Re: silicone for assembly, I just bought this from Ace Hardware. Plumbers grease, 90% silicone, safe for all rubber and plastic. And super slippery stuff! A little goes a long way. I used it today.
...I measured the more meaningful vertical axial movements of the throttle shafts and results are posted in the revised carb measurement chart - post #73, page 4. .002' and .003". Don't know if this is enough slop to be problematic, but guess we'll see soon enough.
...Forgot to check throttle bore measurements. Done now and results posted in said chart above. I think we're OK here as they range from one low 37.93 mm to 38.00 mm and most being close to 38. These probably fall within spec?
Zamak has a lower melting point than bronze....Also had a look at the throttle shaft bushings on the 78/79 carb bodies. I don't know how to tell if they are brass or bronze but they have very fine serrations/splines?.
The outside bushing surface is serrated (too small to photograph) which raises a couple of questions. (letters this time....lol)
- a) I wonder how these were manufactured? I'm thinking probably placed on a locating shaft and pressed into a smaller bore in the softer Zamac carb body material. Can't see that the carbs were cast around these. But who knows?
Yes, that was my original intention with my carbs. Modifying a 10mm (or 3/8") ream, with a long 8mm (or 5/16") shaft, and backwards cut the throttle bore to accept bushings. The details are in that other link posted earlier. The question is: Will 10mm (or 3/8") exceed the OD of the existing bushing?...
- b) These bushings do not extend the full depth of the throttle shaft bore (once again hard to get a pic) but rather sit against a lip the thickness of the throttle bore wall. Maybe after these bushings are pressed into place they, and the carb throttle bore wall lip are machined to 8 mm. Whatever the case may be with that I wonder if there is a repair solution for worn out shaft bushings on these older carb sets. Could one not just ream out a larger bore, even a stopped bottom bore to leave a lip, and then machine and install an 8 mm ID sleeve? If this could be done would maybe save the fate of some sets. I wonder.
- Thinking again (dangerous again) Even if these are cast into place in the shaft bores they are now centered and one should still be able to ream and sleeve shouldn't they? I know Xsbob's concern was pulling the entire bushing and then not having the true centre but what if we just machine the existing centred bushing?
...So we're all studied, measured, and buttoned up again and ready to mount back on the bike.
...If not, these will go into the material collection bin for that Gingery lathe I've been wantin' to get around to.
OK, thanks for that confirmation. IIRC I was further out than that with this set.Your 0.002"-0.003" slop probably isn't enuff to allow the plates to contact the bore at your idle setting. Unless yours is set less than 1/3 turn from fully closed.
When my 74/75's make it back home (should have just bought some bottoming taps for those float bowl screw holes and been done with it), I will get and post the measurements for those as well.It does affect idle and off-idle response. Don't know if just mine are uniquely oblong, or if it's common with our carbs. Kind of a personal project.
Yes, I remember reading through that a few times and that would explain where I got the idea. I will get a picture and rough measurements of the bushing OD / wall thickness from my other 78/79 carb on the bench. All I can do is eyeball it, but it will give an idea of how much there is to play with.The details are in that other link posted earlier. The question is: Will 10mm (or 3/8") exceed the OD of the existing bushing?
I am amazed to say, "absolutely perfectly clear". Not because your explanation is lacking, but that I have absorbed enough about these carbs that it makes total sense. I will photo-document and make notes of all of this. Interesting to have another visual check procedure and a way to preset idle screw better than my, 'ya that looks like the right amount of gap at the bottom' method.Clear as mud???
I'll snap a shot or two of the running 78-79 set's idle screws