Servicing the Slash 2 (/2) Oil Cleaning Slingers
© Copyright, 2012, R. Fleischer
There is very little specific Slash 2 or /2 information on this website. There IS a listing of the rear drive ratios in http://bmwmotorcycletech.info/ringgears.htm. The main reason there is so little SPECIFIC /2 (and other earlier BMW bikes) information is that my huge three ring binder of notes 'disappeared', and it was so many years since I worked on these bikes, that I did not want to furnish possibly faulty memory information. However, there IS a lot of information in the carburetor, electrical's, and other areas of the website that are applicable.
Slingers, background information:
Before the slash 5 boxer engine motorcycle, which is often referred to as an Airhead, began production in late 1969 (and that style of engine continued until the end of production in 1995), the engine in BMW bikes were very different in many respects. After WWII, in general, the street bike models had the camshaft located higher up, and lubrication was not the best, but adequate. The location of the pushrod tubes is a dead giveaway on pre-1970 twin cylinder bikes, as they are ABOVE the cylinders.
For the purpose of this article, I will use Slash 2, or /2, to include all those pre-1970 engines that had no removable and replaceable oil filter element, but had slingers on the crankshaft, and this includes the boxer twins as well as the single cylinder bikes such as the R26 and R27, etc. BMW made all of these various engines for a very long time. The information generally applies to other motorcycles besides those actually identified as /2; that is, generally all BMW motorcycles built before 1970. BMW also built race engines, and these were often very different in layout, so they are NOT included here.
There was NO OIL FILTER such as a paper pleated filter, or anything even close to that, as there is on the 1970+ Airheads. On the /2, the oil from the oil pump was 'filtered' by sending it into closely separated plates or plate and backing, that were part of the crankshaft assembly. One plate is called a slinger, where the harsher of the contaminants would be deposited into a hard layer along the edge of what was actually a shallow cup.
The capacity of the cavities was limited. If the slingers were not cleaned at reasonable intervals (you will NOT think the mileage reasonable! ...30,000 miles!), the slingers would fill-up, clog the oil passageway, & some very expensive engine parts would be ruined.
The over-all condition of the engine, including such as blowby from wear in such as valve guides and piston rings; how the bike was driven; under what conditions & what type of oil; ...all had effects on how fast the slingers filled-up.
The material the slingers gathered/filtered, by centrifugal force, tight spacing, & deposited in themselves ...was rather hard. It was not removed by adding detergent additives to the oil or by the detergent additives any modern oil came with. Oils were not as good back then either, and, in truth, the deposit build-ups DID, SOMEWHAT, depend modestly upon the type of oil used. Modern SG oils work well with the old bikes, but the deposits will still build up as things wear.
The material deposited in the slingers was somewhat magnetic, and consisted mostly of worn engine metals.
In order to clean the slingers, you must disassemble the engine! There is NO OTHER WAY. If you failed to clean the slingers (sometimes you had to replace them, they could be damaged upon removal, depending on where they were in the engine version), you WOULD cause oil starvation and RUIN OR GREATLY DAMAGE THE CRANKSHAFT. This creates a very expensive repair.
I wrote an article on how to do this & posted it on this website in a hidden file, the URL of which I would give out to those needing it. This was done because I did not want to be known as any sort of pre-Airhead expert, & there are web groups devoted to them.
On October 11, 2010, I saw a shorter article, more pertinent & to the point too!, posted on the Airheads List by Mike Arman. I decided to edit it liberally, & post it here. The information here is reasonably complete on how to do the job. I still have mixed feelings about owner's doing this work without a full understanding & following instructions carefully.
To clean the slingers requires some special tools. You will probably want to remove the engine from the frame. You will have to remove everything in front, that means the magneto & generator. The timing chest has a lot of Allen screws & you must heat the cover. You will have to remove the cylinders & pistons. Don't try to remove the rods at this point. Removing of the large flywheel nut is required, locking the flywheel (like one does with an Airhead) in order to undo that nut. You will be removing the oil pump drive nut which is a left-hand thread, and remove the gear (on a taper). You will rotate the crank & remove all 4 of the front cam bearing housing screws, then heat the top of the crankcase quite hot & remove the camshaft with the rear cam bearing.
There is a small bearing forward of the main crank gear; it needs to be heated quite hot & then pulled off. You will have to put the flywheel back temporarily & lock it again so you can do the gear work. You can then remove the front main bearing retainer ...with a heated crankcase. If the old style main bearing retainer is cast iron, it may be cracked.
As Mike pointed out, for the R50S, R69, and R69S you'll need a special tool which keeps the self-aligning rear main bearing aligned. Fasten tool into place, heat the rear of the crankcase, pull the crank forward & "roll" it & the rods out of the crankcase. Remove the rear main bearing which had better be very tight. If it comes off easily, the rear of the crank is necked, this can be fixed at high cost.
Now you can remove & clean the slingers. The deposits are HARD and difficult to remove completely. It may be easier to buy new slingers.
At this point you want to inspect everything & get new bearings (rear main is $$$). If you use standard number 6207 for the main bearings, be sure they have metal cages and 11 or 13 balls ...do not use bearings that have a plastic cage and 9 ball bearings. The other bearings are not very expensive. You will need new gaskets & seals, rear main seal, etc.
If the engine is relatively worn, maybe you need to hone the cylinders, get new piston rings, maybe even pistons. How are the valves, valve seats, valve guides? What about the generator brushes, ignition points, etc? Think about honing the cylinders, touching up the valve seats, new generator brushes, points, condenser, plugs and maybe wires.
Re-assembly is rather involved. Better get a good book. Mike recommended the BMW Blue Book manual.
Maybe you should be in touch with Vetch! ...and/or farm the job out ...or?
NOTE: The singles are different in some ways. No need to get into them here, you would easily see the differences during disassembly. References:
http://www.motorrad-stemler.de check it out for /2 parts sketches...etc.
I don't typically discuss the /2 and /3 bikes; or, really, anything built before December 1969. I also do not "follow" Vech's site, nor the sites for the older bikes. Two reasons. One is that my huge notebook on the /2 and /3 era bikes was somehow lost. The other reason is that these old bikes have a specialized following, some of who are much more knowledgeable than I am ...as my memory has faded on them over the years, as I got further & further away from working on them. However, there are some sources for information, such as a /2 LIST on the internet (and other lists or groups), and in a very few books. One of the books that is just about a must to own is the Barrington Motor Works BMW /2 Restoration and Service Manual. This is a well done book, reviewed by many 'experts' in the field before it was published. The book is roughly $100, and worth it. email@example.com or call 607-664-2673
© Copyright, 2012, R. Fleischer
Return to Technical Articles LIST Page
Return to HomePage
Last check/edit: Friday, November 18, 2016