1981 XJ650 Maxim; Top end corrosion

Hey all, I have yet another post about my 650 for you. When I took the valve cover off to check my clearances, I noticed corrosion on the camshaft and on the.. cam chain guide? That’s what the Haynes manual called the part, see below for the left and right side views.

Left side view:


Right side view:


Camshaft closeup:


The camshaft corrosion seems totally minimal, but the cam chain guide looks concerning to me. I’m also now worried about other parts in the crankcase, since I imagine this corrosion means water entered the case at some point.

Any idea if I should be worried about this? If so, is there some good technique to remove rust from the cam chain guide, or should I look into replacing it?

 

The unfinished surfaces on the camshafts: no problem.

The sides of the upper chain guide: no problem.

Possible problem: if a lot of water got into the engine somehow, and got down into the crankcase, that could be a problem if the engine oil wasn't changed regularly.

Of course, it may not even be that water got into the top end; just the moisture in the air, after 40+ years of exposure, will cause some-what unprotected surface to oxidize. With regular usage, all of the top end parts are covered with an oily sheen, which prevents rust from forming, but if the engine sat unused for a long period of time, the oil coating dropped off, and chemistry did its thing........

 

I think it’s safe to assume that this bike sat unused for a very long time. It came to me with just 3900 miles on the odometer in mid 2024.

I’m relieved to hear you think the chain guide corrosion isn’t a concern, and hopefully it’s just airborne moisture doing its thing. I’ll have to keep an eye out for bottom-end corrosion when I get around to doing clutch maintenance or something.

 

Agree with @chacal, however when I look at the last picture it almost looks like there might be some light rust on the cam lobe, and maybe some scoring on the top of the lobe? Hard to tell if it's that, or if it's just the lighting/angle/reflections of the shot. But I'd look closer at that one.

 

Chain guide is plastic I think. .

 

Well, just about any internal engine corrossion on un-protected surfaces is not going to be a problems; the only thing "down there/in there" that could be of concern are:

a) the crankshaft journals (main and rod)......although since they are much more protected by an oil film, even over long periods they generally won't rust (just like your cam LOBES didn't rust).

b) any shaft ball bearings.


But if the engine didn't actually get lots of water in it (example: someone left the valvecover off the head, and let the engine sit out in the weather where water could build up in the crankcase), then the minor surface rust that did form on any internal parts won't do any (or much) harm, and the difficulty involved in getting to such items in order to inspect them (meaning: full engine teardown) isn't worth the trouble. It
will all be burnished off with the first few dozen rotations of the engine.

HOWEVER, I would suggest doing a few things:

1) upon first real engine run, use some approved-but-cheap engine oil, as you'll want to change it almost immediately (like within the first half-hour or so) to your proper oil-of-choice.
2) I would also install the strongest MAGNETIC drain plug that you can find (like our HCP1656 magnetic drain bolt) and...
3) for extra credit, go to home depot (or online) and buy the strongest small "rare earth" magnet(s) that you can find (these are typically Neodymium) and attach it (them) to the drain plug (you can stack them one on top of each other to multiply their effect) so that the drain plug becomes a "super magnetic" drain plug, and is your best chance to pull out any of the rust particles that will be suspended in the oil.

 

The guide itself (the part that contacts the chain) is a hard rubber or plastic, but the supporting structure is stamped steel........and that is what has rusted in the image shown.

 

I’ve actually been riding the bike all summer, so if there was loose rust to be burnished off, I likely already got it off. I put 1200 miles on it, and I changed the oil once without noticing any corrosion or glitter in the oil (though, I don’t know if I would have seen it either, given I use a black drip pan). That could be why the cam lobes show no signs of rust.

I wouldn’t mind buying a new drain plug though, and a stronger magnet sounds like a good idea. Since I didn’t see corrosion products in the oil before, it’s always possible there’s some sitting in the bottom of the crankcase.

 

Cheers Len.

 

That’s just the lighting. My garage lighting sucks, so I have to use a flashlight to get good photos of anything. There does appear to be some light rust on the sides of the cams, but I saw nothing on the surface that interfaces with the valve shims.