Petcock question

[GS750GUY]

Hi guys and gals!!
I recently rebuilt the petcock on my 78 GS750EC which included replacing the internal rubber gasket and ring. Initially, after reinstalling the petcock it worked beautifully. The selector dial turned nice and easily and smooth. I had no leaks. It worked great!! However, the other day I went to turn the dial and could not even budge it. Finally after backing out the two face plate screws (almost all the way) I could finally move it but it was still very stiff. I decided to investigate by disassembling it and discovered that the internal rubber parts seemed to have swollen and expanded to the point where they almost no longer fit within the petcock. I think this was causing such internal pressure that the dial would not budge. The rubber ring that fits in the groove around the outside parimeter of the dial is very sloppy and the same with the inner rubber gasket that fits under the dial. Has anyone experienced the same thing happening to them? Is this normal? Does it just need to be broken in? I'm afraid that I put so much pressure on the dial lever that I might end up breaking it off.
I appreciate hearing about any past experience with this and any suggestions anyone may have.
Thanks!
GS750GUY

 

[Steve]

If they are the proper o-rings, there should be no problem. Did you get them in a kit intended for this purpose, or did you source them from the hardware store? Many rubber-looking o-rings are not rated for use will gasoline. I think Nitrile is the key word to look for, but I could be wrong.


.

 

[SqDancerLynn1]

My first question would be WHAT did you use for assembly ?? Any type of grease other than silicon grease can cause the rubber to swell. Same goes if you are doing brakes

 

[DanTheMan]

And with brakes, only brake fluid will do, otherwise you contaminate the brake system.

 

[QuaiChangKane]

Not sure about your gaskets, but when I rebuilt my petcock I had a similiar problem.


It seems the o-rings if not lubricated will get very dry (I assume from close proximity to the fuel) and cause significant resistance when trying to turn the valve. I took mine back apart and lubricated the o-rings with silicone grease, and have had no subsequent problems over the last 2 years.


FWIW - if you're trying to source individual o-rings and can't find nitrile o-rings, try looking for an automotive HVAC o-ring assortment. They're usually green instead of black, but they're good stuff and readily available in a variety of sizes.


-Q!

 

[Dave8338]

I had similar problems with the rebuild kit that I installed and after tearing it apart, it found it's way to the trash can and I ordered a new one. $40-$50 and not look at it again for the next twenty years. It is the least expensive insurance I've got on the bike!

 

[feelergaugephil]

I'll give you a huge TIP for FREE.....................

Go buy an IN LINE ON/OFF switch, leave the petcock on "on" and turn the in line switch OFF when not in use, and ON when you want the engine to run....
When the GS petcock gives up and the fuel runs into your crankcases and you try start it, if you get a vapor lock......
Happy stripping of your motor..................

 

[GS750GUY]

Petcock

Petcock

Thanks guys for the advice!!
I did buy this in kit form specifically for this purpose. However, I did use some kind of light weight ........I think it was fishing reel grease.......to lube the rubber parts. That is probably what caused it to swell. I think I will take it apart again and soak the parts in gasoline hopefully to remove the grease and shrink the parts back to original size and then reassemble with silicone lubricant. I think I will also take your advice and put in an inline on/off fuel switch just for safety sake.
I don't know if any parts suppliers read these tech issues or not but would it kill them to include in the package a small instruction sheet to let us amatures know what to use and what not to use when using their products. Or do they just figure we all should know better?
Many thanks!!
Harold.......GS750GUY

 

[txironhead]

No, they WANT you to screw up (factory parts, anyway) so you'll either pay $50+ an hour for the dealership mechanics to work on your bike or be forced to admit your bike is "too old" and buy a new one.

Do you really think it costs the dealership $30 to make a simple, one-piece paper valve cover gasket? They expect people to ride their bikes until the first major repair and trade it in on a new one. I got this bit of enlightenment from a former head mechanic at a Honda dealership.

 

[bwringer]

I had similar problems with the rebuild kit that I installed and after tearing it apart, it found it's way to the trash can and I ordered a new one. $40-$50 and not look at it again for the next twenty years. It is the least expensive insurance I've got on the bike!

I agree completely. The rebuild kits are junk. Buy a new petcock. It's the only way, and it's not at all expensive.

There's no point in screwing around with your fuel delivery system. Even with an on-off valve in the fuel line (which is an invitation to human error), the old petcock is not working correctly after 20 years, and could still lead to a variety of disasters.

At or before the first sign of trouble, replace the petcock so you can think about something else for another 20+ years. Petcocks do not last forever, and I completely fail to understand the mindset that thinks it makes more sense to try and work around an aged, failing, safety critical part than to simply replace it.

The OEM vacuum-operated petcock works very well -- there is nothing deficient about the design, and certainly no reason to replace it with a manual Pingel. Pingels do not last 20+ years either.

A manual petcock actually leaves you far more likely to forget to shut it off and hydro-lock your engine or fill the crankcase with gas -- the floats and needles are simply not designed or able to completely hold back gas for long periods of time. It's also quite easy to forget to turn the gas on, which can create a hazard as you try to merge into traffic. All in all, the vacuum diaphragm is far less fallible than human memory and is just as reliable as a manual petcock.

 

[txironhead]

Put a lot more eloquently than I could have phrased it, but I completely agree. I hate having to remember to turn the fuel on/off.

And having had someone play a nasty trick on me by turning off the fuel on my Shadow and it dying midway through an unprotected left turn at an intersection, I fully agree about the margin of error there, too. BTW, that guy nearly ended up in the hospital. I didn't touch him, but it turned out he turned ALL the bikes (around ten of them) fuel selectors off (mainly metric bikes) at the bike shop I was at. Funny, I never saw him at that shop again......:-D