do NOT put Sil-Glyde on Throttle Shaft Bushings!

[DogBunny]

A couple years ago or so I thoroughly rebuilt/restored three sets of BS34 carb sets for use in future projects. I used brand-new genuine Mikuni throttle shaft seals which I lubed inside and out with Sil-Glyde before installing.

I recently put one of the carb sets into service and discovered intake leaks at the throttle shafts. Disassembled the carb set. The throttle shaft seals had visibly swollen. A brand-new seal should be a perfect fit on the shaft with just a little drag. When removed and inspected the Sil-Glyded seals were visibly loose on a test shaft. I could actually see an air gap where the seal met the shaft. I would guess that the interior diameter of the Sil-Glyded seals was 0.25 to 0.50 mm oversize.

This is making me re-think the use of Sil-Glyde. I always thought that Sil-Glyde was 100% safe and inert on rubber. The tube says: "Ease rebuilding of rubber parts: o-rings, grommets, boots."

I love Sil-Glyde, but obviously I will never put it on a throttle shaft seal again, nor on other tiny or thin critical parts such as carb o-rings.

I have been putting it on throttle shaft seals for years, but on carbs that went into immediate use, where I'm guessing that heat, air flow, and gas vapors dissipated the Sil-Glyde.

As I recall, I got the idea to Sil-Glyde throttle shaft seals from a post made many years ago by a highly respected member of this forum. I have gotten scores of excellent tips, answers and insight from this member which I am extremely grateful for, but this was a bad one. But again, who knew that Sil-Glyde swells rubber?
This same member advocates putting a thin coating of Sil-Glyde on carb diaphragm rubbers. Something to re-think about. Might be very beneficial if it swells and softens an old, slightly stiff, slightly shrunken diaphragm rubber, but I don't think I'd put it on a nice, supple diaphragm rubber.

 

[Bob Kelly III]

Good information there Dogbunny ! THANK YOU !!!!!
....
Bob......

 

[gggGary]

If you are referring to me, You may wish to re-read my posts. I use sil-glyde in many places but NOT critical rubber like carb parts. I use Dielectric silicone compound on diaphragms. Is this a perfect lube? I do not know, but have not found any issues so far. Sil-glyde (from NAPA) is a mix of various greases, not pure silicone. Rubber ages, Opinion; the plasticizers gradually outgas and disappear. any applied compound is only a stop gap and some create more problems than they solve. There's a lot out there about ageing rubber. I have heard anecdotally that the spray on vinyl care products actually hasten the ageing process.

 

[xjwmx]

I put dielectric grease on a non-oem outer seal and 6 mos. later when I finally broke down and replaced all the seals, that seal was literally as hard as plastic. I've used CRC silicone spray on various rubber things, and I don't know if it preserves it, but it doesn't cause anything to harden so far.

 

[fredintoon]

Also, a lot depends on the rubber,
which ain't usually vulcanized tree sap these days, it's more likely an "Elastomeric Polymer" instead and there's thousands of them.
Some of which make better seals than others.
One of my apprentice tasks back in the 1950s was to babysit a test rig that operated O-rings made of various compounds running in first generation
synthetic oils. The O-ring compound acceptance rate was less than 20% swelling in 24 hours.
We couldn't measure the natural rubber O-rings swelling because they were so degraded that they had to be wiped off the test rig mandrel with a cloth.

 

[DogBunny]

Yes gggGary, it was you, and again, huge thanks for all of the hundreds of excellent useful posts that you have made. Sorry for conflating Sil-Glyde with dielectric silicone compound (which I assume is the same thing as silicone grease) in your posts.

I have always had a huge problem with using dielectric grease on anything other than electrical components. That is its specific application. Dielectric grease is electrically insulating and does not break down when high voltage is applied. It seems to me that there should be better rubber-lubricating silicone greases for non-electrical applications. I always thought that Sil-Glyde was it. As I said, the tube says: "Ease rebuilding of rubber parts: o-rings, grommets, boots." But I think that now I am only going to use Sil-Glyde on brake calipers. For all other rubber I am going to start using (non-dielectric) silicone grease.

I quick search reveals a bewildering number of silicone greases sold for myriad purposes. If anyone likes one that they think is particularly pure and inert on rubber please share.

