Boxer Lubrication 101

[boxermania]

The intent of this post is to provide the BMW Boxer owner with the information necessary to understand the fundamental relationship between lubrication and the Boxer engine design. Hopefully after perusing the document, the owner should have gained sufficient knowledge to simplify the selection of the lubricant for his bike based on his/her riding habits at the same time reducing the cost and enhancing the engine durability.

First let’s identify some terms:

Owner’s manual – Provides “basic” recommendations to the new owner. I emphasize basic because one has to understand that these bikes are sold both in Alaska as well as Tierra del Fuego and the lubrication requirements are different in either of the locations. It is a guideline, period.

Air cooled engine – Engine design that enjoys the benefits of simplicity and fewer parts. However it does give up some performance primarily because the thermal range of operation is greater than that of a water cooled engine. Air cooled engines can never sustain the “tight” clearances of water cooled ones, therefore the efficiency will always suffer.

Nikasil – Electrodeposited nickel/silicon carbide matrix which when applied to aluminum cylinders has shown some excellent wear characteristics. Please note that this coating is quite common to the current aluminum engine designs. The reason being that if one makes the cylinder hard to wear, the rings will become the sacrificial component, the upside is that it is easier and less expensive to change rings than cylinders. This is one of the reasons while the boxer engines can go 200,000 miles (with proper maintenance) on the original cylinders.

Break in – A phenomena usually associated with operation and temperature cycles within the engine, that allow the rings to conform to the cylinder in such a way that it minimizes “blowby” or passage of combustion gases into the oil as well as preventing the oil to gain passage to the combustion chamber. Boxers typically use a significant amount of oil during the break in period. Let it be known that the way the bike is ridden plays a significant effect on the duration of the “break in” period, read oil consumption. Some owners will complete the “break in” within the first 5000 miles (stopped oil consumption) others have run 20,000 to 30,000 miles and haven’t completed the “break in”. Let me suffice to say that there are different and conflicting opinions on how to break in a Boxer, but that is a topic best left for another post.

Oil – A liquid whose primary function, amongst others, is to lubricate and act as a heat transfer medium in internal combustion engines.

Organic oil – Hydrocarbon derived (petroleum based). Two organizations, API (American Petroleum Institute) and SAE (Society of Automotive Engineers) regulate the grades and additive packages in the oil.

Organic oil, operational temperature – The rule of thumb is to keep engine oil temperature between 180 F to 220 F to attain maximum engine life. Yes, one can exceed 220 F with the understanding that rotating parts will wear at a faster rate. Once you exceed 260 F the oil viscosity begins to suffer and the engine life will be reduced accordingly.

Synthetic oil – Artificially synthesized lubricants such as esters and polyalpha-olefins. These lubricants, because of their highly refined state exhibit improved viscosity and a wider temperature range at temperature extremes than organic oils. In addition, these lubricants have improved efficiency over the organic variety; therefore they don’t degrade as quickly as the organic oils. It is very important to note that there is no difference in the retention of particulate matter, meaning that the filter will deteriorate (plug) at the same rate as that on the organic lubricant.

Synthetic oil, operational temperature – This oil has improved lubricity across its operational range. Typical range is defined between 170 F to 260 F. Once past 300 F, viscosity begins to suffer with end results similar to those of organic oil.

Grades – The grades have to do with oil viscosity. There are single grades like 30W and multigrade like 10W30. Basically the first one has one viscosity; the second one has a range of viscosities which change according to ambient and operational temperature. It is very important to understand that multigrade oils, because they exist as a blend can never reach the viscosity extremes. So a 10W30 oil will never reach the lower viscosity of a 10W or the higher viscosity of a 30 W.

Additives – Oils used on internal combustion engines use additive packages to minimize sludge, corrosion, mitigate metal to metal contact (zinc), along with friction reducers (moly) and extreme pressure compounds, amongst others. Some of the above are included with the oil to reduce the by-products of combustion.

OK so what now?

Break in - Suggest that one completes the break in with organic oil before going to synthetic. Synthetic oil has more lubricity than organic oil and therefore will increase the break in period (the comment is made regarding the Boxer engines). You want the rings to reach maximum sealing against the cylinder wall as quickly as possible; this in turn will reduce the amount of oil consumption significantly. The break in is accomplished faster if the owner revs through the gears and stays away fro steady state operation.

Organic or synthetic – That will depend on the ridding style and the frequency of use. For instance; if one uses the bike every day, runs through the gears and will run 30 minutes or more, organic will be my choice and there will not be any abnormal wear issues. On the other hand if the bike is used occasionally, the runs are short, with insufficient run time to warm the oil, there are benefits to using synthetic because of the superior lubricity.

Cost – In reality, there is not much of a cost difference. Let’s assume that the synthetic is 2x the cost of organic and assume that the organic oil is changed every 3,000 miles. So in the case of the synthetic you can probably run 6,000 miles before changes, although, because of the particle retention the filter will have to be changed at 3,000 mile intervals. So in the long run the lubricant cost is a washout.

Extreme conditions – If the ambient temperature is consistently above 100 F, I would suggest synthetic oil as the lubricant, since it enjoys a wider temperature range than the organic oil.

And last but not least

What should be my oil level – Middle of the window (sight glass) after a minimum of a 20 minute run, 3 to 5 minutes on the side stand and then onto the center stand. Come back when the bike is cold (15 to 20 minutes) and check the level. Never run the bike below the bottom of the circle as it will reward you with unpleasant and costly results, nor higher than the middle of the glass, as you will be burning the oil of in the combustion chamber acceleration the formation of carbon deposits.

In some instances, one might run for an extended period of time, however, the ambient temperature might be low enough that it will prevent the opening of the thermo valve to the oil coolers, therefore trapping a quantity of oil in the loop from the previous ride.
To your surprise you will find that upon checking, the oil level it is fairly low and your reaction will be to top up to the middle of the window. After the following ride you then find out the oil level is now at the top of the window…Arrgghhh…..the oil coolers loop opened up and the trapped oil went back into the system………I rest my case.

[cone]

very informative. Will you use a synthetic oil in your CBX once restored? I have asked a few people whether I can use a modern oil in my older bikes, R90S R50/2 and a 1936 New Imp and seem to be getting a different answer every time. a BMW mechanic once told me that a monograde 40 is the best oil for an aircooled engine. It is a hassle to keep different types of oil and will be much more convenient to buy one type of oil and use it on all the bikes.

[boxermania]

cone.....no, I plan to use Castrol GTX on the CBX once completed.

[cworley5150]

Ah, just put some oil of some type in her. She will be just fine. Boxers are tough and seem to like Dino oil OK.

(Explanation . . . I'm a little bored and toasted and reading old threads! Great Fun in the wee hours of the morning!)

Good info though, Boxermania.

[ROBOX]

Very interesting. However you did loose me a couple of times. I use fully synthetic and have no problems.

Thanks for the information.

Rich