Slingers

[redavide]

Most of you know a LOT more than I do about slingers, the bottom end of these motors and the history of their design, but as a novice I can't help thinking that design-wise, it just doesn't make sense that you have to pull the crankshaft after the first 30,000 or so miles and then every subsequent 30,000 miles. I have no doubt that the system works well, but that's a pretty stiff requirement to keep it going. The other thing that surprises me is that there isn't even some way to inspect them short of pulling the crankshaft -- you would think the engineers would have thought of some relatively easy way to at least check the condition of the slingers before having to disassemble the whole motor . . .

Anyway, thanks for the major education you've provided -- the explanations and photos, etc. are really great.

[Allan.Atherton]

... I can't help thinking that design-wise, it just doesn't make sense that you have to pull the crankshaft after the first 30,000 or so miles and then every subsequent 30,000 miles... you would think the engineers would have thought of some relatively easy way to at least check the condition of the slingers before having to disassemble the whole motor...
You don't pull the crankshaft every 30K miles. That only happens after 30K miles of neglect and abuse spread over 40 years. That was impossible to take place in the old days. In the bikes' heyday, in regular operation by police and couriers, the slingers only came out in connection with crank bearing replacement at much higher mileages. The "condition" of the slingers was of absolutely no interest, so there was no need to check them.

The modern misconceptions seem amusing: that slingers are filters, need to be checked, should be flush-able. We need to keep in mind how much better these bikes were than anything else at the time. BMW called for a piston to cylinder wear tolerance of 0.12 mm, which at the wear rates cited previously would mean a first rebore at 72,000 miles. The crankshaft bearings were anticipated to last longer, meaning no crank removal or slinger cleaning until ~100,000 miles. Yet, I have two friends who took delivery of Triumph Bonnevilles in England for summer vacation and returned them for rebuilds before they came home.

[Allan.Atherton]

That kind of use fills the slingers prematurely. Uh, don't you mean "abuse"??...
In my case it was more like benign neglect. That is more likely what happens than outright abuse. It was not abuse because most of the 6 previous owners were enthusiasts. One PO is still a force in the /2 world. The PO after him died in a nursing home and had been a founder of a state club. The next PO only had it a year. PO I got the bike from had bought it unseen and was appalled and furious at the condition. People go through life changes, lose interest, become poor, become elderly, and the bike suffers as it changes hands so many times.

[redavide]

...

The modern misconceptions seem amusing: that slingers are filters . . . BMW called for a piston to cylinder wear tolerance of 0.12 mm, which at the wear rates cited previously would mean a first rebore at 72,000 miles. The crankshaft bearings were anticipated to last longer, meaning no crank removal or slinger cleaning until ~100,000 miles.

I didn't mean to imply that a slinger is simply the equivalent of an oil filter, but removing particles and debris from the oil with centrifugal force is one of its functions (intended by its designers), isn't it?

It sure seems more reasonable to wait to deal with the slingers until the crankshaft bearings need attention -- that would seem to be a good design. Here in Italy, even very reputable vintage BMW mechanics think you're absolutely crazy to remove the crankshaft exclusively to replace the slingers. They can hardly imagine that I would consider such a thing.

But, according to Vech, the original BMW service manual calls for slinger replacement at 45,000 miles. I've never seen any mention of required intervals for slinger replacement in any BMW literature (but I haven't seen a lot). Is Vech correct on BMW's official position on slinger replacement intervals?

It's easy for a novice to get confused with this issue when the real experts have a wide range of opinion.

Also, the stories I've read about sudden rod bearing failure, etc. as a direct result of failure to replace slingers make me really paranoid about waiting to attend to the slingers only when there's some other reason to pull the crankshaft (ie: crankshaft bearings). I picture myself standing on the side of the road in the dark with a connecting rod in my hand thinking how I should have replaced those darn slingers earlier . . .

