magnetized shims

Bought some valve shims off fleabay. A bargain indeed, but they are magnetized. Seems like a bad idea to use magnetized shims - does anyone know how to demagnetize small metal discs in the comfort of your own shop?

 

I wouldn't worry about it. You use a magnet to get them out so I'm sure the magnatizim will wear off after they are in for awhile.
Just as a note chacal sells new ones and alot of people here do not like using used shims.

 

You SHOULD NOT use a magnet to get them out (per the factory book among others.) Using a magnet to get them out can magnetize them which IS a bad thing; they will now attract and hold minute bits of metal which will cause premature wear or worse. Chacal sells new aftermarket shims that are indistinguishable from the originals, and for less than half. Plus I would not trust used shims either.

 

Hmmm. What's the big deal with used shims? If they check out with the feeler gauge for the proper tolerances, seems like they'd do the job.

 

Which, now that I think about it, leads me to another question. I had planned on swapping a few of the shims I have in the bike around. Is this also not a good idea?

Por exemple: The exhaust valve on piston#3 needs a 2.85mm shim, which the intake on piston #1 has but does not need anymore (it needs another, different size). Can I use the shim in #1 on #3?

 

You can but I wouldn't. That 2.85 probably ISN'T 2.85 any more. You could mic it and see. Shims are cheap. Resign yourself to a 2-step process; break it down, measure. When you get your shims, install them and re-measure. Chacal ships quick but you can always put the cover back on and ride it until the shims arrive. To remove shims I use a teeny flat-bladed screwdriver to pop them up and then grab them with a pair of hemostats. Be sure to dip the new ones in oil before installing; and be sure to turn the motor over by hand a couple r's when you're done to be sure they all seated properly.

 

Do NOT use magnetized shims! They will attract and hold iron particles that float around in the oil, at one of the highest pressure points in the engine (the cam lobe-shim interface), turning the valve shim into a very very fine grade of sandpaper against your cam lobes, and then you just have a real nightmare of a problem to overcome.

Of all the expenses involved in maintaining a 25+ year old bike, the rather low and infrequent cost of replacing the valve shims is something that I would recommend not cutting corners on!

 

Thank you! The other consideration is the amount of HORRIBLE DAMAGE that will occur if you "spit" a shim. I consider new shims cheap insurance, like an in-line fuel filter.

 

All right, all right. I'll scrap 'em. I never intended to use magnetized shims - that was the reason for starting this thread. Guess nobody knows how to demagnetize small metal discs.

As for cutting corners, that stings a little, fellows. I've already spent close to a thousand bucks getting this bike up to speed in the past year, a lot of it on "corners" that many others might have skipped over.

I'm sensitive. Gonna go cry in my shop now.

 

if you have a soldering gun, lay it on the bench ,pull the trigger and set the shim on the side of it, not the tip you should feel some vibration, count to 10 flip it over count to 10, pick it up and slowly move it away, while the gun is still on
sometimes this works on screwdriver tips, sometimes it don't

 

Oak.....no no no, that comment wasn't directed at you! It's a common question (and temptation) and this questions about re-using shims has been discussed many times before.............

 

Just kidding. I didn't cry in my shop. Really. Anyway, I put in an order for the new shims I needed from you Chac before I even bid on the ebay ones. The question was for future reference. You guys may have saved my valves from certain destruction.

I might try the soldering gun trick on the used shims, just to see if it works. Then I'll throw them away. First I'll spit on them and smash them with a rock.

 

Polock said it himself, in regard to the soldering iron trick; sometimes it works and sometimes it doesn't. You can also "demagnetize" a screwdriver by just smacking it real hard on a flat surface a few times. The problem with either method is that it is NOT "demagnetized" just less magnetized and could still attract minute particles. I'm also guilty of implying that you were considering reusing shims as a cost-cutting measure, and for that I apologize. Like Chacal, just trying to keep you from doing something you will end up regretting.

 

if you heat them bright cherry red with a torch and let them cool slowly
they won't be magnetic at all, they won't be any good for shims either, but hay

 

yeah, heating them bright cherry red always has such a good effect on screwdrivers too.

 

If you had a degauser laying around you could use that (I gots one!) but I like the soldering iron trick, never thought of that. I would not reuse any magnetized shims either. I do, however, reuse shims (after I mic them out), usually from the same bike (if swapping will bring clearances into spec). I'll order replacements for anything I can't swap around. Anything under 0.0005 of stated value has probably worn through the hardened surface and is most likely suspect. Replace them.

 

I was wondering when someone was going to mention those. I was going to suggest Radio Shaft, but I'm not certain they still sell them anymore. Then again, I think I remember seeing something at Home Despot that had two pads on it -- one to magnetize, and the other to demagnetize.

 

I never had a problem using old shims, although I've never seen one so worn down that its dimensions changed significantly. Magnetized shim is bad news, though.

You can crack open an old ac/dc adapter (the bigger, the better). plug it in, move the shim near the flux core for a few seconds and pull it away while the transformer is still on. This works much better than a soldering iron. Commercial demagnetizers (like cassette tape erasers) are based on that principle, but their field is stronger and more directed.

If you have a TV shop in the neighborhood, they will most certainly have a degausser.

That being said... New shims are what, 4-5 bucks a piece?

 

Let it be known: I'm not gonna use the old magnetized shims, whether or not I could demagnetize them. I swear. I'm convinced.

What's "mic"-ing? Measuring the thickness? With a micrometer, I imagine. So as I understand ya, Robert, if you measure the shims (the ones from your bike, not the used ones you bought off ebay, changed your mind, spit on and broke with a rock) and find them within .0005, you're comfortable swapping them around to other valves that need those sizes. Is that .0005 mm, or inches?

 

Inches. They probably aren't smooth to .0005mm.

 

You don't have to heat them until they are cherry red to demagnitize them.
Just heat them in the flame of a propane torch.
Drop them into a can of cool motor oil.
Done.

 

You are correct sir! "Mic" is "to measure with a micrometer." Sorry 'bout that, old school term, new school crew. By the way, I really liked the "spit on and smashed with a rock" bit. We honestly have to cut the ends off bad cables (PC support) to keep people from pulling them out of the trash and trying to re-use them.

 

They don't need to be cherry red just heated to 600 deg. F. There is no problem using old shims. This has been done for years. It is the valve stem and seat that wear, and this is at a very low rate. The shim is made from a harder dissimilar metal to minimize wear.

 

here ya go max
http://es.youtube.com/watch?v=X8ZHQQUusGo

 

Yep I stand corrected. I work with 76% nickle alloys which would have a curie point of 280 C which would be 536 F. So for my alloy it would be correct. But my point was that the shim in this case is the magnet. So if the magnet is heated to 770 C it should lose it's magnetic field and therefore no longer attract the ferrous nut in his experiment.

 

We do that too -otherwise the problem just moves on. I even cut an old helmet in half so no one would use it when trashed. It was not safe.