OLD MAN SLINGER RANT!!

[Seek]

The main source of run-in crud in an engine are the piston rings bedding in. That's is the only part especially designed to be bedded in. The gears, bearings, camshafts and followers, valves etc. already have a precise fit and shouldn't need any bedding. That isn't to say that nothing happens in these parts, but my guess is that it is negligible compared to the piston rings.

The main problem with opinions about subjects like this is a lack of proper data. We have some anecdotes, but nothing that would pass proper scientific standards. Collecting data like that is pretty much impossible of course. What we do know though, when we open up an unknown 60 year old engine, it will be full of surprises. Even when we buy a bike from an auction that looks fabulous from the outside, chances are high that it was just a cosmetic restauration. So, avoiding to clean the slingers is always a gamble on an unknown, ancient engine.

[johnlacko]

Thanks Chuck, for getting that out there. As another old timer who started riding BMWs in 1971, I can tell you that I don’t think I even heard the word ‘slinger’ until the 1990s. Now everyone asks you if you’ve ‘done the slingers yet’ like it was an oil change. When you take an engine completely apart as is needed to reach the slingers, how can you NOT freshen the crank, freshen up the cylinders 1 over and install new pistons, do the valves & guides. Not to mention all the gaskets, seals and bearings. It’s never going to be easier, right? But that little cleaning process could turn into thousands and thousands of dollars of work. Or you can just replace the oil regularly and enjoy it until you ever start to get a trace of a knock, and then spend the same amount as above (adjusted for inflation, as only BMWs owners can appreciate) once that happens. If you’re restoring the bike - then absolutely do it. If not, let it be. With today’s modern synthetics, I think that we might be getting better lubrication on a bad slinger day than we were ever getting with brand new bikes using the old Dino-lube. I just didn’t wanna be the first one to say it, because with the Internet, bringing up a controversial topic is just like an old Western movie - the first one through the door always gets shot! Thanks Chuck, for taking the bullet!

[Seek]

Now of course, be sure to catch the knocking big end before it seizes, breaking the conrod and punching a hole in your crankcase....

[sherman980]

John,
BULLSEYE!! And welcome to the Old Man's club! Will be sending out your Club membership package complete with bulletproof vest shortly!

[sherman980]

Seek,
I can't tell you a broken rod/trashed crankcase can't happen, I've seen a pic or two that says it can (pretty sure the pics were of a race engine, but it's been a while...). But in all my years riding and working on BMWs (and a wide range of other motors), I've never actually seen and touched a broken /2 or earlier BMW rod (slinger equipped motor) much less a case that was broken by one. I have heard "rod knock" on a number of occasions both on BMW and non-BMW motors, and that experience tells me that you USUALLY get a bit of warning before a lower end fails catastrophically. I capped "USUALLY" because like all things in life, shit happens. (Oh, and some of us are deaf at this point in our lives and couldn't hear a knock until there was oil dripping on our shoe from a hole in the crankcase! ) We get up every morning and take our chances. The good news is that we each get to pick what chances we take. So do what makes you feel good so you can enjoy the ride.

Edit: Guessing broken rod/cases are out there and folks will post. But like a previous post noted, an anecdotal event doesn't make it statistically significant. From my original post, BMW had decades of experience with tens of thousands of "slinger" equipped motors. If they believed it was THE important "service issue", guessing they would have emphasized it in their workshop manuals. A full slinger is an "indicator" that your engine needs attention, albeit one you can't easily look at, not the original problem. And to not rebuild a crank with new bearings along with the rest of your motor once you're in there seems like false economy to me.

[Seek]

Very interesting discussion. Thanks for bringing this up!

The situation now is a little different from the situation back when these bikes were new and when BMW . When you buy something you are almost never guaranteed of a proper restauration job. There are just too many cosmetic restaurations that look beautifull, can be used for a short trip around town, but nothing more substantial was done. Or they did a quick top end rebuild, advertise with "engine revision", and nobody looked any deeper.

I agree, that just doing a slinger job, is not likely to end like that. At least you need new bearings, many old cranks also have worn bearing seat, the big end and small might be beyond spec. The bearing seats in the crankcase could very well be worn out etc etc.

The trick is to catch just the right time to dive into the bottom end.

[808Airhead]

Here is a dramatic example. With crankshafts getting harder to find , I think it is good insurance.

[sherman980]

Thomas,
Curious what the background info is to the failure you posted above. Not suggesting things can't go wrong for a variety of reasons, but that looks like it would have given a lot of warning beforehand if it was a big end lube failure. And the piston shows no signs of scoring and small end of the rod isn't discolored from overheating which tells me they were still getting plenty of lubrication. A "clean snap" of the rod like that looks more like an over revved motor failure to me...? Regardless, a bad outcome and more reason to do it all if you decide to do it at all.

[808Airhead]

Chuck, that is a pic I got off of FB, supposedly rod seized and there it is…. I don’t know the whole story. Pretty dramatic failure though!

[Jim D 5112]

So does that mean the pictures are not representative of mechanical failure from lack of having the slingers serviced, cleaned or replaced ?