 

[gggGary]

xjwmx I avoid using the spray silicone on anything critical because the silicone is diluted with "some solvent", that solvent may speed the drying out process we are trying to slow.
This really does get complex as each seal may use different compounds,and even a new seal from an OEM may be different than one made 35 years ago. Perhaps not least because environmental regulations have changed allowable manufacturing techniques.

Mia Culpa I've been here for 7 years now and have gotten more involved and "educated" (occasionally at gun point LOL) as time goes on, my preferred practices continually evolve.

 

[xjwmx]

If there's drying out solvent in it, it's still overwhelmed by non-drying out silicone A good method might be to put some on a q-tip.

If the seals were a persistent problem, some crafty machinist among us could modify the shafts so it was easier to get to the inner seal. Maybe just cut the shaft next to each carb and hold it together with a sleeve over it with set screws.

 

[Paul Sutton]

In the UK the white spirits for thinning paints has a high aromatic content, very aggressive towards rubber. I washed a disc brake dust cover with it and with 1 minute it was twice the size. It took about 4 hours in the scorching sun to shrink back. Swollen rubber usually tears very easily. For cleaning rubber and seals I use the liquid it was designed to retain. i.e. petrol for things carburetor related and oil for engine seals.

Interesting fact from the newspaper: Vaseline will decrease the strength of a condom by 98% within 2 minutes. Perhaps that is why they too have a specialist lubricant, and I do not mean saliva.......

 

[xjwmx]

Well, just buy a condom and rub it on the seals.

 

[mrtwowheel]

I use Walmart Tech Lubricant, similar to WD40, as a cleaning solvent and have seen Orings swell in size from using it, not all Orings.

Scott

 

[retiredgentleman]

I use Sil-Glyde on my car's disc brakes when I replace pads and general clean up of the slide bolts. Excellent for that.
I use dielectric grease on most rubber parts on my bike and car. It is very good for carb boots and carb diaphragms.
I use dielectric grease on my car's sun roof seals and door seals.

Carb shaft seals are quite delicate so I don't use any grease on them.

 

[5twins]

Lately, I've been using red rubber grease. It doesn't seem to be readily available in this country. I found out about it here on this forum, from some of our English members. In fact, I ordered my tub from the U.K. I haven't tried it yet on shaft seals but had planned to. It's not petroleum based, it's vegetable oil based. It's not supposed to harm any kind of rubber.

http://www.redrubbergrease.com/

So far, it's worked well on the things I've tried it on - brake parts (one of it's design purposes), carb boots to ease carb install, and best of all so far, footpeg mounts. My footpegs always seemed to be stuck on any time I went to remove them. The rubber bushings were always stuck to the mounting studs. I'd have to hit them with some spray lube of some sort to break them free. Not any more. Now that they're lubed up with this stuff, they slide on and off easy, even months to a year since the last time they were off.

 

[DogBunny]

I am also huge on red rubber grease. Its specific application, as I understand it, are rubber parts that come in contact with hydraulic fluid. It is "The Only" grease compatible with both rubber and hydraulic fluid i.e. brake fluid. I too got mine from the UK, it is precious, so the only things I use it for are brake parts. It is what is in those little packets that sometimes come with new brake parts -- view link:
http://www.lukekailburn.com/caliperrebuild.html
Two more instructive links:
http://www.redrubbergrease.com/tip-...e-with-rebuild-kit-use-red-rubber-grease.html
http://www.redrubbergrease.com/tips-how-to-brake-caliper-failure-repair-with-rebuild-kit.html
Of course, they are trying to sell more of the stuff, so they go WAY over-board with over-applying it.

I just started three long-term experiments:
One: Took a useless, shrunken, dry, stiff carb diaphragm rubber and covered both sides with Sil-Glyde to see if it will non-aggressively rejuvenate it.
Two: Took some old, stiff, dry carb shaft seals and did the same thing. I don't think I have ever thrown out a useless carb shaft seal. They will be in high demand after the apocalypse.
Three: Took those shaft seals that I ruined in my initial post, and put them in 50% isopropyl alcohol. To see if it will non-aggressively shrink them back to where they are supposed to be.

 

[retiredgentleman]

5twins.................I use to have the same problem with the foot peg mounts. A real struggle to get them off and on. Once I started using a small amount of dielectric grease, it was super easy.
Red rubber grease.....................interesting, I have never heard of it before.

