Any thoughts on synthetic versus conventional oil?
I read someplace that the K engines did not like synthetic so I always stayed with conventional oil.
Using dino oil can exacerbate the sprag clutch issue !! read snobum's verbose comments below for a detailed explanation.
Part 1; Noticeable mechanical damage; you have done the large amount of labor and have the sprag clutch on your workbench:
Sprags not spragging? Look at them carefully. You may see a "polished" flat where it runs on the inner cylinder lightly pressed there by the springs. When the springs get gunked, they end up exerting less force and so less friction for it to "lift itself" over the high point to start wedging.
Part 2: You have the sprag clutch on the workbench and there is NO noticeable mechanical damage nor gunking-up:
The starter clutch is a constantly running device that is designed to transmit force in one direction, and it is not supposed to have any appreciable grabbing engagement until the starter rotates, which is supposed to cause the sprags to move, and that movement is to LOCK the clutch up, so the starter rotates the engine. When the starter is NOT powered, the starter sprag clutch is free-wheeling, with no appreciable friction in its innards. This clutch is a ONE-WAY device. One direction, it locks up, other direction, it rotates freely, with no coupling between the two main parts other than quite minor friction except in the oil film contact involved. I have seen TWO of these sprag clutches (of the later types too!...not the earliest K bike ones that were heavily modified by the factory for later versions) that have failed, withOUT any apparent real wear on any part. I have ONE of these in the shop. I was so curious about it, that I paid the owner to send it to me. I have compared it to a brand-new one, with no good conclusions, beyond the fact that dimensions have not changed enough to mention. My suspicions are STILL that it failed due to unseen-by-the-eyeball microscopic surface glaze, or other type of surface change... on the inner friction 'drum' part (and likely also the sprag parts that contact it). I have not proven this....might be able to at some point. The owner told me he had tried both Seafoam and CD40 additives. Even if I could prove what happened, it likely would not help us all very much (??).
Anecdotally, no one that has used Mobil 1 a TRUE full synthetic, has had a problem...that has been reported to me. It is entirely possible that OIL is THE > major factor.....or not. I do NOT want to imply that wear is not a concern. I HAVE seen worn starter sprag clutches; and the springs, if gunked-up enough, could cause reduced tension. My suspicion is that it was also the OIL that enabled excessive wear, when that is seen, but I cannot be 100% sure about it. The only way I can get a handle on that, is maybe to actually be present at some teardowns, and MEASURE side-play, and so on. I am a bit hesitant to state that it could be a problem, because there is no indication of sideplay wear on the needle bearings in the starter sprag clutch here....that I can see...nor on the ones I have looked at in that particular regard (two of them). Keep in mind that a starter sprag clutch works by friction, and it is not supposed to be friction of metal to metal, but oil film to oil film. Most do not understand how oil films work. There is an in-depth article on my website for anyone who wants details. My guess is that there is more than just one thing at work with the starter clutch problems. I suspect basic failure modes; OIL film failure (the result is mechanical damage as in part 1 above, or failure due to a glaze or gunked springs). I am beginning to think that all the other failures, which manifest themselves as WEAR failures, are due to a combination of oil, perhaps side forces, and maybe there is some sort of production tolerance...and maybe contaminant/protectant problem at work too. I am only too well-aware that MANY have NEVER had a problem with the later starter sprag clutches, and have used fairly conventional oils. My mind jumps to the same situation with camshaft and followers, in the Airheads. Many got HUGE mileages without problems; others, even running the same oils, had problems. I have personally witnessed these engines apart. WHAT was the answer? Seems to be heat treatment variations. For the Classic K bikes, I think we have a combination of effects, and anecdotal evidence TENDS to point towards using a REAL synthetic oil (Castrol Syntec is NOT!), like the Mobil 1 I have been recommending. It may well be that the higher amounts of ZDDP in Mobil 1 is helping with the WEAR failure modes. In addition, in what APPEARS to be the case, Mobil 1's formula does not leave the surfaces such that the sprags do not properly grab. Until someone does a serious laboratory analysis, right down to the surface's molecular analysis, I doubt we will know much more.
Because of the huge amount of labor involved ,...not to mention the $$$$$ parts cost...I personally use ONLY Mobil 1 in my K bike, from WalMart, in 15W50, it comes in 5 quart jugs. I am simply using the oil that the majority of information I have points towards it being much less of any problem. I have nothing against someone using the particular Mobil 1 20W50 oil that has even higher amounts of certain additives (V-Twin version) but I think that the K bikes do not require the thicker oil. Maybe the 20W50 is a bit better if someone rides a lot in the hot Southwest, where temperatures can exceed 100°F relatively often. I don't think the Mobil 1 20W50 is warranted otherwise. I leave my Mobil 1 in my K11 for the entire year; unless I have put more than 8,000 miles on the bike. It really does not need to be changed often, particularly if one does not do a lot of very short commutes; even more particularly in cold weather. I also note that analysis of my oil at changes has shown no wear to speak of, so I quit paying for analysis. My K11 also works hard; so is hard on oil...it hauls a big sidecar. I do change the filter at the same time, but I well understand that I could, without the slightest harm, go for an extra oil change between filters. The in-depth analysis by a lab showed that the additives in Mobil 1 hold up quite well over time and mileage. You get, sometimes, what you pay for. I also use nothing but BMW filters. I have no problem with folks using aftermarket filters, but find them highly variable internally, so I don't use them. NOTE!....K bikes seem to use less oil, if the oil is a quality one, and if the oil level is NOT maintained all the way to the top of the sight glass. I like the middle.
Part 3; fixing an original late model starter sprag clutch (of course, you have to remove it first, not a simple job!):
It has been reported to me by a trusted source that after removing a starter sprag clutch that has failed or gotten intermittent, but exhibits no signs of bad mechanical wear, that it can be repaired by a very thorough cleaning in strong solvents. I have, myself, done this to one, and I also used about a 2000 grit paper in 'polishing' the contacting surfaces; with no further problems from the starter operation; so it was nice to hear that someone had used JUST solvents to effect cures. I would recommend the polishing by super-fine grit paper, as I did, plus VERY thorough solvent cleaning (and scrubbing by turkish toweling with the solvents). I used a 50-50 mixture of MEK and Acetone.
