Topic: 75-77 CB400F -- need diameter of tach cable securing screw...

[mwc400f]

Greetings,

The head of the screw that secures the tach cable to the engine is hopelessly buggered, so I need to drill it out. Does anyone know what the diameter of the threaded portion of this screw is? I don't want to damage the threading in the valve cover by using the wrong drill bit.

Thanks.

[scottly]

Drilling the screw is a last resort, and is not easily done on such a small screw. There are other methods of removing a screw with a damaged head. Post a pic of the damaged screw head.

[KennyRedman]

Is it #15?

https://www.partzilla.com/catalog/honda/motorcycle/1976/cb400f-a-super-sport-400-four/cylinder-head-cover

Can you use some vice grips to grab it?

[mwc400f]

Here's a photo of the screw head. Unfortunately, it's recessed otherwise I would have tried to get at it with vice grips. Yes, it is #15 on that parts list  (a 5x20 screw).

I have JIS screw drivers; unfortunately, this screw was pretty buggered when I got the bike, and a few treatments of penetrating oil and taps at a #2 JIS impact driver seems to have made it worse.

Any suggestions for how to get it out appreciated.

[pekingduck]

I've taken out worse ones.  First, take a hammer or punch, and hammer the high spots down to give it more meat.  Then take just the Phillips tip and hammer it into the slot firmly and it will stay by itself.  Then use the impact driver and don't be afraid to whack it firmly.

If it still doesn't come out, use a sharp chisel and cut a slot on one side.  Then use the chisel in the slot to slowly rotate it out.

[grcamna2]

Here's a photo of the screw head. Unfortunately, it's recessed otherwise I would have tried to get at it with vice grips. Yes, it is #15 on that parts list  (a 5x20 screw).

I have JIS screw drivers; unfortunately, this screw was pretty buggered when I got the bike, and a few treatments of penetrating oil and taps at a #2 JIS impact driver seems to have made it worse.

Any suggestions for how to get it out appreciated.

I've used a sharp 'prick punch' with a small ball pein hammer to remove small tapered head screws similar to that.

[scottly]

You might try cutting a slot in the head with a thin cutoff wheel in a dremel tool, then use a good flat blade screwdriver tip. Don't go to deep, or the head may split in two. There are also screw extractors that are spun backwards and dig into the stripped cross head type screws with a conical bit, but I've never used one myself. Sometimes a left handed drill bit has enough grab to get the screw out without drilling down into the shank of the screw.

[newday777]

Here's a photo of the screw head. Unfortunately, it's recessed otherwise I would have tried to get at it with vice grips. Yes, it is #15 on that parts list  (a 5x20 screw).

I have JIS screw drivers; unfortunately, this screw was pretty buggered when I got the bike, and a few treatments of penetrating oil and taps at a #2 JIS impact driver seems to have made it worse.

Any suggestions for how to get it out appreciated.

Are you using a hand impact driver similar to this type?
Pekingduck is correct in his process to hammer the head flat to push the stripped head material down back into the grooves first then hammer the tip into the head to reform the slots to the tip before putting the hammer impact tool on the tip to impact the screw out.

[newday777]

These screw extractors usually work when all else fails

[goodtryer]

You might also try a Torx bit. I've had some luck with them. Also, try twisting clockwise once in a while as you are trying to extract. You might find that it gives you a tiny extra bit of space to twist back the other way.

Don't forget to use heat in addition to the penetrating oil. Don't get in a hurry. Use a bunch of cycles of penetrating oil and heat. My rate of breaking nuts & bolts & screws has gone way down after getting smarter about this.

Plenty of choices on Amazon. Harbor Freight has them, too.

Good luck!

[bryanj]

DO NOT hit hard as those alloy holder break off and are not cheap to replace

[BenelliSEI]

DO NOT hit hard as those alloy holder break off and are not cheap to replace

READ THIS POST…… easy to break! I’ve done it……

[mwc400f]

As you can see from the photo of the screw, I tried everything suggested. The screw extractor worked like a charm -- it came right out. I suspect the heating and tapping with 1/4" cold chisel + punch broke whatever bond was holding the screw in in the first place. Getting the extractor off the screw once it was out took some effort (it was really on there).

Thanks for your help!

[goodtryer]

Excellent. Always nice when it works out.