 

[TwoManyXS1Bs]

Things seemed simpler 45+ years ago, when seals were mostly rope, rubber, neoprene, and the newly emerging silicone.

...This really does get complex as each seal may use different compounds,and even a new seal from an OEM may be different than one made 35 years ago. Perhaps not least because environmental regulations have changed allowable manufacturing techniques...

Good one, Gary. What do we have nowadays?

This present world of new-fangled organics, rubber materials, sealants and lubes, is another black hole.

Just look at the current state of o-ring material compatabilities:

https://www.marcorubber.com/o-ring-material-selection-comparison.htm
https://www.sealingdevices.com/compatibilty-tables-for-gases-fluids-solids-parker-handbook
http://www.applerubber.com/chemical-compatibility-guide/
http://mykin.com/rubber-chemical-resistance-chart

I've been researching the various silicone greases, another maddening area, due to minimal MSDS reveals of proprietary formulations.

Then, we've got a market awash in fake, counterfeit, substandard products.

Maddening, I tell you.

Best I could figure out about Sil-glyde, is that it's about 30%-60% vegetable oil based, specifically castor oil, which has a good history as a (natural) rubber protectant and restorer. As such, it's supposedly okey-dokey on (natural) rubber products, like the JBindustries diaphragms.

The Red Rubber Grease offering by Castrol claims to be largely vegetable oil based, probably castor oil, which makes it also okey-dokey on (natural) rubber products.

Throw the new-fangled elastomers into the mix, and it's headache time.

Also been trying to compile a list of 100% silicone greases.
More madness. Incomplete, but so far:

Ford Silicone Brake Caliper Grease and Dielectric Compound #190984

(A close substitute)
AGS Dielectric Silicone Grease
Product codes: BT-1K, DS-1, DS-2, DS-4, DS-1BK (765-1190), DSB-1, DSB-1GR, BT-1, BT-1A, BT-1SP, BT-1ASP, DP-1, DP-1A

 

[TwoManyXS1Bs]

...I recently put one of the carb sets into service and discovered intake leaks at the throttle shafts. Disassembled the carb set. The throttle shaft seals had visibly swollen...

If you used carb cleaner to test for leakage, there's a chance that the swelling may have been caused by the cleaner. But, if it was already leaking, that may be a moot point.

I used the Sil-glyde on my seals and new bushings, but put them into immediate service.
No issues, so far...

 

[gggGary]

On foot peg bushings; if they haven't been lubed before remove nut and washer, hit liberally with spray silicone grease, wiggle the peg around a bit. They come right off. This is a place I use sil-glyde all the time. side cover push pegs n' grommets also. Even if it does swell those robbers a bit, and I haven't seen it, that'd be a good thing! I'm anal about the those plastic push pegs I razor off any flash and sharp edges and use fine sand paper to smooth them before sil-glyde. Pretty sure I've saved myself some broken off pegs. another place for spray silicone, before I try to remove covers from an old bike.
+1 on the complexity of this subject, remembering there is no "cure" for aging, hardening rubber.
Any rubber in the brake system is a very special compound, I pretty much stick with brake fluid as a lube and cleaner on that stuff, any "normal grease etc. will swell it to uselessness.
Another one; that old fork oil that stinks so bad? Many Japanese lubricants contain WHALE oil! I heard a large Japanese auto maker had a real tough time designing an automatic transmission fluid to replace the whale oil based one they had been using when the US banned import of whale oil products. Seems that some of the lubrication properties are near impossible to duplicate.
This is one area where the upper midwest is great, our old rubber tends to hold up quite well. I've owned more than one south west vehicle with rubber parts that turned to dust when handled. The Royal Star Venture sat under an Arizona carport for a decade or so, all the plastics and rubber have really suffered.

 

[Mailman]

The last time I had my carburetors apart, I used this product I found in the plumbing section of my local Ace hardware store. Inexpensive and super slippery.

I cringe to think that the first time I rebuilt my carburetors , following a YouTube video for advice, I hosed down my diaphragms with aerosol silicone spray.

 

[xjwmx]

^LOL. How are the diaphragms now? Did it really hurt them? Probably less sensitive than what we're talking about.