[k0og]

I just purchased a Pentax-M 35mm f2.8 lens from the famous auction site for $10 plus shipping, and contrary to the description, it is not in "useable" condition because the aperture blades are badly covered with oil and extremely sluggish. Of course, I let the seller know about this problem and we'll see where it goes. There is a small scratch on the front glass that was described, but it is small enough that this would be a quite useable lens if I can clean the aperture blades.

I've taken several Pentax-M and other brand of lenses apart for cleaning and repairs with no problems. Unfortunately, this one seems to have the lens-mount screws VERY tight and they just won't budge. So, I'm looking for some advice...

Assuming that loctite was used on the screws, I tried a drop of acetone on one of the screw heads, making sure it went around the edges of the head, and kept refreshing it for about 10 minutes as it evaporated, but that did not loosen the screw.

Can anyone recommend a good, safe way to loosen lens-mount screws that may have been installed with loctite? I see no particular signs of loctite, but that is the only explanation I have for why they are so tight.

Thanks.
-Joe-

[konraDarnok]

I doubt there's any thread locking compound on them. I had some that were very tight; the key was a screw driver that fit *perfectly* and persistent application of force, being careful to not strip the head. If you do strip the head or can't find a screwdriver that fits *perfect*, there's also the rubber band trick to get more friction, which I've found effective on stubborn lens screws.

You can also try to put a small vice-grip perpendicular to the screwdriver. If you can keep the screw driver seated square in the head, it will greatly increase the toque you can apply. Barring all that invest in a t-handle.

[k0og]

konraDarnok,

You make a good point about having a screwdriver that will *perfectly* fit the screw head. I will order a proper JIS type "S" set from Moody Tools, and maybe that will do it. I have a jeweller's set that has gotten me by with the other lenses and camera bodies I've worked on, but I guess I just really need the JIS set. It will be a good long-term tool investment.

Thanks for your encouragement!

-Joe-

I doubt there's any thread locking compound on them. I had some that were very tight; the key was a screw driver that fit *perfectly* and persistent application of force, being careful to not strip the head. If you do strip the head or can't find a screwdriver that fits *perfect*, there's also the rubber band trick to get more friction, which I've found effective on stubborn lens screws.

You can also try to put a small vice-grip perpendicular to the screwdriver. If you can keep the screw driver seated square in the head, it will greatly increase the toque you can apply. Barring all that invest in a t-handle.

[Not a Number]

I take it you are keeping the lens even if the seller offers a full refund for the lens return? Otherwise why risk damaging the lens which could cause further disputes if you do return the lens.

I have yet to strip a screw using a JIS driver. Screws on the mount tend to be torqued down tighter for obvious reasons. The usual methods to loosen thread lock is to apply a solvent like acetone or to heat the screw with a soldering iron. Try at your own risk.

[k0og]

Not a Number,

I'll keep the lens. I only paid $10 for it (however, +$10 for shipping!), and have a use for it, so will just consider it a "project" lens. It would not be worth the cost to either me or the seller of shipping it back. Of course, I was not happy about the surprise of oily aperture blades, and that surprised me with a Pentax-M prime lens.

I thought about heating them with a soldering-iron tip (well-cleaned, of course), but realize that I ought to have the proper JIS screwdriver kit anyway. I'll order it from Amazon and will have it in a couple of days with our Prime shipping.

Thanks.
-Joe-

I take it you are keeping the lens even if the seller offers a full refund for the lens return? Otherwise why risk damaging the lens which could cause further disputes if you do return the lens.

I have yet to strip a screw using a JIS driver. Screws on the mount tend to be torqued down tighter for obvious reasons. The usual methods to loosen thread lock is to apply a solvent like acetone or to heat the screw with a soldering iron. Try at your own risk.

[aoeu]

Get the Hozan set.

Hozan JIS-4 JIS Screwdriver Set (NEW 3rd. Gen) - - Amazon.com

[k0og]

Aoeu,

Thanks for the suggestion. When I was searching Amazon earlier I saw those, but could not verify the exact sizes. It appeared to me that I needed the JIS Type S set from Moody Tools that includes sizes 000, 00, 0 and 1, so that's what I ordered.

-Joe-

[Just1MoreDave]

The Hozans seem to have larger diameter handles than the Moodys, which is an advantage. Tapping is supposed to work, but maybe uncomfortable with a lens, even though you shouldn't be tapping that hard. Patience helps me. If the screw doesn't move, I set it down for a few minutes instead of gritting my teeth and adding more brute force.