[Allan.Atherton]

... removing particles and debris from the oil with centrifugal force is one of its functions (intended by its designers), isn't it? It sure seems more reasonable to wait to deal with the slingers until the crankshaft bearings need attention -- that would seem to be a good design.... according to Vech, the original BMW service manual calls for slinger replacement at 45,000 miles. ... the stories I've read about sudden rod bearing failure, etc. as a direct result of failure to replace slingers make me really paranoid...
1. Filtering is not the primary function of the slinger. If it did not have the peripheral bulge, it would not act as a filter. The slinger is primarily part of the lubrication system with a side benefit of filtering.
2. The crankshaft bearings only need attention because the slingers have been full for too long. Full slingers lead not to easy crankshaft removal, but to crankshaft rebuilding, which is becoming very problematic.
3. I do not see that in the BMW Shop Manual. Where did you see that Vech said that?
4. Full slingers could produce rod bearing failure if the overflowing sludge blocked the hole into the crank pin. It would not be very sudden. You would have to keep riding hearing and feeling the bearings going bad. It takes some riding to do this:

[Allan.Atherton]

... Here in Italy, even very reputable vintage BMW mechanics think you're absolutely crazy to remove the crankshaft exclusively to replace the slingers. They can hardly imagine that I would consider such a thing.... Have you checked with the VBMWMO director in Italy, Michelle Varcasia of Rome. He can be reached at michele.varcasia@vintagebmw.org.

... according to Vech, the original BMW service manual calls for slinger replacement at 45,000 miles. I've never seen any mention of required intervals for slinger replacement in any BMW literature... Is Vech correct on BMW's official position on slinger replacement intervals?...
BMW had no position on slinger cleaning. It was not a scheduled maintenance item. It was done whenever the engine was down for overhaul. I don't know where the 45K miles came from, but in practice these days, that is about the maximum miles for a well maintained engine until it is very likely that the slingers are full. That is, if you replace the slingers when you rebuild the engine, and you ride and care for the bike, then it might be safe to go 45K miles. I would not have the same confidence in a bike I had bought with uncertain history.

[Allan.Atherton]

... I picture myself standing on the side of the road in the dark with a connecting rod in my hand thinking how I should have replaced those darn slingers earlier... The rods don't break.
And you will likely not be standing by the road. You will have the luxury of thousands of miles, and years of discussion, hope and denial. Not knowing how full the slingers are, or whether sludge and starvation are already working away on the rod bearings and crank pins, or whether a faint knock means it's already too late and the crank needs rebuilding. And after the knock, there are still more years and thousands of miles before your appointment on the side of the road.

[redavide]

Allan, Thanks for all the info, I appreciate it. Earlier in this thread, you posted several links to sites about slingers. In the first one, Vech states the following "The service bulletins of the era recommended the removal and cleaning, or replacement of the oil slingers every 45,000 miles."

I haven't been able to find anyone else who has seen one of these bulletins or any other official BMW source that makes reference to slinger maintenance intervals, etc.

[Allan.Atherton]

... you posted several links to sites about slingers. In the first one, Vech states the following "The service bulletins of the era recommended the removal and cleaning, or replacement of the oil slingers every 45,000 miles." ...

I did not think it was in the Workshop Manual, as that just mentions removing the slingers as part of disassemby of the enginel. There were a lot of separate Service Information bulletins issued several times a year dealing with changes and new procedures, etc.

Here's John Lacko's site with all the bulletins. These bulletin's are on "Service Information" forms, and must be the same "service bulletins" that Vech refers to.
http://www.beemergarage.com/bulletin.html

Over the years, I have read just about all of them. A bulletin about slingers would be in the first "Group:Engine" section. I have not seen anything about slingers or 45,000 miles in there, and have spent a few more minutes just now and still don't. It's good advice, but I just don't see where BMW said it.

[wicks]

I wonder if a cardio surgeon could get a little camera in there to look.

I only have 13K miles, but have no idea how fresh oil was kept, and it was stored forever.