Hey guys I just started to put fluids in the old girl this weekend in the hopes of getting her running by the end of the week. Went out to do a little more work on her this evening and noticed oil on the rear tire and small little specks on the rear brake disc. Upon off the wheel and disc I could see where there was a very fine film of gear oil down around the six o clock position. I read on one of the K boards that some people have issues with the rear drive seals when using full synthetic and go back to dino gear oil and it goes away. Is this just wishful thinking or would it be worth trying before having to replace seals on the final drive. Anyone with experience in these matters who could pass along some wisdom would be greatly appreciated!
OG

It seems the synthetic oil dissolves some of the grime that the dino oil leaves in place and therefore seems to 'start ' leaks. I think the seal was already faulty, but sealed on dirt which is now removed. Putting in a new seal is not too difficult at all.

Thanks for input Rene! I've ordered the seals and will ad this job to the list. Just wasn't looking forward to doing more seals after the little water pump trauma.

Hey folks,

Just wanted to do a follow up to pass along what I learned with my case study of one. :-) Still waiting on the FD seals so I went ahead and put some BMW 80/90 weight GL 5 dino gear oil in the FD and low and behold there is no more weeping from the unit. I was using Amsoil 75-90 extreme gear oil and the seals are not in good enough condition apparently to hold tight with that. So if your gonna use synthetics, a least Amsoil synthetics, you need to have excellent seal integrity.

J

I've heard of a few cases where using synthetic oil produced leaks at the FD.
Reverting to dino oil "fixed" it.

But I haven't heard of any trouble changing to synthetic oil in the gearbox no matter how long you have used dino oil.

My 2 cents worth.

Hey Blakey,
This has certainly been my experience as I've got Amsoil fluids in the entire bike without issue except the FD.

Which seals did you have to change? I'm new to the K100 and I too have an occasional weep at the rear wheel (oil out that is, not me crying over it).
There's a big O ring and a smaller oil seal inside the bevel box. Swap both?

Cheers

I'm going to go out on a limb and suggest that it would have to be the worst marketing decision of the combined oil companies to continue to market a product that actually but unintentionally 'promotes' leakage in oil seals.

Back in the early '80s companies that made seals introduced a new type of seal which had varying levels of nitrile added to the existing rubber formulae. Buna-N is one type that was introduced around then, also known as NBR. This was in response to some complaints of old style seals potentially leaking under certain conditions when using fully synthetic oils (early Mobil One, for example). The idea was that the more nitrile was in the ploymer the more heat resistant the seals would be to oil leakage but the less flexible the seal potentially would be under certain conditions.

Almost any seal made in the past 29 years and intended for the automotive industry would have these nitriles added. I can't imagine a modern company intending to stay in business would intentionally sell a seal that could leak using synthetic oils. In the trade since the late '70s I have heard of a few instances of leakage, and I have heard of many many people blaming it on the use of synthetic oil. I have never seen this verified scientifically. I reckon it's one of those persistent myths. I have no explanation for your seal not continuing to leak after using a non-synthetic oil. If I have had a seal leak whilst using synthetic oil, simply switching to a non-synthetic oil has never worked for me. I fully recognise that others have had differing experiences. I believe a seal leaks because it's going to leak, regardless. But I often sat in the back of the class and caused trouble.

Well, here we go, I hope this helps, and doesn't "inflame" the situation........ Very good logic TWB, I agree with all your points, and yes the Buna-N has those properties (and compromises) as with all engineering solutions. From my perspective the following points need to be taken into account when dealing with oil leakage issues -
Lip seals with external wipers (as on the bevel drive for our K's) will eventually trap fine dust in the space between the wiper and the lip. This in turn causes wear on the rotating metal part and, eventually, wear on the seal lip, so leakage begins. You are correct TWB, the seal was going to leak anyway, synthetic oil may/may not hasten the process with an already worn/hardened oil seal.
Oil leaking out means dirt can get in, change the seal asap. Also, check for movement of the offending shaft(s) when there is an oil leak. Pointless replacing the seal if bearing damage has already occurred as the relative movement will only cause further reduced seal life.
If you intend to use full synthetic oils, switch seal materials to VITON, much more expensive but engineered to match polymers, poly-alpha-olefins (PAO) and poly-glycol type "oils". A word of warning though, never burn the viton seals as the chemicals given off in the combustion process are hydroflouric acids, which will cause severe burns and irreperable skin damage, as will as the vapours being highly toxic. Plenty of info available by "googling". Regards, Dennis