger increases the amount of oil delivered, so even at low rpm, if the throttle position is increased, more engine oil can be supplied. It is possible to supply more oil.

The Autoroute pump incorporates a number of oil seals, the distributor rotating in conjunction with the engine and the plunger stroking at its centre. In the early years of their use in the 1960s, individual parts could be purchased as spare parts, but the precision of their construction and their proven durability meant that they were eventually supplied as assemblies.

However, no matter how much the reliability is improved, it is difficult to completely reduce the probability of lip wear and damage to zero because of the relationship between the rotating shaft and the oil seal. Also, in the process of reviewing old and out-of-print motorcycles, there are more and more opportunities to recycle immobile motorcycles that have been left for a long time. In such cases, there are examples of engine oil deterioration inside the pump and leakage from the oil seal.

Fortunately, the oil seal, which is the main cause of oil leaks, is a general product that is defined by industrial standards, so there is a possibility that a skilled Sunday mechanic can replace it himself. The oil pump on the Yamaha HS1 90cc twin shown here has a paper gasket in one place, but this can also be reused with a liquid gasket if the old gasket comes off properly.

Slightly exposed areas corrode with moisture and cause oil leaks.

A small oil seal is incorporated in the center of the distributor shaft where the plunger is inserted to ensure an airtight seal and prevent oil leakage. All seals inside as well as outside the pump case can be purchased as standard parts. Incidentally, the oil seal used here is available as a genuine Yamaha part, and if you match it by size, Suzuki genuine parts use the same size.

The bottom right is a pump that was disassembled due to rust on the distributor shaft, the left is a parts collection part that was set in the case cover, and the top right is a pump for an AT90 that was original and unused. As you can see from the parts collection, the oil pump is not located in a place where it is directly exposed to rain and wind. However, being left unattended for many years, moisture-prone elements get into it.

The shaft removed from the parts pump (above) also has some rust, but not as bad as the shaft below. The starter plate is an effective equipment to release the air by forcing the oil out when the pump is empty, but it seems to be a weak point after half a century. However, it seems to be a weak point after half a century, but I can't say that now, so I'll try to find a usable part.

The condition of the pump case itself as well as the distributor shaft was good, so we decided to utilize the oil pump that was supposed to be parted out. The oil seal was replaced and a new pump case cover gasket was installed.

 The amount of stroke of the plunger at idling is adjusted with thin shims. If the stroke is too small, the amount of oil dispensed will be too little, causing seizure, so use a combination of shims to adjust the stroke to a minimum of 0.15 mm, and usually in the range of 0.20 to 0.25 mm.

If the oil leak is due to deterioration of the oil seal, it is relatively easy to repair, but if the internal parts are damaged, it is unfortunately hopeless. If the vehicle has been left for a long time and there is still oil in the pump body, the distributor shaft may not be rusted, but if the oil has been drained out for some reason, the shaft may be rusted.

In some cases, as in the case shown here, corrosion on the exposed parts of the body can be the cause of the trouble. 1960s auto lube pumps have a plastic gear called a starter plate at the end of the distributor shaft. This gear is used to force the pump to perform without the engine working when oil is injected after the inside of the oil pump or oil pipe has emptied for some reason, and under normal conditions, it will spin as the engine works.

There is only a small exposed area on the distributor shaft where the starter plate is mounted, but this is where rust can occur. The oil pump itself is set on the right side of the engine and has a cover, but it is not submerged in oil like the clutch disc, but is exposed to the outside air, and over a long period of time, the surface plating can rust due to continuous exposure to temperature and humidity changes. The oil seal is built into this shaft, but if the surface of the shaft becomes uneven, it will naturally not be able to seal, and this will cause oil leaks inside the pump.In the RZ250/350 era, the oil pump is no longer used and is now a cap, so there is no need to worry about rust in this area since the distributor shaft is not exposed.

The distributor shaft used in the HS1 would have been available as a genuine part in the 1960s, but of course, it is not available now, more than 50 years later. So I replaced the shaft with a pump that I had obtained as a spare part. If the replacement parts cannot be procured, it will be literally immobilized. If you want to drive an old motorcycle, you have to search and procure the out-of-print parts which are difficult to get.

The distributor shaft that I removed from the spare engine was also in better condition than the repaired shaft, although it was starting to rust a little, and after polishing it with compound and setting a new oil seal, it did not leak any oil. I was also able to find an unused oil pump (for the AT90, the same 90cc twin cylinder as the HS1) on the internet, so no worries about auto lube in the future.

For Yamaha 2-stroke owners, the revolutionary auto lube system with separate lubrication is a mechanism that should be passed on to the future. Although non-disassembly is a prerequisite, it is important to know the internal structure and composition of the parts so that you can calmly deal with the problem when it arises.

The oil pump is set on the engine cover which has been painted beforehand. The plastic oil pipe has hardened over the years, so it is best to start the pipe through the cover before installing it on the engine to avoid complications. This way, when the engine starts and the distributor shaft rotates, the engine oil will not leak out of the pump case.

See YAMAHA Moto Index Page
See Accessories for YAMAHA TZR250R
See Accessories for YAMAHA RZ250
See Accessories for YAMAHA RZ350