Topic: Need to heli coil a carb screw CB 550 Anyone know what size I need? See Picture

[Way Way norcal]

I was pulling off these carb float covers to give them a clean and paint and the upper right screw came out and the hole was buggered
Whats the best course of action here?
thanks

[harisuluv]

don't think it's been heli coiled before, that's what it looks like when you strip out the alloy of the body.  the "coil" that is on the threads of the screw are the threads that were in the body. 

if you want to heli coil it now, it would be the same size as the screw (m4?)

[Way Way norcal]

you know I put on my glasses and looked at it with better light and it has NOT been heli coiled.   You are correct.
Is it a M 4?   1.25 pitch?

[harisuluv]

m4, .7.  Before you try to helicoil, about half the time you can just use a slightly longer m4 screw.  There are still some threads that are good and that will solve it.

If that doesn't work, you can just go to m5, but you will have to drill (not tap though) the bowl too.

[Way Way norcal]

I thought I might try a bit longer screw and see if theres a bit more thread in there.
You prefer the drill and tap up to a M5 rather than heli coil it?

[Desert Dan]

I had the same issue on my carbs. The previous own had stripped a number of the bowl screws, I found the best solution was a little longer screw or in extreme cases a little larger diameter screw. I used old air cooled VW carb screws as they are the same diameter and pitch but a little longer and some from later 70's VW's are slightly larger in diameter. I found the aluminum of the carb to be so soft drilling and tapping wasn't necessary.

[Way Way norcal]

thats a huge help!  Thanks

[strynboen]

you can replace them vith umbraco bolts they are easyer to handle..and as be said a bi tlonger then stock helps

[alacrity]

On my pd46a carbs, there is just enough room for a nut above the body flange on the one that was stripped. I selected longer m4 socket head cap screw that was just long enough to reach the nut, create the right amount of clamping pressure, and not bump Into the carb body structure above the flange there

[vorhese]

a glob of red loctite can help too. Dab some on, screw it, let it sit 24 hours, unscrew, and squirt some more on again.  I have stripped rocker threads on a Triumph that hold up just fine with red loctite until I can give them the attention during a  strip down. You just need enough tension to seal the gasket. 

[DaveBarbier]

If that doesn't work, you can just go to m5, but you will have to drill (not tap though) the bowl too.

I don't understand why you said to not tap. After drilling there will be no threads there. Will screwing in the new screw cut its own threads in the soft aluminum?

Oh wait, duh. I get it now. Don't tap the bowl but tap the body. Of course, haha. Now I get it.

a glob of red loctite can help too. Dab some on, screw it, let it sit 24 hours, unscrew, and squirt some more on again.  I have stripped rocker threads on a Triumph that hold up just fine with red loctite until I can give them the attention during a  strip down. You just need enough tension to seal the gasket.

If it were me, I'd definitely avoid red loctite, or even blue for that matter. Red is made to be very strong and possibly (probably?) strip out again once you try and take them out. Or worse, snap the screw. Especially on a part that you need to take off for periodic maintenance. I'd take Harisuluv's advice which it seems you're going to do.


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1978 Honda CB550K