One of my grease zerks got knocked out of the rocker arm assembly on my motorcycle. It’s poor design, the fittings hang low like the teats on a sow and a pot-hole or a curb is perfect for snapping them out. I’m one of a several on the Kawasaki board who’ve had this happen. (Vulcan 900 Classic, by the way).
Not a great idea - you’re right that you’ve created a galvanic couple that can corrode, especially if you ever ride under conditions where you could get salt water on the assembly.
Corrosion from dissimilar metals is definitely a concern here. Fortunately, in this case the fastener isn’t load bearing, but the corrosion cell might eventually eat away at your rocker arm necessitating replacement, especially with that chunk that came out of it. Generally when you use steel bolts on an aluminum housing you either use an insert (which helps to strengthen the internal threads as well as protecting those from forming a corrosion bond), or use a chromed or passivated fastener, and preferably a non-conductive washer shim (Teflon or some ceramic) between the bolt head and parent material. Also, the “stainless” bolts you got from Ace should be considered suspect; most fastening hardware you get from a general hardware store is barely CRES, and fasteners are often counterfeit. Again, this isn’t much of a concern for you as the fastener isn’t load bearing, but if you do have a critical bolted joint you’ll want to use SAE Grade 8 or better from a certified vendor (Fastenal, et cetera).
Also, throw away the split ring washer unless your intent is just to use it as a small diameter washer. So-called “lock” washers made from helical rings do absolutely nothing to prevent a bolt from backing out. I’ve spent a frustrating amount of my professional life showing how these things are useless–and often worse than useless–as a locking mechanism.
Armor the remaining casting. What hit the zerk before might be back (so to speak) later.
Another Kaw forum poster did just what Dag Otto suggested, used hex socket set screws. We all went “Wow!” at that, it is, indeed flush. Then I started to wonder about the “armor” that the hex head supplies, his solution is more flush, my solution puts a strong steel cap on those threads. Not sure what the better option is on that.
If I were to replace the stainless bolts with something less corrosive, what would you suggest? I don’t want to make a future maintenance problem here. I know what a chromed bolt is, of course, but have no idea what a “passivated fastener” is.
The washer, by the way, was intended to eat a bit of the thread depth up, since the 1cm length of the bolt is a little deeper than the zerk. I also hoped it would help keep the bolt from backing out since all the grease those threads seemed to make lock-tite useless.
EDIT: Denver, of course, has no sea air but we do salt our roads in the winter so there is some salt around part of the year.
Well, they work to the extent they’re designed to. Unfortunately, too many people seem to think they’re a replacement for Belleville, wave or star washers and, of course, they’re not. They provide a modicum of spring pressure to resist (key word–not prevent) fasteners loosening under mild vibration conditions, and that’s it.
I’d go with nylon.
As you imply, if it got hit once it can get hit again, and if the stainless gets hit hard enough it’s the aluminum casting that’s going to fail. You do not want that.
Unless you are dumping the machine in salt water for long periods of time I would not be too concerned about electrolisys. I think that is a minor concern.
I would be more concerned that if the aluminum case is much softer than the screw the treads might be stripped. This has happened to me too many times. You really want the screw to be a tad softer.
Nope. Once you’ve torqued the screw down to a minimum of 50% of fastener proof strength (the accepted minimum for any structural joint) the washer has long been flattened, and it provides no more resistance than a standard flat washer. If the tension on the fastener is so light that the spring effect of the spiral washer comes into play the joint is already compromised, and friction on the threads due to tension is probably insufficient to prevent the fastener from backing out, especially in a vibratory load situation. This is exacerbated by the fact that most people put a spiral lock washer on top of a hardened washer to keep it from scratching a finished or painted surface, which totally negates any value the washer has at all.
Star washers are useful only on machine screws (#10 or smaller) in non-critical vibratory applications with non-hardened washers. Load indicating washers aren’t a locking mechanism; they’re just used to indicate when a specified minimum bolt tension has been achieved. Conical or Belleville washers are useful for light dynamic loads with small deflections as it allows you to maintain a consistent tension on the bolt without increasing the tension; very when you need to maintain a specified range of friction with compliance like a sliding or expanding joint.
Critical joints should either use mechanical or adhesive thread locking (locking threads/inserts, cured threadlocker), a positive head lock like lockwire, or for low torque or constant load condition a thru-pin and slotted nut, or jam nut.
I didn’t think about a nylon fill screw but that’s actually a good suggestion. Frankly, if it were me and I didn’t intend to put a zerk back in there, I’d probably just clean the threads and fill it in with a high strength epoxy, which will protect it from further corrosion or damage.
Curiously enough I had the opportunity yesterday to toss a similar comment back into the lap of the speaker after corrosion from dissimilar metals caused dramatic (and entirely anticipated) problems. Unless you are operating in low desert, galvanic corrosion is a real concern even in a moderately humid environment.
No. You always want the thread screws to be harder on the fastener than the nut or material they’re threading into because threads deforming on the fastener will cause the running (installation) torque to vary continuously, whereas once you deform female threads by a pre-installation measurement the running torque will be about the same. The only exception to this is some threaded inserts which are of roughly equivalent hardness to the screw, in which case there is relatively little deformation. The reason you don’t want to screw into an especially soft material is due to galling which can result in unintended thread friction or cross threading; in this case a threaded insert is generally used which intentionally galls the parent material and provides a harder internal thread for engagement.
Well, different situations require different considerations.
Of course I would not install those if I were the manufacturer but I would not be excessively worried about electrolysis unless they are really going to be regularly dumped in salt water.
As a boat owner I know electrolisys and corrosion well. In this case I am not saying they do not exist, just that it would be a minor concern. Those screws will come out relatively soon again. It’s not like a situation were you want to be sure there is no corrosion in ten years. So, yes, the best is always the best but sometimes it is resonable to compromise on order to save time, money, etc.
It’s gonna have to come out again to be greased - I was just gonna fit a zerk in there again, grease everything, and then replace the bolt.
The nylon is a good idea but i do worry about strength. I don’t know how many nylon bolts I’ve sheared off while unscrewing them. I’d be left with a neat, nylon plug threaded in there.
I guess I’ll leave it in there until the next oil change and just check it when I back it out for maintenance. The real solution to this, IMO, would be better design.
Those zerks are made out of steel and are not a problem (except for being in a likely place for breakage). If you’re still concerned you could use a corrosion preventive coating (like… um… grease!) or just wrap some teflon tape on the threads and use a painted aluminum washer.
