Butterfly screws

[BooG]

Those two screws that hold the circular butterfly valve in the carb...I've just replaced them as I'm re-building my carbs. Can you just loctite them in place, or must they be peened? If I have to peen, whats the best technique to use?
Thanks.

[Mike V]

I don't peen mine, just blue Locktite the new screws. The new screws should have a little natural resitance, along with the Locktite should secure them adequately.

http://i428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Bing%20Carb%20Right/81R65RestorationBingCarbRt012.jpg

[Barry]

I would loctite them too - if you have some.

To peen them them you have to be very careful to support the screws on the other side so as not to put undue stress on the shaft. It's a bit of a balancing act holding the carb over a suitable piece of metal in the vice. A few light taps with a small hammer and punch should do it. They should be peened just enough to make sure they won't fall out due to vibration and not so much that they can't be slackened a little to centralise the butterfly.

[Rob Valdez 79 R65]

http://i428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Bing%20Carb%20Right/81R65RestorationBingCarbRt012.jpg

What is that tool, in your picture, Mike?  A magnetic screwdriver, or one of those drivers that has the little "claws" to hold the screw while you work with it?

[Bob_Roller]

You can 'peen', or 'upset' the bit of screw that hangs out on the backside of the throttle shaft, with an automatic center punch .

The ones that are spring loaded  and go snap when you push on them enough .

I did this on my last carb overhaul .

The material of the screw is soft steel, and easily deformed .

[montmil]

Pre-peening, be very sure you have the butterfly flaps right-side up and facing the proper direction. Additionally, sight through the bore to confirm equidistant space around the perimeter of the butterfly and bore prior to the mechanical peening, if that's your choice. Failing that, you'll never get the carbs to play nice.

Monte

PS: It's a magnetic tool.

[Mike V]

Mike V wrote on Today at 01:40:27:

http://i428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Bing%...


What is that tool, in your picture, Mike?A magnetic screwdriver, or one of those drivers that has the little "claws" to hold the screw while you work with it?  

Rob,
That's a wonderful tool! It's a screw-holder with a magnetic opposite end. It has a spring-loaded slot that will hold small screws. I use it constantly. I can send you some information if you're interested.

I would not recommend peening the shaft screws...too risky. If you want extra security take some needle-nose pliars and disturb the exposed threads.  The idea is to keep the screws from completely coming loose and finding the intake channel and being digested. One pad move while peening may leave you with more than you bargained for.

[Flash]

Blue locktite is all you'll need. One piece of advice though, before you tighten the screws all the way, let the shaft close and "center" the butterfly, then finish tightening the screws. That will ensure a better fit and more predictable metering.

[Rob Valdez 79 R65]

I can send you some information if you're interested.

Come on, Mike!  We are always interested in new toys tools!

[bruce_launceston]

I found that before tightening the screws I had to put some pressure on the butterfly lever and tap the face of the butterflies (with the handle of a small screwdriver) to get them so seat correctly.
It is not easy and as Monte said it is very important to sight through the carbs to ensure that the butterflies close completely.

I didn't get it right when I first rebuilt my carbs and you can't get the bike in tune and idling slow if there is any gap.

Use a torch from behind to see how much light leaks through.

I had a friends R100RS in my garage the other day for a carb balance and the first thing we did was readjust the butterflies as he had put new seals on the shafts. We couldn't get them 100% light tight so I tried tuning them anyway.
When it comes to adjusting the airscrews the idle goes up and then you run out of adjustment on the throttle screws and can't get the bike to idle slow enough.

We ran out of time so he took it home to have another go at getting the butterflies to close better.

[bruce_launceston]

BTW his screws were damn tight and he said he didn't remember doing them up that tight, they seem to tighten up in the heat maybe.

I definately would not peen the screws as the threads in the shaft are very fine and soft and would probably tear out next time the screws were removed.
You would then be up for new shafts as well as screws!

[Rob Valdez 79 R65]

You are supposed to grind off the peened end of the screw with a rotary-type tool before attempting to remove them.

[bruce_launceston]

Hi Rob, I guessed that was the correct way to get them out if you know but I have never heard of them being peened before I read this thread.
Are they peened from the factory because I just unscrewed mine when I rebuilt the carbs?

[Mike V]

Bruce,
Yes, they're peened at the factory. It's hard to tell by looking but you won't get them out without grinding...unless you're lucky and tenacious. Here's a quick little pictorial/tutorial in my Photobucket album from my rebuild.

http://s428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Bing%20Carb%20Left/

[Rob Valdez 79 R65]

It is also possible, Bruce, that you are not the first person to rebuild these carbs since the factory.