[OregonJim]

If you hold a can of compressed air upside down and spray it on the screw, it will emit the propellant (refrigerant) which may cool the screw enough to shrink the threads. This has worked for me a couple of times, but not always.

[aoeu]

000 is less common than 2

[wombat2go]

Tee Bars and soft jaws.

I just had same problem on old medium format stuff.

I clamped the jic screwdriver in a lathe dog (top left behind the vice). That thing is designed to grip like nothing else,
....and it make a good handle.
I held the lens in the wooden soft-jaws.
Now it was possible to put a lot of down force while gently rotating until a satisying 'click' was heard on all the screws.

Cheap tools - for the same reason I made the Tee bar shown to left of the screwdriver.
That is an M5 allen wrench, brazed by oxy-acet to minimise softening of the hex tool. The T bar allows good control so the thing is less likely to skate and damage the socket.

[k0og]

Wombat2Go, that's a good idea to get more firm torque. Here's my story...

I received the JIS set from Moody Tools. I attempted to remove the lens-mount screws with my new JIS driver, and could only get one to snap loose, using moderate hand-held force. I decided to use more force on one of them, and it deformed the screw head. I then decided to use even more force on another screw that was in good-looking shape (again, ONLY handheld, no additional torque device as Wombat2Go showed), and the brand-new JIS driver tip simply crumbled! The JIS drivers claim a lifetime warranty, so I sent them a message over 24 hours ago describing the problem, but have not yet heard from them. There is no way the tip should have crumbled, handheld. I'm no superman with an iron grip!

After that frustration, I decided to simply remove the black light shield, which only requires removal of three tiny JIS screws, and they came out very easily. I was then able to unscrew the rear lens element retaining ring, remove the rear element, and could easily get to the aperture blades to begin the cleaning process. As it turns out, it was not necessary to remove the whole lens mount anyway to clean the aperture assembly.

While holding the lens horizontally with the bottom tilted slightly down, I sprayed napthalene (lighter fluid) on the aperture assembly then immediately held the lens vertical thus letting the fluid drip out, while simultaneously actuating the aperture blades. I did this procedure a dozen times, then let it dry. I found that some thick oil was still present on the aperture blades and they were slow to operate, so I did the same procedure with a small amount of acetone, again followed by several flushes of napthalene. That removed all remaining vestiges of the old lubricant. I put it in front of a hair dryer for a few minutes, blowing on the warm (not hot) setting to help evaporate the solvent. I then allowed it to dry for a couple of hours with the aperture blades set at f22. At all points in the process I kept the bottom of the lens downward so that solvents would not run into the upper parts of the lens.

After it dried, and I confirmed that the aperture blades were operating freely, I used a Q-tip with a TINY amount of 91% isopropanol on it to wipe the aperture blades (while stopped down to f22), VERY carefully, not putting much pressure on them. That made them clean looking and removed solvent marks. Then I opened the aperture to f2.8 to get the aperture blades out of the way, and with another fresh Q-tip with a tiny amount of isopropanol on it I wiped the inner lens element in front of the aperture, then quickly turned over the Q-tip to the fresh end and dry-wiped the lens element. I repeated this 3 or 4 times until the lens element was absolutely free of any haze or marks. I then gently blew out the rear of the lens and inspected it in a bright light to remove a couple of residual dust particles. I then cleaned the rear element similarly with isopropanol and a Q-tip, reassembled the lens, and it works perfectly!

Warning: Do NOT attempt to use acetone on any lenses with plastic components! I got away with it on this lens because it is all-metal construction. Acetone will "melt" or at least weaken many plastics.

Here is a bump-on-a-log photo I just took with my "new" $10 SMC Pentax-M 35mm f2.8 lens @ f2.8 with Pentax K100DS, ISO400. This lens focuses perfectly at infinity, shows excellent colors, has nice bokeh even stopped down a bit and even though it only has 5 aperture blades, and seems surprisingly sharp wide open at f2.8. Exposure at all f stops works perfectly now (it did NOT before because of the slow aperture blades!).

I'm a happy camper now!

Thanks to all who commented.
-Joe-

[Not a Number]

Well I'm glad you were able to find a work-around to clean the iris.

How unfortunate with the Moody Tools. I've not stripped or deformed a screw you, even on screws that ultimately I was unable to budge. The only complaints I've seen about Moody Tools are about the ones with plastic handles - the plastic breaks.