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I'm looking to replace the idle speed adjuster screw on my 2150 carb. For easier access from the side, I'd like to use a bolt with a hex head, so I can turn it with a wrench. The present screw is headless, with only a slot for a straight screwdriver.
The existing screw has a nylon insert so it doesn't vibrate loose. Alas, my new bolt has nothing. Any recommendations for some compound I can use? Obviously I don't want a strong threadlocker on there, as I will need to adjust it occasionally. I've seen some fasteners with what looks like a stripe of rubber cement down the side. Something like that would be perfect if I knew what to use.
Threadlock comes in different consistencies. You want the one that stays gooey and does not harden. Seems they are color coded but different companies use different codes. I have a tube of red and it stays gooey. All you need is a drop. The blue is more gluey but can be broken out. I think the yellow is meant for permanent installs. Take a look at the family of thread locker by a single manufacturer though. I can't be sure of the colors used by individual makes. Pick the one that stays gooey.
Blue thread locker is medium duty. Red thread locker is used for high torque suspension components, engine fittings, etc. I don't know if they make a light duty product.
Found some of the various manufacturers' product selector guides to be less than helpful. Permatex had the least bad version. Decided to try purple low strength #24024:
Fingers crossed that it works well. Says it's for small fasteners that require occasional readjustment. My only concern is what happens after you make an adjustment. Does the old stuff continue to grip or do you have to remove the screw and reapply the goop? Not a huge concern, but we'll see what happens. I can gamble the $10.
Found some of the various manufacturers' product selector guides to be less than helpful. Permatex had the least bad version. Decided to try purple low strength #24024:
Fingers crossed that it works well. Says it's for small fasteners that require occasional readjustment. My only concern is what happens after you make an adjustment. Does the old stuff continue to grip or do you have to remove the screw and reapply the goop? Not a huge concern, but we'll see what happens. I can gamble the $10.
Yeah, it will continue to hold after an adjustment. Apply a ring around the bolt as shown and install it and adjust it. I don't think you'll need to reapply it every adjustment.
One suggestion: mark a line across the head to make adjustments easier. One of the reasons spotted screws are still used (especially on mixture screws) is to clearly see how much adjustment you have made.
If you get a longer bolt and put a spring through it, that will hold it. That's what the factory did on some of the carb adjustment screws.
Ooh, you’re a genius. I like this idea. This solves another concern I hadn’t mentioned.
I wanted to use a flanged head bolt. The idea is when using a box end wrench, the flange prevents it from slipping down below the bolt head. The only small flanged head bolt I could find was stainless steel. (If my boss is reading this, even though it looks like aviation hardware from our stockroom, I bought it on eBay. Yeah, that’s the ticket.)
With stainless fasteners, galling is a YUGE issue. Hadn’t mentioned it, figuring you mortals would be using a regular fastener, not aviation grade stuff (that I bought myself). Anti-seize is a must, or thread lock compound designed for stainless (like purple Permatex).
But if I used your spring idea (even though it’s Fall), I could add a washer under the head. It serves the same purpose as the flanged head. The spring is a spare from a carb rebuild kit, for the mixture screws. It works perfectly and no thread lock will be required, although I did add a little anti-seize.
Here are the three options side by side. The original headless screw is in the middle. The stainless flanged head bolt I bought with my own money is on the left. The ordinary screw and washer (ignore the aviation grade cad plating) and spring are at the right:
